Thomas Morgan - founder chromosome theory of heredity



Modern chromosome theory of heredity has created an outstanding American geneticist Thomas Morgan.He and his students worked mainly with the fruit fly Drosophila, having a diploid set of chromosomes 8.As a result of experiments, it became clear that the genes lying in the same chromosome inherited concatenated, i.e.during meiosis fall into one germ cell - gamete.This phenomenon is the essence of the law, later called "the law of Morgan."Morgan and his students has also been shown that every gene in a chromosome occupies a well-defined plot - locus.

Crossing chromosomes as one of the causes of genetic variation



Among the second generation of hybrids, but it was a small number of individuals w
ith evidence of recombination, the genes of which are on the same chromosome.Later, it was found an explanation: the fact that in the prophase of the first meiotic division homologous (paired) chromosomes are conjugated, ie,converging and crossing over occurs between them - crossing.

the point of contact they can rupture and exchange portions, whereby alleles come from one chromosome to another.At the same time the further genes are located, the higher the probability of their recombination, as closely spaced genes are less divided and often is linked inherited.Crossover - the most important source of genetic variability of organisms.

What are the signs of sex-linked, and how they are inherited



set of genes located in the sex chromosomes - X and Y - and not all of these genes encode signs of having any relation to the floor.In humans, 22 pairs of autosomes and one pair of sex chromosomes.Women homogametic on grounds of sex (XX), and men - heterogametic (XY).Localization of the gene in the sex chromosome is called "clutch gene with the floor."

In humans, for example, in the X-chromosome is a dominant gene which determines the normal blood clotting.The same recessive gene leads to hemophilia, whereby blood coagulation is broken.Since the Y-chromosome has no allelic pair for this gene in men hemophilia always appear despite the recessive gene and women - are extremely rare, even if it is its passive carrier (usually present and dominant allele that suppressesrecessive effect).Similarly, inherited color blindness - the inability to distinguish green and red colors.