Hey! Check out that hot beast over there. Sex Determination Wow! She looks cool.

Of the 46 Chromosomes found in a human cell, two of these play an important role in determining which sex the human is. These are referred to as the X and Y chromosomes. Females have two X-chromosomes in each of their cells and males have an X and Y. Stannard & Williamson: ScienceWorld 3

All of the eggs produced by a female have “X” chromosomes, one of which is an X. Half of male’s sperm cells have an “X” chromosome and the other half a “Y” chromosome. If a sperm carrying an X chromosome fertilizes an egg, the offspring will be a Female (XX). If a sperm carrying a Y chromosome fertilizes an egg the offspring will be Male (XY). Stannard & Williamson: ScienceWorld 3

Female Chromosomes Male Chromosomes Stannard & Williamson: ScienceWorld 3 Female Chromosomes Male Chromosomes

Sex Linkage There are some genes that are found on the X chromosome and not on the Y chromosome. These are called sex-linked genes. As there is no homologous gene on the Y chromosome, these genes can operate as a single allele in males. Stannard & Williamson: ScienceWorld 3

Colour blindness is caused by colour blind recessive genes Colour blindness is caused by colour blind recessive genes. This means the genes are found on the X chromosome and it is recessive to the dominant normal colour vision. Normal Vision sees 8 Colour Blind sees spots Normal Vision sees 6 Colour Blind sees spots http://www.toledo-bend.com/colorblind/Ishihara.asp

Try and find a circle, star, and/or square in 3 seconds If a woman with normal colour vision mated with a man with colour blindness her daughters would be for heterozygous blindness but would have normal vision. If her daughters were to mate with males of normal vision, none of their daughters would be colour blind but half their sons would be expected to be colour blind. Try and find a circle, star, and/or square in 3 seconds http://www.toledo-bend.com/colorblind/Ishihara.asp

Answer Colorblind individuals should see the yellow circle. Color normal individuals should see the yellow circle and a "faint" brown square.

Haemophilia Haemophilia is a sex-linked disease that prevents the sufferer’s blood from clotting. Queen Victoria passed hemophilia on to many of her descendants. http://en.wikipedia.org/wiki/Hemophilia

Sex Linked Crosses ALWAYS show the chromosomes