Sex chromosomes and the work of mendel

• How many pairs of chromosomes are there in every human body cell?

  There are 22 pairs of chromosomes.
• What does the 23rd pair of chromosomes determine in humans?

  It determines whether a person is male or female.
• What are the sex chromosomes for males?

  XY
• What characteristic does the Y chromosome cause?

  The Y chromosome causes male characteristics.
• What are the sex chromosomes for females?

  XX
• Why do females develop differently than males according to the chromosome theory?

  Females lack a Y chromosome, which causes male characteristics.
• How is sex determined in humans?

  Sex is determined by a gene carried on the Y chromosome.
• Who is considered the grandfather of genetics?

  Gregor Mendel
• What did Gregor Mendel study to understand inheritance?

  Mendel studied characteristics in pea plants.
• When were Mendel's research results published?

  In 1866
• What were the steps of Mendel's experiments with pea plants?

  1. Crossed a tall pea plant with a dwarf pea plant; all offspring were tall.
  2. Crossed two tall offspring; 75% were tall, 25% were dwarf.
  3. Showed that height was determined by inherited factors.
• What does the ratio of tall to dwarf plants in Mendel's second cross indicate?

  It indicates that the factor for tall plants (T) is dominant over the factor for dwarf plants (t).
• What are the "inherited factors" that Mendel referred to in his experiments?

  They are now known as genes.
• What was not known about genetics during Mendel's time?

  People did not know about DNA.
• How did later scientists link Mendel's work to modern genetics?

  They linked his inherited factors with genes and chromosomes.
• What did some biologists speculate about the X and Y chromosomes?

  They speculated that swapping an X chromosome for a Y could create a new species.