Evolution and Genetic Variation

Genetic variation produced in sexual life cycles contributes to evolution.

Origins of Genetic Variation Among Offspring Behaviour of chromosomes during meiosis and fertilization are responsible for the variations that arise in each generation.

Three mechanisms are examined of which contribute to the genetic variation arising from sexual reproduction:

Independent Assortment of Chromosomes
Crossing over
Random Fertilization

Independent assortment

Meiosis I, which is the first meiotic division results in an assortment of maternal and paternal chromosomes in the two daughter cells. Each homologous pair lines up independently at the metaphase plate; the orientation of the maternal and paternal chromosomes is random. The number of possible combinations of maternal and paternal chromosomes is 2^n, where n represents the haploid number.

References:

1) Biology. Seventh Edition, Neil A. Campbell and Jane B. Reece. Pearson Eduction Inc., publishing as Benjamin Cummings, 1301 Sansome St., San Franscisco, CA

2) Biology. Peter H. Raven, George B. Johnson, Susan Singer, Jonathan Losos. McGraw-Hill Science/Engineering/Math; 7 edition (January 8, 2004)

3) DNA Science: A First Course, Second Edition. David A. Micklos. Cold Springs Harbor Laboratory Press; 2 edition (January 8, 2003)