8.3.2 Homologous Chromosomes: Thanks, Mom and Dad!

Question 1

sexual reproduction

Answer 1

• two diploid parents will produce haploid gametes that can fuse to form a diploid cell that has the same number of chromosomes as the parents

Question 2

meiosis

Answer 2

• two problems must be overcome:
  1. How do we divide our chromosome number by half? Meiotic division produces haploid cells from diploid cells.
  2. How should chromosomes be sorted? In other words, how can we ensure that a copy of each chromosome will be in each cell that results? Diploid cells have twenty-three chromosome pairs which are sorted and split during meiosis. The resulting cells have one chromosome from each pair.
• In the example at the beginning of the lecture, the
  chromosomes in the mom and dad cells were divided to make gametes. The problem with this situation is that if the egg with the chromosome containing the head gene is fertilized by the sperm that also has the head gene, then the offspring will lack the gene for a body.
• Diploid organisms actually have two sets of each
  chromosome. For example, humans don’t simply have
  forty-six different chromosomes. It is more accurate to say that they have twenty-three chromosome pairs. The
  chromosomes within a pair are referred to as homologous chromosomes. In the process of meiosis,
  chromosome pairs are split apart, producing haploid cells, each containing one full set of chromosomes. Homologous chromosomes are split apart into separate cells during meiosis to ensure that a copy of each chromosome is present in the resulting haploid cells.
• The earlier example would not have worked in the first place because the mom and dad did not even have two sets of each chromosome (they only had one set that was doubled).

Question 3

True or false?

Homologous chromosomes are attached at the centromere.

Answer 3

• false

Question 4

Which statement regarding homologous chromosomes is not correct?

Answer 4

• Homologous chromosomes have identical alleles

Question 5

Meiosis in animals serves all but which one of the following functions?

Answer 5

• the production genetically identical daughter cells

Question 6

Homologous chromosomes originate

Answer 6

• during fertilization.

Question 7

A diploid cell with 16 chromosomes

Answer 7

• has 8 chromosome pairs

Question 8

True or false?

All diploid cells have homologous chromosomes.

Answer 8

• true