Tetrad Analysis and Gene Interaction

Question 1

MI Type segregation pattern

Answer 1

4:4 segregation and no crossing over

Question 2

MII Type segregation pattern

Answer 2

2:2:2:2 segregation; both alleles are present in both halves of the ascus; crossing over

Question 3

What are the 4 different MII segregation patterns?

Answer 3

2:2:2:2 (A a A a), 2:2:2:2 (a A a A), 2:4:2 (A a a A), 2:4:2 (a A A a)

Question 4

Independent Assortment

Answer 4

results in 50% parental ditype and 50% non parental ditype

Question 5

What is the map distance b/w centromere and locus limited to?

Answer 5

33 m.u.

Question 6

Complete linkage

Answer 6

results in only parental ditype

Question 7

Parental ditype

Answer 7

all 4 parental; no crossing over; w/ MII segregation there is crossover between locus and centromere, but no crossing over b/w loci

Question 8

Non parental ditype

Answer 8

all 4 recombinant

Question 9

Tetratype

Answer 9

1/2 recombinant and 1/2 parental; single crossing over of 2 chromatids or double crossing over involving three chromatids

Question 10

Distance formula (according to discussion material)

Answer 10

(1/2 (TT) + NPD)/total x 100

Question 11

Penetrance

Answer 11

frequency w/ which a genotype expresses a phenotype; a trait has low penetrance if few individuals w/ the gene express it

Question 12

Expressivity

Answer 12

degree to which a trait is expressed in individuals having the gene; ex: severity of genetic diseases such as cleft palate in humans

Question 13

Sex-limited traits

Answer 13

expression of certain traits is only in one of the sexes; traits encoded by genes on autosomes but character is expressed in one sex; ex: milk production in cows

Question 14

Multiple Alleles

Answer 14

blood groups (A B O groups); IA, IB, i

Question 15

Incomplete dominance

Answer 15

presence of intermediate phenotype (heterozygous is different from homozygous dominant); ex: red, pink, and white flowers