D2.1 Cell and Nuclear Division Flashcards
Explain why some cell divisions produce cells that are unequal in size (hint oogenesis and budding of yeast)
Unequal cytokynesis (splitting of the plasma membrane) occurs during oogenesis- formation of the ovum. An oocyte is an immature egg cell- and when an oocyte divides, the cytoplasmic division that follows is unequal. As a result, a primary oocyte creates a secondary oocyte and a polar body. Similarly, when that secondary oocyte divides- another polar body is formed. However, the polar bodies degenerate and their cytoplasm and cellular content are absorbed by the final ovum. This is because the polar bodies and secondary oocyte form one large ovum- to provide a large enough cytoplasm for storing nutrients and energy for the growing embryo.
In yeast, a single-celled fungus, unequal cytokinesis occurs through budding.
*Mitosis and meisois only occur in eukaryotes. Prokaryotes divide through binary fission.
Suggest why it is essential that nuclear division is a precise process.
it must be a precise process to ensure correct distribution of chromosomes, especially to avoid production of anucleate cells.
Suggest a main advantage of chromosomes being supercoiled during metaphase of mitosis
Supercoiling makes the chromosomes much more condensed, preventing them from becoming tangled or damaged as they are aligned at the metaphase plate and pulled apart during anaphase. This compact state ensures that the genetic material is equally and accurately distributed to the two daughter cells.
Distinguish between terms haploid and diploid
A haploid cell contains one set of chromosomes. This means a haploid cell has 23 chromosomes. However, a diploid cell contains two sets of chromosomes, one set from each parent. In humans, this means diploid cells have 46 chromosomes.
2n vs n, n=23 chromosomes
Define the term bivalent (Hint: BI meaning 2, implying duplication)
Bivalent refers to one pair of duiplicated and homologous chromosomes which are held together by chiasmata during meiosis.
Define the term Chiasmata (plural: chiasma)
The chiasma is the site of crossing over; the exchange of DNA between homologous chromosomes during meiososis
Define Crossing over
Crossing over is the exchange of genetic material between 2 homologous chromosomes during meisosis.
Distinguish between meiosis 1 and meisosis 2
Meiosis 1 forms 2 distinct haploid cells, each containing 1 chromosome from teh homologous pairs
However, meiosis 2 forms 4 distinct haploaid cells, each containing
All gametes produced during meiosis are haploid
What causes trisomy 21? (down syndrome)
An extra chromosome at chrosome 21 (13 or 18) due to meiosis error. The two chromatids in chrosome 21 fail to separate, resulting in both of them going into the daughter cell that forms the secondary oocyte.
How is genetic variation created in meiosis?
Fistly, genetic variation is created through crossing over, where segments of each maternal and paternal chromosomes exchange genetic material. These result in new combinations of genes on the chromosomes of the haploid cells produced.
Secondlty, through random orientation. Random orientation refers to the independent assortment of maternal and paternal homologous chromosomes in meiosis 1. This happens because the way the bivalents (homologous chromosomes held together by chiasma during meisosis)line up at the equator of the spindle in meisosis 1 and it is entirely random. Which chromosome of the given pair goes to which pole is unaffected by the behaviour of chromosomes n other pairs.
Chiasmata also increase genetid variability because the process results in the exhange of DNA between maternal and paternal chromosomes. Crossing over can happen many times and in between different chromatids between each bivalent, producing new combinations of alleles.
Compare and contrast mitotic and meiotic cell division
