IQ1 Reproduction – How does reproduction ensure the continuity of a species?

- Reproduction is the fundamental evolutionary process ensuring the continuity of life.- Only eukaryotes can undergo sexual reproduction, which is more difficult and produces

less offspring, but has one main advantage – VARIATION.- However, both methods have pros and cons, and many species are capable of both!

a) Bacteria- Bacteria are not complex enough to undergo mitosis or

meiosis, so they replicate through binary fission: the cell expands, the naked DNA in the nucleoid region duplicates, and the cell splits in half.

- It is so rapid and effective that bacteria can double exponentially in 20 minutes!

- Replication is controlled by the cell cycle, and occurs until they run out of resources.

- As binary fission produces identical clones, there is no variation (asexual).

- In order to maintain variation, bacteria have three processes to exchange/alter their DNA despite their reliance on asexual reproduction.

- In transformation, a bacterium takes up a piece of DNA floating in its environment. In transduction, DNA is accidentally moved from one bacterium to another by a virus. In conjugation, DNA is transferred between bacteria through a tube between cells.

b) Protists- Protists are any single-celled eukaryotic organisms that are not plants, animals, or fungi,

and they can reproduce both asexually and occasionally sexually.- Protists usually reproduce through mitosis, a more complex form of binary fission.- Due to the added complexity of the nuclear membrane, this takes hours to days instead

of the minutes that bacteria take.- It can occur along any axis that divides the cytoplasm into halves.

- Protists can also reproduce by budding, where the genetic material copies itself once or multiple times into tiny pockets of cytoplasm, which grow whilst still attached to the parent. Budding forms chains of cells, and these can grow into colonies!

- Multiple fission is similar to budding and mitosis, where many daughter cells are formed in a single round of replication.

- In addition, sexual reproduction – through the formation of haploid gametes which fuse into a zygote that undergoes meiosis – originated in Protists.

- Some Protists can also form spores, similar to fungi.- Both of these processes only occur rarely, in stressful and unfavourable conditions.

c) Fungi- Fungi also reproduce both sexually and asexually, and often rely on budding as they are

often colonial organisms. However, they can also be multicellular or unicellular.- Budding in fungi occurs in the same way as in Protists: yeast reproduces in this way.

- The formation of spores is the main way in which fungi reproduce, and this can be either sexual or asexual.

- Spores are tiny, unicellular reproductive cells that are produced in great numbers.- Spores can remain dormant in unfavourable conditions and can travel long distance.- Asexually-produced spores are known as mitospores, and are produced by mitosis.- Mushrooms and mould make spores in mass-production structures called sporangia.

- Sexual reproduction in fungi involves two haploid gametes (only half of the full set of chromosomes) in the underground hyphae coming into contact and ‘mating’.

- This forms zygospores, which are genetically distinct from its parents and undergoes meiosis. Zygospores are only formed rarely in unfavourable conditions.

d) Plants – Asexual and Sexual- Asexual reproduction in plants occurs via a process called vegetative propagation. Any

part of the plant can propagate, and it is easier than sexual reproduction (although many plants do both). There are many different forms:

o Bulbs – modified underground stems made up of layered fleshy ‘scales’.o Tubers – swollen underground stems made up of solid tissue.o Corms – a cross between a tuber and a bulb, typically with multiple nodes and

coated in layers made up from dead leaves (tunics), which can split or be cut.o Runners/Stolons – thin horizontal stems which grow along the ground and sprout

new daughter plants at their ends (nodes) once they reach far enough from the parent plant. They do not grow roots along their length – only at nodes.

o Rhizomes – thicker underground versions of runners.o Suckers – new plant shoots growing from the root systems of an existing plant.

