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 ** 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: ** 
THE ** 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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