Revision Inheritance

DNA Although all humans are similar to each

other, we are also different in many ways

The nucleus of a cell contains a chemical called DNA – deoxyribose nucleic acid which controls which proteins the cell makes

Nobody in the world has the same DNA as you

Chromosomes DNA is coiled up into structures called

chromosomes. All of your body cells have the same

number of chromosomes

Task: How many pairs does each cell have? Where do these chromosomes come from?

Chromosomes Each chromosome contains many genes Each gene has coded information that

controls a particular characteristic Different genes code for different

characteristics of the body

Task: Name three inherited characteristics

1 – chromatid

2 - centromere

3 – short arm

4 – long arm

Task – draw and annotate the diagram to show your understanding of DNA and Genes

Chromosomes

Each chromosome is a very long molecule

of tightly coiled DNA.

The DNA moleculelooks like a

twisted ladder thisspiral shape is

called a DOUBLE HELIX

DNA molecules carry the code that controls what cells are made of and what they do. They are found inside the nucleus of every cell in the body

DNA The DNA molecule looks like a twisted

ladder

Support

Double Helix

Steps

Bases

The double helix ‘ladder’ of a DNA molecule is held together by ‘rungs’ made from pairs of chemicals called bases.

DNA Bases

There are four types of bases, and they are usually identified by their initials.

A

T

C

G

Base pairs hold the two strands of the DNA helix together.

It is the sequence of these bases along a DNA molecule code for different proteins. These proteins control the processes within the cell

DNA Bases

A T

C G

C G

A T

DNA stands for Deoxyribonucleic acid. DNA molecules are coiled up into structures called Chromosomes. Chromosomes are found in the Nucleus of every cell. They contain Bases called Adenine, thymine, cytosine and guanine. The bases pair up. Adenine pairs with Thymine. Cytosine pairs with Guanine. The bases code for Proteins. The code determines the sequence of amino acids. The role of the proteins is to control processes within the cell.

DNA

Chromosomes Chromosomes are found in pairs in the

nucleus of each cell in the body. A small section of DNA is called a gene. Genes are sections of DNA molecules. DNA contains information which codes for proteins. DNA molecules contain pairs of chemicals called bases. The sequence of bases determines what protein the cell makes. Chromosomes are coiled up sections of DNA. Proteins determine the cells function and characteristics

Finger prints Can you name the three different fingerprint

groups?

Whorl Arch Loop

Genetic profiling – why? The analysis of DNA produces a genetic

profile

Everyone's profile is slightly different Police scientists can identify the DNA left

behind at a crime scene It can also be used to identify the Father of

a child

A sample of cells is collected from blood, hair, semen and skin. The cells are broken up and the DNA is extracted. The DNA is cut up by enzymes so that it is left in small pieces and different sizes. A technique called gel electrophoresis separates the fragments. The DNA fragments are placed on a gel bed and an Electric current is passed through the gel. The segments move across the gel and with the smallest moving furthest. A pattern then develops which is The Genetic Profile.

Stages of Genetic Profiling .

Task – is Genetic Fingerprinting a Good Thing? DNA profiling can be used to help solve

crimes It can also identify health problems

Is this infringing on a person? What are the problems?

What do you think? – write an argument For and Against

Genetic Profiling – right or wrong?

Advantages

Show the similarities between two people

Help to solve crimes Determine paternity

Disadvantages

Identity theft wrong convictions Disclosure of

information Human rights/ethical

issues Who owns the sample? Does it get passed on? Does it get kept or

destroyed?

During sexual reproduction, an egg fuses with a sperm. The egg and sperm are called gametes and when they fuse the form a zygote. This process is called fertilisation. When the gametes are formed, the chromosome number is halved. This means that only half of the genes come from the mother and the other half come from the father. A human has 46 chromosomes: 23 from the mother and 23 from the father. During fertilisation, the chromosome number is restored.

Fertilisation

Sperm:

Tip of Head

Tail

Nucleus

Egg:

Nucleus

Jelly coat

Nucleus

Cytoplasm

How is sex determined? In human body cells, one of the pairs of

chromosomes XX, XY, carries the genes which determines sex.

These separate and combine randomly at fertilisation.

What chromosomes are male? XY What chromosome are female? XX

Punnett Square Are used to show the inheritance of sex

chromosomes

Can be used to determine features such as straight hair or curly hair

Allele The description of the genotype eg black hair Genotype Short for the first and second generation in a genetic cross PhenotypeTwo identical alleles DominantA variety of a gene RecessiveThe allele that shows the phenotype whenever it is present F1/F2 Two different alleles Homozygous/HomozygoteThe allele that is hidden whenever a dominant allele is present Heterozygous/Heterozygote The genetic make-up of an individual eg BB

KEYWORDS AND DEFINISIONS

Punnet Square

Practise Punnet Squares Draw punnet squares for the following;

Hair Colour – BB rr Eye colour – Bb Bb Height – Tt tt

Include the names of each stage and the ratio

Parental Phenotype – male/female

Parental genotype – xx/xy

Gametes – x x / x y

F1 genotype – xx, xx, xy, xy

F1 phenotype – male, male, female, female

How is sex determined?

What is a mutation? Genes do not remain the same forever

New genes are rare but do occur by mutation

A mutation is the change in the structure of a gene

This can occur naturally or can be caused by environmental factors

Some mutations do not result in harm however some do

Gregor Mendel One of the most famous scientists of all time

Experimented on “tall” and “dwarf” pea plants that were breeding

He crossed the plants and didn’t get the expected results

This was how he determined dominant and recessive genes

He also determined that most characteristics are controlled by more than one gene

Gregor Mendel At the time, no one took notice of Mendels

results – he did not publish them in a journal 1865 - He presented his results in his home

town of Bruun which was then published in a local paper

Mendels paper was rediscovered in 1900 and his experiments replicated

The structure of DNA and genes was not understood until 1950’s.

Resistance What is resistance?

Soya bean plants have a gene resistant to herbicides

The crops are sprayed with herbicides to kill the weeds but the plant remains unaffected

This results in an increased yield due to a competition for space and nutrients

GM? Plants that show resistance may be cut out

and transferred into another plant

1980 – the potato was modified to show resistance to bacterium in the soil

Therefore it has its own insecticide The gene for the poisons production was

transferred to potato plants which then made the plant resistant to insect pests

Herbicides Why would it benefit plants to be resistant

to herbicides? Weeds compete with crops Herbicides kills the weeds Less chemicals used What would be the problem? Herbicides kill plants too Resistant genes in plants may escape into

the environment – if herbicides cannot kill them, what can?

An argument both for and against the case of Genetic Modification

For

No chemicals Higher yield Tailor made More nutrition Higher income Save natural

resources

Against

Could get out of control

Reduce reliance form developing countries

Economic damage Ethical issues