topic 11

Question 1

what are the 2 types of cells in humans?

Answer 1

somatic cells and gametes

Question 2

what are somatic cells?

Answer 2

• 2 sets of of 23 chromosomes (46 chromosomes)
• diploid cells (2n)

Question 3

what are gametes?

Answer 3

• one set of chromosomes (23 total)
• haploid cells (n)

Question 4

what is a karyotype?

Answer 4

an ordered display of the pairs of chromosomes from a cell

Question 5

role of meiosis in sexual reproduction

Answer 5

meiosis produces gametes (sperm + egg) that then undergo fertilization to produce a zygote, that undergoes mitosis to form somatic cells

Question 6

the 2 chromosomes in each pair are called

Answer 6

homologous chromosomes

Question 7

homologous chromosomes carry the same _____ but not the same ______

Answer 7

genes, alleles of those genes

Question 8

locus

Answer 8

the location of a particular gene on a chromosome

Question 9

an individual has _____ at each gene locus

Answer 9

two alleles

Question 10

after DNA replication, each replicated chromosome consists of

Answer 10

2 identical sister chromatids

Question 11

gonads

Answer 11

sex organs (testes and ovaries)

Question 12

in animal sexual life cycles, gametes are

Answer 12

1. the only haploid cells
2. the only cell type produced by meiosis
3. undergo no further cell division before fertilization

Question 13

difference between animals and other organisms in sexual life cycles?

Answer 13

in animals: only diploid cells can divide by mitosis

in other organisms: both haploid and diploid cells can divide by mitosis

Question 14

in ALL organisms, only _____ cells can undergo meiosis

Answer 14

diploid

Question 15

meiosis is preceded by

Answer 15

the replication of chromosomes
(DNA replication during S phase)

Question 16

meiosis I is known as

Answer 16

reductional division

Question 17

meiosis II is known as

Answer 17

equational division

Question 18

pairing and separation of homologous chromosomes

Answer 18

meiosis I

Question 19

sister chromatids separate

Answer 19

meiosis II

Question 20

sister chromatids

Answer 20

• genetically identical
• joined at the centromere

Question 21

meiosis I occurs in 4 phases

Answer 21

• prophase I
• metaphase I
• anaphase I
• telophase I and cytokinesis

Question 22

prophase I

Answer 22

• 90% time of meiosis
• chromosomes condense
• synapsis (tetrad formation)
• crossing over

Question 23

synapsis

Answer 23

each pair of chromosomes forms a tetrad (group of 4 chromatids)

Question 24

chiasmata

Answer 24

X-shaped regions where crossing over occurs

Question 25

crossing over (genetic recombination)

Answer 25

exchange of DNA segments between non-sister chromatids of homologous chromosomes

Question 26

synaptonemal complex

Answer 26

a meiosis-specific multiprotein complex that forms between homologous chromosomes during prophase of meiosis I

Question 27

metaphase I

Answer 27

• tetrads line up at the metaphase plate, each homologous chromosome facing each pole
• microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad

Question 28

anaphase I

Answer 28

• homologous chromosome pairs separate
• sister chromatids remain attached at the centromere and move as one unit toward the pole

Question 29

telophase I / cytokinesis

Answer 29

• each cell still consists of 2 sister chromatids, and has a haploid set of chromosomes
• in animals: cleavage furrow forms
• in plants: a cell plate forms

Question 30

similar to mitosis

Answer 30

meiosis II

Question 31

mitosis _____ the number of chromosome sets, while meiosis _____ the number of chromosome sets

Answer 31

conserves, reduces

Question 32

3 events unique to meiosis

Answer 32

1. synapsis and crossing over
2. metaphase I - alignment of tetrads instead of individual replicated chromosomes
3. anaphase I - separation of homologous chromosomes instead of sister chromatids

Question 33

4 mechanisms contribute to genetic variation

Answer 33

1. genetic recombination (crossing over)
2. independent assortment of chromosomes
3. random fertilization
4. mutations

Question 34

how many possible combinations are possible due to independent assortment

Answer 34

2^23 = 8 million gametes

Question 35

crossing over produces

Answer 35

recombinant chromosomes

Question 36

mutations

Answer 36

changes in an organism’s DNA, create different versions of genes