Question

People with trisomy 21 develop Down’s syndrome. What law of Mendelian inheritance is violated in this disease? What is the most likely way this occurs?

a) Law of Dominance; through the absence of a dominant allele
b) Law of Segregation; through the failure of chromosomes to separate
c) Law of Independent Assortment; through non-random assortment of chromosomes
d) Law of Unit Characters; through the blending of parental traits

Answer 1

Down's syndrome, occurring due to trisomy 21, violates Mendel's Law of Segregation, being caused by chromosomal nondisjunction during meiosis.

Step-by-step explanation:

People with trisomy 21 develop Down's syndrome, which is the presence of an extra copy of chromosome 21. This does not follow Mendel's Law of Segregation, which states that genes must segregate equally into gametes. The violation occurs due to chromosomal nondisjunction during meiosis, where chromosomes fail to separate properly, leading to gametes with an abnormal number of chromosomes. The likelihood of nondisjunction increases with maternal age, particularly in females over 36. Unlike Mendelian inheritance of single genes, which follows specific predictable ratios, chromosomal disorders such as Down syndrome result from errors in the distribution of entire chromosomes.