Transcript Unit 2 - 5.7 Multi-trait Inheritance.pptx

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
YR
yr
YyRr
YyRr
yr
YyRr
YyRr
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