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Thread: genetics help....

  1. #1 genetics help.... 
    Forum Freshman
    Join Date
    Dec 2008
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    Palomino horses are valued for their beautiful and distinctive coat color; usually a golden yellow or shade of tan with a white or flaxen mane and tail. They result from matings between chestnut coated horses and ‘off white’ coated horses and the palomino coloration is actually intermediate between the coat colors of the parents. In a breeding experiment, several pairs of palomino horses were bred together and produced 19 ‘off white’ offspring, 21 chestnut offspring and 44 palominos.

    (a)
    Determine the genotype of the palomino parents used in this breeding experiment and explain how the presence of these alleles in the genotype contributes to the phenotype.

    (b)
    Show the possible genotypes and phenotypes with respect to coat colour of the offspring produced by matings between palomino horses.

    (c)
    Calculate the expected ratio of each of the phenotypes in the offspring and compare this to the actual ratio of the different phenotypes produced.

    (d)
    A horse breeder wishes to establish and maintain over many generations a herd with as many palomino horses and as few ‘off white’ horses as possible. She wishes to breed from her own horses only. Explain which phenotypes of horse from the herd should be used for breeding in order to maximize the number of palomino horses and minimize the number of ‘off white’ horses in the herd over many generations.

    -------------

    my attempt

    (a) CCr & CCr

    (b) chestnut = CC, palomino = CCr x2, off white = CrCr

    (c) 1:2:1

    (d) breeding CCr with CCr produces CC CCr CCr CrCr so 2 Palomino and 1 off white. Breeding CrCr with CC produces CCr CCr CCr CCr so all Palomino

    I have been told the following for (d) -
    Consider sex ratio, and what sex the off-white horse is. Would she be able to get away with having less white horses if it was any particular sex?
    I don't understand about sex ratio's how how to work it out or the sex of the horses etc.
    Also -
    remember to count the parents as part of the total, since the breeder wants few off-whites. What if the breeder just has palominos and chestnuts? What if the breeder has only a single male off-white which can fertilize many chestnuts?
    CC x CCr = CC CCr CC CCr
    CrCr x CCr = CCr CrCr CCr CrCr
    CC x CC = all CC
    CCr x CCr = CC CCr CCr CrCr
    CC x CrCr = all CCr
    CrCr x CrCr = all CrCr - don't want


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  3. #2  
    Forum Cosmic Wizard spuriousmonkey's Avatar
    Join Date
    May 2005
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    2,191
    I can tell you that with mice the predicted ratios never work.


    "Kill them all and let God sort them out."

    - Arnaud Amalric

    http://spuriousforums.com/index.php
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