Question

Aneuploidy may be the result of a. duplication of a region of a chromosome. b. inversion of a region of a chromosome. c. nondisjunction during meiosis. d. interspecies breeding. e. all of the above.

Short answer

The correct answer is c. nondisjunction during meiosis.

Step-by-step solution

Understand the Concepts

First, understand the terminologies. Duplication of a region of a chromosome means that a part of the chromosome is repeated. Inversion of a region of a chromosome concerns a segment of a chromosome which has been reversed end to end. Nondisjunction during meiosis talks about the failure of homologous chromosomes to separate properly during cell division. Interspecies breeding pertains to reproduction involving organisms of different species.

Evaluate Each Choice

Evaluate each choice. Duplication and inversion results in structural changes in the chromosome, but not necessarily aneuploidy. Interspecies breeding could lead to a variety of outcomes, but not necessarily aneuploidy. Nondisjunction during meiosis, however, directly leads to aneuploidy, as it creates gametes with too many or too few chromosomes.

Choose the Correct Option

From the evaluation in Step 2, it is clear that choice 'c. nondisjunction during meiosis' is the direct cause of aneuploidy, even though the other phenomena could possibly lead to genetic changes. Hence, 'c' is the correct option in this case.

Key concepts

Nondisjunction in Meiosis

When we talk about nondisjunction in meiosis, we refer to a significant error that occurs during the segregation of chromosomes as a sex cell divides. This process has two stages, meiosis I and meiosis II, and nondisjunction can happen at either stage. If chromosomes fail to separate properly, this leads to gametes—sperm or eggs—that have an abnormal number of chromosomes. When such a gamete fuses with a normal one, the resulting zygote may have an incorrect chromosome number, a condition called aneuploidy. For instance, Down syndrome is often caused by an extra copy of chromosome 21, which is a result of nondisjunction.

Understanding nondisjunction is critical because it can have profound implications for an individual’s health and development. Detecting and managing nondisjunction-related conditions require a solid grasp of genetics and meiosis.

Chromosome Duplication

Chromosome duplication is when a segment of a chromosome is copied and attached to the original, resulting in a chromosome with repeated genetic material. This can happen due to mistakes during DNA replication or through a process known as unequal crossing over during meiosis when chromosomes exchange segments.

While chromosome duplication doesn't typically lead to aneuploidy (a change in the number of chromosomes), it can cause genetic disorders if the duplicated segment contains genes. When genes are duplicated, their expression may be altered, potentially leading to developmental issues or health problems. The duplication of a whole chromosome, however, could lead to aneuploidy, as seen in some genetic disorders.

Chromosome Inversion

Chromosome inversion refers to a situation where a chromosome segment is reversed end to end. Imagine a piece of chromosome breaking off, flipping around, and reattaching—but now the genetic sequence is in reverse order. Inversions can be pericentric, involving the chromosome's centromere, or paracentric, not involving the centromere.

This alteration doesn't change the total genetic information or the number of chromosomes, so it doesn't cause aneuploidy. However, it may lead to problems during meiosis if the inversion interrupts the pairing of chromosomes, potentially causing abnormal crossovers. Depending on where genes are located within the inverted segment, this can result in genetic diseases or infertility.

Interspecies Breeding

Interspecies breeding, sometimes known as hybridization, occurs when individuals from different species reproduce. Think of mules, the offspring of a donkey and a horse, as an example of this. Interspecies breeding can introduce a range of genetic variations and is an intriguing topic in evolutionary biology. However, it doesn't typically result in aneuploidy because it involves the combination of distinct species' genetic materials rather than a change in chromosome number.

It's worth noting that most interspecies hybrids are sterile, which means they can't produce offspring. This is due to differences in chromosome number or structure between the parental species, which can interfere with meiotic chromosomal pairing in the hybrids and ultimately prevent the successful creation of viable gametes.