Nondisjunction in Meiosis: Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate during meiosis, resulting in an abnormal chromosome number.
What results when there is an error during meiosis?
Errors can occur during meiosis producing gametes with an extra or missing chromosome. The consequences of this following fertilisation depend on which chromosomes are affected. Often the embryo is not viable, but some of these errors can lead to trisomy conditions or sex chromosome disorders.
What causes errors in meiosis?
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.
During which phase of meiosis are errors likely to occur?
Meiosis II progresses the same way as mitosis, but with the haploid number of chromosomes, ultimately creating 4 daughter cells all genetically distinct from the original cell. Nondisjunction can occur during anaphase of mitosis, meiosis I, or meiosis II.
What happens if mitosis goes wrong?
Mistakes during mitosis lead to the production of daughter cells with too many or too few chromosomes, a feature known as aneuploidy. Nearly all aneuploidies that arise due to mistakes in meiosis or during early embryonic development are lethal, with the notable exception of trisomy 21 in humans.
Which of the following does not undergo mitosis?
While WBCs do retain their nucleus while in peripheral circulation, most are also what we call terminally differentiated, since they can no longer undergo mitosis. Skeletal muscle can undergo hypertrophy, as each cell gets bigger. But skeletal muscle cells do undergo hyperplasia, since no new cells are generated.
Does polyploidy occur in humans?
Polyploid cells are found in diverse taxa (Fox and Duronio, 2013; Edgar et al., 2014), and in fact entire organisms can be polyploid, or polyploid cells can exist in otherwise diploid organisms (endopolyploidy). In humans, polyploid cells are found in critical tissues, such as liver and placenta.
Can sperm cause chromosomal abnormalities?
An estimated 1 to 4 percent of a healthy male’s sperm have abnormal numbers of chromosomes, or aneuploidy, that are caused by errors during cell division (meiosis) in the testis.
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.