Answer to Question #60852 in Genetics for Sanjukta Ghosh

Question

Which of following is/are exception(s) of Law of segregation ? Why?
1. Parental imprinting
2 Random inactivation
3.Maternal effect
4.Incomplete penetrance
5.Nondysjunction
6. Meiotic drive
7.Lethal alleles
Note: You may just explain in a word or two for I understand these phenomena.

Answer 1

Mendel’s Law of Segregation is:
“During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.”
The exception from it is Nondysjunction of chromosomes. In non-disjunction, generally a complete homologous pair moves towards one gamete (in meiosis I) leaving another gamete with no chromosome of this pair. However, it can also occur in meiosis II if the 'replicated chromosome' moves only towards one gamete, leaving the other gamete with no chromosome.