human biology (biol 104) talk twelve: genetics chapters 19, 20, and 21

Human Biology (BIOL 104) Talk Twelve: Genetics Chapters 19, 20, and 21

Basic Concepts of Heredity Genes provide the instructions for all human traits, including physical features and how body parts function Each person inherits a particular mix of maternal and paternal genes Genes and Inheritance

History Genetics is the study of genes.Genetics is the study of genes. Inheritance is how traits, or characteristics, are passed on from generation to generation.Inheritance is how traits, or characteristics, are passed on from generation to generation. Chromosomes are made up of genes, which are made up of DNA.Chromosomes are made up of genes, which are made up of DNA. Genetic material (genes,chromosomes, DNA) is found inside the nucleus of a cell.Genetic material (genes,chromosomes, DNA) is found inside the nucleus of a cell. Gregor Mendel is considered The Father of Genetics"Gregor Mendel is considered The Father of Genetics"

Gregor Mendel Austrian Monk.Austrian Monk. Experimented with pea plants.Experimented with pea plants. Used pea plants because:Used pea plants because: They were available They reproduced quickly They showed obvious differences in the traits Understood that there was something that carried traits from one generation to the next- FACTOR.

Mendel In the mid-1800s, the rules underlying patterns of inheritance were uncovered in a series of experiments performed by an Austrian monk named Gregor Mendel.

Mendel's Plant Breeding Experiments Gregor Mendel was one of the first to apply an experimental approach to the question of inheritance. For seven years, Mendel bred pea plants and recorded inheritance patterns in the offspring. Particulate Hypothesis of Inheritance Parents pass on to their offspring separate and distinct factors (today called genes) that are responsible for inherited traits.

Mendelian Genetics Dominant traits- traits that are expressed.Dominant traits- traits that are expressed. Recessive traits- traits that are covered up.Recessive traits- traits that are covered up. Alleles- the different forms of a characteristic.Alleles- the different forms of a characteristic. Punnett Squares- show how crosses are made.Punnett Squares- show how crosses are made. Probability- the chances/ percentages that something will occur.Probability- the chances/ percentages that something will occur. Genotype- the types of genes (Alleles) present.Genotype- the types of genes (Alleles) present. Phenotype- what it looks like.Phenotype- what it looks like. Homozygous- two of the same alleles.Homozygous- two of the same alleles. Heterozygous- two different alleles.Heterozygous- two different alleles.

Mendel was fortunate he chose the Garden Pea Mendel probably chose to work with peas because they are available in many varieties. The use of peas also gave Mendel strict control over which plants mated. Fortunately, the pea traits are distinct and were clearly contrasting.

To test the particulate hypothesis, Mendel crossed true- breeding plants that had two distinct and contrasting traitsfor example, purple or white flowers. What is meant by true breeding? Mendel cross -fertilized his plants by hand. Why is it important to control which plants would serve as the parents?

For each monohybrid cross, Mendel cross-fertilized true-breeding plants that were different in just one characterin this case, flower color. He then allowed the hybrids (the F1 generation) to self-fertilize.

Typical breeding experiment P generation (parental generation) F1 generation (first filial generation, the word filial from the Latin word for "son") are the hybrid offspring. Allowing these F1 hybrids to self- pollinate produces: F2 generation (second filial generation). It is the analysis of this that lead to an understanding of genetic crosses.

The F1 crossed produced the F2 generation and the lost trait appeared with predictable ratios. This led to the formulation of the current model of inheritance.

Mendel studies seven characteristics in the garden pea

: Statistics indicated a pattern.

Law of Dominance In the monohybrid cross (mating of two organisms that differ in only one character), one version disappeared. What happens when the F1s are crossed?

Alleles: alternative versions of a gene. The gene for a particular inherited character resides at a specific locus (position) on homologous chromosome. For each character, an organism inherits two alleles, one from each parent

How do alleles differ? Dominant - a term applied to the trait (allele) that is expressed irregardless of the second allele. Recessive - a term applied to a trait that is only expressed when the second allele is the same (e.g. short plants are homozygous for the recessive allele). Dominant allele Recessive allele

Probability and Punnett Squares Punnett square: diagram showing the probabilities of the possible outcomes of a genetic cross

Genotype versus phenotype. How does a genotype ratio differ from the phenotype ratio?

Testcross A testcross is designed to reveal whether an organism that displays the dominant phenotype is homozygous or heterozygous.

