Sex Inheritance

11SCI - Genetics

Finn Le Sueur

2024

Sex Determination & Chromosomes

  • Males carry one X and one Y chromosome (XY)
  • Females carry two X chromosomes (XX)
  • Since males can give either an X or a Y chromosomes, the chromosome in the male gamete (sperm) determines the biological sex of the offspring.

Fertalisation & Punnett Squares

  • In humans we need to fuse a sperm and an egg into a fertalised zygote.
  • Therefore, we can visualise sex determination with a Punnett square.
  • Complete this Punnett square and describe the genotypic and phenotypic ratios.
  • Pātai: Does the probability of a particular sex change with each fertalisation? Why / why not?

Answers / Whakatika

  • The genotypic ratio is 1XX:1XY or 50% XX and 50% XY.
  • The phenotypic ratio is 1male:1 female or 50% male and 50% female.
  • The probability does not change with each fertalisation because each fertalisation is an independent event (one not affected by prior events).

Task / Ngohe

  1. Open https://scipadonline.co.nz/lesson/193-lessons
    • Join the class with code QWPR5 if first time.
  2. Complete the lesson on variation.

Fast Finishers: Work on the Inheritance task on Education Perfect.

Finish: Blooket