Session 5: Mitosis & Meiosis Flashcards
How many alleles of a specific gene are found in the G2 phase of the cell cycle? Why?
2, each gene is inherited in 2 alleles because each comes from one parent so there would be 2 different alleles for a trait.
Why do humans have 2 copies of each chromosome?
Humans are diploid so each cell carries 2 copies of each chromosome, one from mother and one from father
What are the phases of the cell cycle? What occurs in each phase?
G0 - Cell is performing its function without actively preparing to divide - rest
G1 - cell grows
S - DNA replication
G2 - Cell prepares for cell division, more growth & organelles and proteins develop
M - Cell division (mitosis or meiosis)
How many DNA molecules are there in one chromosome after G2 phase?
2 DNA molecules (each chromatid consists of 1 DNA molecule)
What are the main cell cycle checkpoints & what occurs at each?
G1 - checks for nutrients, growth factors & DNA damage
G2 - Check for cell size & DNA replication
Metaphase - check for spindle attachment
What are telomeres? What is their function? How would they be identified under a telescope?
They are regions of repetitive DNA found at either end of chromosomes, they appear as white dots under a microscope.
Telomeres protect the end of chromosomes during replication, making sure all genes on chromosomes are copied and no info is lost during replication
What is the function of centromeres?
Sequence that links sister chromatids together
What is G-banding and what do they tell us about chromosomes?
Chromosome banding = thin alternating light & dark regions along length of chromosome
Enzymatic digestion followed by Giemsa stain
- Identify translocations, duplications & loss of specific chromosomes
How is chromosome painting used to identify chromosomes?
Fluorescent markers label different parts of chromosomes
What is an allele?
A variant of a gene
At which stage of mitosis are sister chromatids moved to opposite poles?
Anaphase
At which stage of mitosis do chromosome decondense, spindle fibres disappear and nuclear membrane reforms?
Telophase
At which stage of mitosis does the nuclear membrane break down, spindle fibres appear and chromosomes appear?
Prophase
At which stage of mitosis do chromosomes align and condense at the metaphase plate?
Metaphase
What does mitosis produce after cytokinesis?
2 identical diploid daughter cells are produced with the same chromosome content as parent
What type of cells does mitosis occur in?
Somatic cells
What type of cells does meiosis occur in?
Germ cells
What does meiosis produce after cytokinesis?
4 non-identical haploid cells with 1/2 the number of chromosomes in each cell
How do sex chromosomes find each other
They share similar sequence
During which stage of meiosis are homologous chromosomes paired up?
Prophase 1
What are the implications of recombination?
Genetic variation
What is spermatogenesis?
a meiotic process producing sperm
What is oogenesis?
a meiotic process producing oocytes
Compare oogenesis & spermatogenesis.
- 1 oocyte (2n) gives 1 egg (n) & 3 polar bodies whilst 1 spermatocyte (2n) gives 1 egg (n) and 3 polar bodies
- Length of oogenesis = 12-50 years whilst length of spermatogenesis = approx 60 days
- Oogenesis = non-motile gametes whilst spermatogenesis = motile games
What is aneuploidy? What can cause it?
condition of having an abnormal number of chromosomes in a haploid organism
can be caused by non-disjunction during meiosis or miosis
What is non-disjunction?
A failure to separate pairs of chromosomes lined up at the metaphase plate = produces daughter cells with abnormal number of chromosomes
What is trisomy? What is an example of a condition caused by meiotic trisomy?
3 copies of a chromosome instead of 2.
Eg Down’s syndrome = 3 copies of chromosome 21 instead of 2
What is monosomy? What is an example of a condition caused by miotic trisomy?
Only 1 copy of chromosome rather than 2 - missing chromosome.
Eg Turner’s syndrome = only 1 X chromosome, missing chromosome
What is the difference between meiosis 1 and meiosis 2?
meiosis 2 is cell division without DNA replication
When and how do homologous chromosomes pair up in meiosis 1?
During prophase 1
- Homologous chromosomes pair up forming bivalents
- Crossing over occurs at chiasmata between maternal and paternal copy
- Recombinant chromosomes are formed
