A2 Biology- Genetics

can anyone help me on this question

Guinea pigs, which were homozygous for long, black hair were crossed with ones which were homozygous for short white hair. All the F1 offspring had short, black hair.

using suitable symbols, draw a genetic diagram to explain this result.

Reply 1

barbarellapants

Try doing a punnet Square/diamond diagram using 'B' for Black and 'b' for white and 's' for long and 'S' for short hair - as all the offspring were black and short...they must be the dominant alleles. Cross done (thats the name of those diagrams, isn't it?)

Reply 2

kitch

Reptile

can anyone help me on this question

Guinea pigs, which were homozygous for long, black hair were crossed with ones which were homozygous for short white hair. All the F1 offspring had short, black hair.

using suitable symbols, draw a genetic diagram to explain this result.

Right, black must be dominant, as must be short. So, these are the dominant alleles as the last person pointed out.

B = black
b = white
S = short
s = long

first set of guinea pig therefore has the alleles BB (as there are no white offspring, it cant have a b allele..when they wre crossed they all had at least 1 B allele...also it's homozygous meaning they have the same 2 alleles) and ss for the same reasons.

Second set of guinea pigs have bbSS for again teh same reasons as I stated above.

parents B B s s , b b S S

offspring BbSs BbSs BbSs BbSs

(draw in lines to show how you got all that, doing a cross diagram yes)

They all have the alleles BbSs... therefore short black as B and S are dominant alleles.

Hope that helps.

Reply 3

Reptile

OP

ok thnx, did it :cool:

Reply 4

danni_bella

17

Reptile

can anyone help me on this question

Guinea pigs, which were homozygous for long, black hair were crossed with ones which were homozygous for short white hair. All the F1 offspring had short, black hair.

using suitable symbols, draw a genetic diagram to explain this result.

You should draw up a couple of punnet squares to help you with this problem. I know these questions can be a bit vague, but if you apply the right logic to it, you can usually work them out quite easily.

If you're done this and got the technique down, well done :smile:

However I would advise you remember this for your next exam - they may give you a similar question, word it differently.

A2 Biology- Genetics

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