Family Genetics and Inbreeding

Question 1

Inbreeding

Answer 1

Can calculate Most Recent Common Ancestor (MRCA)

Question 2

Identity by descent (IBD)

Answer 2

Individual is homozygous, receiving 2 copies of allele from same ancestor More IBD = more homozygosity

Question 3

Inbreeding loops

Answer 3

Count round from on parent through ancestors to other parent, child not numbered in loop

Question 4

Coefficient of inbreeding (F)

Answer 4

Probability that a pair of alleles at a locus will be identical by descent

F = ΣN(½)ⁿ

N = number of loops

n = number of ancestors in each loop

As degree of kinship increases, F increases

Question 5

Examples of inbreeding

Answer 5

Pedigree dogs suffer inbreeding depression e.g. syringomelia in King Charles Spaniel

Sunny the bull - 1000’s of offspring from artificial insemination → inbreeding in later generations

Tutankhamun parents were siblings

Smaller populations - more inbred

Consanginious marriage - parents share same blood

Brother - sister mating → child with runs of homozygosity (ROH)

ROH increases risk of severe autism + early onset Parkinsons

Question 6

Anisogamy

Answer 6

Union of 2 gametes that differ in size

Question 7

Patrilineal inheritance

Answer 7

Y chromosome inheritance, differential (pseudo-autosomal) regions recombine with X, many genes lost to X of decayed, remaining genes usually code male traits

SRY active in early development → male

Palindromes where Y can recombine with itself

Mapping Y can show evolution of males

Question 8

Matrilineal inheritance

Answer 8

Chloroplasts + variegated plants: mixture of green and white patches on leaves, branch can be mixed or just one colour

Question 9

Maternal inheritance

Answer 9

Offspring same as egg, irrespective of pollen phenotype

Question 10

Cytoplasmic inheritance

Answer 10

Offspring are a mixture as genes are in the cytoplasm and only passed down through female parent, white/green chloroplasts are passed on at random

Question 11

Maternally inherited bacteria

Answer 11

Wolbachia - passed on through female cytoplasm, can stop male development, makes males infertile or kills adult males

Question 12

Mitochondrial Inheritance

Answer 12

Slow growth mutants in Neurospora - phenotype can be transferred with microinjection of cytoplasm

Crosses between mating types in Chlamydomonas resistant to different drugs - 3 point cross but different gene order each time as mitochondrial map is circular

Leber’s hereditary optic neuropathy (disease) - associated with deletions in mitochondrial genome

Question 13

Hardy-Weinburg Equilibrium

Answer 13

Ratio of zygotes: AA = p²; Aa = 2pq; aa = q²

Populations in H-W are stable

p² + 2pq + q² = 1

Can work out freq. of dominant from freq. of recessives

Question 14

Genetic Drift

Answer 14

Random change in small populations, strength of effect depends on how small pop. is + what allele freq. are

Both effect sampling variance: pq/N

N = pop. size

Genetic drift is greatest when sampling variance is big

Patterns of disease on islands eg. Tristan - retinoblastoma

Question 15

Migration

Answer 15

Gene flow between populations, humans more homogenous between places than any other primate

Admixture for skin colour very rapid in Britain

Question 16

Non-random mating

Answer 16

H-W assumes mating is random but in humans it depends on race, religion, class, education etc

Out-breeeding mechanisms: self-incompatibility in plants, BRUCE effect in mice

Question 17

Natural Selection

Answer 17

H-W assumes all genotypes have same fitness which isn’t true