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dominate/recessive gene question

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dominate/recessive gene question

Postby defhalotones » Tue Dec 02, 2008 12:27 am

In a particular breed of cats, Black (B) is Dominant and white (b) is recessive. What are the chances of producing white kittens when crossing a Bb male with a Bb female?

And......

What are the chances of producing black kittens from the above cross?

I cannot figure this one out...
Help please!
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Postby Darwin420 » Tue Dec 02, 2008 12:43 am

OK, this is simple.

Set up a P square.

B b
B BB Bb

b Bb bb


So, to have a white cat you have a 25% chance of getting one. 75 % for black cats, 50% for black cats with a recessive trait.

Do you understand what I did here?
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Postby defhalotones » Tue Dec 02, 2008 12:56 am

thanks for the answer.

And i sorta know what you did there. I've been taught how to use the punnet square, but do not know how to 'accurately' do it. If you are very bored, could you tell me how you set that up to find the answer using the P-Square? MUCH appreciated
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Postby Darwin420 » Tue Dec 02, 2008 1:18 am

Ok, I am actually trying to study for an ecology and evolution exam but I can spare a few minutes.

Ok, do you know why we use this square? Look up Mendel's peas.

Essentially he was some guy who studied pea plants, where he noticed that there must be something passed on to each generation, because he discovered a huge similarity from parent to progeny. He also noticed that there are traits that are recessive and some that are dominant, which we now know as Alleles.

The P square represents the PROBABILITY of getting offspring with particular traits.

For the example you gave me, we are given two traits, correct? B = black fur and is DOMINANT

b= white fur and is recessive

Also keep in mind that when you cross a dominant characteristic with a recessive, only the dominant trait is expressed (assuming no co-dominance is occurring).

So we cross the two heterogeneous ( i.e. Bb) individuals together to see the probability of obtaining white and black cats.

so we write it like this:

Cat one + cat two
Bb Bb = offspring

So all you gotta do is plug it into the P square.
B b
B BB Bb

b Bb bb



If you are still having troubles google "punnet square" and see if there are some 101's on how to do it.
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Re: dominate/recessive gene question

Postby defhalotones » Tue Dec 02, 2008 7:01 am

thanks a ton Darwin
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