Genetics Flashcards
When becoming domesticated, mammals have an early __?__ in size, then later __?__.
decrease; increase
When becoming domesticated, why do birds have an early increase in size?
Larger size => decreased flight
3 ways the humans pressure has changed natural behaviors of domesticated animals.
- Adaptations to human environment (e.g., husky living in southwest VA; use of horse for transport/riding)
- Beast of burden (castration, confinement, sacrifice)
- Control reproduction & genetic variability (slow vs fast repro)
Domesticated animals fall into 3 categories:
- Breed
- Industrial Stock (very little variability)
- Landrace (very adapted to specific environment/region)
4 steps in the general process to domestication
domestication -> landrace or primitive breed -> standard breed (purebreds!) > industrial breed
Mitosis versus Meiosis
Mitosis: process of cell division which results in formation of two 2n daughter cells identical to parent cell (forms somatic cells).
Meiosis: process during gametogenesis by which one 2n parent cells are reduced into four 1n gamete cells, and crossing over exchange occurs b/w homologous chromosomes (forms gametes).
crossing over: results in recombination + genetic variation/diversity, and influences inheritance (genes present on same chromosome tend to be inherited together (aka “linked genes”).
Allele
specific gene located on each homologous chromosome in somatic cells (two copies of each gene b/c homologous chromosomes = paired: one maternal, one paternal).
E.g., paternal allele = Rr, maternal allele = RR -> -> possible genotypes = RR, RR, Rr, Rr (basic Punnett square)
- genotype determines phenotype.
Incomplete dominance versus Co-dominance
Incomplete dominance: in heterozygote, dominant allele’s phenotype does not dominate over recessive’s (e.g., red flower = R, white flower = r -> Rr = pink flower)
Co-Dominance: two alleles’s phenotypes are fully expressed in a heterozygote (e.g., Roan coat horses- has mixture of fully red and fully white hairs).
Recessive masking epistasis
Epistasis: interactions b/w genes at ≥ 2 loci affecting phenotype of that trait.
Recessive Masking Epistasis = presence of homozygous recessive genotype at loci 1 masks the phenotypic expression of gene at loci 2, whether it’s dominant or recessive.
Ex: Labrador Retriever coat color.
- Each lab receives “B” and “E” gene
- “B” = dominant, “b” = recessive
- “e” = recessive masking gene, where “ee” masks all other genes, but “EE” does not have any masking power.
Somatic cell versus Germline cell mutation
Somatic: mutation will only affect original individual
Germline (includes both gametes & cells from which they are formed): mutation can be passed on to progeny
Autosomal Dominant
very rare in vetmed
- non sex-linked chromosome
- only requires 1 copy of affected gene to cause dz: mutant/normal ; mutant/mutant
- Examples: polycystic renal dz in persian cats, progressive rod/cone degen/atrophy in english mastiffs & bullmastiffs
Autosomal = ?
any of the non sex-linked chromosomes
Autosomal Recessive
- common in vetmed
- must obtain one of each gene from each parent- requires 2 copies of affected genes to express disease
- examples: congenital myasthenia gravis of smooth fox terriers
Describe Penetrance and At Risk
Penetrance = probability calculation - # of individuals with affected genotype that actually express the phenotype
At Risk = is it autosomal recessive or dominant (aka does it require 2 or 1 copies of mutant allele), AND does it have incomplete or complete phenotypic expression?
Polygenetic
an expressed phenotype that is determined by multiple different genotypes
- NOTHING to do with penetrance, and everything to do with external factors
- e.g., hip dysplasia: environment + genetics + diet/exercise/lifestyle
Dermatomyositis
autoimmune disorder that affects the skin - polygenic in nature (3 identified loci)
- also influenced by environment
