Down syndrome (trisomy 21 ) and Edwards syndrome (trisomy...

Name: Problem 13, Chapter 17: Molecular Biology of the Cell
Uploaded: 2021-03-16T11:25:31-08:00
Duration: 1 min 13 s
Channel: Joanna Quigley
Description: Down syndrome (trisomy 21 ) and Edwards syndrome (trisomy 18) are the most common autosomal trisomies seen in human infants. Does this fact mean that these chromosomes are the most difficult to segregate properly during meiosis?

Down syndrome (trisomy 21 ) and Edwards syndrome (trisomy 18) are the most common autosomal trisomies seen in human infants. Does this fact mean that these chromosomes are the most difficult to segregate properly during meiosis?

Key Concepts

Meiosis

Meiosis is the specialized cell division process that produces gametes (sperm and egg cells) with half the number of chromosomes compared to the parent cell. This reduction is achieved through two consecutive cellular divisions, which are critical in ensuring that the resulting gametes have the correct haploid chromosome number for fertilization.

Chromosome Segregation

Chromosome segregation is the process by which chromosomes are accurately distributed to daughter cells during cell division. In the context of meiosis, the careful alignment and separation of homologous chromosomes ensure that each gamete receives the proper number of chromosomes, which is essential for normal development.

Nondisjunction

Nondisjunction refers to the failure of chromosome pairs or sister chromatids to separate properly during meiosis. This error can lead to gametes with an abnormal number of chromosomes, and if fertilization occurs, the resulting zygote may have an extra or missing chromosome, a condition known as trisomy or monosomy, respectively.

Autosomal Trisomy

Autosomal trisomy is a genetic condition where an individual has three copies of one of the autosomal chromosomes instead of the usual two. The occurrence of autosomal trisomies is influenced by both the mechanics of meiosis and biological selection processes, and some trisomies are more commonly observed because embryos with these imbalances can often continue development to birth.

Viability and Selective Pressure

Viability and selective pressure refer to the ability of an embryo with chromosomal abnormalities to survive and develop to term. Although errors in meiosis occur frequently, many result in embryos that are not viable, making certain trisomies, such as those leading to Down syndrome or Edwards syndrome, more commonly observed among live births not necessarily because of segregation difficulties, but due to their relative compatibility with development.

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