5.meiosis Flashcards
Autosomes
Autosomes are any chromosomes in humans that is not a sex chromosome
Sex chromosomes
sex chromosomes are a chromosome responsible for determining the biological sex of an organism. In humans, sex chromosomes can be either an X or Y chromosome.
What is meiosis
Process by which a germline cells gives rise to four genetically different cells. Each daughter cell inherits half of the set of DNA from the parent cell.
Germline cells
- the precursors for gametes
- diploid
- 2n=46
diploid
The number of chromosomes found as homologous pairs in a cell
haploid
one of each pair of homologous chromosomes
features of homologous chromosomes
- same size
- same length
- same centromere position
- share the same genes at a specific gene loci
where does meiosis occur
Meiosis only takes place in the germline cells in the sex organs eg testes and ovaries
GONADS
purpose of meiosis
- produce 4 haploid gametes
- haploid gametes fuse in fertilisation to create a diploid zygote
how many rounds of DNA replication in meiosis
one round
List the stages of meiosis
Interphase
-G1,S,G2
PMAT 1
Cytokinesis
PMAT 2
Final cytokinesis
Prophase 1
- Chromosomes are visible and condensed
- Crossing over between homologous pairs occur
Define Crossing over
Crossing over between homologues pairs of chromosomes is where alleles are exchanged. This creates new allele combinations on sister chromatids (they are no longer genetically identical) which leads to the genetic variation.
Metaphase 1
- Homologous chromosomes align at the equator of the cell
- Independent assortment of chromosomes occurs
Define Independent assortment
Independent assortment of chromosomes is where the chromosomes randomly align on the equator of the cell in their homologous pairs. This creates new chromosomal combinations
Anaphase 1
- Homologous pairs seperate
- Centromere doesn’t divide
Telophase 1
-two nuclei formed, each containing one of the homologous pairs
Prophase 2
- DNA doesn’t replicate
- NO crossing over
- Chromosomes become visible
Metaphase 2
-Chromosomes line up at the equator of the cell (not in pairs)
Anaphase 2
-Centromeres disjoin and sister chromosomes (now called single chromosomes) move to opposite pole of the cell
Telophase 2
-two nuclei form
what are recombinant chromatids
Chromatids that have swapped DNA
importance of fertilisation
In sexual reproduction, following meiosis, the final genetic variation comes from the random fertilisation of gametes.
why is genetic variation important
populations are able to better adjust to changes in the environment eg natural disasters ,food shortages etc
