USF PCB 3063 EXAM 2 QUESTIONS & ANSWERS
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)
-can be described using -frequency distrib. or -normal distrib.
What is a continuous trait? - Answers :Do not fall into discrete categories
What is a meristic trait? - Answers :A continuous trait expressed in whole numbers
Example: How many bristles on a fly's sex comb?
What is Discontinuous trait? - Answers :Traits that fall into 2+ discrete categories
Example: Red-eyed or White-eyed
What is Polygenic Inheritance? - Answers :The transmission of traits governed by 2+
genes
Gene 1
Gene 2 > ---> phenotype
Gene 3
Quantitative Trait Locus (QTL) - Answers :The location on chromosome that affects
outcome of quantitative trait via gene mapping. QTLs may contain +1 gene
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)
-can be described using -frequency distrib. or -normal distrib.
What is a continuous trait? - Answers :Do not fall into discrete categories
What is a meristic trait? - Answers :A continuous trait expressed in whole numbers
Example: How many bristles on a fly's sex comb?
What is Discontinuous trait? - Answers :Traits that fall into 2+ discrete categories
Example: Red-eyed or White-eyed
What is Polygenic Inheritance? - Answers :The transmission of traits governed by 2+
genes
Gene 1
Gene 2 > ---> phenotype
Gene 3
Quantitative Trait Locus (QTL) - Answers :The location on chromosome that affects
outcome of quantitative trait via gene mapping. QTLs may contain +1 gene
