Meiosis 2.1.6 (f,g) Flashcards
what is a diploid cell?
a cell with the normal number of chromosomes
what is a haploid cell?
a cell with half the number of chromosomes
what does mitosis result in?
two genetically identical daughter diploid cells
what is a gamete?
a sex cell
are haploid cells
what is a zygote?
the fertilised egg
are diploid cells
why is meiosis reduction division?
each gamete produced by meiosis are haploid cells
- have half the number of chromosomes than parents
what are homologous pairs of chromosomes?
a pair of chromosomes which are the same size and have the same gene
where do homologous pairs of chromosomes come from?
after fertilisation, one chromosome comes from the dad and one chromosome comes from the mum
what are the products of meiosis?
4 haploid daughter cells which are all genetically unique to each other with a different combination of chromosomes
what is an allele?
different versions of the same gene
they have the same gene loci
what is the gene locus?
the position of an allele on a chromosome
what are the two stages of meiosis?
meiosis I
meiosis II
what happens in meiosis I?
the reduction division:
the pairs of homologous chromosomes are separated into two new cells
product of meiosis I?
two genetically unique haploid cells
what happens in meiosis II?
similar to mitosis:
the individual chromosomes are separated in both of the newly produced cells
product of meiosis II?
four genetically unique haploid cells
prophase I
the chromosomes coil and condense
the homologous chromosomes pair up with each other
centrioles move to opposite poles
nuclear membrane breaks down
crossing over occurs
metaphase I
the homologous chromosomes attach to spindle fibres at their centromeres which lines them up on the metaphase plate
independent assortment occurs
anaphase I
the pair of homologous chromosomes are pulled apart when the spindle fibres contract
telophase I
the nuclear membrane reforms
chromosomes uncoil
cytokinesis occurs to produce two haploid daughter cells
prophase II
the chromosomes coil and condense into sister chromatids bound together by the centromere
the nuclear membrane breaks down
centrioles move to opposite poles of cell
metaphase II
the sister chromatids attach to the spindle fibres and are moved to the metaphase plate
independent assortment happens again
anaphase II
the individual chromatids are pulled apart by the contraction of the spindle fibres to opposite poles
telophase II
the separated chromatids uncoil and the nuclear membrane reforms
cytokinesis occurs to produce four haploid daughter cells
in what ways is genetic variation produced during meiosis?
crossing over
independent assortment of chromosomes
at what stages does crossing over occur?
prophase I
at what stages does the independent assortment of chromosomes occur?
metaphase I
metaphase II
what is crossing over?
when homologous chromosomes pair up in prophase I, their chromatids twist around each other and exchange alleles
this leads to a different combination of alleles
means that the four haploid cells produced at the end will have different allele combinations to their parents
what is independent assortment?
chromosomes line up completely independent of each other both in metaphase I and II
therefore the four haploid cells produced will have a completely random combination of maternal and paternal chromosomes
independent assortment in meiosis I
independent assortment of homologous chromosomes
the paternal and maternal chromosomes pair up randomly
independent assortment in meiosis II
independent assortment of sister chromatids
they can end up in either of the daughter cells so is random
