Crossing Over (3) Flashcards
What is crossing over?
Crossing over is the mutual exchange of pieces of chromosome so that whole groups of genes are swapped between maternal and paternal chromosomes. This takes place in the late prophase of meiosis 1.
Explain the crossing over process? (3)
- The replicated homologous pairs of chromosomes come together in a process called synapsis to form bivalents. They swap pieces of their inner chromatids by breaking and reforming their DNA while they are paired up.
- The points of crossing over where the chromatids break are called chiasmata. singular: chiasma
- In this way some genes from a maternal chromatid change place with some genes from a paternal chromatid, forming a recombinant chromatid. The outer, unchanged chromatids are called parentals.
Why is crossing over important?
The exchange of genetic material produces chromatids with a unique combination of genes. This increases variation among the daughter cells combinations of genetic material. This is why the offspring do not look the same (except for identical twins) or like their parents. as there will be new During this exchange process, mistakes may occur which lead to mutations. Most mutations are harmful but occasionally they may be beneficial. In this way, new genes may be introduced into the genetic make-up of a species which can influence evolution.
Why is meiosis important? (3)
- Gametes are formed by the process of meiosis.
- During meiosis the number of chromosomes is halved so that the chromosome number is kept constant from generation to generation.
- Meiosis results in genetic variation through:
- crossing over
- a random arrangement of chromosomes at the equator of the cell during metaphase.
What are the similarities between meiosis and mitosis? (3)
- Both are types of cell division
- The DNA of the parent cells is replicated in interphase before cell division starts
- In early prophase, the chromosomes become short and fat and are visible as two chromatids joined by a centromere
