Genetics Flashcards
animal genetics
study of the DNA code and its contribution to animal performance
animal breeding
selection of animals to be used in breeding for the next generation
genome
the genetic makeup of the whole animal
the entire set of instructions
genotype
specific to one or two genes
phenotype
manifestation of the genes
- expression of the genotype
- genetic and environmental components
- “genetic potential” dependent on environment
genes
segments of DNA that can be inherited
code for specific proteins made w/in the body
central dogma: one gene codes for one protein
DNA
deoxyribonucleic acid
2 anti-parallel strands of alternating sugar (deoxyribose) and phosphate
linked together by bonds between purine (A, G) and pyrimidine (C, T) nucleotide bases
top strand is the coding strand
karyotype
“a metaphase spread”
to look for gross alterations in chromosome shape or number
replication
make copies of DNA
gene transcription
DNA –> mRNA
mRNA translation
mRNA –> protein coded for by that gene
stops at stop codons
mRNA
messenger ribonucleic acid
single stranded
same code as DNA but replaces T w/ U
protein
made of a chain of amino acids
locus
a specific location on a chromosome (gene or specific DNA sequence)
alleles
alternate forms at the same locus
single nucleotide polymorphism
SNP
mutation
one nucleotide is swapped for another
deletion
a nucleotide is deleted
*frameshift mutation
insertion
an extra nucleotide is added
*frameshift mutation
frameshift mutation
codon reading downstream is altered
myostatin mutation
causes muscle hypertrophy
common in belgian blue breed
“double muscle”
inheritance
1 chromosome from each parent
transfer of genes from parent to offspring
homozygous
same allele at a given locus
heterozygous
different alleles at a given locus
offspring
arise from fusion of male and female gametes
gametes
spermatozoa, oocyte
“germ” cells as opposed to somatic cells
derived through the process of meiosis
mitosis
somatic cell division
meiosis
gametogenesis
sperm and oocytes arise from somatic cells via meiosis
crossing over - exchange of pieces of parental chromosomes
gamete chromosomes are spliced pieces of maternal and paternal chromosomes
punnett square
simple example of dominant/recessive inheritance
each parent contributes 1 allele to offspring
co-dominance
both alleles expressed in heterozygotes
ex. red+white = roan
ex. ABO blood type system - AB is co-dominant both alleles displayed
incomplete dominance
blending of phenotypes
epistasis
phenotypic expression of genes at one locus depends on alleles present at another loci
aka modifying genes
ex. coat color in labs
historical parentage verification
blood group antigens
serum protein polymorphisms
labor intensive
not very robust
DNA based parentage verification
looks at approx. 15 different loci each w/ numerous alleles
PCR amplification of DNA
a few hair follicles are sufficient
99.99% accurate
parentage testing based on polymorphic region of DNA
microsatellite marker
-DNA between genes
-repeated in di, tri, or tetra units TGTGTG…
polymorphism
-difference in DNA sequence btwn individuals
-ie different # of repeats at a specific locus
polymerase chain reaction
PCR
amplifies a specific segment of DNA located btwn specific primers
used in forensics
each primer pair amplifies one locus
-good sites have 8 to 16 different lengths of the repeat
-thus 8 to 16 alleles
parentage testing uses 15 different primer pairs
-15 different loci w/ many different alleles
polygenic inheritance
traits influenced by many genes
sex-linked inheritance
refers to a gene located on the X or Y chromosome and therefore inherited along w, sex chromosomes
x-inactivation
one X chromosome in each female cell is silenced
random process that occurs soon after conception
results in both males and females having the same # of X chromosomes
sex-limited traits
the traits expressed in only one sex (both sexes contain the gene)
eg. milk production - females
cryptochidism - males (lack of testicular descent)
qualitative traits
(think either/or)
can be classified into groups rather than measured on a continuous scale
-coat color, blood group
-genetic control by alleles of one (or a few) genes
-little environmental modifications to the gene effect
quantitative traits
continuous on a measuring scale
traits numerically measured
usually controlled by many different genes
envirionmental effect on expression of genetic potential
ex. growth rate, milk production
heritability
proportion of the difference in individuals that is due to the additive gene effects (NOT environmental)
proportion of phenotypic variation that can be passed to offspring
measure of potential genetic progress that can be made through selection
relationship coefficient
w/in a population animals may being to share similarities in their genetic composition
proportion of genes two animals have in common is known as their relationship
ex. R
full sibs .5
half sibs .25
1st cousins .125
inbreeding
breeding closely related individuals
used to “fix” specific alleles at a locus
increases homozygosity of detrimental recessive genes
inbreeding depression
line breeding
mild inbreeding
breeding related individuals who are removed by greater than one generation
-grand sire + grand daughter, 2nd or 3rd cousins
-need good knowledge of pedigrees to avoid excessive inbreeding
out breeding
mating less closely related individuals compared to the avg of the population
generates heterosis (hybrid vigor)
- inc. heterozygosity
- superiority of outbred individuals relative to the avg performance of their parents
crossbreeding
mating animals of different breeds to take advantage of outbreeding (designer breeds)
sometimes called terminal cross b/c F1’s are predictable but F2’s are unpredictable mixture
rate of genetic change
how fast will genetic selection have an effect
dependent on:
-accuracy of selection
-intensity of selection
-variation in the population
inversely dependent on
-generation interval
= (accuracy x intensity x variation)
generation intervalaccuracy of selection
major influence of heritability
how much is phenotype influenced by genotype
selection intensity
ex. select top 10% or top 2%
large enough population to select only top animals
genetic variation
how much better are the best animals?
if little variation, hard to improve
generation interval
avg age of parents when offspring are born
how long it takes to see results of mating
population genetics
considers the frequency of phenotypes, genotypes and alleles in the whole population being considered
phenotypic frequency
frequency of visible phenotypes (red or black)
genotypic frequency
frequency of allele combination (BB, Bb, bb)
allele frequency
also called gene frequency
frequency of alleles (B or b)
four factors affecting gene frequency in a population
- selection
- mutation
- genetic drift
- migration
selection
A. Natural selection - some animals are more likely to be parents than others in a given environment
- general situation in wild animal populations
B. Artificial selection - human selection of breeding animals
- based on managed choices (may involve culling and replacement)
mutation
generation of new alleles (rare)
genetic drift
loss of certain alleles from a population over time due to chance (problem in small population)
-bottlenecks inc. genetic drift
migration
bringing new breeding stock (w/ different gene frequency)
