What causes nondisjunction during meiosis II?

Nondisjunction in meiosis II results from the failure of the sister chromatids to separate during anaphase II. Since meiosis I proceeded without error, 2 of the 4 daughter cells will have a normal complement of 23 chromosomes. The other 2 daughter cells will be aneuploid, one with n+1 and the other with n-1.

What causes nondisjunction to happen?

Nondisjunction occurs when chromosomes fail to segregate during meiosis; when this happens, gametes with an abnormal number of chromosomes are produced.

What is the most common cause of nondisjunction of chromosomes?

They are caused by nondisjunction, which occurs when pairs of homologous chromosomes or sister chromatids fail to separate during meiosis. The risk of nondisjunction increases with the age of the parents. Nondisjunction can occur during either meiosis I or II, with different results (Figure 7.8).

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What is the result of a nondisjunction during meiosis II quizlet?

If nondisjunction occurs during meiosis II, sister chromatids fail to separate. In this case, 50% of the gametes that are produced are normal haploid gametes, 25% of gametes have an extra chromosome, and 25% are missing a chromosome.

What happens in meiosis 2 of meiosis?

During meiosis II, the sister chromatids within the two daughter cells separate, forming four new haploid gametes. … Therefore, each cell has half the number of sister chromatids to separate out as a diploid cell undergoing mitosis.

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.

How does nondisjunction during meiosis I differ from nondisjunction in meiosis II?

Nondisjunction can occur during meiosis I and meiosis II, resulting in abnormal chromosomes number of gametes. The key difference between nondisjunction in meiosis 1 and 2 is that during meiosis 1, homologous chromosomes fail to separate while in meiosis II sister chromatids fail to separate.

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.

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Where does nondisjunction occur in meiosis?

Nondisjunction can occur during anaphase of mitosis, meiosis I, or meiosis II. During anaphase, sister chromatids (or homologous chromosomes for meiosis I), will separate and move to opposite poles of the cell, pulled by microtubules.

What events during meiosis produces trisomies and Monosomies?

If a gamete with two copies of the chromosome combines with a normal gamete during fertilization, the result is trisomy; if a gamete with no copies of the chromosomes combines with a normal gamete during fertilization, the result is monosomy.

Which describes the cells at the end of meiosis I when nondisjunction occurs during meiosis II select all of the correct statements?

One cell with extra homologous chromosomes and one cell missing a homologous chromosome. Which describes the cells at the end of meiosis I when nondisjunction occurs in meiosis II? The homologous pairs are in separate cells. The cells are haploid.

What occurs during nondisjunction quizlet?

If nondisjunction occurs during meiosis I, homologous chromosomes fail to separate. This produces abnormal gametes that contain two members of the affected chromosome or none at all.

What events occur during meiosis I and meiosis II?

Homologous pairs of cells are present in meiosis I and separate into chromosomes before meiosis II. In meiosis II, these chromosomes are further separated into sister chromatids. Meiosis I includes crossing over or recombination of genetic material between chromosome pairs, while meiosis II does not.

Which event occurs during meiosis II but not during meiosis?

In meiosis I, homologous chromosomes separate, while in meiosis II, sister chromatids separate. Meiosis II produces 4 haploid daughter cells, whereas meiosis I produces 2 diploid daughter cells. Genetic recombination (crossing over) only occurs in meiosis I.

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Which of the following occurs during meiosis II?

In meiosis II, the sister chromatids separate, making haploid cells with non-duplicated chromosomes.