Mitosis And Meiosis Flashcards
What are the stages of the cell cycle and what happens in each? (Simply)
G1-cell contents replicated
S-DNA replicated
G2-cell grows in size
M-mitosis/meiosis (cell division)
What is a telomere?
A repeated equine of base ate each end of a chromosome/chromatid (can be used as a marker as is known)
What is a centromere?
It links the sister chromatids and is made of repeating sequences.
How are chromosomes grouped by scientists?
According to size and shape
What is the basic of mitosis?
Cell division for Somatic cells.
Produces 2 identical daughter cells (same chromosome content as parental cell)
Mitotic growth is needed constantly for tissues such as epidermis and bone marrow
What are the stages of mitosis?
Prophase Premataphase Metaphase Anaphase Telophase
Then cytokinesis
Describe prophase.
Nuclear membrane dissolves
Chromosomes are visible
Kinetochore proteins bind to centromere
Spindle fibres form
Describe premetaphase.
The spindle fibres attach to the kinetochore’s
Describe metaphase.
Chromosomes randomly line up at metaphase plate (middle of cell)
Each chromosome has 2 chromatids
Describe Anaphase.
The kinetochore fibres pull the daughter chromasomes apart separating the chromosomes and breaking the centromere
Describe telophase.
The cytoplasm divides (using cleavage furrow) and the nuclear envelope reforms.
2 daughter cell are formed (containing same genetic info as parent)
What are homologous chromosomes?
Have the same DNA sequence and genes
However the gee may be different variants of each other (alleles)
What is a sister chromatid?
Has the identical DNA and same alleles as they are replications of each other
What are non-sister chromatids?
Have the same genes, but different alleles (not replicated)
What is meiosis main points?
Cell division for germ line cells (sex cells)
Produce 4 non0identical haploid cells
One lot of replication and 2 divisions
Produced gametes
What are the stages of meiosis?
Meiosis 1 = prophase 1, metaphase 1 (this is when variation occurs), anaphase 1, telophase 1
Meiosis 2= prophase 2, metaphase 2, anaphase 2, telophase 2
What happens in prophase 1 of meiosis?
The pairs of chromatids find each other.
What happens in metaphase 1 of meiosis?
The homologous pairs of chromosomes form tetrads. And line up at metaphase plate. Recombination occurs as does random assortment
What is recombination?
Chromatids with near identical sequence find each other.
The chiasmata of these chromosomes can now cross over and so genetic info is swapped. The daughter chronometer are now non identical.
(If sister chromosomes cross this doesn’t matter but it has no effect as they are indentical)
What happens in anaphase 1 of meiosis?
The homologous pairs are pulled apart (pairs seperate not chromosomes)
What happens in telophase one of meiosis?
The two daughter cells form
Each is a haploid cell with 23 unreplicated chromosomes
Hat happens in prophase 2 of meiosis?
The homologous pairs are still crossed over from prophase 1. The envelope disintegrates
What happens in metaphase 2 of meiosis?
The chromosomes pair up randomly. No homologous pairs are present (only 23 in each cell no replicated)
What happens in anaphase 2 of meiosis?
The chromatids are separated by spindle fibres and pulled to poles.
What happens in telophase 2 of meiosis?
Envelope reforms and 4 (2 per telophase 2) non-identical daughter cells are created.
What does meiosis ensure?
Maintains constant number of chromosomes in every generation ( 23 per gamete fuse so 46 per cell)
Generate genetic diversity (random assortment of chromosomes and crossing over of genetic material)
What happen in Spermatogeneis? (Brief overview)
One spermatocyte produced 4 non identical sperm.
Takes around 60 days.
What happens in oogenesis? (Brief overview)
One oocyte produces 1 egg and 3 polar bodies
Takes between 12-50 years
