B2(iii) - Genetics 5.

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X and Y Chromosomes.

Your Chromosomes Control Whether You Are Male or Female.

There are 23 matched pairs of chromosomes in every human body cell. The 23rd pair are labelled XX or XY. They're the two chromosomes that decide whether you turn our male or female.

ALL MEN HAVE X AND A Y CHROMOSOME: XY

THE Y CHROMOSOME CAUSES THE MALE CHARACTERISTICS.

ALL WOMEN HAVE TWO X CHROMOSOMES: XX 
THE XX COMBINATION ALLOWS FEMALE CHARACTERISTICS TO DEVELOP. 

When making sperm, the X and Y chromosomes are drawn apart in the first division in meiosis. There's a 50% chance that each sperm cell gets an X chromosome and a 50% chance it gets a Y chromosome. A similar thing happens when making egg cells. But the original cell has two X chromosome, so each cell has one X chromosome.

Genetic Diagrams Show

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