MCBG Session 3 - Cell Division and DNA Flashcards
1
Q
Outline the G1 phase.
A
- Stage begins immediately after mitosis.
- RNA, proteins, and organelles are synthesised.
2
Q
Outline the S phase.
A
DNA replication occurs, i.e. chromosomes form sister chromatids.
3
Q
Outline the G2 phase.
A
- Mitochondria divide.
- Precursors of spindle fibres are synthesised.
4
Q
Outline Prophase.
A
- Chromosomes condense due to supercoiling, i.e. now visible as long, thin, intertwined threads.
- Nuclear envelope disappears
- Centrioles divide and migrate to opposite poles of the dividing cell
- Spindle fibres form and attach to chromosomes
5
Q
Outline Metaphase.
A
Chromosomes, with spindle fibres attached, line up on the equator of the dividing cell.
6
Q
Outline Anaphase.
A
- Centromeres divide, converting each sister chromatid into a chromosome
- Late in anaphase, the chromosomes migrate toward opposite ends of the cell.
- By the end of anaphase, there is a complete set of chromosomes at each end of the cell.
7
Q
Outline Telophase.
A
- Chromosomes reach the opposite poles of the cell and decondense
- Spindle fibres break down
- New nuclear envelope forms
8
Q
Outline cytokinesis.
A
- Cleavage furrow forms at equator of cell and deepens
- Cytoplasm divides
9
Q
Outline chromosome structure.
A
- Each chromatid consist of one (identical) DNA molecule; each has a p (short) and q (long) arm.
- Telomeres are repeated sequences (TTAGGG) at each end of chromosome/chromatid.
- Centromere links the sister chromatids and consists of repetitive sequences.
10
Q
Elaborate on the different types of chromosome structures.
A
Centromeres link the sister chromatids and consists of repetitive sequences.
- Metacentric
- Submetacentric
- Acrocentric
- Telocentric
11
Q
Explain the groupings of chromosome structure.
A
- Chromosomes are grouped according to size and shape.
- Groups A-G
- X is a ‘C group’
- Y is a ‘G group’
12
Q
Outline meiosis.
A
- In meiosis, members of a chromosome pair separate from each other, and each daughter cell receives a haploid (n) set of 23 chromosomes.
- These haploid cells form gametes (sperm and egg).
- Fusion of two haploid gametes in fertilisation restores the chromosome number to the diploid number of 46, providing a full set of genetic information to the fertilised egg.
- The two rounds of division (meiosis I and meiosis II) accomplish this precise reduction in the chromosome number.
- Meiosis I reduces the chromosome number.
- Before cells enter meiosis, the chromosomes replicate during interphase.
13
Q
Explain what is meant by homologous chromosomes, sister chromatids and non-sister chromatids.
A
- Homologous chromosomes have the same DNA sequence and the same genes (identical genetic loci) but they may have different variants (alleles).
- Sister chromatids have identical DNA and the same alleles.
- Non-sister chromatids have the same genes, but maybe different alleles.
14
Q
Explain recombination.
A
- Meiosis produces new combinations of parental genes in two ways: by random assortment (the result of meiosis I that puts random combinations of maternal and paternal chromosomes into gametes) and by crossing over (the exchange of chromosome segments between homologues).
- When pairs of homologous chromosomes line up in metaphase I, the maternal and paternal members of each pair line up at random with respect to all other pairs.
15
Q
Outline Meiosis I.
A
21
Q
Outline Meiosis II.
A
- Prophase II: Chromosomes re-coil and shorten.
- Metaphase II: Unpaired chromosomes become aligned at equator of cell.
- Anaphase II: Centromeres separate. Daughter chromosomes, which were sister chromatids, pull apart.
- Telophase II: Chromosomes uncoil and nuclear envelope re-forms.
- Cytokinesis: Cytoplasm divides forming 4 daughter cells.
22
Q
Outline the steps involved in spermatogenesis.
A
- In males, the production of sperm, known as spermatogenesis, occurs in the testes.
- Cells called spermatogonia line the tubules of the testes and divide by mitosis from puberty until death, producing daughter cells called primary spermatocytes.
- Primary spermatocytes undergo meiosis, and the four haploid cells that result are called spermatids.
- Each spermatid develops into a mature sperm.
23
Q
Outline oogenesis.
A
- In females, the production of gametes is called oogenesis and takes place in the ovaries.
- Cells in the ovary known as oogonia begin mitosis early in embryonic development and finish a few weeks later.
- Because no more mitotic divisions take place, females are born with all the primary oocytes they will ever have.
- All the primary oocytes begin meiosis during embryonic development and then stop.
- They remain in meiosis I until a female undergoes puberty.
- After puberty, usually one primary oocyte per month completes the first meiotic division, and the secondary oocyte is released from the ovary and moves into the oviduct.
- Cytokinesis following meiosis I does not produce cells of equal size.
- One cell, destined to become the female gamete, receives about 95% of gamete (the ovum) and the non-functional, smaller cells are known as polar bodies.
- If the secondary oocyte is fertilized, meiosis II is completed quickly and the haploid nuclei of the ovum and sperm fuse to produce a diploid zygote.
- The timing of meiosis and gamete formation in human females is different from what it is in males.
- Unfertilized oocytes are lost during menstruation, along with uterine tissue.
