Nondisjunction of chromosomes produces conditions such as T

. Nondisjunction of chromosomes produces conditions such as Turner syndrome (XO) or Down syndrome (trisomy 21). a) When, during meiosis, could this nondisjunction have occurred to produce these conditions? Draw this out to convince yourself of how these could come about during meiosis.

b) Nondisjunction of chromosomes produces an individual with the sex chromosomes XYY. When, during meiosis, could this have occurred and in which parent?

Solution

a) Turner Syndrome is caused due to variation of the chormosome number where in chromosomes are found as univalents at metaphase I of meiosis and during the anaphase I , these univalents ditribute at random.. Turner syndrome is with XO condition which is found in females.

Downs Syndrome is caused due to trisomic condition of chromosome number 21. This pair of chromosome has one extra number, a trivalent structure which is formed during meitic prophase.

b) X is a female chromosome and Y is a male chromosome. XYY Syndrome is caused due to an extra Y male chromosome which happens during anaphase II of meiosis II . This happens during the formation of sperm cells.