Exam 3

Question 1

Causes of GEI

Answer 1

1. Animals of any genetic group have a particular average level of genetic potential for a character and a particular degree of adaptation to a particular environment.
2. The animals’ adaptation to a particular environment determines how much of their genetic potential can be achieved under the stresses of that environment.

Question 2

Transmitting ability

Answer 2

(a measure of genotype for a particular quantitatively inherited character) is the average amount that a large number (infinity) of this animal’s progeny would differ from the progeny of an animal with transmitting ability of zero.

Question 3

selection response

Answer 3

the change in the average of a character due to selection

Question 4

selection differential

Answer 4

the average amount that selected animals differ from the average of the group from which they were selected

Question 5

heritability

Answer 5

a population parameter that is a measure of how well, on the average, that animals’ performance levels (phenotypes) indicate their transmitting ability for the character of concern. (Heritability is a population parameter; individual animals do not have their own individual heritability values).

Question 6

annual selection reponse

Answer 6

the change per year in the average of a character, due to selection

Question 7

generation interval

Answer 7

the average amount of time between generations (can usually be estimated as the average age of the animals when their offspring are born)
always longer than the average age at which animals produce their first offspring
always shorter than the average age at which breeding animals leave the herd
Beef cattle- 5 years
dairy cattle- 3.5 years
horses- 9 years
sheep and goat- 3.5 years
hogs- 2.5 years

Question 8

possible change value of epd

Answer 8

measure of precision of an EPD that defines an interval where there is a .68 probability that this animal’s true transmitting ability is between one PCV below the EPD and one PCV above the EPD

Question 9

phenotypic correlation

Answer 9

phenotypic correlation between two characters, x and y, is a measure of both the degree (low to high) and direction (+ or -) of the correspondence between the phenotypes of the two characters

Question 10

genetic correlation

Answer 10

genetic correlation between two characters is a measure of both the degree (high to low) and direction (+ to -) of the correspondence between the transmitting abilities of the two characters (are almost always numerically larger than phenotypic correlations)
pleiotropy, linkage, or gei

Question 11

causes of genetic correlation- pleiotropy

Answer 11

1. pleiotrophy (major effect) - among the many loci that effect the performance for one character, some (or all of them) may also affect the phenotype of the other character.
   3 types
   a. the two traits mat be (at least partially) measures of the same thing
   b. the phenotype for one of the traits may affect the phenotype expression of the other trait
   c. the product of a gene may be involved in a biochemical pathway that affects both characters

Question 12

causes of genetic correlation- linkage

Answer 12

(minor and temporary) - where among the many loci that affect one of the characters, some may be on the same chromosome and close to loci that affect the other character

Question 13

causes of genetic correlation- gei

Answer 13

where in one environment, animals can meet their nutritional requirements, but, in another environment, increased nutritional requirements for one trait may limit performance of another trait.

Question 14

correlated response to selection

Answer 14

the change in the average of a character due to the selection for another correlated character

Question 15

quantitatively inherited characters

Answer 15

differences among animals for quantitatively inherited characters are due to

1. differences in genotype at many loci
2. environmental influences

Question 16

milk epd

Answer 16

an animal’s milk EPD is its EPD for maternal effects on weaning weight. It is the average amount that its daughters’ progeny are expected (based on the available information) to differ in weaning weight from the progeny of the daughters of an animal whose milk EPD is zero, due to maternal effects.

Question 17

total maternal epd

Answer 17

an animal’s total maternal epd is the average amount that its daughters’ progeny are expected (based on the available information) to differ in weaning weight from the progeny of the daughters of an animal whose total maternal EPD is zero (due to both maternal and direct effects)

Question 18

robertsonian translocation

Answer 18

a common and significant type of chromosome rearrangement that is formed by fusion of the whole long arms of two acrocentric chromosomes (chromosomes with the centromere near the very end).

Question 19

callipyge

Answer 19

like double muscling in cattle- muscular hypertrophy-
its expressed only if the callipyge genes comes from the sire and only from the sire. that is, for the trait to be expressed, the lamb must be heterozygous and receive the callipyge gene from the sire

Question 20

HH in cattle

Answer 20

bulls- polled

cows- polled

Question 21

Hh in cattle

Answer 21

bulls- polled or scurred
cows- polled or scurred

scurs are more common in bulls than in cows, are more common in some breeds than others, and are typically larger in bulls than in cows

Question 22

hh in cattle

Answer 22

bulls- horned
cows- horned

horns are typically larger at the base in bulls than in cows, but not necessarily longer

Question 23

knobs in sheep

Answer 23

knobs are protrusions from the skull resembling horn cores, except that they are usually less than an inch in height and are covered with skin

Question 24

scurs in sheep

Answer 24

scurs are knobs with small horn like coverings; easily distinguishable from horns, because the scurs are small and irregular in shape

Question 25

GEI

Answer 25

There is a genotype-environment interaction (gei) when the difference in the average performance of animals in two different genetic groups is different in two different environments