Meiosis

Question 1

Fertilization

Answer 1

combining of sex cells, or gametes, 2 haploid gametes fuse to form a diploid (2n) zygote

Question 2

Zygotes

Answer 2

cell created by the fusion of two
gametes; fertilized egg

Question 3

Diploid vs haploid

Answer 3

Haploid cells are those that have only a single set of chromosomes (n), while diploid cells have two sets of chromosomes (2n)

Question 4

What type of cells undergo meiosis

Answer 4

germ cells

Question 5

What types of cells are produced

Answer 5

gametes (sex cells)

Question 6

Meiosis I

Answer 6

Preceded by DNA replication in S phase
- Homologous chromosome pairs separate, but the individual chromosomes (sister chromatids) stay together

Question 7

Prophase 1

Answer 7

Chromatin begins to condense
- Synapsis: specific parallel alignment (pairing) of homologous chromosomes
- Tetrad: four chromatids of each pair of homologous chromosomes

Question 8

Prometaphase

Answer 8

Chiasmata: regions of attachment that form between non sister chromatids, crossing over and exchanging genetic material, resulting in recombinant chromatids and increases genetic variability of the products

Question 9

Metaphase 1

Answer 9

Homologous pairs line up on
equatorial (metaphase) plate

Question 10

Anaphase 1

Answer 10

Homologous chromosomes – each with two chromatids – move to opposite poles of the cell

Question 11

Telophase 1

Answer 11

Chromosomes gather into nuclei
- Original cell divides

Question 12

Independent assortment

Answer 12

chromosome pairs align randomly during metaphase I, each haploid cell receives an entire set of genes, but only one from each pair (again, the pair comes from each parent)

Question 13

Meiosis II

Answer 13

Not preceded by DNA replication
- Sister chromatids are separated
- Chance assortment of the chromatids contributes to genetic diversity
- Final products are four haploid daughter cells (n)

Question 14

Prophase II

Answer 14

Chromosomes condense again after brief interphase (but chromosomes do not replicate)

Question 15

Metaphase II

Answer 15

Centromeres of paired chromatids line up along equatorial plate of each cell

Question 16

Anaphase II

Answer 16

Chromatids separate, becoming chromosomes
- Move to opposite poles
- each new cell has different genetic makeup

Question 17

Telophase II

Answer 17

Chromosomes gather into nuclei and cells divide

Question 18

Products

Answer 18

Each of the four cells has a nucleus with a haploid number of chromosomes, DNA replicates once, nucleus divides twice

Question 19

Nondisjunction

Answer 19

• Homologous pairs fail to separate at anaphase I
• Sister chromatids fail to separate in meiosis II
• Result: aneuploidy – chromosomes lacking or present in excess, lack of cohesins cause homologs to go to the same pole

Question 20

Human example of nondisjunction

Answer 20

Down syndrome results from a gamete with two copies of chromosome 21
- After fertilization, there are three copies (trisomy) of chromosome 21

Question 21

Main differences between mitosis and meiosis

Answer 21

mitosis produces two identical daughter cells with the same number of chromosomes as the parent cell, while meiosis produces four genetically different daughter cells with half the number of chromosomes as the parent cell