CHROMOSOMES

GENES

A Credit card has a chip and is in a wallet.

Wallet Cell

Credit card (inside) Nucleus of a cell (inside)

Chip (carrying information)

Chromosomes (carrying information)

Sex cells (gametes)

FERTILISATION

Hypertrichosis

Progeria

MUTATIONS

Why do offspring get half their genes from each parent?

Answer•Because Sex Cells contain half the chromosomes

and they fuse to form a new set of chromosomes.

Why are brothers and sisters similar?

Answer•Because they might have some genes in

common.

How do identical twins form?

Answer• If the early embryo splits appart.

These twins are ‘genetically identical’. What do you think this means?

Answer•They have the same genetic information.

How do you think the differences between identical twins are caused?

Answer• Identical twins have differences in their

environment; this can cause differences between them even before being born. (fingerprints,

weight, etc)

Focus on Chromosomes

Chromosomes

AllelesRecessive - Dominant

Genotypes (Alleles) and phenotypes

Punnett Square

Eyes color of an offspring from parents who have different eye color.

• Father has blue eyes (bb)• Mother has Brown eyes – one recessive blue(Bb)

Possible gametes b b

B Bb Bbb bb bb

Genotype Phenotype (trait) % Bb brown eyes 25% bb blue eyes 25% Bb brown eyes 25% bb blue eyes 25%

6a What percentage of this couple’s children are likely to have Brown eyes?• According to the chart, 50% of the couple’s children will have Brown

eyes.

Possible gametes b b

B Bb Bbb bb bb

6b. Redraw diagram for a man with eye color alleles Bb and a woman with alleles BB. What percentage of this couple’s children are likely to have brown eyes?• According to the chart, 100% of the couple’s children

will have brown eyes.

Possible gametes B b

B BB BbB BB Bb

6c. Redraw diagrams for a man and a woman who both have alleles Bb. What percentage of this couple’s children are likely to have Brown eyes?

• According to the chart, 75% of the couple’s children will have brown eyes.

Possible gametes B b

B BB Bbb Bb bb

Cystic fibrosis is caused by a recessive allele. Two parents are both carriers for the disease and both have alleles Cc (C is the normal allele and c is the allele that causes the disease). What percentage of children would the be likely to have cystic fibrosis?• According to the chart, 25% of the couple’s

children will have cystic fibrosis.

Possible gametes C c

C CC Ccc Cc cc

• The tall trait is dominant (T) in pea plants, while short pea plants is a recessive trait (tt). Use a punnett square and probability table to determine the possible genotypes and phenotypes of offspring from a cross between a tall male pea plant (TT) and a short female pea plant (tt).

Punnett Square

Genotype Phenotype (trait)

%

Benefits of Punnett Square• Predict possible genetic diseases• Combine genes to have new varieties of plants and animal breeds • Can you list another possible benefit?

Whiskers in sealsIn seals, the gene for the length of the whiskers has two alleles. The dominant allele (W) codes long whiskers & the recessive allele (w) codes for short whiskers. a) What percentage of offspring would be expected to have short whiskers from the cross of two long-whiskered seals, one of them with Genotype Ww and the other with WW? b) If one parent seal is a non pure long-whiskered

(Ww) and the other is short-whiskered, what percent of offspring would have short whiskers?

Blue eyesIn humans, brown eyes (B) are dominant over blue (b). A brown-eyed man marries a blue- eyed woman and they have three children, two of whom are brown-eyed and one of whom is blue-eyed. Draw a Punnett square that illustrates this marriage.a) What is the man’s gentoype? b) What are the genotypes of the children?