How Many Possible Genetic Combinations Can Arise From Meiosis?
Learning Outcomes
- Sympathize how meiosis contributes to genetic variety
The gametes produced in meiosis aren't genetically identical to the starting jail cell, and they also aren't identical to 1 another. Equally an example, consider the meiosis II diagram above, which shows the end products of meiosis for a simple cell with a diploid number of iin = iv chromosomes. The four gametes produced at the terminate of meiosis Two are all slightly different, each with a unique combination of the genetic fabric nowadays in the starting cell.
As it turns out, in that location are many more potential gamete types than just the 4 shown in the diagram, fifty-fifty for a simple cell with with merely four chromosomes. This diversity of possible gametes reflects ii factors: crossing over and the random orientation of homologue pairs during metaphase of meiosis I.
- Crossing over. The points where homologues cross over and exchange genetic material are chosen more or less at random, and they will exist dissimilar in each prison cell that goes through meiosis. If meiosis happens many times, as information technology does in human ovaries and testes, crossovers will happen at many different points. This repetition produces a wide variety of recombinant chromosomes, chromosomes where fragments of DNA have been exchanged between homologues.
- Random orientation of homologue pairs. The random orientation of homologue pairs during metaphase of meiosis I is some other important source of gamete diverseness.
What exactly does random orientation mean here? Well, a homologous pair consists of one homologue from your dad and one from your mom, and you take 23 pairs of homologous chromosomes all together, counting the X and Y as homologous for this purpose. During meiosis I, the homologous pairs will separate to grade two equal groups, but it'due south not usually the case that all the paternal—dad—chromosomes will go into one grouping and all the maternal—mom—chromosomes into the other.
Instead, each pair of homologues volition finer flip a money to make up one's mind which chromosome goes into which grouping. In a cell with just two pairs of homologous chromosomes, like the one at correct, random metaphase orientation allows for ii2 = 4 dissimilar types of possible gametes. In a human prison cell, the same mechanism allows for 223 = 8,388,608 different types of possible gametes[1]. And that's not fifty-fifty because crossovers!
Given those kinds of numbers, it'due south very unlikely that any two sperm or egg cells made by a person will exist the same. It'due south fifty-fifty more unlikely that you lot and your sister or brother will exist genetically identical, unless you happen to be identical twins, thanks to the process of fertilization (in which a unique egg from Mom combines with a unique sperm from Dad, making a zygote whose genotype is well beyond ane-in-a-trillion!)[2].
Meiosis and fertilization create genetic variation by making new combinations of gene variants (alleles). In some cases, these new combinations may make an organism more or less fit (able to survive and reproduce), thus providing the raw material for natural selection. Genetic variation is important in assuasive a population to arrange via natural selection and thus survive in the long term.
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Source: https://courses.lumenlearning.com/wm-biology1/chapter/reading-genetic-variation-in-meiosis/
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