Genetic inheritance

1. How genes are inherited? Aims: Why offspring have features inherited from both parents. Understand how to carry out genetic crosses.

2. How Genes are inherited. Brothers and sisters have the same parents but still not look the same. They don’t receive the same genes from their parents. Each parents has two versions of the allele, we cannot be sure which version they are going to pass on. We can draw diagrams to work out the different combinations of alleles that a child could inherit from the parents. All the sperm and the ovum have a different combination of alleles, on all the chromosomes.

3. Twins. There are two types of twins, these are: Identical Non-identical Explain in detail, the difference between the genetic make-up in these twins. What other factors might affect the way identical twins look like, give examples.

4. Predicting Inheritance. (Easy) Practice writing out examples of monohybrid cross diagrams. Try these: (a) genotype TT x genotype tt (b) genotype Rr x genotype Rr (c) genotype aa x genotype Aa Practice working out ratios. Try this: When purebred black-coated Aberdeen Angus cattle (BB) are crossed with purebred red-coated Redpoll cattle (bb) - what is the ratio of black coats to red coats among their offspring?

5. Questions – The best bit! 1. Using the symbols W for normal wings, and w for vestigial (short) wings, write down the following: a) the genotype of a fly which is heterozygous for this characteristic. b) The possible genotype of its gametes. c) The possible genotype of the offspring when two heterozygous flies mate. 2. Using a Punnet square, work out what kind of offspring would be produced if the heterozygous fly mated with one which was homozygous for normal wings. 3. In humans, the allele for red hair , b, is recessive to the allele for brown hair, B. A man and his wife both have brown hair. They have five children, three of whom have red hair, while two have brown hair. Explain how this may happen.

6. Predicting Inheritance. (Hard) Complete the following genetic cross to show the probability of tall pea plants to short pea plants, when two tall pea plants are crossed. Tt Tt a) What is the ratio of tall to short offspring? b) One of the tall offspring is crossed with another short offspring. What would be the genotype of the parent if all the offspring are tall plants? c) Draw a diagram to show the genetic cross for b). A mother who has bent little fingers has three children. Two of them have straight little fingers and one child has bent little fingers. Use a diagram to explain how the children have inherited the shape of their fingers. The allele for bent fingers is (P) is dominant to the allele for straight fingers (p). a) What is the probability of the couples next child having bent fingers. b) Is it possible to predict which of the grandparents had bent fingers? c) Explain the difference of the P allele being dominant over the p allele.