Biology Forums - Study Force

If 2 advantageous mutations (A and B) arise in a population, I understand that an individual with A could mate with a B mutant. Some of their offspring could have both mutations. In an example where these 2 mutations lie on the same chromosome at different loci, I understand that through recombination these mutant alleles can be combined onto one chromosome. Thus lots of offspring will have both mutations.

However, what happens when they are on different chromosomes. Recombination cannot bring them together. I know independent assortment could lead to them both being inherited but then they are free to be separated again during meiosis.

Can you tell me where I'm going wrong? Thank you.

Are the mutations arising for the same trait, or are they mutations for two different traits?

For different traits.

I drew you my conceptual understanding, start from the far top left and read the descriptions. Let me know what you get out of it.

Thank you for that! Brilliant.
However, my question was regarding mutations that lie on different chromosomes. So crossing over won't be able to combine the genes on to one chromosome. Then even if independent assortment does bring the advantageous mutations into one gamete, they could be easily separated in the next generation.

The crossing over that takes place during meiosis only occurs with the same paired chromosome. For example, humans have 46 chromosomes - or 23 chromosome pairs. Chromosome 1 from dad pairs with chromosome 1 from mom during meiosis because they share the same size and properties. So, if there is a mutation on chromosome 1 and a mutation on chromosome 5, they will never combine into a single chromosome because chromosome 1's pair together and chromosome 5's pair together. You could, however, have an offspring that inherits both mutations, but those mutations will always be on chromosome 1 and chromosome 5. In other words, a gamete can have both mutations, but they will be on separate chromosomes. However, this doesn't mean that the offspring will have these traits, especially if they are recessive mutations. For instance, if a sperm has both these mutations, and the sperm combines with an egg that doesn't, the alleles found in the egg may be dominant, and they so the offspring will only be a carrier of the advantageous trait.

Thank you. I understand this.
In my lectures (first year undergraduate), I've been told that one of the advantages of sexual reproduction is that it can combine advantageous mutations (asexual reproduction cannot do this). I can see how this can happen in one individual (whose father had mutation A and whose mother had mutation B). But then I can't see how these mutations can "stick together" in further individuals..

Yes, I agree with this statement as well.


If the offspring inherits mutation A from dad on chromosome 1, and mutation is dominantly expressed over whatever he/she inherits from mom, the individual will express the mutated gene his/her whole life. The same is true for mutation B on chromosome 5. In case the allele is not dominant, it still makes the individual genetically "more fit" as now they are a carrier for an advantageous gene. If the person decides to have kids and reproduce, their kids might express that mutated gene is it can still be passed on even if it's not dominantly expressed.