Which is more similar: sister-sister or mother-daughter

Genetics as it applies to evolution, molecular biology, and medical aspects.

Kaimiddleton
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Which is more similar: sister-sister or mother-daughter

Genetically speaking what is more similar, a girl and her sister or a girl and her mother?

I'm trying to understand this from a point of view of genetic recombination and independent assortment (and whatever else might be relevant).

http://en.wikipedia.org/wiki/Crossing_over
http://en.wikipedia.org/wiki/Independent_assortment

Let me take a stab at an answer. Let's talk about twenty genes.

Code: Select all

``Mom:  A B C D E F G H I JDad:  1 2 3 4 5 6 7 8 9 10``

I want to say that A corresponds to 1, B corresponds to 2, etc. Here is where my understanding of genetics breaks down because I don't know how to communicate about the differences among corresponding genes and homologous chromosomes. But let me guess. Suppose we end up with:

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``Sister1: A 2 C 4 E 6 G 8 I 10Sister2: A 2 3 D E 6 7 H I 10``

Here the sisters share 50% of their genome and each sister share's 50% of her genome with her mom. Is this representative of the general case??

canalon
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No It does not work Like that.

Each person has a pair of each chromosome. 1 from the father one from the mother. The crossing over will mix the father/mother of each parents so In a case of 2 chromosome with 2 genes:
Mother has AB and CD from her mother and ab and cd from her father, the father 12 and 34 from his mother and I II and III IV from his father.
The mother can give AB and Cd (one recombination due to c.o.) and father 1II and III4 (2 crossing over) so the daughter will have:
A B C d
1 II III4

A second daughter can have any combination of the same genes depending on the c.o. events.

On average a daughter will share 50% of her mother genome (and 50% from the dad) and have 25% of a sibling genome (recombination are independant events and give 50% of each parent genome, and it represents 50% of the final genome)
Patrick

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)

Kaimiddleton
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I still have a misconception

I've discussed this with a friend of mine who is a biology professor and he gets the same answer. Interestingly he also talked about the grandparents though I don't completely understand how that comes in to play. But more concisely he wrote me an email:
Try this explanation: Mom gives half her genes to each offspring, but the half that they get is random regarding which of each pair of homologous chromosomes. Because this is random, each child will share only about half of the genes Mom donates; i.e., 1/4 of Mom's total genome. Same for Dad.

I also did a google search and found this:
http://www.genomenewsnetwork.org/articl ... ncer.shtml
The hypothesis driving the study was that if getting cancer at a young age is somehow related to certain genes, then the risk must be greater among sisters and brothers of patients with some form of childhood cancers than in the population as a whole, because siblings share around 25 percent of their genes.

So 25% sibling similarity is the answer. The misconception that I'm still struggling to overcome is this: the sisters share only 1/4 of Mom's total genome; they also share 1/4 of Dad's total genome. So wouldn't you add 1/4 + 1/4 to get 50% sibling similarity?

canalon
Inland Taipan
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Joined: Thu Feb 03, 2005 2:46 pm
Yep,

And that is wher I made a mistake. I should not try to answer while struggling to read my statistics book, I mix up everything.
Each daughter has 50% of her mother genome, half of which is shared with her sister so you got 25% of the mother genome common. But the same is true for the father, so they also share 25% of the father genome, so in total they have 50% of their genome in common. So sibling similarity as you said is 50%.
Patrick

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)

Kaimiddleton
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Well ... now you disagree with the two other sources I cite who say sibling similarity is 25%. Are they wrong?

mkwaje
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Hmmm... this is getting confusing but I see the different points. Here is my two cents: in simple terms, daughter = 50% mom + 50% dad

but the other daughter can possibly have a different set of 50% genes from father and and mother. True, they both have 50% genes from mother and father but they have different sets; therefore they are not 50% similar

I honestly don't know if that explanation does make sense?

rvidal
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Theres a table that relates the percentages at the bottom of this website:
http://www.dnatesting.biz/Sibling/sibling.html

loveangel
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so does it means that we inherit more of our mother's than our father's?

kiekyon
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loveangel wrote:so does it means that we inherit more of our mother's than our father's?

yep

mkwaje
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Location: Philippines
Interesting... theoretically we should inherit 50% from father and 50% from mother, but as my professor once told me, there are other extrachromosomal DNA that affects the fertilized egg -- and of course these came all from the mother. That's why they say that the intelligence of the child is 60% mother and only 40% father. Is this really true? any violent reactions?

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