How was Biology Paper 42 MAY/JUNE 2017?

[Metallic9896]

now we can hope they give us some marks for this. I mean it does make sense

It really does. I looked it up the moment I came back home and it seems that there are 3 distinct versions with their own reasons of white color in cats. From Wikipedia:

• The "C" gene codes for the enzyme tyrosinase, the first step in pigment production. Its recessive alleles determine whether a cat is a complete albino (pink-eyed) or a temperature sensitive albino. The temperature sensitive albino genotypes are cbcb Burmese (sepia), cscs Siamese (pointed), and cbcs Tonkinese (mink). The cscs gene can turn a cat's eyes blue due to a reduced number of melanocytes, affecting pigmentation of the eyes. If a cat has the dominant C allele, then the cat is non-albino and full pigment production occurs.
• The white masking gene, W/w. The "W" gene prevents the normal replication and migration of pigment-producing cells during embryologic development. As a result, WW and Ww cats have a greatly reduced number of melanocytes and appear white, no matter what other color genes it may carry. Only a cat that is homozygous recessive (ww) will express normal pigmentation. Thus, W is epistatic to the other coat pigmentation genes. Some cats with the W allele of this gene are deaf and/or have depigmentation of the iris of one or both eyes, resulting in blue eye color. White cats are also more likely to get skin cancer.
• The white spotting or piebald spotting gene, S/s, has variable expression, so that an SS cat often has more extensive white patching than an Ss cat. It is this gene that creates the familiar white blaze across the face, a white bib, tuxedo pattern, or dappled paws. A hypothetical Sb allele ("gloving gene") may cause the mittens in Birman and Snowshoe breeds. Some researchers believe that there are separate white spotting genes for distinct forms of white pattern, such as the white locket that some cats have on their neck or bellies.

The first one is typical albinism found in humans as well. Although you and I would be inclined to say we are right, but this one says that the recessive alleles determine the white coat, whereas in our paper they said that the A in Aa (the dominant allele) determined it and that when it was aa, the color WOULD show. This mirrors the second bullet point where the dominant allele causes the lack of color. And the reason for this seems to be out of our syllabus but the explanation you and I gave seems more in line with the possible explanaiton CIE would expect. So hopefully we'll get marks.

It is also possible that CIE fabricated a fictional scenario for the sake of the question, in which case both explanations would be correct and ours would be the closest the ones Wikipedia gave. So good scene. XD

 

[Metallic9896]

However, I'm still disappointed that CIE gave this in the question paper. If my theory is correct and the question was about this white masking gene, then that is about 'epistasis', which the syllabus says in 16.2 b)

use genetic diagrams to solve problems involving monohybrid
and dihybrid crosses, including those involving autosomal
linkage, sex linkage, codominance, multiple alleles and gene
interactions (the term EPISTASIS does not need to be used;
knowledge of the expected ratio for various types of epistasis
is not required. The focus is on problem solving)

Granted that they didn't expect us to use the word epistasis, it still makes no sense for them to teach us half the situation and expect queestions on it. Either include it fully in the syllabus or don't give related questions. Or, our teachers should've taken out their time to teach us some situations of epistasis "problem solving" as CIE says. This is present in detail in the OCR/AQA boards from what I can tell when I used their notes to revise but I skipped this part.

 

[MariaKhan243]

2004 base pairs.
I don't remember a blood cell question... can you give more detail...?

I wrote 2004 before ugh

 

[darks]

It really does. I looked it up the moment I came back home and it seems that there are 3 distinct versions with their own reasons of white color in cats. From Wikipedia:

• The "C" gene codes for the enzyme tyrosinase, the first step in pigment production. Its recessive alleles determine whether a cat is a complete albino (pink-eyed) or a temperature sensitive albino. The temperature sensitive albino genotypes are cbcb Burmese (sepia), cscs Siamese (pointed), and cbcs Tonkinese (mink). The cscs gene can turn a cat's eyes blue due to a reduced number of melanocytes, affecting pigmentation of the eyes. If a cat has the dominant C allele, then the cat is non-albino and full pigment production occurs.
• The white masking gene, W/w. The "W" gene prevents the normal replication and migration of pigment-producing cells during embryologic development. As a result, WW and Ww cats have a greatly reduced number of melanocytes and appear white, no matter what other color genes it may carry. Only a cat that is homozygous recessive (ww) will express normal pigmentation. Thus, W is epistatic to the other coat pigmentation genes. Some cats with the W allele of this gene are deaf and/or have depigmentation of the iris of one or both eyes, resulting in blue eye color. White cats are also more likely to get skin cancer.
• The white spotting or piebald spotting gene, S/s, has variable expression, so that an SS cat often has more extensive white patching than an Ss cat. It is this gene that creates the familiar white blaze across the face, a white bib, tuxedo pattern, or dappled paws. A hypothetical Sb allele ("gloving gene") may cause the mittens in Birman and Snowshoe breeds. Some researchers believe that there are separate white spotting genes for distinct forms of white pattern, such as the white locket that some cats have on their neck or bellies.

The first one is typical albinism found in humans as well. Although you and I would be inclined to say we are right, but this one says that the recessive alleles determine the white coat, whereas in our paper they said that the A in Aa (the dominant allele) determined it and that when it was aa, the color WOULD show. This mirrors the second bullet point where the dominant allele causes the lack of color. And the reason for this seems to be out of our syllabus but the explanation you and I gave seems more in line with the possible explanaiton CIE would expect. So hopefully we'll get marks.

It is also possible that CIE fabricated a fictional scenario for the sake of the question, in which case both explanations would be correct and ours would be the closest the ones Wikipedia gave. So good scene. XD

Hmmmm we just have to wait and see i do feel like our answer is correct. Usually questions like this will contribute in lowering the grade threshold.

 

[MariaKhan243]

I also wrote about tyrosinase and the intermediates to get melanin and that it wad absent many people didnt remember it in my center

 

[harriet 12345]

did anyone do 41? is there a thread anywhere

 

[darks]

For me it was tougher that may/june 2016. I think grade boundry will be low for this one. What do you think? How was it for you? My guess for gt is 55-60 considering difficuly and gts of past few years..

EXACTLY 55 IT IS!

 

[Metallic9896]

EXACTLY 55 IT IS!

You called it mann!!! Haha nice. I saw those files too but are they legit for sure?

 

[darks]

You called it mann!!! Haha nice. I saw those files too but are they legit for sure?

For sure. O/A level resources fb page is trusted 100%. He posted ms too.