USF PCB 3063 Exam 2 Questions and Answers Fully Solved Latest Update 2025-2026
What is Epistasis? - Answers Masking or alteration of the expression of alleles of one gene by an allelic
combination of another.
Modifies the normal phenotypic ratio of a dihybrid cross (9:3:3:1)
What is the phenotypic ratio of a normal dihybrid cross? - Answers 9:3:3:1
What are the types of epistasis? - Answers Recessive, Dominant, Complementation, Duplicate Gene
Action, Suppression
Recessive Epistasis (Give expected ratio, example, gene sequence) - Answers 9:3:4 ratio.
Example: Coat color in mice
White Precursor--Gene A--> Black --Gene B--> Agouthi
Dominant Epistasis (Give expected ratio, example, gene sequence) - Answers 12:3:1
Example: Color of Summer Squash
White Precursor-Gene A (STOP)->Green--Gene B--> Yellow
Complementation Epistasis (Give expected ratio, example, gene sequence) - Answers 9:7
Example: Flower Color of Pea Plants
White Precursor-Gene A--> White Interm.--Gene B-> Purple
Duplicate Gene Action (Give expected ratio, example, gene sequence) - Answers 15:1
Example: Fruit Shape in Capsella Bursa
Narrow--Gene A OR Gene B---> Heart
Suppression (Give expected ratio, example, gene sequence) - Answers 13:3
Example: Feather Color in Chicken
C=Colored c=white I=Inhibitor i= uninhibitor
White--Gene C AND Gene i ---> Colored
Does Epistasis Violate Mendelian Law? - Answers NO. Principles of Segregation and Independent
Assortment are NOT violated
, How do we know that a phenotype is Dihybrid (Controlled by two genes)? - Answers When Phenotypic
Ratios are expressed in 16ths, 2 gene pairs are controlling phenotype
What is Sex-Limited Inheritance? - Answers Expression of a specific phenotype is ABSOLUTELY LIMITED
by the sex of the invidiual
What is Sex-Influenced Inheritance? - Answers Expression of a specific phenotype is INFLUENCED by the
sex of the individual
Give an example of Sex-Limited Inheritance - Answers Tail and Neck Plumage in Fowl
H = Hen Feathering h= Cock Featherin
(HH, Hh, hh)--> Hen Feathering in FEMALES
(HH, Hh)--> Hen Feathering in MALES
(hh)--> Cock Feathering in MALES
Give an example of Sex-Influenced Inheritance - Answers Pattern Baldness in Humans
B = Bald B'= Non-Bald
(BB)--> Baldness in FEMALES
(BB', B'B') --> Non-Baldness in FEMALES
(BB, BB') --> Baldness in MALES
(B'B') --> Non-Baldness in MALES
Describe how Index Finger Length is an example of a Sex-Influenced Inheritance - Answers L is dominant
in FEMALES
L is recessive in MALES
Exposure to Testosterone in Utero-->Shorter Index Finger
Shorter Index Finger-->Higher rate of Physical Aggression in MALES
No correlation in Females
What is Quantitative Genetics? - Answers study of numerically described traits
-usually controlled by >1 gene
-significantly influence by environment
(e.g. height, metabolic rate, weight, duration of behavior)
What is Epistasis? - Answers Masking or alteration of the expression of alleles of one gene by an allelic
combination of another.
Modifies the normal phenotypic ratio of a dihybrid cross (9:3:3:1)
What is the phenotypic ratio of a normal dihybrid cross? - Answers 9:3:3:1
What are the types of epistasis? - Answers Recessive, Dominant, Complementation, Duplicate Gene
Action, Suppression
Recessive Epistasis (Give expected ratio, example, gene sequence) - Answers 9:3:4 ratio.
Example: Coat color in mice
White Precursor--Gene A--> Black --Gene B--> Agouthi
Dominant Epistasis (Give expected ratio, example, gene sequence) - Answers 12:3:1
Example: Color of Summer Squash
White Precursor-Gene A (STOP)->Green--Gene B--> Yellow
Complementation Epistasis (Give expected ratio, example, gene sequence) - Answers 9:7
Example: Flower Color of Pea Plants
White Precursor-Gene A--> White Interm.--Gene B-> Purple
Duplicate Gene Action (Give expected ratio, example, gene sequence) - Answers 15:1
Example: Fruit Shape in Capsella Bursa
Narrow--Gene A OR Gene B---> Heart
Suppression (Give expected ratio, example, gene sequence) - Answers 13:3
Example: Feather Color in Chicken
C=Colored c=white I=Inhibitor i= uninhibitor
White--Gene C AND Gene i ---> Colored
Does Epistasis Violate Mendelian Law? - Answers NO. Principles of Segregation and Independent
Assortment are NOT violated
, How do we know that a phenotype is Dihybrid (Controlled by two genes)? - Answers When Phenotypic
Ratios are expressed in 16ths, 2 gene pairs are controlling phenotype
What is Sex-Limited Inheritance? - Answers Expression of a specific phenotype is ABSOLUTELY LIMITED
by the sex of the invidiual
What is Sex-Influenced Inheritance? - Answers Expression of a specific phenotype is INFLUENCED by the
sex of the individual
Give an example of Sex-Limited Inheritance - Answers Tail and Neck Plumage in Fowl
H = Hen Feathering h= Cock Featherin
(HH, Hh, hh)--> Hen Feathering in FEMALES
(HH, Hh)--> Hen Feathering in MALES
(hh)--> Cock Feathering in MALES
Give an example of Sex-Influenced Inheritance - Answers Pattern Baldness in Humans
B = Bald B'= Non-Bald
(BB)--> Baldness in FEMALES
(BB', B'B') --> Non-Baldness in FEMALES
(BB, BB') --> Baldness in MALES
(B'B') --> Non-Baldness in MALES
Describe how Index Finger Length is an example of a Sex-Influenced Inheritance - Answers L is dominant
in FEMALES
L is recessive in MALES
Exposure to Testosterone in Utero-->Shorter Index Finger
Shorter Index Finger-->Higher rate of Physical Aggression in MALES
No correlation in Females
What is Quantitative Genetics? - Answers study of numerically described traits
-usually controlled by >1 gene
-significantly influence by environment
(e.g. height, metabolic rate, weight, duration of behavior)
