Mitosis and Meiosis

Question 1

Mitosis

Answer 1

somatic cell formation

-prophase, metaphase, anaphase, telophase

Question 2

Meiosis

Answer 2

gamete formation

-reproductive nuclear division

Question 3

prophase

Answer 3

• chromosomes condense (thicken, coil) from chromatin form - become individually visible
• nucleoli disappear and nuclear envelope breaks up
• centrosomes move to either pole
• microtubules form spindle apparatus (starting at centrosomes) + attach to kinetochore proteins ( called kinetochore microtubules)
• spindle moves chromosomes toward cell equator

Question 4

Metaphase

Answer 4

46 chromosomes line up on cell equator

Question 5

Anaphase

Answer 5

• as the spindle microtubules shorten, the kinetochores are pulled away from each other - causing separation of centromeres, which results in separation of chromatids
• 46 chromatids migrate to each pole
• cytokinesis (division of cytoplasm) begins

Question 6

Telophase

Answer 6

• chromosomes uncoil to chromatin
• nucleoli, nuclear envelope reappear
• spindle disassembles
• cytokinesis completes (or may end after telophase ends)

Question 7

Meiosis

Answer 7

produces games (ovum and sperm)

• 1 cell (2n)produces 4 genetically dissimilar gametes (n)
• involves interphase and 2 cell divisions Meiosis 1 and Meiosis 2
• b/w meiosis 1+2 = interkinesis not interphase (no DNA replication)

Question 8

Meiosis 1

Answer 8

reduction division = 2n to n

prophase 1, metaphase 1, anaphase 1, telophase 1

Question 9

Prophase 1

Answer 9

• homologous chromosomes attach together = tetrads (4 chromatids in a row)
• crossing over occurs

Question 10

crossing over

Answer 10

• piece 1 chromatid exchanges with matching piece from a chromatid of the homologous chromosome ie. non sister chromatid
• acts to increase genetic diversity
  eg. you pass on your dad’s black hair with your mom’s blue eyes

Question 11

Metaphase 1

Answer 11

23 tetrads line up along cell equator

Question 12

Anaphase 1

Answer 12

tetrads (homologous chromosome pairs) separate and migrate to opposite poles ie. 1 homologous chromosome ( with 2 sister chromatids) goes to each pole

• chromatids don’t separate
• telophase 1 follows

Question 13

After meiosis and cytokinesis

Answer 13

each new cell has 23 diff chromosomes (1/2 the number of Xms) = n

• these cells do not have homologous chromosomes
• chromosome 1-23 from mom or dad (randomly segregated)

Question 14

Meiosis 2

Answer 14

same as mitosis except with 23 chromosomes instead of 46

• prophase 2
• metaphase 2 (23 chromosomes line up at equator)
• anaphase 2 (23 chromatids migrate to each pole)
• telophase 2
• cytokinesis (same for mitosis/meiosis (beings in anaphase/anaphase1/anaphase 2, and continues through telophase/telophase 1/ telophase 2)

Question 15

why meiosis?

Answer 15

need to turn diploid germ cells into haploid gametes
-germ cell: primary oocyte/spermatocyte, 2n
(meiosis 1)
-intermediate: secondary oocyte/spermatocyte, n
(meiosis 2)
-gamete: (ovum/spermatozoon),, n
-note 2 oocyte is ovulated / spermatozoa ejaculated

Question 16

fertilization

Answer 16

spermatozoon (n) contacts and penetrates 2 oocyte (n)= fertilization

• triggers completion of meiosis 2 in 2 oocyte-forms ovum (egg)
• then female and male pronuclei unite
• new cell = zygote 2n

Question 17

pronucleus

Answer 17

nucleus of sperm/ egg post-fertilization but prior to fusion