Question

Please explain the Chromosome Theory of Inheritance. Explain how Mendal’s law of segregation and law of independent assortment relate to the above theory. How does crossing over disrupt these laws? Please use the term “linkage group” in your answer and explain how that term relates to all of the above. (500 word minimum).

Answer 1

Chromosome Theory of Inheritance;

In 1902 and 1903, Sutton and Boveri published independent papers proposing what we now call the chromosome theory of inheritance. This theory states that individual genes are found at specific locations on particular chromosomes, and that the behavior of chromosomes during meiosis.

these theory can explain Mendel’s laws of inheritance.

Observations that support the chromosome theory of inheritance include:

• Chromosomes, like Mendel's genes, come in matched (homologous) pairs in an organism. For both genes and chromosomes, one member of the pair comes from the mother and one from the father.
• The members of a homologous pair separate in meiosis, so each sperm or egg receives just one member. This process mirrors segregation of alleles into gametes in Mendel's law of segregation. it state that When an organism makes gametes, each gamete receives just one gene copy, which is selected randomly. This is known as the law of segregation.
• The members of different chromosome pairs are sorted into gametes independently of one another in meiosis, just like the alleles of different genes in Mendel's law of independent assortment. it state that endel's law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.

The chromosome theory of inheritance was proposed before there was any direct evidence that traits were carried on chromosomes, and it was controversial at first. In the end, it was confirmed through the work of geneticist Thomas Hunt Morgan and his students, who studied the genetics of fruit flies.

linkage group, in genetics, all of the genes on a single chromosome. They are inherited as a group; that is, during cell division they act and move as a unit rather than independently. The existence of linkage groups is the reason some traits do not comply with Mendel’s law of independent assortment (recombination of genes and the traits they control); i.e., the principle applies only if genes are located on different chromosomes. Variation in the gene composition of a chromosome can occur when a chromosome breaks, and the sections join with the partner chromosome if it has broken in the same places. This exchange of genes between chromosomes, called crossing over, usually occurs during meiosis, when the total number of chromosomes is halved.

Sex linkage is the tendency of a characteristic to be linked to one sex. The X chromosome in Drosophila flies and human beings, for example, carries a complete set of genes; the Y chromosome has only a few genes. Eggs of females carry an X chromosome; sperm of males may carry an X or a Y. An egg fertilized by a sperm with an X chromosome results in a female; one fertilized by a sperm with a Y chromosome results in a male. In offspring with the XY chromosome pair, any trait carried by the X chromosome will appear unless there is a corresponding gene (allele) on the Y chromosome. Examples of sex-linked traits in man are red–green colour blindness and hemophilia. These traits are controlled by genes on the X chromosome and thus occur much more frequently in men than in women because there is no allele on the Y chromosome to offset them. See also sex chromosome.