Mitosis and Meiosis Flashcards
what stage of the cell cycle is DNA polymerase active?
S phase. DNA polymerase is involved in DNA synthesis
what is meiosis?
special type of cell division used solely to produce gametes – oocytes and sperm.
where does meiosis occur?
occurs in the gonads (ovaries and testis)
why is meiosis required?
required to produce gametes that are haploid, to allow fertilisation and production of a diploid zygote. This results in genetic variation within the gene pool.
what are the stages of meiosis?
(Meiosis I and Meiosis II), each with their own prophase, metaphase, anaphase, and telophase stages
what is meiosis I?
the first metabolic division is a reduced division, in which homologous chromosomes are separated, thus reducing the number from diploid to haploid
what happens during prophase 1?
the chromosomes condense, the nuclear membrane dissolves, homologous chromosomes from bivalents and crossing over occurs
what happens during metaphase 1?
spindle fibres from opposing centrosomes connect to the bivalents at their centromeres and align them along the middle of the cell
what happens during anaphase 1?
the spindle fibres contract and split the bivalent. homologous chromosomes move to opposite poles of the cell
what happens during telophase 1?
chromosomes decondense, the nucleus may reform and the cell undergoes cytokines to dorm two daughter cells
when does crossing over occur?
during prophase 1
what is crossing over?
The homologous pairs of chromosomes line up in register, matching the location (locus) of the corresponding genes together. As the chromosomes condense, crossing over sites are formed (between the maternal and paternal chromosomes) and random exchange of genetic material occurs between the homologous chromosomes.
what causes abnormalities in chromosome numbers?
nondisjunction. This means one daughter cell will have both chromosomes of the homologous pair, instead of one. So one daughter cell will have an extra chromosome (24 chromosomes), whilst the other daughter cell will have one less
what is gameteogensis?
the process by which spermatozoa and ova are formed. Meiosis is a crucial part of gametogenesis, but the timing of events and size/number of gametes produced vary between the testis and the ovary.
