X and Y chromosomes

• What chromosomes do males have?

  X and Y chromosomes
• What characteristic does the Y chromosome control?


  Male characteristics
• What chromosomes do females have?

  Two X chromosomes
• What does the XX combination allow for?


  Development of female characteristics
• What happens to the X and Y chromosomes during sperm formation?


  They are drawn apart in the first division of meiosis
• What is the probability of each sperm cell getting an X chromosome?


  50%
• How many X chromosomes does the original cell have when making eggs?


  Two X chromosomes
• What is the physical size comparison between the Y chromosome and the X chromosome?


  The Y chromosome is physically smaller than the X chromosome
• Is it possible for individuals to have more than one Y chromosome?


  Yes, individuals can have one X and two Y chromosomes
• What is the key takeaway regarding X and Y chromosomes?


  XX gives female characteristics and XY gives male characteristics
• How can you determine the probability of offspring being male or female?

  • Use a genetic diagram
  • Show possible gametes from each parent
  • Fill in combinations in the diagram
  • Calculate the ratio of male to female outcomes
• What do genetic diagrams model?


  Possible genetic outcomes from crossing different genes or chromosomes
• What do you place down the side of a genetic diagram?


  Possible gametes from one parent
• What do you fill in the middle squares of a genetic diagram with?


  Letters from the top and side that line up with that square
• What does the presence of two XX results and two XY results indicate?


  There’s the same probability of getting a boy or a girl
• What does the 50:50 ratio in genetic diagrams represent?


  The probability of male or female offspring in each pregnancy
• What are the steps to create a genetic diagram?


  1. Place possible gametes from one parent down the side
  2. Place possible gametes from the other parent along the top
  3. Fill in the middle squares with combinations
  4. Analyze the results for probabilities
• What do the criss-cross lines in a more complex genetic diagram represent?


  All the possible ways the X and Y chromosomes could combine
• What do the bottom circles in a genetic diagram show?

  The possible combinations of the offspring
• What is a common focus of genetic diagrams seen in exams?

  They often concentrate on a gene instead of a chromosome
• What should you not worry about when looking at genetic diagrams?


  They aren’t as scary as they look