biology 6.2 - sexual reproduction and meiosis

What is a zygote?

It is created when 2 gametes join at fertilisation and develops into a new organism

What us meiosis?

A type of cell division that happens in reproductive organs to produce gametes

What are haploid cells?

Chromosomes with only 1 complete set of chromosomes (e.g. in humans = 23 chromosomes)

What is a reductive division?

When the number of chromosomes divides resulting in the mother cell having the full number of chromosomes whilst the daughter cells are haploid cells

What is the end result of meiosis?

4 genetically different cells

How many divisions are there in meiosis and is there a reductive division?

There are 2 divisions and meiosis 1 is the reductive division

What happens in interphase?

The DNA unravels and replicated to form sister chromatids (2 armed chromosomes)

What happens in prophase 1?

• Chromosomes condense and arrange themselves into homologous pairs (e.g. chromosome 1 from mum and dad)

• Crossing over occurs

• Centrioles move to opposite side of the cell forming spindle fibres

• Nuclear envelope breaks down

What happens in metaphase 1?

• Homologous pairs attach to spindle fibres by their centimetres

• Chromosomes line up along the eqyatri if the cell

What happens in anaphase 1?

The spindles contract so pull the pairs apart so one chromosome gives to each pole

What happens in telophase 1?

Nuclear envelope forms around each set if chromosomes

What is the result if cytokinesis 1?

There are 2 haploid cells as the homologous pair have been separated to each new cells only has one chromosome from the original pair

What happens in prophase ll, metaphase ll, anaphase ll and telophase ll?

Similar to in mitosis but in anaphase the sister chromatids are separated so each daughter cells inter it one chromatids form each chromosome

What is crossing over?

During prophase 1 when the homologous pairs come together the chromatids twist around each other and sections of chromatids swap over so the chromatids now have the same genes but a different combination of alleles

What is independent assortment?

During metaphase 1 when the homologous pairs line up along the equator and in anaphase 1 when they are pulled apart it is completely random whether each pole get the mother of fathers chromosome resulting in each of the 4 daughter cells have a different combination of maternal and paternal chromosomes