Unit 4, topic 1.2: Cellular replication and variation Flashcards
Types of cell division in Eukaryotes
Mitosis and Meiosis
Mitosis and miotic division
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
Process of Mitosis
- Interphase
→ Occurs before mitosis, DNA replication occurs, producing 2 chromosomes - Prophase
→ Chromosomes pair up - Metaphase
→ Chromosomes line up on the equator using the miotic spindle - Anaphase
→ Sister chromatids pull apart - Telophase
→ Cell pinches down the middle - Cytokinesis
→ Cells divide and 2 new identical daughter cells have been produced
Homologous chromosomes
A pair of chromosomes with the same gene sequence, one coming from the mother (maternal), the other coming from the father (paternal)
Sister chromatids
the identical copies formed by the DNA replication of a chromosome, with both copies joined together by a common centromere
Role of homologous chromosomes in Meiosis
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
Independent assortment
the random alignment and distribution of chromosomes during meiosis
important mechanism for producing variation in gametes
Genetic variation through Meiosis
Independent assortment and crossing over/recombination
Process of meiosis
MEIOSIS I:
1. Prophase 1
→ homologous chromosomes pair up, replicated chromosomes appear as two sister chromatids
→ crossing over may occur at this time
- Metaphase 1
→ Independent assortment occurs - Anaphase 1
→ homologous pairs separate, pulled apart by spindle fibers - Telophase 1
→ intermediate cells are produced
MEIOSIS II
→ second division occurs with same steps as Meiosis I, allowing more gametes to be produced
Crossing over and recombination process
- 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
How many chromosomes do humans have?
46 → 23 paternal, 23 maternal
making 23 homologous pairs
Haploid cells (N)
Contain only one set of chromosomes (n)
Diploid cells (2N)
Contains two sets of chromosomes (2n)
Processes producing sex cells
Spermatogenesis and Oogenesis
Process of spermatogenesis
- Spermatogonium
→ growth (mitotic cell division) - Primary spermatocyte (2N)
→ 1st Meiotic division (meiosis I) - Secondary spermatocyte (N)
→ Second meiotic division (meiosis II) - Spermatids (N)
→ Maturation - Sperm (N)
Spermatogenesis
Process by which mature sperm are produced → daily in the testes
Oogenesis
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
Process of Oogenesis
- Oogonium
→ growth (Mitotic cell division) - Primary oocyte (2N)
→ Meiosis I (produces first polar body) - Secondary oocyte (N)
→ Meiosis II (Produces 2nd polar body (N)) - Mature ovum (N)
steps 1 + 2 are completed in the fetus
steps 3 + 4 are completed in the adult
Polar bodies (Oogenesis)
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
Differences between Oogenesis and Spermatogenesis
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
Random fertilization
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
