Meiosis Flashcards
What are gametes?
They are the sperm cells in males and egg cells in females
Hows a diploid zygote formed?
In sexual reproduction two haploid gametes join together ar fertilisation to from a diploid zygote, which divides and develops into a new organism
Definition of homologous chromosomes
A pair of chromosome one from the mum and one from the dad that pair up with each other inside a cell during meiosis. They have the same size and genes although they could have different version of the genes called alleles
Why do gametes have a haploid number of chromosomes?
As theres only one copy of each chromosome
Why are cells formed by meiosis are all genetically different?
Because each new cell ends up with a different combination of chromosomes
Definition of meiosis
Its a type of cell division that happens in the reproductive organs to produce gametes
What does meiosis begins with?
Interphase - during interphase, the cell’s DNA unravels and replicates to produce double armed chromosomes called sister chromatids
What is Meiosis 1
Its the reduction division (it halves the chromosome number) - it has 4 stages Prophase, Metaphase, Anaphase, Telophase
What happens in Prophase 1
> The chromosome condense, getting shorter and fatter
Homologous chromosome pair up - 1 with 1, 2 with 2 etc…
Crossing-over occurs
Centrioles start moving to opposite ends of the cell, forming the spindle fibres
Nuclear envelope breaks down
What happens in Metaphase 1
> The homologous pairs line up across the centre of the cell and attach to the spindle fibres by their centromeres
What happens in Anaphase 1
> The spindles contract, pulling the pairs apart (One chromosome goes to each end of the cell)
What happens in Telophase 1
> A nuclear envelope forms around each group of chromosomes
> Cytokinesis occurs and two haploid daughter cells are formed
What happens in meiosis 2
The 2 daughter cells undergo Prophase 2, Metaphase 2, Anaphase 2, Telophase 2 and cytokinesis
What is the difference between meiosis 1 and meiosis 2
In meiosis 2 half theres half the number of chromosomes
What happens in Anaphase 2
The sister chromatids are separated- each new daughter cell inherits one chromatids from each chromosome. Four haploid daughter cells are produced.
What leads to genetic variation
- crossing over of chromatids
2. independent assortment of chromosomes
Describe crossing over of chromatids
> During Prophase 1 of meiosis 1, homologous pair of chromosomes come together and pair up.
The chromatids twist around each other and bits of chromatids swap over.
The chromatids still contemn the same gene but now have a different combination of alleles
how does crossing over of chromatids lead to genetic variation
Because each cell has different chromatid and therefore a different set of alleles, which increases genetic variation in potential offspring
How does independent assortment of chromosomes lead to genetic variation?
The shuffling of chromosomes leads to genetic variation in any potential offspring
