12.3

Question 1

Interpret data from testcrosses to infer unknown genotypes.

Answer 1

o Cross the individual with an unknown genotype (e.g. P_) with a homozygous recessive individual
o All offspring will be dominant if the unknown genotype was homozygous dominant
o If unknown genotype is heterozygous, then some of offspring will be homozygous recessive

Question 2

What is polygenic inheritance

Answer 2

 Occurs when multiple genes are involved in controlling the phenotype of a trait
 The phenotype is an accumulation of contributions by multiple genes
 These traits show continuous variation and are referred to as quantitative traits

Question 3

What is pleiotropy

Answer 3

 Refers to an allele which has a >1 effect on phenotype
* Effects are difficult to predict because a gene that affects 1 trait often performs other, unknown functions
 Can be seen in human diseases such as cystic fibrosis or sickle cell anemia
* Multiple symptoms can be traced back to one defective allele

Question 4

Explain how ABO blood type is an example of multiple alleles

Answer 4

 A blood type can have a genotype of IAIA or IAi
 B blood type can have a genotype of IBIB or IBi

Question 5

Explain how ABO blood type is an example of codominance

Answer 5

 AB blood type has a genotype of IAIB
 IAIB individuals express both the A carbohydrate and the B carbohydrate

Question 6

Incomplete dominance

Answer 6

 Heterozygote is intermediate in phenotype between the 2 homozygotes
* Crossing black cats to white cats produces grey F1

Question 7

Codominance

Answer 7

 Heterozygote shows some aspect of the phenotypes of both homozygotes
* Crossing black cats to white cats produces spotted F1

Question 8

Provide examples of environmental influence on gene expression

Answer 8

o Coat color in Himalayan rabbits and Siamese cat
 Allele produces an enzyme that allows pigment production only at temperatures below 33ºC

Question 9

Discuss how epistasis changes Mendelian ratios

Answer 9

o Gene at one locus alters the phenotypic expression of another gene at a second locus
 Example
* When one gene depends on another to produce its phenotype
* B=black and b=brown but E=deposits pigment while e=does not deposit pigment so when you have B_ee, pigment is not deposited and you get a yellow dog