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March 09, 2021, 06:33:10 pm

Author Topic: Confusion on Independent Assortment + Confirming Random Seg & Crossing Over  (Read 207 times)  Share 

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Sadge

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Hey all,

I just wanted to confirm (while I'm at it) if my understanding of Crossing Over, Independent Assortment and Random Segregation and the manner in which they aid genetic variation is correct since I'm very uncertain at the moment (especially for independent assortment)

Crossing Over
Process where DNA is exchanged between non-sister chromatids of homologous chromosomes at the chiasmata during Prophase I. This aids genetic variation by creating a new combination of alelles not present in either parent

Random Segregation

Process whereby chromatids from homologous pairs are randomly and equally separated into gametes during Anaphase I and II. This aids genetic variation by creating genetically distinct gametes with each gamete having an equal chance of inheriting the paternal or maternal allele for a specific gene

Independent Assortment

My confusion comes from seeing several descriptions:

a) In anaphase, homologous chromosomes are independently sorted from one another into gametes

b) In metaphase , homologous chromosomes align randomly along the equator of the cell

As such, I'm unsure how it should be defined. Is it simply a rule concerning how alleles are separated so that they all allele combinations have the same frequency of occurring? Or am I missing something else entirely?

Thanks for the help

Bri MT

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Hey,

Welcome to the forums!

The way you're talking about these things is very definitional. There's nothing wrong with that,  but I wanted to check that you're understanding what's going on here:

Crossing over:
You create new combinations of alleles on the one chromosome.  This is super super useful e.g. if you have a "good" and "bad" allele next to each other you can separate them.

Random segregation:
Equally likely to get each version of the gene (I.e no allele favourtism). Again, this is super important so the offspring have a mix of traits.

Independent assortment:
Both a & b are talking about the same thing.  The chromosomes line up on the equator independent 50/50 chance for each one what side they're on.  This means when they get separated, they're independently sorted into gametes.

where this rule originally came from: getting allele A for gene 1 doesn't influence the likelihood of getting allele B for gene 2 (this applies as long as they are on different chromosomes). Otherwise, there would be relatively few chromosome combinations the offspring would be likely to inherit.


^ don't use these as formal definitions but I hope this helps your understanding :)

Sadge

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Thanks for helping!