VCE Biology Question Thread

[dyskontent]

Because the trait is recessive, their genotype is certain. Therefore we don't count them

Just to clarify a bit

Molly's parents are heterozygous - Aa
This means the offspring can be AA, Aa, Aa, aa (each have a quarter chance)

However, since Molly does NOT show the trait, we know for certain she is not genotype |aa|
This means she is one of Aa, Aa, AA
Out of these three, two are heterozygous so 2/3 is the answer

[RazzMeTazz]

Just to clarify a bit

Molly's parents are heterozygous - Aa
This means the offspring can be AA, Aa, Aa, aa (each have a quarter chance)

However, since Molly does NOT show the trait, we know for certain she is not genotype |aa|
This means she is one of Aa, Aa, AA
Out of these three, two are heterozygous so 2/3 is the answer

Thankyou so much! I understand it now

[RazzMeTazz]

I did this question on the online 'Study On Biology' (Image attached below)
and  I got the correct answer, but I was guessing.

I don't understand how you would know which allele is dominant over the other. Would 'I' (no colour production) be dominant over the allele 'G' (yellow fruit) ?
Because the genotype has both the dominant alleles and so I was unsure which dominant allele would express itself phenotypically.

[dankfrank420]

That isn't a multiple allele system, it's a dihybrid cross. However, these genes affect the expression of one another, so therein arises the confusion.

You have to sort of think of it as a series of questions. Firstly, ask yourself if the phenotype will contain colour. If it does, you ask yourself which colour.

In this case, the phenotype will not contain colour as the genotype is heterozygous and therefore the "no-colour" allele will be expressed. You don't need to ask yourself the second question because it doesn't matter what colour Gene 2 codes for, as it will not be expressed either way.

[RazzMeTazz]

Would t be correct to say that for a monohybrid cross, crossing over will not increase genetic variation?
As there are only two possible alleles anyway?

[Rachelle]

Can someone please explain lethal alleles? Is there such thing as both lethal traits that are dominant and recessive? What is the difference?
Also how does a back cross work? Or what is involved?

[RazzMeTazz]

How would you explain why linked genes tend to be inherited together?

[RazzMeTazz]

If a characteristic is controlled by two or more genes (polygenes) will it always show continuous variation? or is it possible for polygenic inheritance to also result in discontinuous variation?

[grannysmith]

Can someone please explain lethal alleles? Is there such thing as both lethal traits that are dominant and recessive? What is the difference?
Also how does a back cross work? Or what is involved?

Recessive lethal alleles leads to the immediate death of an organism (they don't survive) if they inherit two copies of the recessive allele and hence are homozygous recessive for that trait. Dominant lethal alleles are less likely to be inherited as the parent would not survive for long (or at all for that matter). However, recessive lethal alleles can be found in heterozygotes that are carriers for that trait.

Back crosses involve a cross between a heterozygote and one of its parents.

How would you explain why linked genes tend to be inherited together?

Linked genes are found on the same chromosome. Unless crossing over occurs, they tend to be inherited together. The further away their gene loci are the more likely recombination will occur.

[RazzMeTazz]

I read that "X-linked dominant traits are more common in females as either X-chromosome may have the dominant allele "

is this correct?
isn't it just as possible for hemizygous males to have one copy of the dominant allele?

[soNasty]

I read that "X-linked dominant traits are more common in females as either X-chromosome may have the dominant allele "

is this correct?
isn't it just as possible for hemizygous males to have one copy of the dominant allele?

They're more common in females because they can be either and to be X linked dominant.

[RazzMeTazz]

What is the purpose of X-inactivation ?
thanks!

[Rachelle]

Back crosses involve a cross between a heterozygote and one of its parents.

What is the purpose of a back cross?

[Rachelle]

Recessive lethal alleles leads to the immediate death of an organism (they don't survive) if they inherit two copies of the recessive allele and hence are homozygous recessive for that trait. Dominant lethal alleles are less likely to be inherited as the parent would not survive for long (or at all for that matter). However, recessive lethal alleles can be found in heterozygotes that are carriers for that trait.

So why is it referred to as a mutation?

[The Usual Student]

I understand this is incredibly complicated but can someone explain cellular respiration to me? Or link me to a video about it.