From the monohybrid crosses, Mendel derived 4 hypotheses.combined, we now refer to these as Mendels Principle of Segregation There are alternative forms of genes, now called alleles For each characteristic, each organism has two genes Gametes carry only one allele for each inherited characteristic Alleles can be dominant or recessive A A pair of homologous chromosomes, each in the unduplicated state (most often, one from a male parent and its partner from a female parent) B A gene locus (plural, loci), the location for a specific gene on a specific type of chromosome C A pair of alleles (each being one chemical form of a gene) at corresponding loci on a pair of homologous chromosomes D Three pairs of genes (at three loci on this pair of homologous chromosomes); same thing as three pairs of alleles

Basic Concepts of Heredity 1.Genes Humans have ~21,500 Chemical instructions for building proteins Locus: specific location on a chromosome 2.Diploid cells contain two copies of each gene on pairs of homologous chromosomes. 3.Allele: each version of a gene 4.Homozygous condition: identical alleles Heterozygous condition: different alleles 5.Dominant allele: Effect masks recessive allele paired with it

Basic Concepts of Heredity 6.Genetic representations Homozygous dominant (AA) Homozygous recessive (aa) Heterozygous (Aa) 7.Genotype: Inherited alleles Phenotype: Observable functional or physical traits

Genetic Tools: Testcrosses and Probability female gametes (n) (eggs) C c C c C C c cc c Cccc male gametes (n) (sperm) CcCc C Cc C CCCc c cc c Cccc F 2 phenotypes CCCc cc 3 dominant (CC, Cc, Cc) 1 recessive (cc) F 1 phenotype s Cc F 1 offspring: Cc C c F 1 offspring : C c C C CCCc c c cc alleles segregate c c Parent: homozygous dominant c c C C Cc CC C C Cc Parent: homozygous recessive

Mendels principles apply to the inheritance of many human traits Family Pedigrees Dominant Traits Recessive Traits FrecklesNo freckles Widows peakStraight hairline Free earlobeAttached earlobe

Pedigree analysis reveals Mendelian patterns in human inheritance In these family trees, squares symbolize males and circles represent females. A horizontal line connecting a male and female (--) indicates a mating, with offspring listed below in their order of birth, from left to right. Shaded symbols stand for individuals with the trait being traced.

A family pedigree Shows the history of a trait in a family Allows researchers to analyze human traits Dd Joshua Lambert Dd Abigail Linnell D_ John Eddy D_ Hepzibah Daggett D_ Abigail Lambert dd Jonathan Lambert Dd Elizabeth Eddy Dd ddDd dd FemaleMale Deaf Hearing

Genes can lead to inherited diseases A gene which doesnt function on an autosomal chromosome can lead to devastating diseases Autosomal chromosomes are 22 pairs of chromosomes which do not determine gender Such diseases can be caused by both a dominant or a recessive trait

Autosomal Recessive Disorders Tay-Sachs Disease: Jewish people in USA (E. Euro descent) Not apparent at birth 4 to 8 months Neurological impairment evident Gradually becomes blind and helpless Develops uncontrollable seizures/paralyzed Allele is on Chromosome 15 Lack of enzyme hexosaminidase A (Hex A) Lysosomes dont work, build up in brain From the wikimedia free licensed media file repository

Autosomal Recessive Disorders Cystic Fibrosis Most common in USA (Caucasian) 1 in 20 caucasians is a carrier Mucus in bronchial and pancreas thick/viscous Breathing and food digestion problems Allele is on chromosome 7 Cl ions can not pass through plasma membrane channels Cl ions pass water goes with it. No water, thick mucus Location of CFTR gene Human chromosome 7

Autosomal Recessive Disorders Phenylketonuria (PKU) Affects in in 5,000 newborns Most common nervous system disorder Allele is on chromosome 12 Lack the enzyme needed for the metabolism of the amino acid phenylalanine A build up of abnormal breakdown pathway Phenylketone Accumulates in urine. If diet is not checked, can lead to severe mental retardation From the wikimedia free licensed media file repository

Autosomal Dominant Disorders Neurofibromatosis Very common genetic disorder Tan spots on skin Later tumors develop some sufferers have large head and ear and eye tumors. Allele is on chromosome 17 Gene controls the production of a protein called neurofibromin This naturally stops cell growth From the wikimedia free licensed media file repository

Autosomal Dominant Disorders Huntington Disease Leads to degeneration of brain cells Severe muscle spasms and personality disorders Attacks in middle age Allele is on chromosome 4 Gene controls the production of a protein called huntington Too much AA glutamine. Changes size and shape of neurons From the wikimedia free licensed media file repository

DNA: A Double Helix Deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: Adenine (A) Guanine (G) Thymine (T) Cytosine (C) Forms a double helix Structure discovered by Watson and Crick DNA is built of four kinds of nucleotides.

