crossing over Flashcards
1
Q
crossing over
A
- mutual exchange of pieces of chromosome
- takes place in late prophase 1
- replicated homologous pairs come together (called synapsis) to form bivalents
- swap pieces of inner chromatids by breaking and reforming their DNA while paired
- points where chromatids break are called chiasmata
- recombinant chromatid, outer called parentals
2
Q
why is crossing over important
A
- produces chromatids with unique combination of genes
- there will be new combinations of genetic material
- mistakes may lead to mutations
- mostly harmful but may be beneficial
3
Q
importance of meiosis
A
- gametes are formed
- chromosome count kept constant from generation to generation
- genetic variation (crossing over, random arrangement of chromosomes)
4
Q
similarities between mitosis and meiosis
A
- both are types of cell division
- DNA of parent cell is replicated in interphase
- in early prophase chromosomes become short and fat
- joined by centromeres
5
Q
where does it occur
A
- development of zygote to embryo
- to form mature organism
- meristematic tissue
- growing regions of bones, skins
- sporangia (spores)
- testis and ovaries (gametes)
6
Q
purpose of the process
A
- chromosome number in daughter cells kept the same as in parent cell
- development of an adult organism from a single to zygote
- growth and repair of tissues
- regeneration of body parts
- asexual reproduction
- half the number of chromosomes
- diploid parent cell reduced to haploid daughter cells
- prevents chromosome numbers doubling
7
Q
difference in process
A
- one cell division
- prophase : no bivalents formed, no crossing over
- metaphase : centromeres split
- anaphase : chromatids move to each pole
- two daughter cells formed with same number of chromosomes as parent
- somatic cells
- involves two cell divisions
- prophase 1 : bivalents formed and crossing over occurs
- anaphase : chromosomes move to opposite poles
- four daughter cells with half chromosome count as parent
- gametes are formed
