Meiosis (3.3, 10.1) Flashcards
Aneuploidy
An abnormal number of chromosomes in a cell.
Types of aneuploidy
- Autosomal aneuploidy (eg. trisomies)- Sex chromosome aneuploidy- Polyploidy
Give two examples of autosomal aneuploidy
Downs syndrome (Trisomy 21)Edwards syndrome (Trisomy 18)
Give two examples of sex chromosome aneuploidy
Klinefelter syndrome (extra X chromosome in men) eg. XXYTurner syndrome (missing X chromosome in women) eg. XO
Non-disjunction
Refers to the chromosomes failing to separate correctly in meiosis, resulting in gametes with one extra, or one missing chromosome.
Trisomy
A genetic disorder where an individual has an additional copy of a chromosome (i.e. three instead of two).
Monosomy
A zygote with only one homologue.
What can influence non-disjunction?
The age of the parents. There is a particularly strong correlation between maternal age and non-disjunction.
What is Meiosis?
Cell division for the production of gametes (sex cells). It occurs in the ovaries and testes and involves the division of a diploid cell into four genetically distinct haploid nuclei.
Stage that precedes Meiosis
Interphase - Here the DNA is replicated to produce chromosomes consisting of two sister chromatids.
Meiosis 1
The division of homologous chromosomes into two intermediate cells (i.e. diploid -> haploid).This stage is where mutations may occur that result in an abnormal number of chromosomes eg. Downs Syndrome.
First stage of Meiosis 1
Prophase 1 (P1) - The chromosomes condense and the nuclear membrane dissolves. The homologues chromosomes pair up in synapsis to form bivalents. Crossing over can occur.
Second stage of Meiosis 1
Metaphase 1 (M1) - The bivalents line up at the equator randomly. This results in independent assortment.
Third stage of Meiosis 1
Anaphase 1 (A1) - The bivalents separate and the homologous chromosomes move to opposite poles of the cell.
Last stage of Meiosis 1
Telophase 1 (T1) - Chromosomes decondense. The nuclear membrane may reform. Cell divides in cytokinesis to form two haploid (n) daughter cells.