Meiosis

Question 1

Crossing Over

Answer 1

• allows homologous chromosomes of maternal and paternal origin to exchange DNA segments
• no loss or gain of nucleotides

Question 2

Basis of Meiotic Cell Division

Answer 2

• results in four daughter cells
• gametes produced though 2 rounds of nuclear divison
• DNA replication in prophase 1 is the same as mitosis

Question 3

Meiosis 1

Answer 3

• prophase 1: chiasmata (point of contact in crossing over) present
• prometaphase 1: spindle attach to kinetochores on chromosomes
• metaphase 1: homologous pairs line up in the center of the cell
• anaphase 1: homologous pairs separate, sister chromatids do not separate
• telophase 1 and cytokinesis: prepare to move into prophase 1

Question 4

Anaphase 1 (more detailed)

Answer 4

• two homologous chromosomes separate
• centromeres do not split here
• chromosomes are at each pole, 23 at each end

Question 5

telophase 1 (more detail)

Answer 5

• nuclear envelope briefly reappears
• cytoplasm divides, two separate cells produced
• blends into prophase 2

Question 6

Meiosis 2

Answer 6

• prophase 2: nuclear envelope breaks down, chromosomes condense
• prometaphase 2: spindles attach to kinetochores
• metaphase 2: chromosomes align in the center of cell
• anaphase 2: sister chromatids separate
• telophase 2 and cytokinesis: nuclear envelope reforms, cytoplasm divides

Question 7

Connection between mitosis and meiosis

Answer 7

• meiosis 1: maternal and paternal homologs separate
• meiosis 2: sister chromatids separate, similar to mitosis
• this similarity suggests that meiosis evolved from mitosis

Question 8

Cytoplasmic Division

Answer 8

• in females division is unequal in both divisions, most of the cytoplasm in retain in one oocyte, small amounts are in polar bodies which are non-functional
• males are fairly equal, during sperm development most of the cytoplasm is eliminated, remaining is the nucleus in the head and the flagellum

Question 9

Non-disjunction

Answer 9

• failure of a pair of chromosomes to separate in anaphase
• results in gametes that have an extra or no copy of the chromosome
• more common in meiosis 1
• down syndrome is a non-disjunction