Genetics: Pedigrees & Inbreeding

Question 1

what is autosomal recessive

Answer 1

two copies of an abnormal gene must be present in order for the disease or trait to develop

Question 2

what is the probability of offspring of two carriers being affected

Answer 2

0.25

Question 3

what is the pattern of inheritance of autosomal recessive

Answer 3

appears in one generation and not the parents –> horizontal pattern

Question 4

why is autosomal recessive the most common form of inherited disorder

Answer 4

persistent of the mutant allele in unaffected carriers

Question 5

what form of inheritance is this

Answer 5

autosomal recessive

Question 6

what form of inheritance is this

Answer 6

autosomal dominant

Question 7

what type of inheritance is this

Answer 7

x-linked recessive

Question 8

what is autosomal dominant inheritance

Answer 8

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

Question 9

what is the probability of offspring to be an affected individual in autosomal dominant inheritance

Answer 9

0.50

affected offspring have an affected parent (every generation affected)

Question 10

what type of inheritance pattern is autosomal dominant

Answer 10

vertical pattern

Question 11

what are examples of AD

Answer 11

polycystic kidney disease

Question 12

what are x-linked recessive disease

Answer 12

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.

Question 13

when are x linked recessive traits passed

Answer 13

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

Question 14

what are examples of x-linked recessive

Answer 14

progressive retinal atrophy in dogs

Question 15

what is non-mendelian appearance locus heterogeneity

Answer 15

same trait can be due to distinct mutations in different chromosomal loci

Question 16

what is an example of locus heterogeneity

Answer 16

hypertrophic cardiomyopathy

Question 17

how is hypertrophic cardiomyopathy caused

Answer 17

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

Question 18

what is allelic heterogeneity

Answer 18

different mutations in the same locus cause different phenotypes

Question 19

what is an example of allelic heterogeneity

Answer 19

double muscling in cattle

Question 20

what causes double muscling in cattle

Answer 20

myostatin gene

many variants from full dysfunction to partial compromise of function

Question 21

what is genetic imprinting and what is an example

Answer 21

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)

Question 22

what is phenocopy and what is an example

Answer 22

an environmentally induced phenotype that mimics one usually produced by a specific genotype

ex. deafness (many causes), congenital cataracts

Question 23

what is anticipation and what is an example

Answer 23

the tendency for some genetic disorders to manifest at an earlier age and or to increase in severity with each succeeding generation

Question 24

how can some diseases act as a quantitative trait

Answer 24

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

Question 25

how is type II diabetes in burmese cats a good example of a disease that is a quantitative trait

Answer 25

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

Question 26

what is the general definition of inbreeding

Answer 26

the mating of relatives more closely related than the average for the population

Question 27

what is the effect of inbreeding

Answer 27

leads to increased homozygosity

Question 28

what does increased homozygosity lead to

Answer 28

1. prepotency: performance of offspring is more like own performance (increased uniformity)
2. expression of deleterious recessive alleles with major effect (HH halotypes of Holstein-Friesian)
3. inbreeding depression: same as concept b but for quantitative traits

Question 29

what is F

Answer 29

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

Question 30

what is F̅

Answer 30

a population parameter (not individual animal level)

provides information about the loss of diversity (or accumulation of homozygosity) in a population

Question 31

what is f

Answer 31

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

Question 32

what is the inbreeding coefficient

Answer 32

probability that both genes of a pair at any locus are identical by descent

Question 33

what is the inbreeding coefficient if an animal is mated to its own parent

Answer 33

25%

Question 34

what is the inbreeding coefficient if an animal is mated to its half sib

Answer 34

12.5%

Question 35

what is the inbreeding coefficient if an animal is mated to its full sib

Answer 35

25%

Question 36

what is the inbreeding coefficient of an animal mated to a single common great grand parent

Answer 36

3.1%

Question 37

what is an acceptable level of pedigree inbreeding

Answer 37

aim for levels <6.25% on average in a population

most cattle breeds have F < 10%