5.1-2 Meiosis only

Question 1

What is meiosis?

Answer 1

• a process that creates haploid gamete cells in sexually reproducing diploid organisms

Question 2

What does meiosis result in, in terms of daughter cells?

Answer 2

• results in daughter cells with half the number of chromosomes as the parent cell

Question 3

We know that meiosis results in daughter cells with half the number of xmes as the parent cell. Use this information with humans as an example.

Answer 3

• humans are diploid: 2n=46
• meiosis produces sperm and eggs that are haploid: n=23
• involves two rounds of cell division (meiosis I and meiosis II)

Question 4

Meiosis is similar to mitosis, but there are some key differences. What occurs in mitosis?

Answer 4

• occurs in somatic cells
• 1 division
• results in 2 diploid daughter cells
• Daughter cells are genetically identical

Question 5

Meiosis is similar to mitosis, but there are some key differences. What occurs in meiosis?

Answer 5

• forms gametes (sperm/egg)
• 2 divisions
• results in 4 haploid daughter cells
• each daughter cell is genetically unique

Question 6

What are three key events in meiosis that are unique?

Answer 6

• Prophase I (synapsis and crossing over)
• metaphase I (tetrads (homologous pairs) line up at the metaphase plate)
• anaphase I (homologous pairs separate)

Question 7

What occurs in interphase?

Answer 7

Cell goes through G1, S (DNA is copied), and G2

Question 8

What occurs in Prophase I? (3)

Answer 8

Synapsis: homologous chromosomes pair up and physically connect to each other forming a tetrad

• crossing over (recombination) occurs at the chlasmata and DNA is exchanged between homologous pairs
• every chromatid that is produced has a unique combination of DNA

Question 9

What is the chlasmata?

Answer 9

• region where non-sister xmes are connected

Question 10

What occurs in metaphase I? (2)

Answer 10

• independent orientation: tetrads line up at the metaphase plate
  —the recombinant chromosomes randomly assort themselves at the equator

Question 11

What occurs in Anaphase I? (2)

Answer 11

• pair of homologous chromosomes separate

- sister chromatids are still attached

Question 12

What occurs in Telophase I and cytokinesis? (3)

Answer 12

• nuclei and cytoplasm divide
• there is now a haploid set of xmes in each daughter cell
• each cell has one member of each homologous pair

Question 13

What occurs in interkinesis?

Answer 13

Period of time between meiosis I and meiosis II

Question 14

What occurs in Prophase II? (2)

Answer 14

• no crossing over (bc odd #]

- spindle forms

Question 15

What occurs in metaphase II? (2)

Answer 15

• chromosomes line up at the metaphase plate

- because of crossing over in meiosis I, the chromatids are unique

Question 16

What occurs in anaphase II?

Answer 16

• sister chromatids separate and move towards opposite poles

Question 17

What occurs in telophase II and cytokinesis? (3)

Answer 17

• 4 haploid cells
• nuclei reappear
• each daughter cell is genetically unique

Question 18

What are three ways that Meiosis leads to genetic variation?

Answer 18

1. Crossing over
2. Independent assortment of chromosomes
3. Random fertilization

Question 19

How does crossing over lead to genetic variation? Which stage does crossing over occur? (4)

Answer 19

• (recombination) occurs and DNA is exchanged between the homologous pairs
  — every chromatid produced therefore had a unique combination of DNA
• produces recombinant xmes which therefore exchange genetic material
• occurs at prophase I

Question 20

How does independent assortment of chromosomes lead to genetic variation?

Answer 20

• chromosomes are randomly oriented along the metaphase plate during metaphase I
• each can orient with either the maternal or paternal chromosomes closer to a given pole

Question 21

How does random fertilization lead to genetic variation?

Answer 21

• any sperm can fertilize any egg

Question 22

Meiosis followed by fertilization ensures ___ _____ in sexually reproducing organisms, and provides genetic variation that plays a role in _____ ______.

Answer 22

Genetic diversity, natural selection

Question 23

Meiosis is driven by the interaction of ______ components and uses ____ _____ that is required for the _____ and ______ of living systems.

Answer 23

1. Sub cellular (organelles)
2. Free energy (energy available to do work)
3. Growth
4. Reproduction