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
0 P2 2pq q2
1 P2+(pq/2) pq q2
2 P2+(3pq/4) Pq/2 q2+(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

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:
 RBC = 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)
1. 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 FA = ½ RBC, Where RBC is the
coefficient of relationship between the full sib parent (B and C) of A
2. 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+FA)
n = number of arrows which connect the individual through one parent back to the common
ancestor and back again to his other parent
FA 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
FE = ½ RGH (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

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

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