meiosis Flashcards
what is meiosis
cell division that produces gametes (haploid cells)
what happens in prophase 1
meiosis
-DNA condenses and becomes visible as chromosomes
DNA replication has already occurred so each chromosome consists of two sister chromatids joined together by a centromere
-The chromosomes are arranged side by side in homologous pairs
-As the homologous chromosomes are very close together the crossing over of non-sister chromatids may occur
-In this stage centrioles migrate to opposite poles and the spindle is formed
-The nuclear envelope breaks down and the nucleolus disintegrates
what happens during metaphase 1
meiosis
-pair of homologous chromosomes line up along the equator of the spindle, with the spindle fibres attached to the centromeres
-The maternal and paternal chromosomes in each pair position themselves independently of the others; this is independent assortment
-This means that the proportion of paternal or maternal chromosomes that end up on each side of the equator is due to chance
what happens during anaphase 1
meiosis
-The homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite ends of the spindle
-The centromeres do not divide
what happens in telophase 1 meiosis
-The chromosomes arrive at opposite poles
-Spindle fibres start to break down
-Nuclear envelopes form around the two groups of chromosomes and nucleoli reform
-Some plant cells go straight into meiosis II without reformation of the nucleus in telophase I
what happens in cytokinesis phase 1 meiosis
-This is when the division of the cytoplasm occurs
-The end product of cytokinesis in meiosis I is two haploid cells
what happens in prophase 2
meiosis
-The nuclear envelope breaks down and chromosomes condense
-A spindle forms at a right angle to the old one
what happens during metaphase 2
meiosis
-Chromosomes line up in a single file along the equator of the spindle
what happens during anaphase 2
meiosis
-Centromeres divide and individual chromatids are pulled to opposite poles
-This creates four groups of chromosomes that have half the number of chromosomes compared to the original parent cell
what happens during telophase 2
meiosis
-Nuclear membranes form around each group of chromosomes
what happens during cytokinesis phase 2
meiosis
Cytoplasm divides as new cell surface membranes are formed creating four haploid cells
how meiosis produce genetic variation?
-independent assortment of homologous chromosomes and sister chromatids
-results in new combination of alleles
how does a cell become specialised
undergo a process called differential gene expression. This process allows cells to become specialized, as their structure determines their function.
what are gametes
genetically different haploid cells
what is synapsis
the pairing of homologous chromosomes
what is a tetrad
4 sister chromatids of paired homologous chromosomes
what does meiosis end with
4 genetically different haploid daughter cells each containing one set of chromosomes
what are homologous chromosomes
pair of chromosomes that have the same genes but different alleles
-one maternal one paternal
what is independent assortment
chromosomes /chromatids separating from each other independently leading to genetic variation
