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X and Y chromosomes and genetic screening (CCEA)Sex determination in humans

Sex is controlled in humans by the X and Y chromosomes. Genetic screening involves testing people or groups of people for the presence of a particular allele or other genetic abnormality.

Part of Combined ScienceGenetics

Sex determination in humans

Sex is determined in humans by the 23.

In females, there are two X chromosomes.

So, female = XX.

In males, one X and one Y chromosome.

So, male = XY.

An image of a complete set of chromosomes is known as a karyotype.

forms gametes (sperm and egg cells).

All eggs contain one X chromosome.

50% of sperm contain one X chromosome and 50% contain one Y chromosome.

Human sex chromosomes

During , there is a 50% chance that a sperm containing an X chromosome will fuse with the egg; this would result in a baby girl 鈥 XX.

There is also a 50% chance that a sperm containing a Y chromosome will fuse with the egg; this would result in a baby boy 鈥 XY.

Within a population there will be equal numbers of females and males.

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