Animal Breeding Flashcards
Genetics
science of heredity
Breeding
-selective mating of animals to increase the possibility of obtaining desired traits in the offspring
-refers to genetic change; goal to improve not simply reproduce
Heredity
transmission of genetics or physical traits of the sire and dam to the offspring
Gregor Mendel
-Austrian monk who conducted basic breeding experiments using garden peas
-“founder of modern genetics”
Sir Robert Bakewell
-father of animal breeding
-established factors paramount to sound animal breeding with objective selection
-used inbreeding and progeny testing
What animals did Bakewell use
-lecister sheep
-shire horses
-english longhorn cattle
What factors did Bakewell establish
- Establish a definite goal
- Breeding the best to the best
- Use proven sires
Gene
-normally appear in diploid (2n) pairs in each body cell of individual organisms
-located on chromosomes
Chromosomes
rodlike bodies found in the nucleus of the cell that contain genetic information
-occur in sets of 2
-all livestock are diploid (2n)
Alleles
two genes occupying corresponding loci in homologous chromosomes that affect the same hereditary trait but in different ways
Homozygous
same alleles (RR or rr)
Heterozygous
different alleles (Rr)
Genotype
genetic makeup of the animal
-for any pair of alleles, 3 genotypes are possible (2 homozygous (dominant and recessive) and 1 heterozygous)
Phenotype
the characteristics of the animal that can be seen and measured
Gametes
-germ or sex cells
-contain a single set of unpaired chromosomes (haploid, n)
-female = ovum
-male = sperm
Mammal female sex chromosomes
-carried by gametes
-homogametic (XX)
-produce ova with only X chromosomes
Mammal male sex chromosomes
-carried by gametes
-heterogametic (XY)
-produce sperm with X or Y chromosome
Avian female sex chromosomes
-carried by gametes
-heterogametic (ZW)
-produce ova with Z and W chromosomes
Avian male sex chromosomes
-carried by gametes
-homogametic (ZZ)
-produce sperm with only Z chromosomes
Dominant cattle traits
-black coat
-polled
-normal size
-normal muscling
Recessive cattle traits
-red coat
-horned
-dwarf
-double muscled
Dominant horse traits
-normal hair
-bay color
Recessive horse traits
-curly hair
-non-bay colors
Dominant poultry traits
-white skin
-feathered shanks
Recessive poultry traits
-yellow skin
-clean shanks
Dominant sheep traits
-wool
-white wool
Recessive sheep traits
-hair
-black wool
Dominant swine traits
-erect ears
-black hair
Recessive swine traits
-droopy ears
-red hair
Horned vs. Polled
-dominant gene = polled (P)
-recessive gene = horned (p)
Swine hair color
-dominant = black (B)
-recessive = red (b)
Poultry skin color
-dominant = white (W)
-recessive = yellow (w)
Incomplete dominance
one allele for a specific trait is not completely expressed over its paired allele.
-causes a 3rd phenotype that is a combination of the phenotypes of both alleles
ex.) shorthorn cattle coat color
-Red coat = RR
-White coat = WW
-Roan coat = RW
Sex-linked
certain traits are associated with a gene that is carried by only the male or only the female parent.
ex.) Feather growth in broiler chickens
-Slow feather growth = dominant (F) on the Z chromosome
-Fast feather growth = recessive (f) on the Z chromosome
Epistasis (overdominance)
the phenotypic expression at one locus depends on the genotype at a different locus
-the extension locus has two alleles E and e
-the dilution locus has two alleles D and d
Black cattle color (epistasis)
-EE or Ee
-dd
EEdd or Eedd
(black non-diluted cow)
Red cattle color (epistasis)
-ee
-dd
eedd
(red non-diluted cow)
Smoke/silver cattle color (epistasis)
-EE or Ee
-Dd
EEDd or EeDd
(black partially diluted cow)
Yellow cattle color (epistasis)
-ee
-Dd
eeDd
(red partially diluted cow)
White parks cattle color (epistasis)
-EE or Ee
-DD
EEDD or EeDD
(black fully diluted cow)
Charlais cattle color (epistasis)
-ee
-DD
eeDD
(red fully diluted cow)
Semi-lethal factors
cause death in only some of the affected genotypes (rare in livestock and poultry)
Lethal factors
cause death in all affected individuals
ex.) overo lethal white in horses
-O/O = lethal white foal
-n/O = carries a single copy for the frame overo, display overo markings
-n/n = solid colored horse
Natural selection
represent forces of selection that are not decided by humans
-acts on alleles that contribute to survival and reproductive success (also called fitness)
-not being able to cope with the situation results in reduced fitness
Artificial selection
allows humans to play a role in selection and decide which animals are allowed to have offspring and which are not
-a set of rules designed by humans to govern the probability that an individual survive and reproduces
Gene frequency
the frequency of an allele at a particular locus in a population, expressed as a percentage.
