Gametogenesis

Gametogenesis Gametogenesis is the creation of gametes. In males, it is spermatogenesis, creation of sperm. In females, it is oogenesis, creation of ova.

Spermatogenesis Occurs in the testes. Meiosis occurs and the result is four, non-identical cells, each with 23 chromosomes that will develop into sperm.

Oogenesis Occurs in the ovaries and in the oviducts. After Telophase I and II, the cytoplasm is not equally divided. One of the new cells gets the majority and it survives, while the other one, a polar body, gets broken down.

Key Terms Diploid: Having the full chromosome number (46 in humans). Haploid: Having half the full chromosome number (23 in humans).

Karyotype A karyotype is a pictorial representation of a person’s chromosomes. An example is shown to the right.

Karyotype The X and Y chromosomes are known as the sex chromosomes. They determine a person’s gender. XX is female, while XY is male. It is the dad who determines the baby’s gender as he can produce sperm carrying the X chromosome or sperm carrying the Y chromosome.

Non-Disjunction

Non-disjunction Non-disjunction is the failure of chromosomes (or tetrads) to separate during anaphase I or II in meiosis. The resulting cells will not have the correct number of chromosomes.

Non-disjunction If it happens in meiosis I, all the resulting cells will be affected. If it happens in meiosis II, only half will be affected.

Having extra chromosomes is bad! Having too many or too few chromosomes is a bad thing. Down Syndrome is caused by having an extra chromosome 21.

Having extra chromosomes is bad! Klinefelter’s Syndrome occurs when an individual receives two X chromosomes and a Y chromosome. The result is an infertile male with varying degrees of feminity.

Missing chromosomes is bad! Turner Syndrome occurs when the individual only gets one sex chromosome, an X, from their mother. The result is an infertile female with a broad chest, poor breast development, low set ears, short stature and poor hearing amongst other things.