Homeschool student needs help!!

K

KRUCK

Registered Member
Okay guys (and gals) this is my 1st post...please be nice :)

A rough-coated male guinea pig is crossed with a homozygous smooth-coated female (rr). Their offspring are rough-coated and smooth-coated in a 1:1 ration. Use a Punnett square to calculate the genotype of the male parent.

This is really confusing to me! HELP!!
 
Okay, you know the female is homozygous recessive for smooth coat, and you are given that the progeny are a 1:1 ratio of rough (dominant: so can be RR or Rr) and smooth (can only be rr). So, the progeny will have to be Rr if rough, since they can only receive a recessive allele from the mother (there is no other possibility). Smooth coats will be double recessive, of course.

So, try out the two possible combinations for male genotype (rough coat means RR or Rr). RR (male) + rr (female) would lead to only Rr progeny, meaning 100% rough coat, by Punnett square analysis.

---R----R
r--Rr---Rr
r--Rr---Rr

The other option of Rr X rr leads to a 50-50 ratio of smooth-rough coated progeny.

---R----r
r--Rr--rr
r--Rr--rr

I hope that helps.
 
The male is Rr.

Why?

Me explain for you.

1:1 ratio means that for every rough hamster, there will be a smooth hamster. So, the litter must be divided equally.

When one does a Punett square, one used a sample litter of 4 offspring.

So, we must have 2 roughs and 2 smooths.

The mother is homogenous recessive. That means she has two rr alleles, allowing her to display the recessive trait of smoothness.

The father is rough and rough is the dominant trait. So he must be either homogenous dominant or heterogenous dominant; he can be RR or Rr, since R only needs one allele to be displayed as roughness.

So the two possible Punett squares are RR with rr and Rr with rr.

Which one gives the result of an equally divided litter? The second one, with the Rr father, does.

Me would give you drawing of me own, but file is too big for attachment. Me suggest you draw it yourself and check.
 
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