meiosis Flashcards
meiosis
cell division of sex cells
karyotype
a complete set of chromosomes arranged according to shape size and number in a organism
where does meiosis take place in animals
in the gonads (reproductive cells) , testes in the male and ovaries in the female
what is are cells produced by meiosis
gametes [ gametes are formed through the process gametogenesis]
in the male sperm cells are produced, through the process spermatogenesis and in the female egg cells are produced , through the process of oogenesis
what are plant gametes called
spores
where does meiosis occur in plants
in the anthers to produce pollen grains in the male and in the ovary to produce ovules in the female
interphase
DNA replication takes place where the chromosomes duplicate and the genetic material is doubled
the two copies of chromosomes are called homologous pairs
meiosis 1
a reduction division where the diploid cell is separated to create 2 haploid cells.
prophase 1
- the spindle is formed
- the chromatin network contracts and the single threaded chromosomes become visible
- the nuclear membrane and and nucleolus disappear
- the chromosomes arrange themselves and pair homologously
- the homologous chromosomes lie next to each other and at the chiasma ( a point along the chromatid) the chromatids cross over and genetic material is exchanged
metaphase 1
- the spindle extends across the whole cell
- the homologous pair arrange themselves at the equator
- the spindle fibers attach to the centrosome of the homologous pairs
anaphase 1
the spindle contracts and the homologous pairs separate and they move tp the opposite ends of the cells poles
telophase 1
the spindle disappears
the nucleus membrane and nucleolus form
the cytoplasm divides thus forming 2 haploid cells with different genetic materials due to crossing over
meiosis 2
- the 2 daughter cells from meiosis 1 divide again
- the centromeres of these daughter cells separate resulting in 4 haploid cells
prophase 2
- nucleus membrane and nucleolus disappear
- spindle threads form
- the daughter cells are now visible as chromatids
metaphase 2
- the spindle threads extends across the cell
- the sister chromatids arrange themselves at the equator
- the spindles attach to the centromeres of the daughter cells
anaphase 2
the spindle fibres contract ,then separating the sister chromatids and pulling them to the opposite poles of the cell
Telophase 2
-the spindles disappear
-the nucleus membrane and nucleolus reform
-the cytoplasm divides thus resulting in 4 haploid daughter cells
the new daughter cells are genetically different from each other
genome
set of genes in a organisms haploid set of chromosomes
what is the importance of meiosis
- it ensures genetic variation
- it prevents the doubling effect of fertilisation
- it results in the formation of mature gametes in the process of gametogenesis
gametogeneiss
process whereby gametes are formed
explain how the random arrangement of chromosomes results in genetic variation
- at the equator each homologous chromosome pair is randomly arranged , which results in the random separation of chromosomes
- the paternal and maternal chromosomes randomly move to opposite poles of the cell, this ensures that the combination of genetic material received by each gamete is random
explain how crossing over allows for genetic variation
crossing over results in the exchange of genetic material between the paternal and maternal homologous chromosome pairs , a new genetic combination occurs between the exchanged chromosomes , this ensures that all the gametes have a unique gene combination
so when the gametes of the same parents come together for fertilisation the resultant offspring will have a unique karyotype thus ensuring variation in the offspring
what is non-disjunction
when one pair of chromosomes does not separate and the one cell receives two copies of chromosomes and the other cell doesnt
explain where does non-disjunction occur
it happens during anaphase 1 when the homologous chromosomes do not separate or in anaphase when the sister chromatids do not separate
