Cell Reproduction Flashcards
What is a genome?
All the DNA of a cell.
How many chromosomes do humans have in each nucleus of each somatic cell? How many pairs is that?
46 single-stranded chromosomes, 23 pairs.
What are somatic cells?
All the cells in a body that are not gametes.
How many chromosomes are in the nucleus of a gamete?
23
What are the sub-phases of interphase?
G1 phase, S phase, and G2 phase.
During what phase of cell division is the DNA replicated?
S phase of interphase.
After DNA is replicated, the G2 phase begins. What occurs in this phase?
The two chromatids formed by S phase combine into a double-stranded chromosome, and the centrosome is duplicated.
What is the centromere?
The part where the two chromatids of replicated DNA are attached to each other, forming one molecule.
What is an aster?
A radial array of short microtubules extending from each centrosome during mitosis.
When does the DNA become condensed, and centrosomes migrate to opposite ends of the cell?
During prophase.
What is the name of the apparatus of microtubules that control the chromosome movement during mitosis?
The mitotic spindle, or spindle apparatus.
What occurs during prometaphase?
The nuclear envelope fragments, so the chromosomes begin to migrate. Some of the spindles attach to each kinetochore of all the chromosomes.
During which phase are the chromosomes all convened at a “plate” in the centre of the cell?
Metaphase
During which phase do the microtubules begin to pull single chromatids away from the centre of the cell by depolymerizing at their kinetochore ends?
Anaphase
During which phase does the cell elongate because of the lengthening of non-kinetochore microtubules?
Anaphase
What occurs during telophase?
Two nuclei form at opposite ends of the cell, with nuclear envelopes re-formed from the fragments and from other portions of the endomembrane system. The spindle apparatus breaks down completely and the chromosomes begin to de-condense.
How is cytokinesis different in plants than in animals?
In plants, daughter cells are not cleaved at a cleavage furrow, but a cell plate made out of vesicles forms between them and becomes the new cell wall.
What is binary fission?
A process of cell division by which prokaryotes reproduce. The chromosome is replicated beginning at the origin of replication, and the two origins produced move apart. Then the new cell is pinched off.
What are the three checkpoints of the cell cycle control system?
G1, G2 and M.
What are all the phases and sub-phases of the cell life cycle in order?
Interphase: G0 phase, G1 phase, S phase, G2 phase.
Mitosis: Prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis.
How many centrioles are in a centrosome?
2
What is genetic variation?
The difference in appearance shown by offspring of the same parents.
What is a locus?
A specific place on a chromosome which signifies a particular gene.
What does the equation 2N=4 signify?
The inheritance of a set of chromosomes from each parent. There are 2 versions of each chromosome inherited, making a homologous pair. Since there are 2 chromatids in a chromosome, there will be 4 chromatids passed on to the offspring which code for the same genes.
What is a karyotype?
An ordered display of the pairs of chromosomes.
What is a homologue?
A pair of chromosomes, both of which code for the same genes, and are the same length.
True or false: females have sex chromosomes XY and males have XX.
False. The opposite is true.
What are autosomes?
The pairs of chromosomes which are not sex chromosomes.
To what do the terms haploid and diploid refer?
‘Haploid’ means there is only one chromatid (or single-stranded chromosome) in a cell that codes for a set of genes (written as n). ‘Diploid’ means there are two, forming a pair (written as 2n).
True or false: a zygote produces somatic cells by mitosis to eventually develop into an adult.
True. The individual only produces gametes by meiosis after it reaches sexual maturity.
What does the expression 2n -> 1n signify?
The process of meiosis.
What does the expression 1n -> 2n signify?
The process of fertilization.
What are the three main types of sexual life cycles?
Animal, plant/algae, and fungi/protist.
What is a gametophyte?
A haploid organism (plant or alga) that develops from a spore made by a diploid sporophyte. It can make haploid gametes by mitosis, since it is already haploid.
Describe the sexual life cycle of most fungi.
- They start as single-celled diploid zygotes
- The zygote undergoes meiosis
- The haploid organism produced grows and produces gametes by mitosis
- The gametes are fertilized and a new diploid zygote is produced
True or false: animals can produce haploid cells by mitosis.
False. Animal cells must undergo meiosis in order to produce gametes.
What are the two stages of meiosis?
Meiosis I (in which homologous chromosomes separate) and meiosis II (in which sister chromatids separate).
How many daughter cells does meiosis produce?
4
2nDS -> 1nDS -> 1nSS is an expression referring to stages of meiosis. Explain.
2nDS means that before meiosis begins, there are homologous pairs of two chromosomes that are each made up of two chromatids, meaning they are double-stranded. 1nDS means that after Meiosis I, the chromosomes are still double-stranded, but there is only one in each cell that codes for certain genes (no more homologous pairs). 1nSS means that equational division has occurred. After Meiosis II, the chromosomes have become single-stranded - there is only one chromatid of each kind in a cell. The cell is now haploid and non-identical to the other daughter cells.
What is ‘crossing-over’?
A genetic rearrangement between non-sister chromatids involving the exchange of corresponding DNA segments. This is completed while homologues are in synapsis, in Prophase I.
What is synapsis?
The physical connecting of homologues along their lengths by the synaptonemal complex during Prophase I.
What do you call a group of four chromatids, or a pair of chromosomes, in Prophase I?
A tetrad
What is a chiasmata?
An ‘x’-shaped region at which crossing-over occurs in a tetrad.
What occurs during metaphase I of meiosis?
- Tetrads line up at the metaphase plate
- Microtubules attach to the kinetochores of each tetrad.
What occurs during anaphase I of meiosis?
Pairs of homologues (tetrads) separate and move toward opposite poles, guided by the spindle apparatus.
Describe what happens during telophase I and cytokinesis of meiosis.
Two haploid daughter cells are formed in the same manner as mitosis, with the nuclear envelope re-forming and everything. No chromosome duplication occurs between meiosis I and meiosis II.
What occurs during prophase II of meiosis?
A spindle apparatus re-forms and DS chromosomes move toward the metaphase plate.
Describe what happens during metaphase II of meiosis.
- Chromosomes convene at the metaphase plate
- The chromatids of each chromosome are not exactly the same, because of crossing-over in prophase I
- Microtubules attach to kinetochores
Describe what happens during anaphase II of meiosis.
- The proteins at the centromere break down so that the sister chromatids can separate
- The chromatids move toward opposite poles
What is the point of telophase II and cytokinesis in meiosis II?
The point is to re-form the nuclei in each of the four daughter cells and to split them up.
True or false: meiosis produces genetically identical sex cells.
False. They are all different from the parents and from the rest.
What are alleles?
Alternate versions of a gene.
What is independent assortment?
The random arrangement of homologues across the metaphase plate in metaphase I. Each parent’s homologues could be on either side of the plate.
What is random fertilization?
It means that absolutely any sperm can fuse with any ovum, and there is no pattern. This contributes to genetic variation.
What are the three events that contribute to genetic variation in sexually reproducing organisms?
Crossing-over, independent assortment, and random fertilization.
