Genetics: Pedigrees & Inbreeding Flashcards
what is autosomal recessive
two copies of an abnormal gene must be present in order for the disease or trait to develop
what is the probability of offspring of two carriers being affected
0.25
what is the pattern of inheritance of autosomal recessive
appears in one generation and not the parents –> horizontal pattern
why is autosomal recessive the most common form of inherited disorder
persistent of the mutant allele in unaffected carriers
what form of inheritance is this
autosomal recessive
what form of inheritance is this
autosomal dominant
what type of inheritance is this
x-linked recessive
what is autosomal dominant inheritance
A pattern of inheritance in which an affected individual has one copy of a mutant gene and one normal gene on a pair of autosomal chromosomes
what is the probability of offspring to be an affected individual in autosomal dominant inheritance
0.50
affected offspring have an affected parent (every generation affected)
what type of inheritance pattern is autosomal dominant
vertical pattern
what are examples of AD
polycystic kidney disease
what are x-linked recessive disease
X-linked recessive inheritance is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be always expressed in males (who are necessarily homozygous for the gene mutation because they have one X and one Y chromosome) and in females who are homozygous for the gene mutation, see zygosity.
when are x linked recessive traits passed
never passed from father to son
males are much more likely to be affected than females –> only need one copy
all affected males in a family are related through their mothers
trait or disease is typically passed from an affected grandfather through his carrier daughters
what are examples of x-linked recessive
progressive retinal atrophy in dogs
what is non-mendelian appearance locus heterogeneity
same trait can be due to distinct mutations in different chromosomal loci
what is an example of locus heterogeneity
hypertrophic cardiomyopathy
how is hypertrophic cardiomyopathy caused
mutation in one of 9 distinct sarcomeric genes that causes an abnormal protein in the myocytes
affected proteins include B-myosin heavy chain, myosin binding protein-C, cardiac troponin-T, tropomyosin
what is allelic heterogeneity
different mutations in the same locus cause different phenotypes
what is an example of allelic heterogeneity
double muscling in cattle
what causes double muscling in cattle
myostatin gene
many variants from full dysfunction to partial compromise of function
what is genetic imprinting and what is an example
either the maternal or paternal copy of the gene is epigenetically silenced via methylation of the gene during gametogenesis
insulin like growth factor 2 (IGF2)
what is phenocopy and what is an example
an environmentally induced phenotype that mimics one usually produced by a specific genotype
ex. deafness (many causes), congenital cataracts
what is anticipation and what is an example
the tendency for some genetic disorders to manifest at an earlier age and or to increase in severity with each succeeding generation
how can some diseases act as a quantitative trait
some diseases require several interacting dysfunctions to result in expression of the susceptibility plus the existence of a favourable environment (microbial challenge) to be expressed
how is type II diabetes in burmese cats a good example of a disease that is a quantitative trait
burmese cats have a risk of disease that is 3x higher than other pedigree breeds
if there is a breed predisposition to a certain disease, it suggests an inherited contribution to the occurence of disease
there is an inherited component but it is not a simply inherited trait
what is the general definition of inbreeding
the mating of relatives more closely related than the average for the population
what is the effect of inbreeding
leads to increased homozygosity
what does increased homozygosity lead to
- prepotency: performance of offspring is more like own performance (increased uniformity)
- expression of deleterious recessive alleles with major effect (HH halotypes of Holstein-Friesian)
- inbreeding depression: same as concept b but for quantitative traits
what is F
inbreeding as measure of shared ancestry
characteristic of an individual (probability that any two alleles in an individual have been inherited from a single common ancestor)
indicates risk of inbreeding depression and disease
not a measure of genetic diversity
what is F̅
a population parameter (not individual animal level)
provides information about the loss of diversity (or accumulation of homozygosity) in a population
what is f
system of mating
an index of deviation from random mating (propensity for assertive mating among relatives)
not a measure of diversity in a population
not informative about any individual
what is the inbreeding coefficient
probability that both genes of a pair at any locus are identical by descent
what is the inbreeding coefficient if an animal is mated to its own parent
25%
what is the inbreeding coefficient if an animal is mated to its half sib
12.5%
what is the inbreeding coefficient if an animal is mated to its full sib
25%
what is the inbreeding coefficient of an animal mated to a single common great grand parent
3.1%
what is an acceptable level of pedigree inbreeding
aim for levels <6.25% on average in a population
most cattle breeds have F < 10%
