Down syndrome, a trisomy of chromosome 21, is the most common anomaly of chromosome number in humans. The majority of cases result from nondisjunction during maternal meiosis I.
What is the effect of nondisjunction in meiosis?
Nondisjunction in meiosis can result in pregnancy loss or birth of a child with an extra chromosome in all cells, whereas nondisjunction in mitosis will result in mosaicism with two or more cell lines. Aneuploidy may also result from anaphase lag.
What is most likely caused by nondisjunction during meiosis?
Mitotic nondisjunction can cause somatic mosaicism, with the chromosome imbalance only reflected in the direct offspring of the original cell where the nondisjunction occurred. This can cause some forms of cancer, including retinoblastoma.
What is the result of nondisjunction?
Nondisjunction: Failure of paired chromosomes to separate (to disjoin) during cell division, so that both chromosomes go to one daughter cell and none go to the other. Nondisjunction causes errors in chromosome number, such as trisomy 21 (Down syndrome) and monosomy X (Turner syndrome).
How do nondisjunction errors in meiosis lead to aneuploidies such as trisomies and Monosomies?
Aneuploidy is caused by nondisjunction, which occurs when pairs of homologous chromosomes or sister chromatids fail to separate during meiosis. The loss of a single chromosome from a diploid genome is called monosomy (2n-1), while the gain of one chromosome is called trisomy (2n+1).
Which process would cause nondisjunction if it occurred during meiosis quizlet?
Nondisjunction can occur during anaphase of meiosis I or meiosis II. If it happens during meiosis I, an entire bivalent migrates to one pole (Figure 8.22a). Following the completion of meiosis, the four resulting haploid cells produced from this event are abnormal.
What is nondisjunction quizlet?
Nondisjunction refers to the failure of pairs of chromosomes or sister chromatids to separate during meiosis or mitosis.
Which of the following processes is the most likely to lead to production of a mosaic?
Anaphase lagging is the most common way by which mosaicism arises in the preimplantation embryo. Mosaicism can also result from a mutation in one cell during development, in which case the mutation will be passed on only to its daughter cells (and will be present only in certain adult cells).
Is Down syndrome caused by nondisjunction in meiosis 1 or 2?
Trisomy 21 or Down syndrome (DS) is one of the most common chromosomal abnormalities. The majority of full trisomy 21 is caused by chromosomal nondisjunction occurring during maternal meiotic division (∼90%). Errors occur more frequently in the first maternal meiotic division than the second (73% vs.
What occurs during nondisjunction and the effect of the resulting cells?
There are three forms of nondisjunction: failure of a pair of homologous chromosomes to separate in meiosis I, failure of sister chromatids to separate during meiosis II, and failure of sister chromatids to separate during mitosis. Nondisjunction results in daughter cells with abnormal chromosome numbers (aneuploidy).
Which of the following conditions is caused by aneuploidy?
Chromosomes in Down syndrome, one of the most common human conditions due to aneuploidy. There are three chromosomes 21 (in the last row). Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46.
How can nondisjunction lead to aneuploidies?
In meiosis, nondisjunction can take place either during anaphase I or during anaphase II. In either case, it can lead to gametes that have an incorrect number of chromosomes. If a male and a female gamete combine to form a zygote and either one of the gametes has aneuploidy, then the zygote will also have aneuploidy.
Why does aneuploidy in animals generally result in phenotypic abnormalities?
Why does aneuploidy in animals generally result in phenotypic abnormalities? … It results in an imbalance of gene products from affected chromosomes, which alters normal development. It results in an imbalance of gene products from affected chromosomes, which alters normal development. You just studied 10 terms!