Chapter 3: Extensions to Mendel’s Laws Learning Objectives

Question 1

o Conclude from the results of crosses whether a single gene or multiple genes control a trait

Answer 1

 F2 phenotypic ratio for dihybrid crosses = 9:3:3:1

Question 2

o Infer from the results of crosses the existence of interactions between alleles of different genes including: complementation, epistasis, and redundancy

Answer 2

	F2 Phenotypic Ratios:
•	Complementary: 9:7
•	Recessive Epistasis: 9:3:4
•	Dominant Epistasis 1: 12:3:1
•	Dominant Epistasis II: 13:3
•	Redundancy: 15:1

Question 3

o Predict from the results of crosses whether a gene is polymorphic or monomorphic in a population

Answer 3

 Depends on dominance relations for each affected trait

Question 4

o Explain how continuous traits, like human height and skin color, are controlled by multiple alleles of multiple genes

Answer 4

 Continuous trait: gene interaction with each other and environment produces phenotypic variation
 A continuous trait can have any value of expressions between two extremes because of a combination of genetics and environment

Question 5

o Recognize when a given phenotype is different individuals does not correspond to the same phenotype

Answer 5

 In incomplete penetrance, a phenotype is expressed in fewer than 100% of individuals having same genotype
 In variable expressivity, a phenotype is expressed at different levels among individuals with same genotype

Question 6

o Categorize allele interactions as completely dominant, incompletely dominant, or codominant

Answer 6

 Complete: hybrids resemble one of two pure-breeding parents
 Incomplete: hybrid resembles neither parent; phenotype is intermediate between both parents
 Codominant: hybrid shows trait from both pure-breeding parents

Question 7

o Recognize progeny ratios that imply the existence of recessive lethal alleles

Answer 7

 2:1 ratio indicates recessive lethal (instead of 3:1)