Linkage inheritance of the genes. The groups of linked genes. Complete and incomplete linkage of genes.

Date: 2015-10-07; view: 425.

According to theory by T.Morgan, the genes, which lie in one chromosome, form a group of linked genes. Thereby, number of groups of linked genes is the same, as a number of chromosomes in haploid kit of chromosomes. Genes that belong to one group of genes inherit together.

Distance between genes in the group of linked genes of can be different. Than more distance, that more probability of crossing over is, and that more often genes are inherited separately. The unit of distance between genes in the group of linked genes is Morgan. One Morgan is such distance between genes, when probability of crossing over is equal one percent. Maximum distance between loci by the gene in one group of linked genes is equal to 50%.

If genes lie very closely to one another, they are considered closely linked. Probability of crossing over between they is equal to 0%. This phenomenon is named as complete linkage of genes. If genes lie far off from each other, for instance, on the distance of some Morgans, the crossing over is possible. These genes are identified as not closely linked genes. It is phenomenon of incomplete linkage of genes.

The distance between genes within one group of linked genes is defined by probability of arising of crossing over posterity. For example, as a result of cross of gray fly (A) with long wings (B) and black fly (a) with shot wings (b) the filial generation is arise. The flies of filial generation are: gray flies with long wings (41,5%), black flies with shot wings (41,5%), black flies with long wings (8,5%), and gray flies with shot wings (8,5%). The flies, those are like parents are named as crossing over posterity. The flies, those are unlike parents are named as uncrossing over posterity. The distance between loci of genes A and B is equal of 17 Morgans.

P AB//ab x ab//ab

G n.c.o. AB, ab ab

c.o. Ab, aB ab

F1 AB//ab, ab//ab, Ab//ab, aB//ab

41,5%, 41,5%, 8,5%, 8,5%