1 Genetic omelettes and the death of evolution of new species Maladaptation

2 Genetic consequences of inbreeding 1) decrease in heterozygosity, no change in P (allelic diversity) (the more related the individuals, the faster the loss of H) 2) increases the probability of a zygote receiving identical alleles (homologous alleles), which will result in increased expression of recessive alleles. 43e-1

3 Genetic consequences of inbreeding 3) increased phenotypic expression of deleterious alleles (strongly selected against) - often results in decreased size, reproduction, vigor, etc., which decrease fitness (i.e., inbreeding depression) -e.g., sickle cell anemia, cystic fibrosis, Tay-Sachs, hemophilia, phenylketonuria, etc. - Genetic load 4) increase in phenotypic variability resulting from a deviation from the mean genotypes in non-inbred individuals 43e-1

4 Inbreeding coefficient Sewall Wright (1923) F = the probability that an individual will receive two equal alleles, at a specific locus, that are from the same ancestor. Autozygous = alleles that are identical by descent allozygous = not identical by descent F = probability that an individual will be autozygous at a given locus 1 - F = probability that an individual will be allozygous at a given locus 43e-2

5 Calculate Junior’s inbreeding coefficients from this pedigree: AB CD MomDad AC CC C =.5 Sis Junior (or could be DD from Dad) Probability of C from Dad to Sis to Junior =.25 Probability of C from Dad (through Sis) to Junior =.50 Probability of Jr. inheriting CC from Dad =.25 X.50 =.125 Probability of Junior inheriting DD from Dad =.125 F = =.25= probability of Jr. being autozygous 31

6 Calculation of F from sib mating 31e AB CD What is F? A =.5 A =.25 Identical by descentProbability AA.25 x.25 =.0625 BB “ CC “ DD “ F = 4 x.0625 =.25 parents sibs --

7 Calculating F in a non-inbred population 51-1 Non-inbred gene pool, F 1 generation C1C2C1C2 1 grandparent Non-inbredInbred F 2 C1C2C1C2 C1C1C1C1 N e = number of breeding individuals 2 N e = number of alleles in the gene pool Probability of drawing any first allele, say C 1, = 100% Probability of drawing the same allele again = F = 1 2N e allozygous autozygous

8 Calculating F in a Non-inbred population, cont. F noninbred = 1 which is approximately 0 in an ideal pop. 2N e Probability of drawing autozygous alleles = 1 = F t 2N e = p (C 1 ) * p (C 1 ) Probability of drawing allozygous alleles = N e 51-2

9 Relationship of F and H When H 0 = 1 (i.e., no initial inbreeding), F = 0 so: F t = 1 - H t I.e., inbreeding and heterozygosity are inversely related. * * 50 Bottom line: all real-world populations tend to become completely homozygous because of genetic drift AND completely inbred

10 Outbreeding depression due to regional adaptation Hunting results in extinction of Czech ibex Translocation of ibex from nearby Austria Ibex Turkey X Ibex Czech-Austria (fall rut) (spring rut) fertile hybrids that rutted in fall, gave birth in February (coldest month) extinction of population 51A

11 OUTBREEDING: Outbreeding = crossing of unrelated invididuals. Hybrid vigor = Heterosis = increased fitness due to outbreeding. which is why: stray dogs look like mutts and not like AKC poodles you see wild-type fruitflies on your rotting apple

12 Consequences of inbreeding: Results of an early experiment on inbreeding in rats (Ritzema-Bos 1894) 55-top

13 Juvenile mortality increases after 1 generation 55-bottom % juvenile mortality * * F=0.25; e.g., wild-caught male x daughter

14 Ralls and Ballou: Examination of zoo pedigrees Infant mortality in 41 of 44 species was higher in the inbred animals (7 orders, 21 families and 36 genera)

15 Summary 43f3 Inbreeding: 1) Inbreeding depression a) decrease in fertile matings b) decrease in litter size c) increase in juvenile mortality 2) Inbreeding does not always result in inbreeding depression a) selfing plants b) Tamil tribes of India c) European Bison 3) Positive aspects a) derive offspring without deleterious alleles b) fix alleles (domestic stock)

16 Usual outcome of inbreeding: THE F VORTEX increased F declining N e (decreased H) (increased genetic drift) Inbreeding depression decreased Ndecreased r (reproductive rate) Extinction 75

17 How much inbreeding is tolerable? If F = 1 and N e = 4 M F 2N e M + F Then F = 1 F = M F 8F 8M M + F 60a Important!

18 How much inbreeding is tolerable? F = F 8M Research on domestic farm animals: natural selection for performance can balance inbreeding depression if the ΔF is no more than 1% per generation. So, F = 0.01 is a tolerable level of inbreeding 60a

19 How much inbreeding is tolerable? F = F 8M If F = 0.01 is a tolerable level of inbreeding, then.01 = so F = 25 and M = 25 8F 8M or, N e = 50 60a Magic number!

20 Number of females Number of males tolerance.005 tolerance What happens to the ‘magic number’ when sex ratios are unequal? N m 8N f + F = Conclusion: 15 = smallest number of effective individuals of one sex 60

21 Population bottlenecks Population size Time bottleneck H = = expected proportion of H o retained after a 2N e 1-generation bottleneck H t = H o t = proportion of H o retained t generations after 2N e a bottleneck if N e at t=0 = 4, then H t=1 = = 7 i.e. 1/8 of original H 2 x 4 8 was lost in 1 generation 61A