Meiosis: Sources of Genetic Variation

Question 1

The different combinations of chromosomes following meiosis
The number of possible chromosomal combinations resulting from meiosis is equal to..

Answer 1

2n
n is the number of homologous chromosome pairs
For humans: the diploid number for humans is 46 then the haploid number or number of homologous chromosomes is 23 so the calculation would be:
223 = 8 388 608 possible chromosomal combinations

Question 2

aving genetically different offspring can be advantageous for natural selection
Meiosis has several mechanisms that increase the genetic diversity of gametes produced

Both crossing over and independent assortment (random orientation) result in different combinations of alleles in gametes

Question 3

Meiosis creates genetic variation between the gametes produced by an individual through crossing over and independent assortment
This means each gamete carries substantially different alleles
During fertilization any male gamete can fuse with any female gamete to form a zygote
This random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a unique combination of alleles
There is an almost zero chance of individual organisms resulting from successive sexual reproduction being genetically identical

Question 4

The different combinations of chromosomes following fertilisation
In random fertilisation, any two gametes may combine

Therefore the formula to calculate the number of combinations of chromosomes after the random fertilisation of two gametes is

Answer 4

2n)2
n is the haploid number and 2 is the number of gametes

Therefore in humans, when the haploid number is 23, the number of combinations following fertilisation is (223)2­­ = 70368744177664

This explains why relatives can differ so much from each other. Even with the same parents, individuals can be genetically distinct due to variation at the meiosis and fertilisation stage (as well as other possible mutations and crossing-over)

Question 5

Several sources of genetic variation have been outlined above. It is also worth remembering that genetic variation can occur on an even smaller scale than chromosomes. Mutations can occur within genes. A random mutation that takes place during DNA replication can lead to the production of new alleles and increased genetic variation.Don’t worry about the effects of crossing over when you are calculating different chromosomal combinations. This is not something you are expected to take into account when using the formulas outlined above.