Inbreeding and outbreeding

This powerpoint gives a clear picture on inbreeding and also about outbreeding of higher organisms. This also explains the advantages and disadvantages of the above said topics. the methods of inbreeding and reasons for inbreeding also given in this powerpoint.

1. DR.N.C.J.PACKIA LEKSHMI NICHE INBREEDING AND OUTBREEDING

2. INBREEDING Introduction Reproduction implies replication Biological reproduction always yield reasonable carbon copy of parent unit Sexual reproduction practiced by majority of animals, plants and microorganisms It produces diversity needed for survival in a world constant change ( ie ., evolution) Sexually reproducing individuals may have individuals which are unisexual or bisexual. Bisexuality is common in plants and lower animals. Higher animals are unisexual, i.e., separate male and separate female sexes exist. Sexual reproduction performs the basic function of providing a great variety of genotypes. Great variety of genotype has much higher evolutionary significance Living organisms fundamentally following two systems of mating occur: inbreeding and outbreeding

3. INBREEDING The process of mating of individuals which are more closely related than the average of the population to which they belong. Production of offspring through matings between related parents Biparental : two different individuals are involved Leads to deviations from H-W equilibrium by causing a deficit of heterozygotes Inbreeding is affected by restrictions in population size or area which brings about the mating between relatives Extreme inbreeding – Intragametophytic selfing – mating between gametes produced from the same haploid individual Generation AA Aa Aa P 2 2pq q 2 1 P 2 +(pq/2) pq q 2 2 P 2 +(3pq/4) Pq/2 q 2 +(3pq/4)

4. 100% homozygosity in one generation – eg ..some ferns and mosses (fern: Archegonium and anthridium ) Does not change allele frequency by itself It does increase homozygosity but does not bring about a change in overall gene frequencies Mating between two heterozygotes as regards two alleles A and a – result in half of the population homozygous for either gene A or a and half of the population heterozygous like the parent but the overall frequencies of A and a remain constant Aa X Aa 1 AA : 2Aa : 1aa It brings about recessive gene to appear in a homozygous state ( aa ) Homozygous recessive are phenotypically differentiated from the dominant population

5. COEFFICIENT OF RELATIONSHIP (R) Expression of the amount or degree of any quality possessed by a substance Also a degree of physical or chemical change normally occurring in that substance Characterizes the percentage of genes held in common by two individuals due to their common ancestory Each individual gets only a sample half of his genotype from one of his parent The sum (Ʃ) between two individuals through common ancestors is the coefficient of relationship and is represented by R: R BC = The coefficient relationship between the full sibs B and C and is calculated as follows: I.e., individuals B and C contain 1/2x1/2 = ¼ of their genes in common through ancestors D i.e., individuals B and C contain 1/2x1/2 = ¼ of their genes in common through ancestors E the sum of these two, the coefficient of relationship, between the full sibs B and C = ¼+1/4=1/2 = 50 %

6. INBREEDING COEFFICIENT In diploid organism each gene has two alleles occupy the same locus – called identical genes If they descended from the same gene; such genes are homozygous at the lcous Such homozygosity also caused when two allels in a diploid organism are not descended from the common gene but the alleles of identical origin are brought together through mating between first cousins- such alleles are similar alleles The probability that the two alleles in a zygote are identical by descent is measured by inbreeding coefficient (F) If the parents B and C are full sibs, i.e., B and C parents are 50% related, the inbreeding ccoefficient of individual A can be calculated by the equation F A = ½ R BC , Where R BC is the coefficient of relationship between the full sib parent (B and C) of A If the common ancestor are not inbred, the inbreeding coefficient is calculated by the equation: F = Ʃ(1/2) n1+n2+1 where n1 is the number of generations from one parent back to the ancestor and n2 is the number of generations form the other parent baCk to the same ancestor

