duquesne's Bio 3/4 Question Thread

[duquesne9995]

Does crossing over occur in Prophase 1 or Metaphase 1? Because I got prophase 1 from one source but my teacher said metaphase 1 =\

[Jenny_2108]

Does crossing over occur in Prophase 1 or Metaphase 1? Because I got prophase 1 from one source but my teacher said metaphase 1 =\

Prophase I

Metaphase I is independent assortment

[duquesne9995]

Need help on this question:

In a population of laboratory mice white colour is recessive to brown. A large population of these mice that consisted of 47% white and 53% brown were allowed to breed randomly for several generations. After several generations of breeding the population still showed the same percentages of 47% white and 53% brown. From this data is would be reasonable to conclude that:
A. the heterozygous phenotype is lethal
B the population is undergoing genetic drift
C. selection has favoured the recessive allele
D. the two phenotypes are selected for equally under laboratory conditions

The answer is D but why wouldn't it be A?
Thanks

[Russ]

A is plausible because there's no evidence that rules it out, but there's no evidence supporting it. You don't know whether heterozygotes have a different phenotype to the homozygous dominant or not, so you can't draw a conclusion

[duquesne9995]

^^^Thank you

I'm stuck on this multi choice question too. I was thinking 2/3 chance that II-3 is Bb and then 1/2 chance that III-2 is Bb and then 1/4 chance of white haired because III-1 is Bb? 2/3 * 1/2 * 1/4 = 1/12?  What have I done wrong?

[duquesne9995]

Bump, and also this question (attached) The answer is A and I can kind of see why but just wondering why is option D wrong? Thanks 

[Jenny_2108]

^^^Thank you

I'm stuck on this multi choice question too. I was thinking 2/3 chance that II-3 is Bb and then 1/2 chance that III-2 is Bb and then 1/4 chance of white haired because III-1 is Bb? 2/3 * 1/2 * 1/4 = 1/12?  What have I done wrong?

Look like doing probability in methods
I got 1/6. Whats the ans?

Bump, and also this question (attached) The answer is A and I can kind of see why but just wondering why is option D wrong? Thanks 

If after 25 generations, there is no variation, so there will be no fall in average body size => D is wrong

[duquesne9995]

^^^Thank you

I'm stuck on this multi choice question too. I was thinking 2/3 chance that II-3 is Bb and then 1/2 chance that III-2 is Bb and then 1/4 chance of white haired because III-1 is Bb? 2/3 * 1/2 * 1/4 = 1/12?  What have I done wrong?

Look like doing probability in methods
I got 1/6. Whats the ans?

It is 1/6. How do you get 1/6?

[Jenny_2108]

^^^Thank you

I'm stuck on this multi choice question too. I was thinking 2/3 chance that II-3 is Bb and then 1/2 chance that III-2 is Bb and then 1/4 chance of white haired because III-1 is Bb? 2/3 * 1/2 * 1/4 = 1/12?  What have I done wrong?

Look like doing probability in methods
I got 1/6. Whats the ans?

It is 1/6. How do you get 1/6?

Here is what I did
So you know genotype of III1 is Bb, now we find genotype of III2

II4 is BB, II3 is B-
Thus III2 is B-

Bb x B-
III1 and III2's offsprings can be BB, B-, Bb, -b => BB, BB, Bb, Bb, Bb, bb
Therefore, the chance of bb is 1/6

[duquesne9995]

^^^Thank you

I'm stuck on this multi choice question too. I was thinking 2/3 chance that II-3 is Bb and then 1/2 chance that III-2 is Bb and then 1/4 chance of white haired because III-1 is Bb? 2/3 * 1/2 * 1/4 = 1/12?  What have I done wrong?

Look like doing probability in methods
I got 1/6. Whats the ans?

It is 1/6. How do you get 1/6?

Here is what I did
So you know genotype of III1 is Bb, now we find genotype of III2

II4 is BB, II3 is B-
Thus III2 is B-

Bb x B-
III2 can be BB, B-, Bb, -b => BB, BB, Bb, Bb, Bb, bb
Therefore, the chance of bb is 1/6

Sorry, I'm still a little confused, what do those ^^^ mean? 

[Jenny_2108]

Here is what I did
So you know genotype of III1 is Bb, now we find genotype of III2

II4 is BB, II3 is B-
Thus III2 is B-

Bb x B-
III2 can be BB, B-, Bb, -b => BB, BB, Bb, Bb, Bb, bb
Therefore, the chance of bb is 1/6

Sorry, I'm still a little confused, what do those ^^^ mean? 

B- means the genotype can be BB or Bb
Similarly, -b means the genotype can be bb or Bb

I just write B- because we don't know whether their genotype is BB or Bb

[aishuwa1995]

Bb x B-
III2 can be BB, B-, Bb, -b => BB, BB, Bb, Bb, Bb, bb
Therefore, the chance of bb is 1/6

but individual III2 is black so it can't have genotype bb?
EDIT: wouldn't it be 1/4 or 0? I'm confused 

[Jenny_2108]

Bb x B-
III2 can be BB, B-, Bb, -b => BB, BB, Bb, Bb, Bb, bb
Therefore, the chance of bb is 1/6

but individual III2 is black so it can't have genotype bb?
EDIT: wouldn't it be 1/4 or 0? I'm confused 

Sorry, I mean when III1 and III2 mate, their offsprings' genotypes can be BB, B-, Bb, -b => BB, BB, Bb, Bb, Bb, bb
Thus, the chance of white hair is 1/6

I edited my early post

I was typing quickly and wrote wrong. Sorry about confusion, thiskid and duquesne9995

[aishuwa1995]

Bb x B-
III2 can be BB, B-, Bb, -b => BB, BB, Bb, Bb, Bb, bb
Therefore, the chance of bb is 1/6

but individual III2 is black so it can't have genotype bb?
EDIT: wouldn't it be 1/4 or 0? I'm confused 

Sorry, I mean when III1 and III2 mate, their offsprings' genotypes can be BB, B-, Bb, -b => BB, BB, Bb, Bb, Bb, bb
Thus, the chance of white hair is 1/6

I edited my early post

I was typing quickly and wrote wrong. Sorry about confusion, thiskid and duquesne9995

I'm still kind of lost..did you use a punnet square Ennjy?

[duquesne9995]

thiskid, are you good with III-1 is Bb and III-2 is B_ ?
Then cross them. Do Bb x B_ and Ennjy is saying that when you do this cross, the genotypes that you get are:
BB, BB, Bb, Bb, Bb, bb and so there are six genotypes and the chance of bb is 1/6.

Hey but Ennjy when you do Bb x B_ if you split it into the two possibilities: Bb x BB and Bb x Bb, I get:
Bb x BB
= 1/2 BB, 1/2 Bb
and then Bb x Bb
= 1/4 BB, 1/2 Bb, 1/4 bb
So that's where I'm getting confused...