- In addition, humans use artificial forms of vegetative propagation to farm plants:o Cuttings – part of a plant is removed and planted and develops into a new plant.o Grafting – part of one plant (scion) is removed with a wedge-shaped cut and

bound to a different plant with wax so that they fuse into ‘one’ plant.o Layering – a lower branch of a plant is bent to the ground and partially covered

with soil. Eventually it develops roots and the original branch can be cut.

o Tissue Culture – like a very small cutting of stem cells grown in a test tube.- Sexual reproduction methods in plants are divided between non-vascular plants (e.g.

mosses, hornworts and liverworts) and vascular plants (e.g. ferns, gymnosperms, and angiosperms).

- Non-vascular plants (bryophytes) don’t have conductive tissues or woody tissues, and hence need water for reproduction and have limited growing potential.

- Alternation of generations is a reproductive technique which originally evolved in algae. In bryophytes, it involves the sexually-reproducing gametophytes giving rise to the asexually-reproducing and gametophyte-dependant sporophytes.

- The gametophytes produce haploid sperm (with two flagella) which require water to swim to the eggs. The gametes join to form a zygote which grows into a sporophyte.

- The sporophytes contain sporangium, usually in the form of small capsules on top of thin stalks growing from the female gametophyte, and the spores that are released from this capsule spread and grow into new gametophytes.

- Vascular plants also reproduce using the alternation of generations, but it is a lot more complicated and the sporophytes (not gametophytes) form the ‘plant’ part.

- Ferns are the simplest form of vascular plants, and reproduce in basically the same way involving spores and water-reliant gametes. The gametophytes are tiny hermaphroditic growths, and the ‘fern’ part is the sporangium.

- The more complex vascular plants all rely on pollen in order to reproduce without needing water. Pollen is made up of tiny male gametophytes which can drift through the air or are carried by vectors to the female gametophytes (ovum), where they join and develop into seeds.

- Gymnosperms (including conifers, ginkgoes, and cycads) are the first plants to evolve pollen and use seeds. Instead of flowers they have cones – small soft male cones producing pollen, and large hard female cones with ovum on the outside. The ovum become seeds, which are protected until they are ready by the cone.

- Angiosperms are flowering plants, and they reproduce exactly like gymnosperms except the cones are replaced by flowers. They are the most diverse plant phylum!

- There are two main types of angiosperms: monocots (grasses) and dicots (broad-leafed). Monocot flowers have parts (petals, sepals, stamen) arranged in threes, while dicot flowers have parts arranged in fours or fives.

- Flowers can form single units (e.g. roses, lotus, or magnolia) or groups/clusters called inflorescences (e.g. lavender, grevillea, or cowslip).

- Male flowers have stamen (pollen-producing anthers on tall filaments) and female flowers (unlike cones) hide their ovum in ovaries accessible by the tall style with an opening (stigma) at the top.

- Flowers with both male and female parts are called ‘perfect flowers’, and the height of the stamen vs the style determines if the flower is self-pollinating.

- Imperfect flowers (or perfect flowers that don’t want to self-pollinate) rely on animals such as birds, bats, and insects to carry pollen, which is why flowers are colourful, sweet-smelling, and nectar-producing.

- There are a wide variety of pollination ‘tricks’ – some flowers have co-evolved with pollinators (e.g. wasp orchid, bees + foxgloves) or have very complex mechanisms such as the passion-flower, and some (e.g. grasses) just use the wind like gymnosperms.

- This process is called cross-pollination and is very useful to ensure genetic variation!- Once the pollen reaches the ovum and fertilisation takes place, the ovum develops into

a seed (like gymnosperms) and the ovary becomes a fruit. Fruits can be designed to protect seeds (also like gymnosperms) or to get them eaten for mobility and nutrients.

e) Animals – Asexual, External and Internal- Asexual reproduction in simpler animals occurs through fragmentation or budding.- Fragmentation is where the body of an organism breaks into two or more types, each of

which develops into a new organism due to the presence of stem cells.- Budding occurs when genetically identical small organisms grow on the parent organism.

They may separate later or remain attached to the parent.- In more complex organisms, parthenogenesis can also take place. Parthenogenesis is the

development of an egg in the absence of fertilization and occurs in reptiles and insects.

- Sexual reproduction in animals relies on the meeting of haploid gametes in a process called fertilization. The combined gametes form a diploid zygote which multiplies into a new animal through meiosis.

