law Thomas Morgan



Every living organism has a set of genes and chromosomes.When this gene is significantly higher.They number about 1 million.Much less chromosomes - only 23 pairs.Each chromosome contains from three to five thousand genes.They form a group of clutches.This group falls into one reproductive sex cells (gametes) by reducing cell division (meiosis).

genes of one linkage group is not subject to the law of independent inheritance.Organisms, characterized by two pairs of features do not split phenotype in a ratio of 9: 3: 3: 1.And give a 3: 1 ratio.That is the same as when monohybrid cross.

Laws of linked inheritance set Thomas Morgan.American biologist used a fruit fly Drosophila as an object of scientific study.This species has a
diploid set of chromosomes 8 and is very useful for research.

experience with Drosophila



One - female with gray body and normal wings.Other - male.He has short wings and a dark body color.As a result, crossing the first generation will have normal wings and gray color.Because the gene which determined gray color dominates a gene determining a dark color.At the same time, a gene that is responsible for the normal development of the wings will be stronger than the gene, because of which originally had a short male, undeveloped wings.

the advantages of gray and the normal length of the wing meets the body flies set of linked genes.They are on the same chromosome with those genes that cause dark body and short wings.This is the inheritance of genes called entangled.As a result of crossbreeding and hybrid flies homozygous (ie, pure-blooded organism, producing one kind of germ cells), most descendants will be as close as possible to the parent form.

However, the clutch may be impaired as a result of crossing-over (from the English. Crossingover - crossing).In this case, there is a mutual exchange of individuals homologous regions homologous chromosomes.These strands (chromatids) are broken and are connected in a new poryadke.Tak there are new combinations of alleles of different genes.This mechanism is very important as it provided variability of the population and, therefore, it becomes possible to natural selection.

The greater the distance between the two genes, the more possible gap.Accordingly, the genes can not be inherited together.Exactly the opposite is happening all with closely spaced genes.Since Morgan was made one of the greatest discoveries.It is known that the value of the distances between the genes directly affect the degree of cohesion within the chromosome.Accordingly, the genes are arranged in it in a particular linear sequence.