18.1: Chromosome Combinations Animation Video
Transcript:
Chromosome Combinations
An important part of a person’s sexuality is biological sex. Biological sex is determined by a person’s sex chromosomes. These two sex chromosomes are referred to as X and Y.
Almost all human offspring receive two copies of every gene, one from the female parent and one from the male parent. This includes the parents’ sex chromosome.
Males inherit a Y chromosome from their fathers and an X chromosome from their mothers. Females inherit an X chromosome from each parent. The odds of a fetus receiving different chromosome combinations from their parents can be calculated using a Punnett Square.
To use a Punnett Square, you place the two chromosomes from the female parent above the columns of the square and the two chromosomes from the male parent next to the rows of the square. By combining the chromosomes from each column and row, you can see the chances that each offspring has for a specific biological sex.
This Punnett Square shows a cross between one male and one female parent.
In this example, there is a two in four chance that the offspring in the cross will have two X chromosomes, and will thus have the biological sex of female. There is a two in four chance that the offspring will have the biological sex of male, with one X chromosome and one Y chromosome.
In most pregnancies, there is a 50% chance that the baby will be male, and a 50% chance that the baby will be female.