Atypical Meiosis (SEC 4.5 PG 127)

Meiosis is the process that creates sex cells. During it the chromosomes are split evenly into different cells turning diploid cells into haploid cells.

Once in a while an error may occur.

A homologous pair does not get split and uneven haploid cells are created. This kind of error is called a non-disjunction.

If a gamete with too many or too few chromosomes takes part in fertilization, a zygote with more or less chromosomes than 46 is created. IF the zygote survives, it will have a syndrome of some sort.

Down Syndrome: 47 chromosomes – 3 copies of chromosome 21 (trisomy of

chromosome 21). Affects Male and Females. All have similar facial features. Mild to severe mental and physical disabilities.

Turner Syndrome: 45 chromosomes – Only 1 of the X chromosome (monosomy of sex

chromosome ‘X’). Only females. Cannot reproduce.

Trisomic Syndrome: 47 chromosomes – 3 copies of the X chromosome (trisomy

of the ‘X’ sex chromosome). Only females. Develop sexually and can reproduce, often taller and

thinner than average females.

Klinefelter Syndrome: 47 Chromosomes – 2 ‘X’ chromosomes and one ‘Y’ chromosome. Only Males. Develop sexually, but have less testosterone than normal, cannot

reproduce.