The number of possible genetic combinations that can arise from meiosis is determined primarily by the independent assortment of homologous chromosome pairs. This number is calculated by the formula:
2n2^n2n
where nnn is the number of homologous chromosome pairs (haploid number).
Explanation
- During meiosis, homologous chromosomes line up and separate independently, resulting in gametes that carry different combinations of chromosomes.
- For humans, with a diploid number of 46 chromosomes, the haploid number nnn is 23.
- Therefore, the number of possible chromosome combinations in human gametes is:
223=8,388,6082^{23}=8,388,608223=8,388,608
This means there are over 8 million possible combinations of chromosomes just from independent assortment alone
Additional Sources of Variation
- Crossing over (recombination) during prophase I of meiosis further increases genetic variation by exchanging segments between homologous chromosomes, creating new allele combinations.
- Random fertilization multiplies the variation further since any sperm can fuse with any egg. The total number of possible combinations after fertilization is:
(2n)2=22n(2^n)^2=2^{2n}(2n)2=22n
For humans, this is:
(223)2=246≈7×1013(2^{23})^2=2^{46}\approx 7\times 10^{13}(223)2=246≈7×1013
which accounts for the immense genetic diversity seen in offspring even from the same parents
Example for Other Species
- For a species with a diploid number of 16 (haploid n=8n=8n=8), the number of possible combinations from meiosis is:
28=2562^8=25628=256
and after fertilization:
(28)2=216=65,536(2^8)^2=2^{16}=65,536(28)2=216=65,536
combinations
Summary
Aspect| Formula| Human Example (n=23)
---|---|---
Possible combinations from meiosis (independent assortment)| 2n2^n2n|
8,388,608
Possible combinations after fertilization (random fusion of gametes)|
(2n)2=22n(2^n)^2=2^{2n}(2n)2=22n| ~70 trillion (7 x 10^13)
Thus, meiosis alone can generate millions of different genetic combinations, and combined with fertilization, the potential diversity is astronomical, ensuring genetic uniqueness in sexually reproducing populations
