X and Y chromosomes

• How many chromosomes are there in a human body cell?

  46 (23 pairs)
• What is the name of the 23rd pair of chromosomes?

  Sex determining chromosomes
• What do the sex determining chromosomes decide?

  Whether you will be male or female
• What combination of chromosomes do all males have?

  XY
• What combination of chromosomes do all females have?

  XX
• What percentage of eggs have an X chromosome?

  100%
• What percentage of eggs have a Y chromosome?

  0%
• What percentage of sperm have an X chromosome?

  50%
• What percentage of sperm have a Y chromosome?

  50%
• What do the letters at the top and side of a Punnett square show?

  The gametes of the parents
• What do the pairs of letters in the boxes of a Punnett square show?

  The possible gametes of the offspring
• Why is the probability of having a boy 50%?

  2 out of 4 possibilities include a Y chromosome
• What are the genetic keywords and their definitions?

  • Gene: Section of DNA controlling a characteristic
  • Allele: Different versions of a gene
  • Characteristic: Feature of an organism
  • Homozygous: Two of the same alleles
  • Heterozygous: Two different alleles
  • Dominant: Expressed if present
  • Recessive: Needs both alleles to be expressed
  • Genotype: The alleles an organism has
  • Phenotype: Physical features of an organism
  • Genetic Inheritance: Passing genes to offspring