- Fertilization can occur through one of two methods:o External fertilization occurs in an external water environment.o Internal fertilization occurs inside the body in a home-made water environment.

f) Mammal Fertilisation, Implantation, and Hormonal control- Gametes are formed through either oogenesis (meiosis where only one of the four eggs

survives) before the female is born or spermatogenesis (meiosis where all sperm cells survive) throughout the life of the male.

- All of a female’s oocytes are produced before she is born, but they then need to mature in the follicles. When the female reaches puberty, the oocytes completes meiosis I.

- At ovulation, the oocyte then completes meiosis II and grows bigger and full of nutrients, becoming an ovum (mature egg) that is then released from the ovarian follicles.

- The follicle it came from becomes a corpus luteum, which releases ovarian hormones.

- Fertilization in all mammals is internal, occurring in the female reproductive tract (usually the uterine tube). There is a five-day window after ovulation when this occurs.

- The sperm die in a variety of ways on the journey, but thousands still reach the ova.- They break through the outer layer (corona radiata) with an acrosomal reaction and

enter the zona pellucida, where only one sperm can enter before the corona radiata hardens and becomes impermeable. The sperm nucleus then fuses with the egg nucleus.

- Once a sperm fertilizes an ova, a series of chemical changes occur to ensure successful zygote production.

- After fertilization the zygote divides into a morula (a 3-4 day old ball of cells) and then a blastocyst (4-5 day old hollow ball of cells connected to the trophoblast).

- The trophoblast secretes enzymes to connect to the endometrium (uterine wall) and develops into the placenta, while the connected blastocyst develops into a gastrula, then an embryo. Human Chorionic Gonadotrophin (HCG) is produced (pregnancy test).

- By 8 weeks the embryo has grown enough to develop human features and be a foetus.- The hormones that maintain pregnancy are produced by the pituitary and ovaries.

Hormone Function ProductionGonadotropin (GnRH) Triggers the release of FSH and LH HypothalamusFollicle-Stimulating Hormone (FSH) Ensures the egg development PituitaryLuteinizing Hormone (LH) Causes ovulation (egg release) PituitaryOestrogen Supports foetal growth, increases blood

flow and triggers positive feedbackOvary

Progesterone Causes the regrowth of the uterine lining, inhibits FSH/LH and contractions

Ovary/Placenta

- Gestation is divided into three trimesters of three months each. The first trimester is just cell division and differentiation, the second trimester is the formation of organs, and in the third trimester the baby is fully formed and just needs to grow bigger.

- The process of childbirth is called parturition and occurs via positive feedback under hormonal control. Positive feedback involves a response which amplifies the change.

- In the case of childbirth, foetal growth causes stretching of the uterine walls which is detected by stretch receptors, triggering the release of hormones.

Hormone Function ProductionOestriol Inhibits progesterone production PlacentaOxytocin Triggers ‘nurturing’ feelings, causes

contractions, helps lactationPituitary

Prostaglandins Triggered by contractions, causes contractions (positive feedback)

Foetus

Endorphins Calming and pain relieving, allows the mother to ‘survive’ birth

Pituitary

Adrenalin and Noradrenalin Inhibits contractions (at low levels), spikes trigger foetal ejection reflex

Adrenal glands

Prolactin Central to breast milk production Pituitary

g) Technological Manipulation of Reproduction in Agriculture- The manipulation of plant and animal reproduction in agriculture has expanded as

knowledge of biological processes had developed and as the need to produce food more efficiently and cheaply increases. This is where selective breeding is utilized.

- Selective breeding (the manipulation of plant and animal reproduction to select important characteristics) has been carried out since agriculture began over 10,000 years ago. Traditional methods are still used, but there are many better ones now too.

- Artificial pollination is where pollen (or whole anthers/stamen) are removed from one parent flower and applied to the stigma of the other parent flower.

