X and Y Chromosomes, and Genetic Diagrams

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  • Created by: Davwi
  • Created on: 11-03-19 20:50

X and Y chromosomes

  • There are 23 pairs of chromosomes in every human body cell. Of these, 22 are matched pairs of chromosomes that only control charcteristics. The 23rd pair are labelled ** or XY. They're the two chromosomes that decide your sex- whether you turn out male or female.
  • Males have an X and a Y chromosome: XY (the Y chromosome causes male characteristics).
  • Females have 2 X chromosomes: ** (the ** combination allows female characteristics to develop).
  • When making sperm, the X and Y chromosomes are drawn apart in the first division of meiosis. There's a 50% chance that eac sperm cell gets an X chromosome and a 50% chance each chromosome gets a Y chromosome.
  • A similar thing happens when making eggs, but original cell has 2 X chromosomes so all the eggs have one X chromosome.

Genetic diagrams

  • To find the probability of getting a boy or a girl, you can draw a genetic diagram.
  • Genetic diagrams are just models that are used to show all the possible genetic outcomes when you cross together different genes or chromosomes.
  • Put all the possible gametes from one parent down one side, and those from the other parent along the top.
  • Then in each middle square fill in the letters from the top and side that…

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