Interactions of allelic genes

Date: 2015-10-07; view: 558.

F2 AA, 2Aa, aa

G A, a A, a

P2 Aa x Aa

F1 Aa

G A a

P1 AA x aa

G.Mendel laws of heredity

First law - the law of unit characters.

As a result of crossing of homozygous dominant and homozygous recessive organisms the unit character heterozygous filial generation is formed.

Second law - the law of segregation.

As a result of crossing of two heterozygous the filial generation is formed whit segregation 3 dominant to 1 recessive (phenotype) and 1 dominant homozygous to 2 heterozygous and 1 recessive homozygous (genotype).

Third law - the law ofindependent assortment.

When there are two pairs of contrasting characters, then the distribution of each pair to the gametes is independent of the distribution of the pair of characters, or that each of a pair of characters may combine with either character of the other pair.

There are some types of allelic genes interactions:complete dominance, incomplete dominance, over dominance, codominant alleles.

Complete dominanceis such type ofallelic genes interactions in which one gene is dominant, and other allelic gene is recessive. For example yellow and green color of peas pod.

Over dominance is such type ofallelic genes interactions in which dominant gene expression is more in case of heterozygous (Aa) than in case of dominant homozygous (AA). For example the length of fly's wings is more in case of heterozygous (Aa) than in case of dominant homozygous (AA). A – is gene of long wings, and a – is gene of short wings.

Codominant alleles occur when rather than expressing an intermediate phenotype, the heterozygotes express both homozygous phenotypes. An example is in human ABO blood types, the heterozygote AB type manufactures antibodies to both A and B types. Blood Type A people manufacture only anti-B antibodies, while type B people make only anti-A antibodies. Codominant alleles are both expressed. Heterozygotes for codominant alleles fully express both alleles. Blood type AB individuals produce both A and B antigens. Since neither A nor B is dominant over the other and they are both dominant over O they are said to be codominant.

The example of codominant alleles Vh and Vf, which are determinant the pictures on leaves.