Cellular replication and variation Flashcards
chromatid
one of the two identical parts of the chromosome after S phase of interphase
centromere
point where the two chromatids touch, and where the microtubules attach
haploid number
cellular condition where there is one type of chromosomes in a set (n)
homologous pairs
matching pair of chromosomes
diploid number
where there is two sets of chromosomes (2n = 46 humans)
ploidy level
the number of complete sets of chromosomes in an organism
polyploid
more than two full sets of chromosomes
aneuploidy
the presence of an abnormal number of chromosomes in a cell
meiosis
nuclear division resulting in daughter cells having half as many chromosomes
happens in sex organs: ovaries and testes and results in variation
mitosis
nuclear division resulting in daughter cells having the same number and type of chromosomes as the parent cell
happens in asexual reproduction resulting in identical genetics
Stages of meiosis
Interphase, prophase I, Metaphase I, Anaphase I, Telophase and cytokinesis I, prophase II, metaphase II, telophase and cytokinesis II
Interphase
Longest part of the cycle
Interphase G1: produces protein, repairing damage and cells increase in size and volume as more cell organelles are produced
DNA Synthesis phase: cell synthesizes and replicates its DNA, however number of chromatins remain the same (semiconservative replication)
G2 phase: growth of cell and replication of the organelles; prepares for cell division of mitosis or meiosis
Prophase I
the condensation of chromosomes consisting of two chromatids becoming visible
chromosomes seen as x-shapes and are identical copies
disappearance of the nucleolus and nuclear membrane, and formation of mitotic spindle.
Metaphase I
Bivalents line up across the equator of the cell, attached to the spindle fibres at the centromeres.
Anaphase I
Chromosomes in each bivalent are pulled by the spindle fibres to opposite poles. The centromeres do not divide.
Telophase and Cytokinesis I
The cell splits into two, each cell gets one chromosome from each pair. In animal cells, two new nuclear envelopes form
Prophase II
New spindle is formed perpendicular to that of the original cell
Metaphase II
Individual chromosomes, each consisting of wo chromatids, migrate to the equator of the spindle and attach at the kinetochore proteins that surround the centromeres
Telophase and Cytokinesis II
the spindle fibres disappear, the cell divides across its equator and a new nuclear membrane is formed around the chromosomes
crossing over / recombination
the exchange of chromosome segments between non-sister chromatids in meiosis. Crossing over creates new combinations of genes in the gametes that are not found in either parent, contributing to genetic diversity.
independent assortment A
• During metaphase I, the bivalents move to the metaphase plate. The homologous pairs orient themselves randomly at the equator. In each cell that undergoes meiosis, the arrangement of the chromosomes is different. The number of variations is dependent on the number of chromosomes making up a set with the possible number of alignments equalling 2n, where n is the number of chromosomes per set.
independent assortment B
During metaphase II, there is further random distribution and subsequent separation of the sister chromatids.
random fertilisation
Genetic variation is also introduced by random fertilisation of the gametes produced by meiosis. Any of the genetically unique sperm generated by a male may fertilise the genetically unique egg produced by a female
spermatogenesis
formation is sperm cells in male testes (DO MORE STUDY)
