Crossing-Over Flashcards
The process of crossing-over
A homologous pair of chromosomes before crossing-over
It takes place in Meiosis 1 of Prophase
Homologous chromosomes come to lie close together
Homologous chromosomes (consisting of 4 chromatids in total) involved in crossing over is referred to as a bivalent
A pair of homologous chromosomes after crossing-over
The chromosomes separate in such a way that each has one original chromatid and one chromatid with some genetic material from its homologous partner
Chromatids interwinding
One chromatid of each chromosome overlaps with a chromatid of its homologue (or homologous partner)
The points of crossing-over are called chiasmata (singular chiasma)
What is Crossing-Over used for
Crossing-Over results in an exchange of genetic material so that each chromosome has genetic material from both parents
The cells (usually gametes) produced will therefore be different from each other
This, therefore results in variation in the offspring
Why the cells produced during meiosis are genetically different
Firstly, Crossing-Over during the Prophase 1 results in the exchange of genetic material
Secondly, during Metaphase 1, the chromosomes arrange themselves along the equator of the cell randomly
The importance of Meiosis
Leads to the formation of haploid gametes in some organisms and haploid spores
The halving effect of meiosis neutralizes the doubling effect of fertilization, thus maintaining a constant chromosome number
Crossing-Over introduces genetic variation. Genetic variation results in offspring that are better adapted to a particular environment ensuring a better chance of survival
