1. Atypical Meiosis (SEC 4.5 PG 127)

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

3.  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.

4.  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.

5.  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.

6.  Turner Syndrome:  45 chromosomes – Only 1 of the X chromosome (monosomy of sex chromosome ‘X’).  Only females.  Cannot reproduce.

7.  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.

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