Exam 3 Flashcards
Causes of GEI
- 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.
- The animals’ adaptation to a particular environment determines how much of their genetic potential can be achieved under the stresses of that environment.
Transmitting ability
(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.
selection response
the change in the average of a character due to selection
selection differential
the average amount that selected animals differ from the average of the group from which they were selected
heritability
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).
annual selection reponse
the change per year in the average of a character, due to selection
generation interval
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
possible change value of epd
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
phenotypic correlation
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
genetic correlation
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
causes of genetic correlation- pleiotropy
- 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
causes of genetic correlation- linkage
(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
causes of genetic correlation- gei
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.
correlated response to selection
the change in the average of a character due to the selection for another correlated character
quantitatively inherited characters
differences among animals for quantitatively inherited characters are due to
1. differences in genotype at many loci 2. environmental influences
milk epd
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.
total maternal epd
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)
robertsonian translocation
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).
callipyge
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
HH in cattle
bulls- polled
cows- polled
Hh in cattle
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
hh in cattle
bulls- horned
cows- horned
horns are typically larger at the base in bulls than in cows, but not necessarily longer
knobs in sheep
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
scurs in sheep
scurs are knobs with small horn like coverings; easily distinguishable from horns, because the scurs are small and irregular in shape
GEI
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