7. 3. In case the common ancestor are inbred, the inbreeding coefficient is calculated as follows F = Ʃ(1/2) n1+n2+1 (1+F ancestor) 4 . The coefficient of inbreeding is also calculated by counting the number of arrows connecting the individual through one parent back to the common ancestor and back again to his other parent by the following equation: F = Ʃ(1/2) n1 (1+F A ) n = number of arrows which connect the individual through one parent back to the common ancestor and back again to his other parent F A is the inbreeidng coefficient of the common ancestor Eg ., the inbreeding coefficient for A in the following arrow diagram can be calculated by following method: B and C are the parents of A. there is only one pathway from B and C and that goes through ancestor E. Ancestor E is inbred, because its parents (G and H) are full sibs and are 50% related. The inbreeding coefficient can be calculated as F E = ½ R GH (R = the coefficient of relationship between the full sibs G and H)

8. PANMIXIS – Random mating If the breeder assigns no mating restraints upon the selected individuals, their gametes are likely to randomly unite by chance alone Wind or insect carry pollen from one plant to another in essentially a random manner Even livestock such as sheep and range cattle are usually bred panmicticly The males locates females as they came into heat, copulate with and inseminate them without any artificial restrictions as they forage for food over large tracts of grazing lands This mating method is most likely to generate the greatest genetic diversity among the progeny

9. ASSORTATIVE MATING In sexually reproducing organism, the most rapid inbreeding system is that between brothers and sisters who share both parents in common – called full sib mating Produces inbreeding coefficient of 25% in the first generation – reduced in succeeding generations since some alleles are identical Within 10 generations, full sib mating can produce an inbreeding coefficient of 90% Other inbreeding systems are half sib mating, parent offspring mating, third cousin mating – called genetic assortative matings Parents of each mating type are sorted and mated together on the basis of their genetic relationship. Assortative mating is of phenotypic type i.e., the mating between two like phenotypes, two like dominant or two like recessive phenotype If it continues for many generations, eliminates the heterozygotes and the resulting will be homozygous dominant or homozygous recessive

10. DISASSORTATIVE MATING Mating of unlike phenotypes and genotypes and tends to maintain heterozygosity Mating between homozygous and an heterozygous individual for sex locus Also results from dichogamy – producing mature male and female reproductive structures at different times Fertilization between plants with different phenotype is favoured Maintains heterozygosity within a diploid breeding population

11. LINE BREEDING Special form of inbreeding utilized for the purpose of maintaining a high genetic relationship to a desirable ancestor A possesses more than 50% of B’s gene D possesses 50% of B’s gene and transmits 25% to C; B also contributes 50% of genes to C-hence C contains 50+25 = 75% B’s genes transmits to C and transmits half of them to A; B also contribute 50% to A – Hence A contains 50+37.5 = 87.5% of B’s gene

12. GENETIC EFFECTS Results genetically in homozygosity Produces homozygous stocks of dominant or recessive genes and eliminates heterzygosity In each generation, heterozygosity is reduced by 50% and after 10 generation – total elimination of heterozygosity from the inbred line and production of two homozygous or pure lines In humans, in happens very slowly

13. EFFECTS OF INBREEDING Occurrence of genetic disorder – due to the development of homogygous recessive Physical and health effects Reduced fertility Increased genetic disorders Fluctuating facial asymmetry Lower birth rate Higher infant mortality and child mortality Smaller adult size Loss of immune system function Increased cardiovascular risks Haemophilia in royal families Increases hearing impairment

14. Reasons for inbreeding Royalty, religion and culture, socioeconomic class and geographic isolation and small population Religion and culture plays major role – many muslims and hindu societies practices unions of first cousin – advantage – bride’s relationship with her Mother in law and the up keep of the family’s property Another incentive to close relative marriages concers brides wealth and dowry To keep their property and land In royal families – to preserve royal blood lines

15. APPLICATION OF INBREEDING Inbreeding causes homozygosity of deleterious recessive genes which may result in defective phenotype – so in human society, the religious ethics unknowingly and modern social norms consciously have condemned and banned the marriages of brothers and sisters Plant and animal breeders also avoid inbreedings in the individuals due to this reason Inbreeding results in homozygosity of dominant alleles – it is a best mean of mating among hermaphrodites and self pollinating plant species for several families. Animal breeders also use inbreeding to produce best race of horses, dogs, bulls, cattles etc… Eg ., modern race horse – descendents of three Arabian stallions and mated with several local mares of the slow heavy type – fast runners of F1 was selected and inbred and stallions of F2 appear as beginning point in the pedigrees of almost all modern race horses – called line breeding. Merino sheep – fine wool producer – result of 200 yrs of inbreeding

