Activity- Happy Families

• Mum and Dad are both heterozygous for the tongue rolling gene. They can both Roll their tongues.

• A tub with 10 blue (roller) and 10 red (non roller) beads represents each parent.

• Work in pairs to pick out at random one bead from each tub. Record the child as RR, RB, BB.

• Replace the beads after recording.• Record 12 children. How many rollers and non rollers

did you expect, and how many did you get?

Punnet square

1. Use a punnet square to find out how many children you expect to be tongue rollers in the family where the parents are both Rr (H……..ous)2. Now use a genetic diagram with punnet square to show the offspring of Rr X rr. Give the phenotype ratio of the children

Using test crosses to find genotype

Activity 2- Deepak’s guinea pigs

• Answer the questions on the A4 coloured work cards.

What are sex chromosomes?Humans cells contain one pair of sex chromosomes, which control gender.

Males have one X andone Y chromosome (XY).

Y chromosomes are very small and contain 78 genes, whereasX chromosomes are larger and contain a 900–1,200 genes.

Because females can only produce X gametes, it is the sperm that determine the sex of the offspring at fertilization.

X chromosome

Y chromosome

Females have two X chromosomes (XX).

Boy or girl?

Sex chromosomes

• Show with a punnet square why the chances of a boy or girl are the same.

• Just copy stage 4 of the “how is sex inherited” slide

The rest of the slides in this powerpoint are extension ideas!

• Sex linked genes• Incomplete dominance• Co-dominance• Multiple alleles

Extension/for interest(!)- genes on the X chromosome (sex linkage)

• Colour blindness is a recessive allele on the X chromosome.

• Males are much more likely to be colour blind than females.

• Boys get their colour blindness from their mother even if the father is colour blind.

• Girls with colour vision can be carriers• EXPLAIN ALL OF THE ABOVE WITH A GENETIC

CROSS AND PUNNET SQUARE

For example, when a red Mirabilis jalapa plant (also called the snapdragon or ‘Four o'clock flower’) is crossed with a white Mirabilis jalapa plant, all the offspring flowers are pink because both the red and white alleles are expressed.

What is incomplete dominance?Sometimes two different alleles are neither fully dominant or recessive to each other.

In heterozygous individuals, this creates a phenotype that is an intermediate mix of the other two. This is called incomplete dominance.

What is co-dominance?The human ABO blood group system is controlled by three alleles: A, B and o. A and B are dominant while o is recessive.

In heterozygous individuals who have both A and B alleles, both are fully expressed, creating an extra phenotype.

What is the pattern of inheritance of the ABO blood system?

This is called co-dominance.

Co-dominance in humans

Syllabus

• interpret genetic diagrams, including family trees; some disorders are inherited.

• Polydactyly – having extra fingers or toes – is caused by a dominant allele of a gene and can therefore be passed on by only one parent who has the disorder.

• Cystic fibrosis (a disorder of cell membranes) must be inherited from both parents. The parents may be carriers of the disorder without actually having the disorder themselves. It is caused by a recessive allele of a gene and can therefore be passed on by parents, neither of whom has the disorder.

• Embryos can be screened for the alleles that cause these and other genetic disorders