- Artificial insemination is when semen is extracted from a male with superior traits and is stored and transported wherever breeders want to be inserted into multiple females (e.g. Belgian Blue cows with ‘double muscle’). It can be used to improve the reproductive rate of endangered species.

- Hybridisation is the breeding of two different gene pools (breeds or variants) of plants or animals. When the offspring is superior to its parents, this is called ‘hybrid vigour’ (e.g. Merino x Border Leicester = First Cross Lambs). It can also occur within a genus (e.g. horse x donkey = mule).

- Cloning is the process by which genetically identical copies of an organism are made without using the process of sexual reproduction.

- In animals it is done through removing the diploid nucleus from the somatic cell of one animal (e.g. a sheep) and placing it in the denucleated egg of another sheep.

- In plants, it is done through the process of tissue culturing, when some of the plant’s tissue is taken and grown into a new plant using nutrient solutions.

- Transgenic species occur when a gene from one species of crop is extracted, formed into a recombinant plasmid, and placed in bacteria.

- The bacteria multiplies to create multiple copies of the gene, which can then be injected en masse into a second, unrelated crop species (e.g. cold-water salmon).

- Transgenics increases the genetic variation within a species by adding new alleles, as well as increasing crop yield and species range, but can cause problems if the transgenic organisms outcompete the ‘natural’ organisms leading to less variation.

IQ2 Cell Replication – How important is it for genetic material to be replicated exactly?

a) What are Chromosomes?

- All prokaryotic and eukaryotic DNA is basically identical, possessing the same structure and function. The only difference is the way it is packaged into chromosomes.

- In eukaryotes, chromosomes are many tight bundles of nucleic matter made up of 40% DNA and 60% histone. Different species have different numbers of chromosomes.

- Histone is the protein which binds chromosomes like a cotton reel. There are 1.65 loops of DNA around each nucleosome (a single unit of 8 histone proteins). The mass of DNA and histone is called chromatin, and when the cell is not replicating the fixed chromosomes unwind into a chromatin mass.

- Scientists in the 20th century discovered that DNA (not histone) was the heredity part.

- Prokaryotic DNA is found in a single chromosome which floats freely in the cytoplasm.- The chromosome is called the nucleoid region and is attached to the cell membrane.- They are compact with no junk DNA or repetitive sections, and only Archaea has histone.- Plasmids are small circular pieces of DNA which are not contained in the chromosome

and which replicate independently. They can be transferred between cells to provide the cell with a selection advantage, but are not necessary for survival.

b) The DNA Molecule- DNA is a double helix polymer made of two anti-parallel (5’ to 3’ and 3’ to 5’) strands.

The strands are made up of monomers known as nucleotides.- Nucleotides are made of three smaller molecules: a phosphate group (H3PO3), connected

to a pentose sugar (C5H10O5), & connected to one of 4 nitrogenous bases.- The bases are divided into single-ring pyrimidines (adenine and guanine) and double-ring

purines (thymine and cytosine). They connect via complementary base pairing.- A-T pairs through 2 hydrogen bonds and G-C pairs through 3 hydrogen bonds.

- The four bases do not occur in equal amounts, but A is equal to T and G is equal to C.

- The typical double-stranded DNA found in cells is called dsDNA or B-form DNA.- In order for the bases to be ‘facing’ each other and this able to pair, the strands must be

running in opposite directions (antiparallel). Phosphate bonds to the 5’ (five-prime) end of the deoxyribose molecule with a covalent bond.

- As the antiparallel chains lengthen, the atoms arrange themselves into the most stable energy configuration, resulting in the ‘twist’ in the double helix.

c) DNA Replication – Mitosis and Meiosis- The cell cycle has three main components: Interphase, Mitosis, and Cytokinesis.- DNA replication occurs at the Interphase of the cell cycle.- It has 3 components: Initiation, Elongation, and Termination.- Helicase ‘unzips’ the DNA which is needed for replication in sections called replication

forks. The 5’ to 3’ strand is the leading strand and the 3’ to 5’ strand is the lagging strand. DNA polymerase can only move in the 5’ to 3’ direction.

