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Bio A2 - genetics

(Put this here too, 'cos not many people go in the science subforum)

Hi. Can anyone help me with these?
1. Suggest 2 reasons why a recessive allele may not have been eliminated by natural selection from a population? (I've put heterozygous advantage for one, but can't think of another). [2 marks]
2. You are provided with a sample of 150 F2 seeds, describe how you could germinate these to observe the phenotypes of the seedlings. (Is this just wanting an experimental method? [3 marks]
3. Explain how a genetic error can lead to abnormal metabolism of the amino acid phenylalanine. [4 marks]

Many thanks, and rep for help! :smile:

Reply 1

Elles

Ellie4

1. Suggest 2 reasons why a recessive allele may not have been eliminated by natural selection from a population? (I've put heterozygous advantage for one, but can't think of another). [2 marks]

balanced polymorphism (oh, or do you mean that by heterozygous advantage?)? preferential transmission? have you done the p2 & q2 etc. equations that account for low levels of carriers of recessive conditions in the population?

2. You are provided with a sample of 150 F2 seeds, describe how you could germinate these to observe the phenotypes of the seedlings. (Is this just wanting an experimental method? [3 marks]

presumably, yes.. just how to germinate.. odd Q. then maybe how you would devise criteria for classfiying phenotypes?

3. Explain how a genetic error can lead to abnormal metabolism of the amino acid phenylalanine. [4 marks]

they want to know about the condition PKU (Phenylketonuria).. google it? (defective enzyme i think.. i never did like metabolism.. :tongue:

) all babies are tested at birth now.. can cause major problems if not picked up, otherwise, you can just avoid it in your diet & only becomes an issue again when pregnant.

Reply 2

Ellie4

Thanks elles :smile:

Rep to come to you too.

Reply 3

undiscovered

I love genetics, it's my favourite area of the spec! Those Qs seem harder than what I've come across though!

Reply 4

Ellie4

SiAnY

I love genetics, it's my favourite area of the spec! Those Qs seem harder than what I've come across though!

Mine too, defo the most interesting. Especially when compared with respiration and photosynthesis!

God yeah!

Elles

they want to know about the condition PKU (Phenylketonuria).. google it? (defective enzyme i think.. i never did like metabolism.. :tongue:

) all babies are tested at birth now.. can cause major problems if not picked up, otherwise, you can just avoid it in your diet & only becomes an issue again when pregnant.

I doubt they want to know specifics - just the general automated response about enzyme tertiary structure being altered by a mutation in the DNA. Something crap, like:

An alteration in the DNA sequence will change the codon sequence of the RNA which may, in turn, affect the primary structure of the translated protien. If the primary structure is altered, then secondary and tertiary structural elements will also be modified. Since enzyme activity relies upon the active site adopting a specific tertiary structural conformation, alterations in the globular (tertiary) protein structure may result in a change in the shape of the active site - such that its specific substrate can no longer bind and be metabolised in the usual fashion. If the mutation occurs in a gene coding for enzymes involved in phenylalanine biosynthesis, then normal phenylalanine metabolism may be compromised.

Ben

Reply 7

Elles

Ben.S.

I doubt they want to know specifics - just the general automated response about enzyme tertiary structure being altered by a mutation in the DNA. Something crap, like:

ah right.. i gave specifics? :redface:

i just remember the baby part & name PKU for some reason.. came up in our metabolism course.

anyway, yes, what you said all perfectly explains generically how a mutation can alter enzyme activity. :smile: