Question regarding Biology

[Zheng1337]

Okay, so long story short, I had a quiz in Biology today on Genetypes, Phenotypes and the Punnett Square.

On the back page, there were application questions worth 6 marks in total. The question involved 2 rabbits, 1 male, 1 female. S represented the dominant trait, short hair. s represented the recessive trait, long hair. These 2rabbits have 8 children, 7 of which have short hair and 1 with long hair.

The female rabbit has 2 possibilites for genotypes, SS and Ss. The male has only 1, ss.

So the question asks what I expect the genotype of the female rabbit is in this situation. I write down SS, but the answer was Ss. It was marked wrong, and I'm okay with that, but I'm not understanding why it cannot be SS. After all, the punnett square provides possible combinations for the gametes of 2 parent cells. These results are not certain; there will always be chances that the actual offspring don't show the same results as the punnett square.

My logic behind the SS answer was that with SS, the punnett square would be SS x ss. This is a phenotypic ratio of 8 short:0 long. If the answer was Ss for the female rabbits geneotype, the phenotypic ratio would be 2 short:2 long or 4 short:4 long. I'm not quite sure as to how I came to this result, but being that 8:0 is closer to 7:1 than 4:4, I thought that there would be a greater chance that SS would be the geneotype. Please correct me if I'm wrong.

I talked to the teacher about this, and she seemed a little skeptical, but she said that she would research it.

On another note, I'm been debating with most of my teachers over marks lately. Is this a bad thing to do? I'm concerned that this could cause resentment from my peers and cause my teachers to annoyed with me.

EDIT: And if you were wondering why I was arguing over marks on a quiz of all things, it's because I got 3/6 on the application part due to this. I was worried that this would have a extremely negative effect on the average in the class. I'm already getting 82...which isn't great considering I want to major in Biology for the career I want to have.

 

[Austin343]

If you cross SS with ss, every offspring will be Ss. That's because you have to get one allele (S or s) from each parent. Since one parent is SS, the only one it can give to its child is an S, and the other parent, being ss, can only give an s. Therefore, the only genotype possible is Ss. Hopefully that's clear!

 

[Famine]

Okay, so long story short, I had a quiz in Biology today on Genetypes, Phenotypes and the Punnett Square.

On the back page, there were application questions worth 6 marks in total. The question involved 2 rabbits, 1 male, 1 female. S represented the dominant trait, short hair. s represented the recessive trait, long hair. These 2rabbits have 8 children, 7 of which have short hair and 1 with long hair.

The female rabbit has 2 possibilites for genotypes, SS and Ss. The male has only 1, ss.

So the question asks what I expect the genotype of the female rabbit is in this situation. I write down SS, but the answer was Ss. It was marked wrong, and I'm okay with that, but I'm not understanding why it cannot be SS. After all, the punnett square provides possible combinations for the gametes of 2 parent cells. These results are not certain; there will always be chances that the actual offspring don't show the same results as the punnett square.

My logic behind the SS answer was that with SS, the punnett square would be SS x ss. This is a phenotypic ratio of 8 short:0 long. If the answer was Ss for the female rabbits geneotype, the phenotypic ratio would be 2 short:2 long or 4 short:4 long. I'm not quite sure as to how I came to this result, but being that 8:0 is closer to 7:1 than 4:4, I thought that there would be a greater chance that SS would be the geneotype. Please correct me if I'm wrong.

I talked to the teacher about this, and she seemed a little skeptical, but she said that she would research it.

The teacher is right to mark you wrong.

If you cross an SS organism with an ss organism, all of the offspring will be Ss. These means that they all have the dominant phenotype, but carry the recessive one - in this case they'd all be short-haired. There's 0 possibility of a long-haired organism here and, since there's 1 long-haired organism you know that the female cannot be SS.

And this leaves only one possibility - that she's Ss.


You're also misunderstanding the ratios here. 4:0 means there's zero possibility of any offspring of the latter type - with all the offspring being the former. 2:2 means that, for any given progeny, there's a 50:50 chance of it being either type - and what offspring they've already had has no bearing on what offspring follow, just like coin tosses. The coin doesn't remember what its last flip was, and nor do the sperms know what the last foetus was.

On another note, I'm been debating with most of my teachers over marks lately. Is this a bad thing to do? I'm concerned that this could cause resentment from my peers and cause my teachers to annoyed with me.

Enquiry is the root of all science, and science comes from the Latin "scire" - "to know".


Incidentally, I'm a geneticist.