- On the leading strand of DNA, the enzyme DNA primase adds a primer fragment of DNA, then the enzyme DNA polymerase binds to the primer and attaches free nucleotides (produced in the nucleolus) in the 5’ to 3’ direction.

- The lagging strand is copied using Okazaki fragments, where multiple primers are attached and the gaps between them are filled in the 5’ to 3’ direction.

- DNA ligase then binds the two new double-strands of DNA, both of which contain an old strand and a new strand of DNA.

- Telomeres are protective DNA structures at the end of chromosomes, like the plastic cap on a shoelace. They prevent chromosomes from sticking together and are made up of a repeating sequence of bases (TTAGGG).

- When DNA is replicated, 25-200 bases in the telomere are broken off. When the strand of DNA ‘runs out’ of telomere, it stops replicating and the cell dies.

- Interphase is divided into three sections – the G1 phase where it grows/functions, the S phase where DNA replicates, and the G2 phase where the DNA is checked for errors.

- Mitosis (Prophase, Metaphase, Anaphase, and Telophase) all occurs in the fourth section, the M phase. The end of the M phase is cytokinesis.

- Mitosis is also known as cell nuclear division or binary fission. It is the process whereby cells reproduce by dividing in half and making two identical diploid daughter cells.

- The four phases of mitosis and cytokinesis are each necessary for cell division:o Prophase: The chromosomes are doubled; nuclear envelope dissolveso Metaphase: The chromosomes align along the middle with spindle fibreso Anaphase: The sister chromatids separate and are drawn away on the fibreso Telophase: Two new nuclear membranes form and spindles disappearo Cytokinesis: The cytoplasm splits to form two complete new daughter cells

- For sexual reproduction there is a second type of cell division – meiosis, which makes haploid sex cells (reductive duplication). It starts with prophase (like mitosis) where the DNA is doubled and forms into 92 chromosomes (double the normal amount).

- At this point two pairs of homologous chromosomes (a pair from each parent) exist in every cell. In meiosis, these line up in homologous pairs in a process called synapsis.

- During synapsis some genes cross over between the homologous pairs. This means instead of 46 pairs each containing two identical chromatids, there are 92 unique chromosomes! These then separate into 4 daughter cells through ‘double mitosis’.

IQ3 DNA and Polypeptide Synthesis – Why is polypeptide synthesis important?

- Polypeptide synthesis has two main parts – transcription and translation.- During transcription mRNA (messenger RNA) is made based on the DNA code, and

during translation the mRNA bonds to rRNA in the ribosomes and is matched to 3-base tRNA pieces (transfer RNA) which are each attached to an amino acid.

- There are two types of DNA – introns and exons. Exons are Expressed as genes (coding DNA) and introns are ‘junk DNA’ (non-coding DNA).

- However, introns still have important jobs – for instance, as promoters alerting the mRNA where to start transcribing when a specific protein is needed, or as terminators to stop transcription and protect the end of the mRNA thread.

- Some proteins are made constantly (cell respiration, haemoglobin etc.) while others are only occasionally needed (hormones etc.)

a) Transcription in detail- Transcription is the copying of the DNA code into a piece of mRNA, allowing the code to

be taken outside the nucleus even though the DNA is kept safely inside.- First, the DNA where the genes to be transcribed are gets unravelled using RNA

polymerase. The genes are made up of triplets which are transcribed into codons.- Random nucleotides attach to the template strand to form a piece of mRNA, going from

the promoter intron to the terminator intron and containing both introns and exons.- The mRNA leaves the nucleus through nuclear pores and is edited by the spliceosome

enzyme to remove the non-coding introns. The coding exons start with the codon AUG.- Once edited, the mRNA travels to a ribosome for translation.

b) Translation in detail- Translation is the process of changing from the ‘DNA language’ of bases (recorded on

the mRNA) to the ‘amino acid language’ of proteins.- First, ribosomes bind to the mRNA. The tRNA binds to the E-site, adds its amino acid to

the polypeptide chain at the P-site, and detaches from the ribosome (now with no amino acid) at the A-site.

