3. Mitosis & Meiosis Flashcards
What type of cells undergo mitotic cell division?
Somatic cells
What is the product of mitosis?
2 identical daughter cells with exactly the same chromosomal content as the parent cell. Diploid cells with 23 pairs of chromosomes.
Just before meiosis, what does the DNA look like in G2?
Chromosomes are replicated and sister chromatids are joined by a centromere. Not visible at this point as not condensed.
What are the 5 stages of mitosis?
Prophase, Prometaphase, Metaphase, Anaphase & Telophase
What happens in prophase which makes the DNA visible?
chromosomes condense
At what stage do the spindle fibres attach to the centromeres?
Prometaphase
What happens in metaphase?
The chromosomes line up along the metaphase plate
In what phase does the nuclear envelope reappear in mitosis?
Telophase
What differs during anaphase in mitosis and meiosis I?
In mitosis, the chromosomes are pulled apart and each chromatid is pulled to a different side of the cell.
During meiosis I, homologous chromosomes are separated. These are then separated into chromatids during meiosis II.
What are telomeres and where are they located?
They are repeated sequences of DNA which are at each end of chromosome/chromatid. They protect DNA from degradation.
What are the names for different position of the centromere, starting from central and working upwards.
Metacentric (central), submetacentric, acrocentric and telocentric (not in humans)
During meiosis, when does crossing over/recombination occur?
Prophase I
What is a bivalent or tetrad and when can it be seen?
It is when 2 replicated chromosomes, homologous pairs line up on the metaphase plate during metaphase I of meiosis.
What are the 2 processes which lead to genetic variation in meiosis?
- Random assortment of homologous pairs on metaphase plate.
2. Crossing over and exchanging of genetic information
What is the product of meiosis?
4 non identical haploid (n) daughter cells
How many chromosomes do the dividing cells have at the end of meiosis I?
Haploid (n) = 23 chromosomes
How many chromosomes do the haploid daughter cells have after meiosis?
23 chromosomes (not paired)
What is the difference in cell division in spermatogenesis and oogenesis?
Spermatogenesis produces 4 sperm (n) from 1 spermatocyte (2n) whereas oogenesis produces 1 egg (n) and 3 polar bodies from 1 oocyte (2n)
What is a common cause of aneuploidy?
Non-disjunction of chromosomes during metaphase
What will the be the result of non-disjunction at the first post-zygotes mitotic division?
46,N will divide to produce one monosomy cell line and one trisomy cell line. The monosomy cell line is usually lost.
What is the result of non disjunction at later mitotic cell divisions?
46N will produce one monosomy cell line and one trisomy cell line. The monosomy will be lost and the trisomy will be combined with the normal cells. MOSAIC karyotype.
What is mosaicism?
The presence of 2 or more cell lines in an individual
What determines the degree of mosaicism?
When the non-disjunction takes place, later mitotic divisions will affect fewer cells.
What will be the effect of non-disjunction in meiosis 1 ?
All offspring will have the wrong chromosome number. Half will be monosomy and half will be trisomy when fertilised.
What happens if there is non-disjunction in meiosis II?
Half of the offspring will have the wrong chromosome number ( one trisomy and one monosomy) and have will be normal.
What is a robertsonian translocation?
When 2 acrocentric chromosomes q arms fuse and p arms are lost, so the indictable will have 45 chromosomes.
What gene is responsible for the initiation of male sex?
SRY gene on the Y chromosome
23 unduplicated structures are seen to travel to each pole, what cell division is this?
Meiosis II.
Duplicated in meiosis I
46 in mitosis
During mitosis, when does the Nucleolus disappear?
During prophase when the chromosomes are condensed and will only return when chromosomes decondense.
What are the consequences of faulty meiosis ?
- infertility
- mental retardation
- miscarriage