-genetic changes in populations are produced by changes in gene frequency
Mutations
the change in the gene that causes a sudden change in the phenotypic expression of that gene
Selection
a potent force in changing the frequency of a gene or genes in a population
Genetic drift
when the frequency of a gene may be very different in a larger population from which the smaller population was derived
Qualitative traits
non-measurable traits that may be of great value to purebred producers but little value to commercial producers
ex.) coat color, ear carriage, horns
Quantitative traits
measurable traits that measure the “quantity” of products produced by the animal
-great value to commercial breeders
ex.) weaning weight, pounds of milk, average daily gain
Level of heritability
how likely the trait will be passed down
Reproductive level of heretibility
low
Growth and milk level of heretibility
medium (ADG, FE, lbs. milk)
Carcass level of heretibility
high (marbling)
Wool level of heretibility
very high (low environmental impact)
Expected progeny difference (EPD)
the prediction of how future progeny of each animal are expected to perform relative to the progeny of other animals of the same breed
Calving ease direct (CED)
predicts the average difference in ease with which a sire’s calves will be born when he is bred to first-calf heifers
-higher value = greater calving ease (want higher EPD)
-more accurate than BW
-expressed as a %
Birth weight (BW
predictor of a sire’s ability to transmit birth weight to his progeny compared to that of other sires
-want a low EPD
Weaning weight (WW)
predictor of a sire’s ability to transmit weaning growth to his progeny compared to that of other sires
-want a larger EPD = more $
Yearling weight (YW)
predictor of a sire’s ability to transmit yearling growth to his progeny compared to that of other sires
-want a larger EPD
Scrotal circumference (SC)
predictor of the difference in transmitting ability for scrotal size compared to that of other sires (size of testicles)
-larger circumference = more sperm/more fertile = daughters start estrus/puberty earlier
Maternal milk (milk)
predictor of a sire’s genetic merit for milk and mothering ability
-that part of a calf’s weaning weight attributed to milk and mother ability
-want a larger EPD
-could not be a good thing if resources are low and the cow is depleting her resources producing a lot of milk
Marbling (Marb)
expressed as a fraction of the difference in USDA marbling score of a sire’s progeny compared to progeny of other sires
-want a great marbling score
Ribeye Area (RE)
expressed in square inches and is a predictor of the difference in ribeye area of a sire’s progeny compared to progeny of other sires
-larger ribeye = more muscling = more to sell
-want a larger number
Carcass weight (CW)
expressed in pounds and is a predictor of the difference in hot carcass weight of a sire’s progeny compared to progeny of other sires
-want a higher number
Actual data
a measurement of an animal’s performance with no consideration of environment or contemporary group comparisons
Adjusted data
standardized to a certain age and/or mature age-of-dam basis (on the actual bull not the offspring)
Birth weight (BW) of the bull
the weight of the animal at birth, measured in pounds
Adjusted weaning weight (ADJ WW)
weaning weight reflects both the milking ability of the dam and the growth potential of the calf
-in order to compare calves of different ages and from different aged dams the actual reported weight is adjusted to a constant number of days of age (205 days)
Adjusted yearling weight (ADJ 365)
in order to compare calves of different ages it is necessary to adjust the actual reported weight to a constant number of days of age (365 days)