- There are 20 main amino acids which link together in long chains called peptides like letters forming words, which in turn link together to form polypeptides and proteins like words making up sentences.

- Every amino acid except methionine (the ‘start’ amino acid) has 2-6 triplets/codons/ anticodons which code for it, ensuring that small single-nucleotide mutations are more likely to be harmless.

c) Effects of Environment on Phenotype- However, DNA is not the only thing which affects the expression of genes and hence the

phenotype of the organism – the environment can also have a strong effect.- Environmental factors such as drugs/chemicals, infections, temperature and light, and

many other factors can trigger the expression or suppression of a gene.- Temperature can affect the pigmentation of animals, such as Siamese kittens which are

born white but produce black pigment when the gene is activated by heat, or Himalayan rabbits which are white above 35oC but develop black pigment when the C gene is activated by cold – allowing them to absorb more heat and keep warm!

- Light can affect the Vitamin D production levels of humans and the chlorophyll production of plants, as well as activating the human melanin-producing genes and affecting the development of butterflies – caterpillars exposed to red light grow bright wings, green light grows dark wings, and blue light grows pale wings.

d) Proteins: Structure and Function- Protein structure depends first on amino acid order, then on how it folds. Chaperonins

are proteins which ‘supervise’ the folding of other proteins to prevent denaturing.- Proteins can be fibrous or globular. The structure of a protein is critical to its function.- They have many functions in our cells. Some main ones include:

o Enzymes facilitate and speed up reactions by lowering activation energy.o Antibodies are produced by white blood cells to target specific pathogens.o DNA-Associated proteins include transcription factors which regulate gene

expression, and histones which organise chromosome structure.o Contractile proteins are the proteins which allow the body to move.o Structural proteins (like titin and keratin) make up tissues which need strength.o Hormones control the activity of cells and are not always protein-based. Protein

hormones (like insulin) are water-soluble and bind to the outside of cells.o Transport proteins (like haemoglobin and ion channels) are responsible for active

and passive transport outside or through cellular membranes.

- Protein structure is divided into four main types based on increasing complexity – primary, secondary, tertiary, and quaternary.

o Primary proteins are simple polypeptide chains direct from the ribosomes, and are non-functional and only used to make more complex proteins.

o Secondary proteins are when hydrogen bonds form in this polypeptide chain, causing it to form a simple alpha helix (coiled) or beta pleated (zigzag) shape.

o Tertiary proteins are when more bonds and more complex bonds form, folding the polypeptide into a unique 3D structure.

o Quaternary proteins are formed from multiple polypeptide chains in secondary or tertiary form all bonded together, making an even more complex 3D structure.

IQ4 Genetic Variation – How can the genetic similarities and differences within and between species be compared?

- Genetics is the study of heredity, and scientists who study it are called geneticists.- A gene is a portion of the genetic code located in a certain locus, and an allele is the

particular form of the gene with a specific DNA code.- Every gene is located at a particular chromosomal locus (plural: loci) on either the p arm

or q arm, and it will always be at that same locus for every member of the species (no matter what alleles they have).

a) Theoretical Genetics: Problem-Solving- The Law of Segregation states that you get only one-half of each of your parent’s genetic

code – for each allele, you get one from either your mum’s mum or your mum’s dad, plus one from either your dad’s mum or your dad’s dad.

- The Law of Independent Assortment states that the random allele you get from any gene is not connected to the other alleles (e.g. just because your mother is small with brown hair doesn’t mean you can’t be tall with brown hair or short with red hair). This is because the chromosomes undergo crossing-over and random alignment during meiosis.

- Because of segregation and independent assortment working together, there are millions of different ways that your parents’ genotype can combine, making it practically impossible for two siblings to be genetically identical (unless they are identical twins from the same zygote).

- In addition, there is the possibility of germline mutations (permanent change to the genetic information), either spontaneous or induced by a mutagen. These come in many different forms and if they are survivable, they produce new alleles which can be evolutionarily favourable (and hence last) or unfavourable (and hence die out).

