Human Genetics part 2

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?

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.

Turner’s Syndrome Usually, a woman has two X chromosomes. However, in women with Turner’s syndrome, one of these chromosomes is absent or abnormal. With appropriate medical treatment and support, a girl or woman with Turner’s syndrome can lead a normal, healthy and productive life. Treatment aims to correct any physical defects and help bring about puberty.

XXY Male (Extra X)

Klinefelter’s Syndrome A male with Klinefelter syndrome has an additional X chromosome, which causes infertility, low testosterone and other characteristics such as development of breast tissue. The chromosomes are present in every cell of the body and the extra X chromosome cannot be removed. Treatment includes lifelong testosterone therapy and cosmetic surgery to remove enlarged breast tissue. Options for men with Klinefelter syndrome to have their own children are becoming more widely available.

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.

Revisit Meiosis? https://www.youtube.com/watch?v=qCLmR9-YY7o Crash Course Biology (be sure to pause the video and rewind if needed)

Nondisjunction

How can siblings look alike but not exactly the same if they come from the same parents?

Crossing over The chromosomes during prophase I undergo crossing over, where parts of the homologues randomly switch places.

Importance of crossing over The gene combinations that a person gets from his or her parents will be different, to varying degrees, than the combination a sibling may get.

More sibling similarities

What other chromosomal disorders can arise? Deletion Inversion Translocation Duplication

Chromosomal mutations Deletion Duplication Inversion Translocation

Problems with chromosomes Duplication: copied parts of chromosome A B C D A B C D

Problems with chromosomes Deletion: missing parts of chromosome A B C D A D

Problems with chromosomes Inversion: parts of chromosome tched A B C D A C B D