16. OUTBREEDING Mating involves individuals that are more distantly related – outcrossing or outbreeding – negative genetic assortative mating Involves crossing individuals belonging to different families or crossing different inbred varieties of plants or crossing different breed of livestock Increases heterozygosity and enhances vigour of progeny – i.e., hybrid have superior phenotypic quality but often has poor breeding value The two inbred parents homozygous for different genes, if crossed produce F1 progeny – heterozygous F1 progeny or hybrid – improved general fitness, resistance to diseases or it may show remarkable growth and vigour The superiority of hybrid over parent – heterosis – coined by Shull The terms heterosis and hybrid vigour are used as synonyms Shull – the developed superiority of the hybrid – hybrid vigour Heterosis – mechanism by which this superiority is developed According to Whaley – hybrid vigour denotes the manifest effects of heterosis

17. Cross breeding and mule production Mating of individuals from entirely different races or even different species – cross breeding Produces sterile hybrids in comparison to normal outbreedings Mule – a hybrid of a male donkey ( Equus asimus , 2n = 62) and a female horse ( Equus caballus , 2n = 64) The hybrid from the reciprocal cross (i.e., female donkey or jenny and male horse or stallion) – hinny Mule shows hybrid vigour and served mankind Sexually sterile and have to produce everytime a new Donkey stallions –imported from Europe by Indian army for breeding mules Two kinds of mules used by Indian army; 1. general service type and 2. mountain artillary type – very important as they are firm footed animals that can carry heavy loads on steep himalayan mountain terrain

18. Manifestation of heterosis Heterosis – increase in size and productivity Eg.,some crosses of beans certain F1hybrids contain greater number of nodes, leaves and pods than their parents but the gross size of plant remain unaffected In some hybrids – the growth rate is increased but there occur no increase in size of mature plant Greater resistance to diseases, insect infestation and increased tolerance to erratic climatic condition are some eg of heterosis effect of plants Shull - Corn or maize hybrids – diverse parentage – greater hybrid vigour Problem is inbred lines are infertile – modified by a method called double cross method (Jones) Double cross method – four inbred lines (A.B.C and D) Single cross is made between A and B by growing two lines together and removing the tassels from line A – Cannot self fertilize – received only B pollen Same method is followed for C and D in another locality The yield of single cross hybrid is usually low because inbred parent lacks vigour and produces small cobs Plants germinate from single cross seeds – vigorous hybrids with large cobs and many kernels Double cross – using pollen from the CD hybrid on the AB hybrid

19. Genetic basis of heterosis Two hypothesis Dominance hypothesis of heterosis – holds that increased vigour and size in a hybrid due to combination of favourable growth genes by crossing two inbred races Eg ., Quinby and Karper – heterosis in sorghum – observed that heterozygote is significantly late in maturity and produces a greater weight of grain than either of the homozygote parents Keeble and Pellow – studied two varieties of pea both semi-dwarf, one with thin stem and long internodes and the other with thick stem and short internodes The F1 hybrid – taller than either of parents, combining the long internodes of one parent and many nodes of the other Over dominance hypothesis of heterosis – proposed by Shull and East independently in 1908 Increases with diversity of uniting gametes Heterozygote is superior to either homozygous Vigour increases in proportion to the amount of heterozygosity

20. Application of heterosis Exploited at commercial scale both in plants and animals In plants – applied to crop plants, ornamentals, fruit crops More important in vegetatively propogating plants In fruit plants and ornamental plants – if heterosis is achieved – may maintained for long Sometime intermediate phenotypes are preferred General purpose cattle can be produced by crossing beef type with a dairy type – offspring produce an intermediate yield of milk and have a fair meat when slaughtered Similar in chicken – egg type with meat type Plants – disease resistance

21. Evolutionary significance of inbreeding and outbreeding Both provide raw material to natural of selection Inbreeding allows natural selection to operate on successive genes – but not permit the introduction of good mutations from outside Outbreeding provides an oppurtunity for the accumulation of good trait of different races in one individual or line It expresses good qualities of the races and masked the deleterious recessive alleles Both provide new allelic combinations which may be good or bad for the natural selection