The Human Karyotype & Nondisjunction

1. The Human Karyotype & Nondisjunction

2. What’s a Karyotype?? • Scientists use a microscope to take pictures of the condensed chromosomes during metaphase. • They can match up the homologous chromosomes by size and shape. • This arrangement of chromosomes is called a KARYOTYPE.

3. A closer look at a karyotype… The human karyotype has 23 pairs or 46 chromosomes Sex chromosomes

4. Remember, Meiosis results in the formation of FOUR daughter cells from ONEparent cell. • Meiosis results in the formation of GAMETES (either eggs or sperm) which are then combined together to form a new individual.

5. The gametes come together… Egg (N), haploid Sperm (N), haploid Embryo (2N), diploid

6. Uh Oh! Problems with Meiosis… • Usually Meiosis occurs with NO PROBLEMS. BUT, sometimes sex cells (gametes) are formed with irregular chromosomes numbers!! • Nondisjunction: Homologous chromosomes DO NOT SEPARATE during meiosis. Gametes are produced with the WRONG NUMBER of chromosomes!!

7. Nondisjunction

8. Down Syndrome • Results from having 47 chromosomes instead of 46 • People with Downs Syndrome have 3 copies of chromosome 21 • Have similar facial features, mental and physical disabilities

9. Turner Syndrome • Female born with only 1 “X” chromosome (instead of 2) • Do not develop into puberty (therefore, they can’t reproduce) • Sometimes females have 3 “X’s”… these women CAN reproduce but are often taller and thinner than women with “normal” chromosome number

10. Klinefelter Syndrome • Males born with 2 “X” chromosomes and 1 “Y” • Produce less testosterone (Sex hormone) and can’t father children