Would nondisjunction in meiosis i or ii form a gamete that could cause calix’s calico fur?
Question: Would nondisjunction in meiosis i or ii form a gamete that could cause calix’s calico fur?
Calix is a rare male calico cat with a beautiful coat of orange, black and white patches. Calico cats are usually female because their fur color is determined by the X chromosome, and females have two X chromosomes while males have one X and one Y. However, some males can inherit an extra X chromosome from their parents, making them XXY. This is a result of a genetic error called nondisjunction, which occurs when chromosomes fail to separate properly during cell division.
Nondisjunction can happen in either meiosis I or meiosis II, the two stages of cell division that produce gametes (sperm and egg cells). In meiosis I, the homologous pairs of chromosomes (one from each parent) are separated into two daughter cells. In meiosis II, the sister chromatids (identical copies of each chromosome) are separated into four daughter cells. Each daughter cell should have one copy of each chromosome, or 23 in humans.
If nondisjunction happens in meiosis I, both sister chromatids of one homologous pair will go to the same daughter cell, while the other daughter cell will get none. This means that one cell will have two copies of the same chromosome, and the other will have none. If this cell goes on to fertilize or be fertilized by a normal gamete, the resulting offspring will have either three or one copy of that chromosome, instead of the normal two. This is called trisomy or monosomy, respectively.
If nondisjunction happens in meiosis II, one sister chromatid will fail to separate from the other and both will go to the same daughter cell, while the other daughter cell will get none. This means that one cell will have two copies of the same chromosome, and the other will have none. However, the other two daughter cells will be normal, with one copy of each chromosome. If the abnormal cell goes on to fertilize or be fertilized by a normal gamete, the resulting offspring will have either three or one copy of that chromosome, depending on which cell was involved. This is also called trisomy or monosomy, respectively.
So, which type of nondisjunction could cause Calix's calico fur? The answer is either one, as long as it involves the X chromosome. If nondisjunction happens in meiosis I in Calix's father, he could produce a sperm cell with two X chromosomes and another with none. If he mates with a normal female cat with two X chromosomes, she could produce an egg cell with one X chromosome. If the sperm cell with two X chromosomes fertilizes the egg cell with one X chromosome, the offspring will be XXY, a male calico cat like Calix.
If nondisjunction happens in meiosis II in Calix's father, he could produce a sperm cell with two X chromosomes and another with none, as well as two normal sperm cells with one X chromosome each. If he mates with a normal female cat with two X chromosomes, she could produce an egg cell with one X chromosome. If the sperm cell with two X chromosomes fertilizes the egg cell with one X chromosome, the offspring will be XXY, a male calico cat like Calix.
Therefore, both meiosis I and meiosis II nondisjunction can result in a male calico cat like Calix, as long as it affects the X chromosome in his father's sperm cells.
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