- Point mutations can be silent (the mutated triplet still codes for the same amino acid, producing the same protein), missense (the mutated triplet codes for a different amino acid, producing a different protein), or nonsense (the mutated triplet is a STOP or START and no protein is produced at all).

- Mendel was the first to conduct genetic experiments and hence was the ‘father of genetics’, and he established the two Laws above and the Principle of Dominance.

- The Principle of Dominance is that for every gene, there is a dominant allele (form of a gene) and a recessive allele. Later, co-dominant alleles were also discovered.

- On the most basic level, traits are always controlled by a pair of genes on a pair of homologous chromosomes (one from mum, one from dad). Polygenic traits are controlled by multiple interacting pairs of genes.

- The generations are represented by the letter F for filial – e.g. F2 is the child of F1.- A punnet square is used to depict the genotypes of the parents in a monohybrid cross

and to estimate the probabilities of different genotypes in their offspring (F generation).- A monohybrid cross involves one gene (one trait) with one pair of alleles per parent. It

shows the separation of alleles into sex cells and then their recombination into a new allele pair in each child.

- A test cross is the cross of a suspected heterozygote with a recessive homozygote to determine the unknown genotype.

- There are many different types of traits which can be predicted using a monohybrid cross: autosomal, sex-linked, co-dominant, incomplete dominant, and traits caused by multiple alleles.

- Most traits are autosomal (occurring on chromosome 1-22) and can be predicted very simply using a punnet square.

- The dominant gene is represented by a capital letter (T, A, etc.) and the recessive is a small letter (t, a, etc.). A carrier has the recessive gene but it isn’t expressed.

- Sex-linked traits are traits which are present on the X chromosome but not the Y chromosome (as Y has only 83 genes while X has 1000). As such, inheritance in females is the same as autosomal, but males can only inherit traits from their mothers.

- They are represented by a Y, and an X with the dominant/recessive letters in superscript.

- Co-dominant traits are traits which are caused by two dominant traits in the same organism, leading to both being expressed in equal amounts. This causes traits such as spotted/patched coats, and is represented by 2 different capital letters.

- Similarly, incomplete dominant traits are traits which when both are present in the same organism, they ‘combine’ to produce an entirely new phenotype. This causes traits such as pink flowers from a white/red cross, and is represented by 2 different small letters.

- About 30% of genes have two possible alleles, about 70% have only one allele, and a small handful of genes have multiple alleles. An example of this is blood groups.

- Blood groups are represented by a small letter i for recessive allele and a capital letter I with A or B superscript for the two codominant alleles.

Genotype Phenotype Blood GroupIA IA

Homozygous Dominant AIB IB BIA IB Codominant ABIA i Heterozygous AIB i Bi i Homozygous Recessive O

b) Allele Frequency and SNPs- The rate at which an allele occurs in a population is known as the allele frequency, and is

expressed as a percentage. A population is any group of interbreeding organisms.- Gene flow is the exchange of alleles between populations via migration and

interbreeding. The amount of gene flow is established by comparing allele frequencies between the populations. If they are different enough, they may be different species!

- In order to carry out effective statistical analysis, multiple genes must be studied.- The Hardy-Weinberg principle (or Hardy-Weinberg Equilibrium/HWE) allows the allele

frequencies for each gene to be placed in punnet squares and multiplied to produce the frequency of their offspring. If the alleles are p and q, the HWE equation is p2 + 2pq + q2

- It only works on a stable population at equilibrium; i.e. where there is randomised mating, no gene flow, no evolution, and no generation overlap (parent-child incest).

- SNPs (single nucleotide polymorphisms) are regions of the genome which have a single nucleotide change between members of the same species. They must be present in at least 1% of the population.

- They usually occur in the non-coding regions (in coding regions they are called substitution point mutations) and there are over 100 million known in humans.

- They can act as biological markers and can be charted in pedigrees. Their effects are unknown, but scientists are beginning to theorise that they may be associated with higher risks of cancer/other diseases, and can even affect gene expression.

