Principles of Inheritance and Variation Test - 10

Segregation of homologous chromosomes occurs during gametes formation. During gametes formation reduction division of meiosis division occurs in which number of chromosome reduce to half.

A chromosome with sub-terminal centromere near the middle is called acrocentric chromosome. In acrocentric chromosome one arm is larger and other is shorter.

Linkage is the non-separation of two genes present on same chromosome. Segregation is the separation of two allels from each other. So segregation is opposite to linkage.

After the discovery of Mendel’s laws of inheritance, scientists turned naturally to the problems of mechanics of the processes they observed. The “what” of earliest twentieth century rapidly gave way to a concern with “how”?

A pair of papers by Sutton as early as 1902 and 1903 (only two and three years, respectively, after the re­discovery of Mendel’s landmark papers initiated the modem age of genetics) clearly pointed the way to a physical basis for the science of heredity. The chromosomal theory of inheritance was proposed independently by Sutton and Boveri in 1902.

Plotting of specific genes on the chromosome is known as chromosome map or linkage map or genetic map. It shows the position of genes on chromosome in respect to others.

When two genes are situated very close to one another on chromosome, hardly any cross-over are produced. Such genes are called linkage and do not separate from each other during gamete formation.

Sex chromosomes of human beings are heteromorphic as they are of different size. Y chromosome is smaller than X chromosome in size.

The bridge between one generation and the next generation are sperm and ovum. Both sperm and ovum contribute equally in heredity. The somatic diploid cells two chromosomes as well as two mendelian factors of each types.

In diploid cells both chromosomes and genes occur in pairs. Two alleles of gene pair are located on homologous sites on homologous chromosomes.