DNA Replication Adenine (A) always base pairs with thymine (T) Guanine (G) always base pairs with Cytosine (C) ALL Down to HYDROGEN Bonding Requires steps: H bonds break as enzymes unwind molecule New nucleotides (always in nucleus) fit into place beside old strand in a process called Complementary Base Pairing.

DNA: A Double Helix adenine A thymine T base with a single-ring structure sugar (deoxyribose) guanine G cytosine C base with a double-ring structure base with a single-ring structure base with a double-ring structure

DNA: A Double Helix Nucleotides can line up in any order Specific nucleotides form base pairs, which are hydrogen molecules bonded together A and T G and C Chemical rules determine which nucleotide bases in DNA can pair up. one base pair p408

Passing on Genetic Instructions DNA replication Semiconservative replication Many enzymes and proteins involved in this process, e.g., DNA polymerases Hydrogen bonds between the strands are broken Strands unwind Each strand becomes the template for a new strand of DNA

Passing on Genetic Instructions A Parent DNA molecule; two complementary strands of base-paired nucleotides. B Replication begins; the two strands unwind and separate from each other at specific sites along the length of the DNA molecule. C Each old strand serves as a structural pattern (a template) for the addition of bases according to the base- pairing rule. D Bases positioned on each old strand are joined together into a new strand. Each half-old, half-new DNA molecule is just like the parent molecule.

Passing on Genetic Instructions Gene mutations Changes in the nucleotide sequence of genes Two common kinds of gene mutations Base-pair substitution An incorrect nucleotide is paired with an exposed base during DNA replication; may be repaired If not repaired, one amino acid might replace another during translation; e.g., sickle-cell anemia Deletion A base is lost

Passing on Genetic Instructions part of DNA mRNA transcribed from DNA Threonine ProlineGlutamate Lysine resulting amino acid sequence base substitution in DNA altered mRNA Threonine ProlineValineGlutamate Lysine altered amino acid sequence deletion in DNA altered amino acid sequence altered mRNA ThreonineProlineGlycineArginine

Figure 3.6a Mutations

Passing on Genetic Instructions Expansion mutation Nucleotide sequence is repeated many times Huntingtons disease Fragile X syndrome Transposable elements Bits of DNA can move from one location to another in same DNA molecule or in different one Neurofibromatosis Genetic disorder

DNA into RNA: The First Step in Making Proteins RNA Ribose sugar, a phosphate group, and one of four nitrogenous bases: Adenine (A) Guanine (G) Uracil (U) Cytosine (C) Single-stranded

DNA into RNA: The First Step in Making Proteins Transcription forms Ribosomal RNA (rRNA) Plus protein and it forms the ribosomes Messenger RNA (mRNA) Carries the code for proteins Transfer RNA (tRNA) Picks up a specific amino acid for the growing polypeptide chain mRNA is eventually translated into a protein

DNA into RNA: The First Step in Making Proteins Transcription Gene serves as a template for RNA synthesis Process occurs in the nucleus using RNA polymerases Begins at promoter region 5' capped end for protection and binding to the ribosome Joins nucleotides together until a termination sequence is reached Pre-mRNA: contains introns and exons Exons: sequences for the proteins In transcription, DNA is decoded into RNA

gene region RNA polymerase, the enzyme that catalyzes transcription A forming RNA transcript DNA template winding up DNA template unwinding B DNA into RNA: The First Step in Making Proteins

transcription site growing RNA transcript C D

DNA into RNA: The First Step in Making Proteins Each cell determines which genes are active or inactive Some genes switched on and off throughout a persons lifetime Some turned on only at certain times Some turned off permanently before birth Regulatory proteins Speed up or halt transcription May bind with noncoding DNA sequences and affect the transcription of a neighboring gene Gene transcription can be turned on or off.

Codons Three nucleotide bases on mRNA Sixty-four codons make up the genetic code Most amino acids have more than one codon Start codon AUG; establishes the reading frame for translation Stop codons: UAA, UAG, and UGA The Genetic Code

DNA mRNA codons mRNA amino acids ThreonineProlineGlutamate Lysine B

tRNA and rRNA Has a hook for the attachment of an amino acid Anticodon base pairs with the codon Sixty-four codons; fewer tRNAs, due to redundancy of the genetic code Example, amino acid proline codons: CCU, CCC, CCA, CCG anticodon amino acid attachment site trp

tRNA and rRNA Two subunits are built in the nucleus from rRNA and proteins Shipped to the cytoplasm Combine into ribosomes during translation rRNAs are ribosome building blocks. tunnel small ribosome subunit large ribosome subunit assembled ribosome +

