XAMPLE 2: The parents in the family above produce another son, this time with two Y chromosomes and normal tooth enamel. In which parent did the nondisjunction occur? Explain and/or illustrate.
I am not sure how to explain what parent the nondisjunction occurred from in example 2 part 1.
- Sometimes nondisjunction will occur in a parent that has normal chromosome numbers and result in an offspring that has abnormal number of chromosomes. The
phenotype of the affected offspring will often allow geneticists to determine in which parent and during which division of meiosis the nondisjunction occurred. In each of the examples below, assume the parents have a normal diploid chromosome complement.
EXAMPLE 1: A man with the X-linked dominant condition “brown tooth enamel” and a woman with normal tooth enamel produce a son with brown tooth enamel. Let’s call the allele for brown tooth enamel “XB” and normal tooth enamel “Xb”.
- In which parent did the nondisjunction occur? Explain and/or illustrate
- Did nondisjunction occur at meiosis I or II? Explain and/or illustrate.
- What sex chromosomes are in the child’s somatic cells?
EXAMPLE 2: The parents in the family above produce another son, this time with two Y chromosomes and normal tooth enamel.
- In which parent did the nondisjunction occur? Explain and/or illustrate.
The nondisjunction occurs in the father in which during the second meiotic division nondisjunction occurs and fails to transfer 1 copy of the Y chromosome in each sperm. Both Y chromosomes are transferred to one sperm which combines with a normal X chromosome-containing egg.
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