Is this sufficient? (1 Viewer)

[LuthienAdrianna]

These are my puny notes for the syllabus point 2.6 - Explain the relationship between dominant and recessive alleles and phenotype using examples:

The phenotype of an organism is the visible physical outcomes of gene expression, or the non-visible physiological outcomes of gene expression. a recessive allele will only express itself if two such alleles are present in the organism i.e. tt results in a short phenotype. Dominant alleles express themselves whether the organism is homo/heterzygous for the characteristic i.e. a tall phenotype results from Tt or TT.

Is there anything missing or incorrect or weird about this? I know the answers but I always have trouble putting them down in words. -_-''

TIA

 

[danieljarvis]

the info is right.. but when you say recessive will only express itself in homozygous form and give your example.. you cant say tt codes for short phenotype, youll have to say short is the recessive allele in pea plants and then give an example of the genotype. ( if asked ).

cos as far as i know short phenotype would be dominant in other organisms.

Note: any letter can be used for displaying genotype. Tt or Rr would be preffered over Oo or Xx as upper case and lower are more easily distinguishable

 

[LuthienAdrianna]

Thankyou! =)

 

[elisabeth]

DON'T say recessive alleles are only expressed if there are 2 of them... because what about sex linked recessive charachteristics? Instead say that recessive alleles are only expressed in the absence of dominant alleles.

 

[LuthienAdrianna]

Oh... we actually haven't done sex-linkage yet, so I'm just making notes from what we've done.

 

[elisabeth]

Well, still, it's a better technical definition, especially since I've fallen into the habit of answering posts with the 2005 HSC in mind But sex linkage is dead easy, just refers to genes inherited via the sex chromosomes. So if it's on the X chromosome, and there's no corresponding gene on the Y chromosome, a man (XY) only has one chance to get an allele... so a female would need 2 recessive alleles for a gene (XrXr) but the guy only needs one (XrY) ie. it's expressed because there are no dominant alleles present, not because you need 2

I realise I may be talking to myself there, but meh. All exam practise. And maybe that explains it briefly for you.

 

[LuthienAdrianna]

*changes notes* =)