Abnormal Meiosis

What each of the human chromosomes look like

Karyotype: A photomicrograph of chromosomes arranged according to a standard classification

In other words… Chromosomes are digitally arranged so that they are matched with their homologue or “partner” chromosome. Homologue chromosomes are the same size, shape, and carry the same genes, and one is inherited from each parent. They are numbered according to size.

Sex determination with karyotype This karyotype has 23 exact pairs, which means the person is female. Note that #23 chromosomes are both X.

Normal human male Note that #23 chromosomes are X and Y.

Is this person female or male?

Is this person female or male?

Trisomy 21 Abnormality shown in karyotype Note that there are three copies of #21 chromosome. This person has Down Syndrome.

Photos of Down Syndrome patients from the National Down Syndrome Society

Correlation between mother’s age and Trisomy 21 incidence

Monosomy X Abnormality shown in karyotype Note this person only has 1 copy of the X chromosome. This female has Turner’s syndrome. Occurs 1 in 2500 females

XXY Male (Extra X) Affected individuals have at least two X chromosomes and at least one Y chromosome. The most common sex chromosome disorder This male has Klinefelter’s syndrome. Occurs 1 in 500 males

How are DNA samples obtained for karyotypes?

Amniocentesis: obtaining amniotic fluid which has cells from the fetus

Chorionic villi sampling: removing cells from the chorion with fetal tissue

If there are chromosomal number abnormalities, how do they form? Meiosis: the process of creating sperm or egg from a diploid cell If there is a mistake when chromosomes are separating, then the resulting sperm or egg will have too many or too few chromosomes.