meiosis Flashcards
what is the difference between mitosis and meiosis
mitosis : cell division that produces somatic cells ; for growth, tissue repair and asexual reproduction ; diploid cells produced
meiosis : cell division that produces gametes ; leads to genetic variation in offspring ; haploid cells produced from diploid cells
define homologous chromosomes
the set of one maternal chromosomes and one paternal chromosome that pair up with each other inside a cell during meiosis
what are the characteristics of homologous chromsomes
same genes
same place
same length
same size
different alleles
centromeres in same place
outline meiosis
prophase 1
metaphse 1
anaphase 1
telophase 1
cytokinesis
prophase II
metaphase II
anaphase II
telophase II
cytokinesis
what happens during meiosis 1
reduction division
homologous chromosomes are separated, placed in different cells
results in two haploid cells
what happens during meiosis 2
like mitosis
sister chromatids are pulled apart at the centromere, one is placed in each daughter cell
results in four haploid gametes
what happens during prophase 1
chromosomes condense
centrioles move to opposite ends of the cell forming the spindle
nucleolus and nuclear envelope break down
homologous chromosomes pair up forming bivalents - a pair of associated homologous chromosomes
what is crossing over
happens in prophase 1
results in exchange of genetic information between the maternal and paternal chromosomes
results in a new combination of alleles in gametes
what happens during metaphase 1
homologous chromosomes line up along the equator of the cell
spindle fibres attach themselves to the centromere
independent assortment
what is independent assortment
the orientation of homologous chromosomes when they pair up is random and independent of any other pair
cells produced after meiosis 1 will contain a mixture of maternal and paternal chromosomes –> same genes but different alleles
what happens during anaphase 1
spindle fibres shorten
homologous chromosomes are pulled apart to opposite poles
chromatids stay joined together
crossed over sections lead to increased variation
what happens during telophase 1
chromosomes reach the poles of the cell
nuclear envelope reforms
chromosomes uncoil
what happens during prophase 2
chromosomes condense
centrioles move to opposite ends of cell forming the spindle fibre
nucleolus and nuclear envelope breaks down
what happens during metaphase 2
individual chromosomes line up along the equator of the cell
independent assortment of sister chromatids
what happens during anaphase 2
spindle fibre shorten
chromosomes are pulled apart to opposite poles
what happens during telophase 2
chromatids reach the poles of the cell
nuclear envelope reforms
chromosomes uncoil and form chromatin again
genetically different due to independent assortment and crossing over
