When teaching a class about trisomy 21, the instructor would identify the cause of thisdisorder as:A. nondisjunction.B. X-linked recessive inheritance. C. genomic imprinting.D. autosomal dominant inheritance.
Answer: ARationale: Trisomy 21 is an example of a genetic disorder involving an abnormality in chromosomal number due to nondisjunction. X-linked recessive inheritance disorders, such as Genomic imprinting disorders, such as Prader-Willi syndrome, involve expression of only the maternal or paternal allele, with the other being inactive. Autosomal dominant inheritance hemophilia and Duchenne muscular dystrophy, involve altered genes on the X chromosome. disorders, such as neurofibromatosis and achondroplasia, involve a single gene in the heterozygous state that is capable of producing the phenotype, thus overshadowing the normal gene.
A. Nondisjunction.
Trisomy 21, also known as Down syndrome, is a genetic disorder caused by the presence of three copies of chromosome 21, instead of the normal two copies. This is due to nondisjunction, which is an error that occurs during cell division where chromosomes fail to separate properly. As a result, one of the resulting cells has an extra chromosome while the other cell is missing a chromosome, leading to the production of gametes with an abnormal number of chromosomes. This condition is not inherited in a traditional sense, but rather occurs spontaneously during cell division in the early stages of fetal development.
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