"A single characteristic that is controlled by two or more genes"
What is Polygenic inheritance ?
Polygenic inheritance, also known as quantitative or multifactorial inheritance, refers to inheritance of a phenotypic characteristic (trait) that is attributable to two or more genes . Those characters or traits which show continuous phenotypic variation are found to exhibit quantitative differences (in terms of number of genes).
Examples of Polygenic inheritance
Height,skin colour,hair and eye colour ,intelligence,etc. are the examples of polygenic inheritance .These characters are determined by more than one gene.
Characteristics of Polygenic inheritance :
Human skin colour : Human skin colour is a good example of polygenic inheritance. Lets assume that two genes determine the skin colour of an individual(AABB from father and aabb from mother -- means a very dark father and very fair mother).The 'dominant' alleles (A, B) control dark pigmentation in the skin, which means these alleles contribute increased amount of melanin .The 'recessive' alleles of the two genes (a, b) control light pigmentation in the skin, which means lower amounts of melanin are present.
Note: An individual inherits two alleles for each gene, one from each parent. If the two alleles are the same, the individual is homozygous for that gene( ex: AA or aa). If the alleles are different, the individual is heterozygous (ex:Aa or Bb).
A genotype with all the 'dominant' genes (AABB) has the maximum amount of melanin and so produces very dark skin. A genotype with all 'recessive' lower case genes (aabb) has the lowest amount of melanin and produces very light skin.
Example -- AABB × aabb
Male (AABB) contributes AB gametes to the offspring and the female (aabb) contributes ab gametes to the offspring .So the child will inherit AaBb genes from the parents and the skin colour will be moderate with two dominant alleles and two recessive alleles.
AaBb × AaBb
If the male with AaBb genes mate with the female with same AaBb genotype then,the possible gametes from the male are (AB or Ab or aB or ab).Similarly the possible gametes from the female are (AB or Ab or aB or ab) since both the male and female are of same skin colour .
What is Polygenic inheritance ?
Polygenic inheritance, also known as quantitative or multifactorial inheritance, refers to inheritance of a phenotypic characteristic (trait) that is attributable to two or more genes . Those characters or traits which show continuous phenotypic variation are found to exhibit quantitative differences (in terms of number of genes).
Examples of Polygenic inheritance
Height,skin colour,hair and eye colour ,intelligence,etc. are the examples of polygenic inheritance .These characters are determined by more than one gene.
Characteristics of Polygenic inheritance :
- In polygenic inheritance each gene has a certain amount of effect and more the number of dominant genes the more is the degree of expression of the character.
- The effect of each contributing gene is additive or cumulative unlike in case of Mendelian inheritance where only the dominant 'gene' expresses itself and determines the trait.
- There is no dominance involved (which means one gene will not override the influence of the other gene)
Human skin colour : Human skin colour is a good example of polygenic inheritance. Lets assume that two genes determine the skin colour of an individual(AABB from father and aabb from mother -- means a very dark father and very fair mother).The 'dominant' alleles (A, B) control dark pigmentation in the skin, which means these alleles contribute increased amount of melanin .The 'recessive' alleles of the two genes (a, b) control light pigmentation in the skin, which means lower amounts of melanin are present.
Note: An individual inherits two alleles for each gene, one from each parent. If the two alleles are the same, the individual is homozygous for that gene( ex: AA or aa). If the alleles are different, the individual is heterozygous (ex:Aa or Bb).
A genotype with all the 'dominant' genes (AABB) has the maximum amount of melanin and so produces very dark skin. A genotype with all 'recessive' lower case genes (aabb) has the lowest amount of melanin and produces very light skin.
Example -- AABB × aabb
Male (AABB) contributes AB gametes to the offspring and the female (aabb) contributes ab gametes to the offspring .So the child will inherit AaBb genes from the parents and the skin colour will be moderate with two dominant alleles and two recessive alleles.
AaBb × AaBb
If the male with AaBb genes mate with the female with same AaBb genotype then,the possible gametes from the male are (AB or Ab or aB or ab).Similarly the possible gametes from the female are (AB or Ab or aB or ab) since both the male and female are of same skin colour .
For any character in an offspring the father and mother contributes equal number of genes/alleles.In this case, assume that the alleles from the female gamete are on LHS and alleles from male gamete are on RHS.If father contributes two dominant alleles (AB) from his genes and mother also contributes two dominant alleles(AB) then the offspring will have all dominant genes (AABB).The more the number of dominant genes the darker will be the child.If the recessive genes are more in number (ex:aabb) then the child will be fair.So according to this example we can understand that the child born to a moderate coloured male and female (with genotype AaBb) can be very dark(4) or dark(3) or moderate(2) or light coloured(1) or very fair(0). The ratio for the same is 1:4:6:4:1
