meiosis Flashcards
Are the gametes haploid or diploid?
haploid
What are homologous chromosomes?
matching pairs made of one maternal and one paternal chromosome containing same genes at same places on the chromosome
What are specialised organs such as ovaries and testes called?
gonads
What is meiosis used for?
sexual reproduction which increases genetic variation
What 2 stages cause genetic variation?
-in crossing over
-in independent assortment
interphase
chromosomes duplicate
prophase 1
-chromosomes , supercoil becoming condensed and visible
-nuclear envelope, breaks down -spindle fibres form from centriole
-homologous chromosomes pair up forming bivalents
-crossing over occurs
metaphase 1
- homologous pairs ofchromosomes align on the cell equator
-spindle fibres attach to the centromeres
-Independent assortment (segregation) . The position of each bivalent is independent of all the other chromosomes- the maternal and paternal chromosomes can be on either side of the equator
anaphase 1
homologous chromosomes are pulled up by the spindle fibres to the poles, but not pulled apart. This causes genetic variation by independent assortment
telophase 1
-nuclear envelope reforms -chromosomes uncoil
-the cells undergo cytokinesis
-cells are now 2 haploid daughter cells
prophase 2
-chromosomes recondense
-Nuclear envelope breaks down again
-Spindle fibres reform
metaphase 2
- single chromosomes are aligned on the equator by spindle fibres by centromeres
anaphase 2
-chromatids are split apart by the spindle fibres
-Chromatids move to the poles of the cells
(same as in mitosis)
telophase 2
-chromatids uncoil
-Nuclear envelopes reform
-Cell undergoes cytokinesis
-Four genetically different haploid daughter cells are produced
how does crossing over increase genetic variation?
homologous
