Lecture 10

Question 1

Epistasis

Answer 1

an allele at one gene locus interacts in such a way that it masks the phenotypic expression of the alleles of another gene locus

Question 2

Recessive epistasis

Answer 2

the presence of the aa genotype masks the expression of the other two phenotypes
Ratio is 9:3:4

Question 3

Dominant epistasis

Answer 3

An inhibitory locus with alleles - only one copy of the dominant needed to mask
12:3:1

Question 4

Other ratios for gene interaction

Answer 4

9: 7 (needs two caps on both)
9: 6:1 (Both caps:one or the other caps: no caps)
13: 3 (dominant epistasis –>need rec on one and one of the caps)
15: 1 (one or both are caps: no caps)

Question 5

Autosomal Linkage

Answer 5

Don’t assort independently, use test cross.

If the the ratio is not (sig diff) 1:1:1:1 it’s linked!

Question 6

cis arrangement

Answer 6

ab

= AB are on the same chromosome and ab are on the other

Question 7

trans arragement

Answer 7

aB

• Ab are on one together and aB are on the other

Question 8

Crossing over and exchange

Answer 8

During meiosis, crossing over (chiasma) occurs

exchange or recombination of maternal and paternal chromatids occurs

Question 9

Map distance

Answer 9

Relative distances between gene loci on the same chromosome are measured by recombination frequency. 1 cM = 1% recombination
Map distance = number of recombinant offspring over the total number of offspring times 100
50 or more map unit rule! 50%