Random Segregation and Crossing Over HELP!!! (1 Viewer)

Mr_Kap

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Question: Sexual Reproduction leads to greater variation within a species. Identify the two sources of variation that occurs within meiosis ans explain what they are and how they lead to a greater number of genetic variance within offspring. 6 MARKS

This was my answer which received 4/6. I lost a mark on each of the explanation/definition of what they are but the teacher won't tell me why they were wrong. Any help would be greatly appreciated.


Answer:


The two sources of variation that occur within meiosis are: 1) Crossing Over 2) Random segregation

Crossing Over

This is the process in which homologous chromosomes exchange segment of genes with eachother, leading to a resultant which has a different order of genes to the ones of the parent. This leads to a greater number of variation within offspring as the crossing over is random, meaning this mixing and matching will lead to unique chromosomes. This in turn leads to each member of species being variated from others.

Random Segregation

The alleles that undergoe meiosis randomly segregate, meaning that each haploid gamete has only one allele. This process is random and can lead to countless possibilities of which has what allele. Hence, this increases the genetic variations within offspring as males and females carry numerous gametes which are all different from eachother, so in reproduction when the gametes make the zygote, the possibilities of offspring are numerous.
 
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I believe you got most parts of it. Would make sense to talk about future offspring. Such as when these genetically different offspring then breed with other genetically different offspring, the gene combination becomes more diverse. Therefore more genetically diverse 'versions' of this species will breed in the future and due to crossing over and random segregation there are increased combinations in genes in the population.

Please tell me there is a marking criteria or even better a sample answer?
 

Mr_Kap

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I lost a mark for the actual 'definition' of random segregation, and another mark for the actual 'definition' of crossing over.

Can anyone tell me what was wrong with my definitions for both????

Sadly, there is no sample answer or marking guidlines.
 

Mr_Kap

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How is my crossing over definition wrong then? That's bullshit. Stupid teacher.

How can I prove my definition for crossing over is correct.

Can anyone find a valid source that says this??
 

rand_althor

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How is my crossing over definition wrong then? That's bullshit. Stupid teacher.

How can I prove my definition for crossing over is correct.

Can anyone find a valid source that says this??
Page 170 of the Biology in Focus HSC Textbook:

"in crossing over, homologous chromosomes exchange genes and so the resulting combinations of alleles on chromatids differ from those originally on the parent chromosomes"
 

Red_of_Head

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You need to mention how the two parents will have unique genes, and thus lead to further variation through sexual reproduction.
Also include that the resultant offspring will have a wildly different genetic sequence, leading to further variation when they themselves reproduce.
 
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Flop21

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You need to mention how the two parents will have unique genes, and thus lead to further variation through sexual reproduction.
Also include that the resultant offspring will have a wildly different genetic sequence, leading to further variation when they themselves reproduce.
I've just realised I can't really explain when all this happens. Could someone outline when meiosis occurs, specifically the segregation and then crossing over?

Before or after fertilisation? I thought meiosis produced sex cells, but then the chromosomes split and form again with a maternal / paternal pair right?? So that happens after fertilisation??
 

el_manu

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I've just realised I can't really explain when all this happens. Could someone outline when meiosis occurs, specifically the segregation and then crossing over?

Before or after fertilisation? I thought meiosis produced sex cells, but then the chromosomes split and form again with a maternal / paternal pair right?? So that happens after fertilisation??
BUMP!!

Someone please answer this. I need to know this
 

BlueGas

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I've just realised I can't really explain when all this happens. Could someone outline when meiosis occurs, specifically the segregation and then crossing over?

Before or after fertilisation? I thought meiosis produced sex cells, but then the chromosomes split and form again with a maternal / paternal pair right?? So that happens after fertilisation??
SOMEONE PLEASE help me please. I need this before next week.
Meiosis is the process in which normal body cells are converted to sex cells, this is fairly simple. The stages of meiosis that lead to the creation of gametes and the inheritance of genes are:
- The chromosomes (which therefore include the genes) make a complete copy of itself (duplicate). The single stranded chromosomes become double stranded, linked at the centre by a centromere.
- In the first meiotic division, the homologous chromosomes separate, but the double-strands of the chromosomes are still joined.
- In the second division, the chromatids of the chromosomes separate and form 4 gametes altogether.

So as you can tell gametes form by meiosis, where recombination of genetic material takes place as a result of crossing over and random segregation. Crossing over and random segregation occur before fertilisation, basically before fertilisation they exchange genes, strands, etc. Then a fertilised egg is formed when when a female sex cell (egg) and a male sex cell (sperm) fuse. When this fusion occurs, random fertilisation occurs.

Random fertilisation: is the process when a random (one of the 4 gametes) from a male and female fuse, these two different gametes randomly fuse. Many different combinations are possible, and this causes variation.

Hope this helps!
 

Flop21

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SOMEONE PLEASE help me please. I need this before next week.
Just found this out through practising past papers.

"Crossing over would occur during the first stages of meiosis, represented in the diagram by B (picture of 2 diploid chromosomes, just after duplication)."
 

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