Turn on thread page Beta
    • Thread Starter

    hey guys..
    the specification (edexcel) states:

    explain the inheritance of two non-interacting unlinked genes;

    understand autosomal linkage and recombinants in relation to meiosis

    plz somebody help me!!!!!!!!!!!!!!!!! plzzzz

    thanks in advance!!!

    have you got the nelson book?

    The non-interacting unlinked genes bit is just a dyhibrid cross (its under that header in the NAS textbook).

    Basically, if you get two organisms with homozygous alleles for two different characteristics - one organism with all dominant alleles, the other with all recessive alleles - and breed them you will get a 9:3:3:1 ratio of phenotypes in the second generation of offspring.

    Its a lot easier to explain with an example. Okay, say we have some pea plants. Two unrelated characteristics (i.e. the alleles for which are NOT linked) could be their height (tall or dwarf) and the shape of their seeds (round or wrinkled).

    The alleles are as follows;
    T - tall (dominant) t - dwarf (recessive)
    R - round seeds (dominant) r - wrinkled seeds (recessive)

    We take one tall pea plant with round leaves (TTRR - remember they are homozygous) and one dwarf pea plant with wrinkled leaves (ttrr) and breed them.

    Parents: TTRR x ttrr

    F1: All TtRr

    If we now breed these: TtRr x TtRr

    The gametes present are: TR, Tr, tR, tr in equal ratios for both of the pea plants.

    If you now draw a punnit square with these four gametes going along the top and down the side and work out the genotypes and finally phenotypes which are formed you will get;

    9:3:3:1 - Tall and round : Tall and wrinkled : Dwarf and round : Dwarf and Wrinkled

    The two middle phenotypes are new (i.e. they did not exist in their parents) and this is called recombination.

    I hope this helps - im still trying to get my head around the second bit myself, but ill get back to ya when i understand it.

    (Original post by KP Nuts)
    I hope this helps - im still trying to get my head around the second bit myself, but ill get back to ya when i understand it.
    me too, it seems everyone is doing genetics this afternoon..

    argh have you got to the bit about interacting unlinked genes? :confused:

    Nope, but i dont like the look of it. Have a look at my other question - u might be able to help...
Turn on thread page Beta
Updated: June 16, 2005
The home of Results and Clearing


people online now


students helped last year

University open days

  1. Bournemouth University
    Clearing Open Day Undergraduate
    Wed, 22 Aug '18
  2. University of Buckingham
    Postgraduate Open Evening Postgraduate
    Thu, 23 Aug '18
  3. University of Glasgow
    All Subjects Undergraduate
    Tue, 28 Aug '18
How are you feeling about GCSE results day?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.