Multi-trait Inheritance Biology 11: Section 5.7
Learning Goals Students will complete dihybrid crosses Students will use product law to predict offspring traits Students will know the difference between discontinuous and continuous variation
Law of Independent Assortment If genes are located on separate chromosomes they are inherited independently of one another This happens because alleles assort themselves independently (recall meiosis) i.e. genes that control pea shape are inherited independently of those that control pea colour Can use a Punnett Square to predict genotypes and phenotypes for multiple traits
Punnett Squares Can be used to show inheritance of two traits Pea genotypes: Parent 1 – YYRR, Parent 2 - yyrr Gametes of Parent 1 – YR, Parent 2 - yr YR yrYyRr yrYyRr
To Do: Review Tutorial 1 on pages 211 and 212 Complete practice questions on page 212 (we’ll take these up)
Probability Punnett Squares can be used to determine the probability of inheriting a certain trait Probability = # ways an event can occur / total # possible events The probability of each event is not affected by results of other events
Product Law The probability of two random events both occurring the product of the individual probabilities of each event i.e. A couple’s chance of having a girls is 50% (½) for the first birth Change of the second birth being a girls is also 50% (½) The chance of having 2 girls is ½ x ½ = ¼ or 25% Probability predicted by the Product Law is the same as that predicted by the Punnett Square
Example 2 Determine the phenotypes and genotypes of the offspring when the parents are both heterozygous for both traits
Discontinuous Variation Genes that control two or more characteristics do not interact with each other i.e. pea plants: tall or short, green or yellow
Continuous Variation Product of one gene affects the product of another gene i.e. skin colour, height, hair colour, eye colour Traits display incomplete dominance
To Do: Read section 5.7 Complete questions 2-8 on page 214 Define additive allele