What phase does nondisjunction occur?


What phase does nondisjunction occur?

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.

How is Klinefelter syndrome caused?

Klinefelter syndrome can be caused by: One extra copy of the X chromosome in each cell (XXY), the most common cause. An extra X chromosome in some of the cells (mosaic Klinefelter syndrome), with fewer symptoms. More than one extra copy of the X chromosome, which is rare and results in a severe form.

What is nondisjunction and when does it occur?

Nondisjunction means that a pair of homologous chromosomes has failed to separate or segregate at anaphase so that both chromosomes of the pair pass to the same daughter cell. This probably occurs most commonly in meiosis, but it may occur in mitosis to produce a mosaic individual.

How does Klinefelter syndrome occur during meiosis?

The 47,XXY karyotype of Klinefelter syndrome spontaneously arises when paired X chromosomes fail to separate (nondisjunction in stage I or II of meiosis, during oogenesis or spermatogenesis). Maternal and paternal meiotic nondisjunction each account for approximately 50% of Klinefelter syndrome cases.

What is the result of nondisjunction during 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 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).

When does Klinefelter syndrome occur?

In a typical situation, if an X sperm meets an egg holding an X, the resulting baby will be a female (46, XX). If the sperm holds a Y chromosome when it meets the egg, the resulting baby will be a male (46, XY). Klinefelter syndrome happens when there is an extra X chromosome in the genetic code.

What is the karyotype for Klinefelter syndrome?

Klinefelter Syndrome (47, XXY) is a chromosomal variation in males in which one extra X chromosome is present, resulting in a 47,XXY karyotype.

What process occurs during meiosis that can result in chromosomal disorders?

Disorders of chromosome number include the duplication or loss of entire chromosomes, as well as changes in the number of complete sets of chromosomes. They are caused by nondisjunction, which occurs when pairs of homologous chromosomes or sister chromatids fail to separate during meiosis.

What are 3 disorders due to nondisjunction?

Chromosomal Abnormalities Patau’s Syndrome (trisomy 13) Edwards Syndrome (trisomy 18) Down Syndrome (trisomy 21) Klinefelter Syndrome (XXY)

What would happen if during meiosis?

During meiosis one cell? divides twice to form four daughter cells. These four daughter cells only have half the number of chromosomes? of the parent cell – they are haploid. Meiosis produces our sex cells or gametes? (eggs in females and sperm in males).

Why does Klinefelter syndrome only occur in males?

Klinefelter syndrome only affects males. It happens because of a difference deep inside the body’s cells, in microscopic strings of DNA (what make up genes) called chromosomes. Chromosomes are tiny, but they play a huge role in who we are — including deciding our gender, how we look, and how we grow.