Meiosis Flashcards
Definition of Diploid
Double the number of chromosomes as the haploid number. Normal number of chromosomes in cells.
Definition of haploid
Half the number of chromosomes as a diploid cell.
Definition of bivalent
2 homologous chromosomes that are paired up/connected.
definition of homologous chromosomes
The same chromosomes with different alleles.
definition of independent assortment
chromosomes/chromatids can end up at either end of the nucleus which causes variation
definition of crossing over
When two homologous chromosomes swap some alleles which causes variation.
definition of chiasma
point at which 2 homologous chromosomes cross over
definition of random fertilisation
Any sperm could fertilise the egg and any egg could have matured. This produces variation. Happens after meiosis.
what do mutation cause?
variation
describe crossing over
each half of a chromosome is the same (one half copied itself) homologous chromosomes then cross over at the chiasma. Alleles are then swapped.
when is crossing over most likely to happen?
on long chromosomes
why is variation good?
produce new characteristics that can help species survive. Deal with changes.
describe independent assortment
chromosomes can end up at either end of the nuclei so when it divides lots of different combinations are possible. During anaphase 1, chromosomes are separated so each daughter cell ends up with different combinations of maternal and paternal chromosomes.
describe random fertilisation
Any sperm can fertilise the egg. Any egg can mature. Happens after meiosis. each sperm/egg is different because of independent assortment.
compared to the start what happens to the number of chromosomes in meiosis?
it is half (haploid cells)
what are the similarities and differences between homologous chromosomes?
similarities- bonding pattern, length, genes
differences - Alleles (maternal and paternal)
what happens during prophase 1
chromosomes condense, nuclear envelope disintegrates, nucleolus disappears, spindle fibres are made. Homologous chromosomes pair up forming bivalents.
what happens during metaphase 1
the bivalents line up along the metaphase plate. Spindle fibres attach to the centromere of each one.
what happens during anaphase 1
the bivalents are separated and one of each homologous pair is pulled to each pole.
what happens during telophase 1
Chromosomes assemble at each pole and the nuclear membrane reforms. The cell undergoes cytokinesis and 2 cells are formed.
what happens during prophase 2
the chromosomes in the nuclei of the two daughter cells condense and become visible again. The nuclear envelope breaks down and spindle formation begins.
what happens during metaphase 2
Individual chromosomes of each daughter cell assemble on the metaphase plate. Spindle fibres attach to their centromeres.
what happens during anaphase 2
the centromeres divide to separate the chromatids. One chromatid from each chromosome is pulled to each pole
what happens during telophase 2
The chromatids assemble at the poles, uncoil and form chromatin again. Cytokinesis divides each cell into 2, forming 4 daughter cells in total
What are the differences between mitosis and meiosis?
Mitosis 1 genetically identical daughter cells 2 daughter cells are diploid 3 no crossing over 4 stages are P M A T 5 chromosomes are separated in A1 into 2 chromatids 6 cytokinesis happens once.
what is the diploid and haploid number of chromosomes in a normal human cell
diploid - 46
haploid - 23
Out of mitosis, meiosis 1 and meiosis 2 which ones have reduction division?
Meiosis 1 only
Out of mitosis, meiosis 1 and meiosis 2 which ones have genetic variation?
Meiosis 1 and meiosis 2
How is the second division in meiosis different to mitosis?
The separating chromatids of a pair are not the same
