Unit 4, topic 1.2: Cellular replication and variation

Question 1

Types of cell division in Eukaryotes

Answer 1

Mitosis and Meiosis

Question 2

Mitosis and miotic division

Answer 2

Produces two identical daughter cells from parent cell, responsible for growth and repair in multicellular organisms and reproduction in single-celled and asexual eukaryotes

Miotic division continues throughout life for cell replacement and repair of tissues

Question 3

Process of Mitosis

Answer 3

1. Interphase
   → Occurs before mitosis, DNA replication occurs, producing 2 chromosomes
2. Prophase
   → Chromosomes pair up
3. Metaphase
   → Chromosomes line up on the equator using the miotic spindle
4. Anaphase
   → Sister chromatids pull apart
5. Telophase
   → Cell pinches down the middle
6. Cytokinesis
   → Cells divide and 2 new identical daughter cells have been produced

Question 4

Homologous chromosomes

Answer 4

A pair of chromosomes with the same gene sequence, one coming from the mother (maternal), the other coming from the father (paternal)

Question 5

Sister chromatids

Answer 5

the identical copies formed by the DNA replication of a chromosome, with both copies joined together by a common centromere

Question 6

Role of homologous chromosomes in Meiosis

Answer 6

Prophase 1: homologous chromosomes pair up
→ replicated chromosomes appear as two sister chromatids are held together at the centromere

Metaphase 1: Independent Assortment
→ Homologous pairs line up in the middle of the cell independently of each other resulting in paternal and maternal chromosomes sorting into gametes

Question 7

Independent assortment

Answer 7

the random alignment and distribution of chromosomes during meiosis

important mechanism for producing variation in gametes

Question 8

Genetic variation through Meiosis

Answer 8

Independent assortment and crossing over/recombination

Question 9

Process of meiosis

Answer 9

MEIOSIS I:
1. Prophase 1
→ homologous chromosomes pair up, replicated chromosomes appear as two sister chromatids
→ crossing over may occur at this time

2. Metaphase 1
   → Independent assortment occurs
3. Anaphase 1
   → homologous pairs separate, pulled apart by spindle fibers
4. Telophase 1
   → intermediate cells are produced

MEIOSIS II
→ second division occurs with same steps as Meiosis I, allowing more gametes to be produced

Question 10

Crossing over and recombination process

Answer 10

• Occurs in the first stage of meiosis
• Non-sister chromatids become entangled and segments may be exchanged
• results in the recombination of alleles (variations of the same gene) producing greater variation in offspring

Question 11

How many chromosomes do humans have?

Answer 11

46 → 23 paternal, 23 maternal
making 23 homologous pairs

Question 12

Haploid cells (N)

Answer 12

Contain only one set of chromosomes (n)

Question 13

Diploid cells (2N)

Answer 13

Contains two sets of chromosomes (2n)

Question 14

Processes producing sex cells

Answer 14

Spermatogenesis and Oogenesis

Question 15

Process of spermatogenesis

Answer 15

1. Spermatogonium
   → growth (mitotic cell division)
2. Primary spermatocyte (2N)
   → 1st Meiotic division (meiosis I)
3. Secondary spermatocyte (N)
   → Second meiotic division (meiosis II)
4. Spermatids (N)
   → Maturation
5. Sperm (N)

Question 16

Spermatogenesis

Answer 16

Process by which mature sperm are produced → daily in the testes

Question 17

Oogenesis

Answer 17

Process which occurs during the growth in the womb, future egg sex cells are made in the ovaries → no new eggs produced after birth

Release of the egg cells stops at menopause, when menstruation halts and the person is no longer fertile

Question 18

Process of Oogenesis

Answer 18

1. Oogonium
   → growth (Mitotic cell division)
2. Primary oocyte (2N)
   → Meiosis I (produces first polar body)
3. Secondary oocyte (N)
   → Meiosis II (Produces 2nd polar body (N))
4. Mature ovum (N)

steps 1 + 2 are completed in the fetus
steps 3 + 4 are completed in the adult

Question 19

Polar bodies (Oogenesis)

Answer 19

a small haploid cell which is formed at the same time as an egg, however cannot be fertilized
they naturally disintegrate after oogenesis process is complete

Question 20

Differences between Oogenesis and Spermatogenesis

Answer 20

Oogenesis:
Initiated → during fetal development
Cytokinesis → unequal, producing polar bodies
# of Gametes → one ovum, one polar body
Ceases → at menopause
release → midpoint of menstrual cycle

Spermatogenesis:
Initiated → during puberty
Cytokinesis → equal
# of Gametes → four sperm cells
Ceases → never, continues to death
Released → released during intercourse

Question 21

Random fertilization

Answer 21

during sexual reproduction, the male gamete and female gamete that fuse to produce an offspring are selected randomly from the pool of male and female sex cells