Do now!Can you stick the sheets in please?

In the right order!

Tests!

• Check Mr Porter has added your marks up correctly

• Calculate the percentage mark for each test by multiplying the out of 25 mark by 4

• Fill in the “Science assessment tracker” on the front of your folder

• In your books write a target for the next unit.

Last lesson

• Understand the difference between species, breeds, varieties

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

Today’s lesson

• How genetic information is transferred

• How genes work

How is genetic information transferred?

I dunno. I’m a

sheep.

How is genetic information transferred?

Sex!

Let’s start at the very beginning

Sexual reproduction

• Requires two parents, a male and female.

Sexual reproduction

• Both have sex organs

Sexual reproduction

• The sex organs make sex cells (gametes)

Sexual reproduction

• In male animals the sex cells are called sperm, made in sex organs called testes (testis is singular)

I can stay alive in the vagina for up to 3 days waiting for

an egg to be released.

Sexual reproduction

• In female animals the sex cells are called eggs, made in sex organs called ovaries.

An egg is released from the ovaries about every 28 days. This is

called ovulation.

Sexual reproduction

• During sexual reproduction the sperm and egg join together (fertilisation)

I will die after about 2 days if not

fertilised.

External fertilisation

In some animals fertilisation takes place outside the body.

External fertilisation

In some animals fertilisation takes place outside the body.

Some sperm may get washed away so I

produce a lot of eggs so at least some get

fertilised.

External fertilisation

In some animals fertilisation takes place outside the body.

I don’t look after my eggs either so many get killed before they have chance to develop into

fish.

Mendelian genetics

Mendelian genetics

Gregor Mendel (1822 – 1884) was a monk who was very interested in plant breeding.

Peas

Mendel took one pea plant that always produced wrinkled peas and used this plant to pollinate another pea plant that always produced smooth peas

Peas

He found that the plants produced (called the F1 generation) all had smooth peas.

He called this (smooth) the dominant characteristic

F1 Generation

Peas

When two plants of the first generation (F1) were cross-pollinated, 75% of the offspring (F2 plants) had smooth peas and 25% had wrinkled peas.

He said the wrinkled peas had the recessive characteristic.

F1 Generation

F2 Generation

Genes

We can now explain Mendel’s results using what we know about genes.

A gene can be defined as a region of DNA that controls a hereditary characteristic.

Chromosomes, genes & DNA

Chromosomes are X-shaped objects found in the nucleus of most cells. They consist of long strands of a substance called deoxyribonucleic acid, or DNA for short. A section of DNA that has the genetic code for making a particular protein is called a gene.

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!

Let’s try some questions!