genetics Flashcards
Heterosis
For any pair of breeds for any trait, the hybrid vigor is the average amount that the average of the F1’s exceeds the average of the two pure breeds
3 main advantages of cross-breeding over straight breeding
1) Heterosis
2) Blending desirable breed effects into a composite animal
3) Use of specialized sire and dam types.
2 main types of livestock production systems
Straight breeding
Crossbreeding
Straightbreeding systems
Non-crossbred parents
must rely on changes in breeding values
Crossbreeding Systems
use crossbred dams an/or sires
can rely on breeding values and genetic values
For any livestock production systems 3 items to keep in mind
1) How much heterosis is present and how?
2) Animals are composites of parental types
3) How we use sire and dam types is important ( breed complementarity)
Maternally Influenced traits
Genetic value of dam influences phenotype of offspring over and above her donation of alleles
4 concepts to remember
1) Progeny breeding values
2) Progeny heterosis
3) Dam breeding value
4) Dam heterosis
HVm=
Hybrid vigor or maternity
2 types of environmental effects
Permanent
Temporary
Breeding value
The sum of all the effects of the alleles that an animal possesses that affect a particular trait.
Twice the amount that a very large group of progeny would deviate from the population average for that trait.
Cream Dilution CC=
Fully pigmented horse
Cream Dilution Cc=
Black pigment not usually affected- sometimes will dilute to smokey
Sorrel or Chestnut to palomino
Bay to buckskin
Cream Dilution cc=
completely dilutes any color to creme
cremello,perlino, smokey creme
Extension Gene ( E and e)
EE or Ee= some amount of black hair
ee= sorrel or chestnut
Agouti Gene ( A and a)
AA or Aa= black restricted to points
mane, tail
ex) bay
Dun Dilution ( D and d)
DD or Dd=
Sorrel or chestnut to red dun
bay to dun
black to grullo
Primitive marks
Darker markings
dorsal stripe down back
stripes on legs
withers stripe
Graying locus ( G and g
GG or Gg = on any base color born dark and turn progressively gray ( head first)
gg - not grey
Tobiano T
dark cover usually covers one or both flanks
generally, all four legs are white
color is more regular with oval-shaped spots
head markings are like a solid colored horse
may be predominantly dark or white
tail is often two colors
Frame overo (Ff)
White arranged horizontally framed by contrasting color
white usually doesn’t cross the top line between tail and withers
legs are usually solid, extensive white on the face
White areas are usually crips and easily traced
markings are asymmetrical
lots of glass eyes
all homozygous individuals die within the first week of birth.
Sabino ( Sb and sb)
Roaned effect of the hair coat
patchy, flecked areas of alternating colored and white hair
Usually have four white legs that extend up to their torso in a ragged pattern
lots of white on the face
outline of the markings are ill-defined
Slashed white overo ( Spl and spl )
Rarest form of overo patterning
four white legs
lower torso and chest usually white
many are deaf
Leopard/Appaloosa ( Ap and ap )
Several patterns included
any coat color
sparse mane and tail hair
variations in pigment concentration
Dominant white ( W or w )
WW- embryonic lethal
ww- all nonwhite horses
Ww- masks all other coat color genes
Reproductive trait h2 level
lowly heritable ( 15% or less)
Production trait h2 level
moderate heritable ( 15-45%)
Product trait h2 level
highly heritable ( > 45%)
Breeding value
animals worth as a parent ( can be passed on to offspring(additive))
Dominance effects
interaction between alleles at a locus= not passed on but hybrid vigor
Epistatic effects
interaction between genes at different loci= not passed on but hybrid vigor
(nonadditive)
The basic model for quantitative genetics
P=G+E
