The phenomenon of unequal separation in meiosis is called nondisjunction. If nondisjunction causes a missing chromosome in a haploid gamete, the diploid zygote it forms with another gamete will contain only one copy of that chromosome from the other parent, a condition known as monosomy.
Why is it important for chromosomes to separate during meiosis?
Because meiosis creates cells that are destined to become gametes (or reproductive cells), this reduction in chromosome number is critical — without it, the union of two gametes during fertilization would result in offspring with twice the normal number of chromosomes!
What happens during meiosis that ultimately would result in there being an extra or missing chromosome?
Figure 7.8 Following meiosis, each gamete has one copy of each chromosome. Nondisjunction occurs when homologous chromosomes (meiosis I) or sister chromatids (meiosis II) fail to separate during meiosis. … The most common trisomy is that of chromosome 21, which leads to Down syndrome.
What is the failure of chromosomes to separate during mitosis?
Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division.
When sections of chromosomes are lost it is called a?
segment is lost; or by translocation, when a segment changes from one location to another in the same or a different chromosome. These are the processes by which chromosomes evolve.
What chromosome is affected in Klinefelter syndrome?
Klinefelter syndrome (sometimes called Klinefelter’s, KS or XXY) is where boys and men are born with an extra X chromosome.
What is the difference between meiosis 1 and meiosis 2?
There are two divisions in meiosis; the first division is meiosis I: the number of cells is doubled but the number of chromosomes is not. This results in 1/2 as many chromosomes per cell. The second division is meiosis II: this division is like mitosis; the number of chromosomes does not get reduced.
What is the result of nondisjunction?
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 are the stages of mitosis?
Today, mitosis is understood to involve five phases, based on the physical state of the chromosomes and spindle. These phases are prophase, prometaphase, metaphase, anaphase, and telophase.