IQ5 Inheritance Patterns in a Population – Can population genetic patterns be predicted?

a) DNA Sequencing and Profiling- The Human Genome Project was a worldwide project to sequence the order of all the

nucleotides in the human genome. Once the project was complete, scientists could use reverse-transcriptase to discover what DNA made up genes for specific proteins.

- DNA sequencing and profiling can be used for paternity tests, forensic investigation, identifying bodies after disasters or from history, and finding the pedigrees of animals.

- The sequences of DNA used for sequencing/profiling are called short tandem repeats (STR) because they are unique to each person and are more similar the more closely related they are. However, to be useful they have to be in large quantities.

- In a polymerase chain reaction (PCR) the original DNA is mixed with the Taq DNA polymerase enzyme (from heat-loving bacteria) and put through a rapid heating/cooling cycle to cause it to duplicate. This is called DNA amplification.

- Gel electrophoresis is used to produce DNA profiles or ‘fingerprints’ from the amplified DNA. A gel is made with small pits in one end, and the amplified DNA is placed in the pits in a solution with fluorescent dye. An electric current is passed through the gel, causing the DNA to spread through it. The shorter fragments travel further, and due to the dye they are visible as bands. This is the ‘fingerprint’, which can then be compared to others.

- DNA sequencing is used to find the order of bases in a person’s genome for more precise identification.

b) Data Analysis in Conservation, Disease, and Evolution- Conservation genetics is the application of genetics to preserve species through

maintaining variation to allow populations to adapt to changes in their environment.- It focuses on analysing the different alleles of each gene which are present in a

population. More alleles more genetic diversity more chance of survival.- The minimum viable population (MVP) is the smallest population capable of continued

survival in the wild. If a population is smaller than the minimum, it will have so few alleles left that even if it increases again the new population will not be genetically diverse enough to survive.

- This occurs due to genetic drift – the loss of random alleles in a population (as opposed to natural selection which is the loss of unfavourable alleles).

- The African cheetah is one example of a population which needs genetic conservation. There are only around 7000 left in the wild, divided among 33 populations of <100.

- This is due to two significant genetic bottleneck events: the last ice age, and human poaching. This has led to cheetahs having an incredibly low genetic diversity.

- Before genetic screening, captive breeding programs attempted to increase cheetah numbers. However, there was a 85% failure rate and 30-40% cub mortality due to low sperm count (10x below big cat average) and 75% malformed sperm.

- Due to genetic screening, these problems were found to be caused by inbreeding, which was particularly severe due to the genetic bottleneck. This spurred worldwide collaboration between breeding programs to ensure unrelated individuals could mate.

- After the Human Genome Project was completed in 2003, researchers focused on discovering what each genes caused, especially diseases and disorders.

- They did this through mapping the human haplotypes (the genes inherited together from a single parent) through the use of SNP’s as ‘tags’ for genes and comparing groups of individuals with and without each SNP. In 2005, they published the ‘HapMap’.

- The process is called genome-wide association studies (GWAS), and they have discovered the genes associated with prostate cancer, Parkinson’s disease, macular degeneration, Crohn’s Disease, and type II diabetes.

- In the field of evolution, the most useful tool to discover how closely-related two species are is DNA hybridisation. In this process, single strands of DNA are allowed to anneal together (connect) and are then heated to separate them.

- The higher the temperature needed to separate the DNA, the more the two strands must have bonded, and hence the more similar they must be to each other.

- If the DNA of two species are similar, the species must be closely related. This can be used to construct evolutionary diagrams which help us trace the development of life.

- Another process for discovering relationships between species is the mitochondrial protein Cytochrome C, which is common to all eukaryotes.

- Closely related species (e.g. humans and chimps) have the same sequence of 104 amino acids which make it up, but more distantly related species (e.g. humans and flies) have variations. The sequence is examined using mass spectroscopy.

- The final and most complex method of examining genomic similarities and differences between species is literally comparing the genetic sequence of their entire genomes.