The Three Stages of Translation Initiation Initiator tRNA with AUG attached binds to mRNA codon AUG binds with the small ribosome subunit Large ribosome subunit binds to form the initiation complex Elongation Peptide bonds form between incoming amino acids Termination Stop codon; detachment of the new polypeptide

start codon (AUG) initiator tRNA first amino acid of polypeptide peptide bond 1 2 Ribosome subunits and an initiator tRNA converge on an mRNA. A second tRNA binds to the second codon. A peptide bond forms between the first two amino acids. The Three Stages of Translation

The first tRNA is released and the ribosome moves to the next codon. A third tRNA binds to the third codon. A peptide bond forms between the second and third amino acids. The second tRNA is released and the ribosome moves to the next codon. A fourth tRNA binds the fourth codon. A peptide bond forms between the third and fourth amino acids. The process repeats until the ribosome encounters a stop codon in the mRNA. 3 5 6 4

The Three Stages of Translation Polysomes Cluster of ribosomes all translating the same mRNA at the same time Where do the new polypeptide chains go? Some stay in the cytoplasm Others modified in the ER to be sent out of the cell polysomes

The Three Stages of Translation polysomes ribosome subunits tRNA Convergence of RNAs mRNA polypeptide Translation A

Human Variation With origins in Africa, modern man has spread around the globe. In doing so, modern man adapted to the surroundings.

Human Variation Arms and legs are longer and thinner in warm areas of the planet shorter and thicker in cold regions. Conserves heat in cold regions by reducing surface area Skin pigmentation is darker the nearer the equator to protect the skin from UV.

The additive effects of two or more genes on a single phenotype Visual Summary 9.5 Multiple genes Polygenic inheritance Single trait (e.g., skin color) Polygenic Inheritance

Human Variation There is a gradient of melanosome size and number in dark, intermediate, and light skin; in addition, melanosomes of dark skin are more widely dispersed. This diagram is based on one published by Sturm et al. (1998) and summarizes data from Szabo et al. (1969), Toda et al. (1972), and Konrad and Wolff (1973) based on individuals whose recent ancestors were from Africa, Asia, or Europe. PLoS Biology | http://biology.plosjournals.org

Human Variation A traditional skin color map by based on geographical location on a global scale. Taken from: PLoS Biology | http://biology.plosjournals.org

Three genes inherited separately The dark-skin allele for each gene (A, B, and C) contributes one unit of darkness to the phenotype and is incompletely dominant to the other alleles (a, b, and c). An AABBCC person would have very dark skin An aabbcc person would have very light skin Figure 9.22 aabbcc (very light) AABBCC (very dark) AaBbCc Eggs Sperm Polygenic Inheritance

Ice age Europe (18,000 years ago) Glacial ice 2km thick covers much of Northern Europe and the Alps. Sea levels are approx. 125m lower than today and the coastline differs slightly from the present day. Human populations that began their migration from Africa 60,000 years earlier were stopped by the ice.

Ice age Europe (18,000 years ago) Due to the cold and the need for food, the populations of the day waited the ice age out in the three locations shown on the map. These were the Iberian Peninsula, the Balkans and the Ukraine.

After the Ice age 12,000 years ago 12,000 years ago, the ice retreated and the land has become much more supportive to life. The three groups of humans had taken refuge for so long their DNA had naturally picked up mutations These three major population groups account for approx 80% of Europe's present-day population

Peoples from Africa that had moved to the Middle East developed the new technology of agriculture and began moving back into Europe. This was the last migration of human population into Europe. Body shape and skin pigmentation all changed due to environmental pressure on the genomes of these separate populations Finally, from 8,000 years ago

The concept of racism Racism has many meanings: All of them come down to the belief that some group of people are better than others. In most cases, the motivation to conquer a region comes first, the racist ideology comes later Came about because people thought that a different genetic trait was inferior to one(s) they processed.

The concept of racism They also believed that their group identity was inherited and could not be changed A view which has no basis in genetics In the 1940s the Nazis exterminated 11 million Jews, gypsies and other groups But not before theses groups were declared inferior. Most people now regard racism as unethical Denies basic human rights, results in crime and human conflicts.

Central High School in Little Rock, Ark. 1957. Elizabeth Eckford : Used with permission from the media file repository of USHistory.com

Systemic Power and Race P 3 = power X Power X Power Power 1 = Power over people of color Power 2 = Power which gives and preserves privilege and advantages for white people Power 3 = Power which socializes all of us into the racial rules Racisms ultimate power to control and racialize all of us

The concept of racism Human populations have always been variable. adapt and change under selective pressure Skin pigmentation is determined by a selective environmental pressure due to the total amount of sunlight a population exists with. Taught hatred for different populations of people

Final thought

The end! Any Questions?

human biology (biol 104) talk twelve: genetics chapters 19, 20, and 21

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inherited traits

inheritance slide

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