Family Genetics and Inbreeding - 15

what can we calculate to investigate inbreeding and ancestors in common?

Most Recent Common Ancestor (MRCA)

what is inbreeding?

the mating of relatives

• if an individual is homozygous by virtue of receiving two copies of the allele from the same ancestor, the alleles show identify by descent (IBD)

what does inbreeding look like in a pedigree?

matings appear as loops

• Alfonso XII of Spain should have had 128 ancestors, he had 8

• Tutankhamun - result of a brother/sister mating, had severe skeletal problems

what does inbreeding cause?

a loss of heterozygosity

• the variation becomes subdivided into distinct inbred lines rather than being scattered throughout the population as a whole

what is the most extreme example of inbreeding in humans?

• brother-sister mating

what is the coefficient of inbreeding?

F = sum of N(1/2)n

• F = the probability that a pair of alleles at a locus will be identical by descent, every inbred pedigree has a loop in it that links the two mates through their shared ancestors

• N = number of loops

• n = number of ancestors in each loop

  • e.g. in brother sister mating, (the child is not counted) - parent → shared ancestors → other parent

  • e.g. cousin mating - value of F decreases, F can build up over generations (1/16 for cousin marriages), each pathway goes through 5 ancestors

what is an inbreeding depression?

caused by the increase in homozygosity of rare deleterious alleles

what are some examples of inbreeding in animals?

• pedigree dogs - suffer from inbreeding depression

  • Border collies - congenital myopathy (wasting of the muscles), hip dysplasia, eye anomaly (blindness)

  • King Charles spaniel - selected for flat faces, causes syringomelia (lost 1/9 of genetic diversity)

  • Bulldogs - changed in phenotype overtime

what did long-term monitoring studies in song sparrows show?

the immune response (determined using a scratch test) decreased with inbreeding

how can we prevent inbreeding in animals?

Programmes in zoos

• use of studbooks

• captive breeding programmes with other zoos (outbreeding)

what are some examples of inbreeding in humans?

• all populations in the end are inbred, some more than others - if on a small island or village, there is little to no option but to mate with someone who shares a recent ancestor

• leads to local patches of high frequency of recessive disease

  • e.g. Finland - 33 unique genetic diseases such as VLINCL, tracing back to a single male in a pedigree

  • can estimate using diversity of surnames in a population

what are runs of homozygosity?

lengths of homozygous genotypes that are present in an individual due to parents passing on identical haplotypes to their offspring

• common in people living on islands of Croatia than the mainland Croatia

• having more runs are associated with human diseases such as colon cancer