Read pages 6 to 9 and write 10 multiple choice questions (each with 4 possible answers) on the subject of species, breeds, varieties,

selective breeding and cross-breeding.

FINISH for HOMEWORK due next Friday 23rd October

We will also be having a genetics (8A) test that day.

Mr Porter apologises that he has not marked all your books (IB evening Wednesday night). He’ll collect them in again Monday and mark them Monday night.

Last lesson

• How genetic information is transferred

• How genes work

Genes

Our DNA contain two genes (one from our mother and one from our father) for each characteristic (eye colour, hair colour etc.)

Obviously the best looking

Alleles

Different genes for the same characteristic (e.g. eye colour) are called alleles.

For example, you all have two genes (alleles) for eye colour

Pron: “Al – eels”

Which colour eyes?

Which colour eyes?

Your eye colour depends on which genes you have. Lets look at the genes for brown and blue eyes.

The brown eye gene (B) is dominant and the blue eye gene (b)is recessive

Which colour eyes?

If you have the alleles for eye colour of Bb, you will have brown eyes (because the brown gene is dominant).

(heterozygous)

Which colour eyes?

If you have BB, you will also have brown eyes.

(homozygous)

Which colour eyes?

Only if you have bb will your eyes be blue (both genes are recessive)

(homozygous)

Which colour eyes?

Your combination of genes (BB, Bb or bb) is called your genotype.

The colour of eyes you actually have is called your phenotype

Cats don’t eat their own poo,

dogs do!

An example

Let’s imagine your mother has Bb genotype and your father also has Bb.

BbBb

An example

Half your mother’s eggs will have B genes and half b (eggs are gametes and only contain one of each pair of genes)

B b

eggs

An example

Half your father’s sperm will have the B gene and half the b gene too.

B b

Sperm!

Gene diagram (Punnett square)

We can look at the possible combinations on a gene diagram

Sperm with B

Sperm with b

Egg with B

Egg with b

Gene diagram (Punnett square)

Here are all the possible combinations for a fertilised egg

Sperm with B

Sperm with b

Egg with B

BB Bb

Egg with b

Bb bb

Gene diagram

This means that there is a 75% chance the baby will have brown eyes (BB or Bb) and only a 25% chance the baby will have blue eyes (bb)

Sperm with B

Sperm with b

Egg with B

BB Bb

Egg with b

Bb bb

BROWN

BROWN

BROWN

BLUE

phenotypegenotype

Pure breeding

If one parent has both dominant genes(BB), any baby will have to have brown eyes. We say the parent is pure breeding.

Sperm with B

Sperm with B

Egg with B

BB BB

Egg with b

Bb Bb

BROWN

BROWN

BROWN

BROWN

phenotype

WARNING!

WARNING!

This is a simplified explanation. In reality eye colour is a little more complex than this. Please do not go home and accuse your mother of sleeping with the cable guy if both your parents have blue eyes and you have green or brown!

Summary and word sheets

Let’s try some questions!