MONOHYBRID CROSS-GENETICS?

Discussion in 'Genetics' started by ryuu, Nov 14, 2009.

  1. ryuu

    ryuu Guest

    1 a. When two parents which are hybrid for brown eyes are crossed, what ratio of the offspring will show the dominant characteristic? How many will show the recessive characteristic?

    b. What is the phenotype and genotype of the F2 if the P1 is a pure strain with one parent dominant and one recessive?

    2. In cats the gene for short hair is dominant over the gene for long hair (Angora). A short-haired tom cat is mated with an Angora female. She bears eight kittens,six-short haired and two with long hair.How do these numbers compare with the expected ratio? If you mated these same cats four more times and obtained a total of forty offspring, would you expect the results to be a closer approximation of the expected ratio? Explain.

    OKAY, I don't understand how to do this. I know that I have to use the Punnet Square and everything. But, firstly I am getting confused about what variables to give them and how to give them the variables. Also, I solved these but I am not sure about my answers. I think that they are wrong. PLEASE CAN YOU HELP FAST? THANKS A LOT! :)
  2. ammiel

    ammiel Guest

    1 monohybrid means you are looking as a single gene with 2 alleles.
    Hybrid means it is heterozygous Bb.
    Bb x Bb gives the standard 1:2:1 genotype ratio in a monohybrid cross
    1 BB
    2 Bb
    1bb

    #1b Both parents are purebreds, one dominant and one recessive
    P1 AA x P1 aa => F1 Aa 100% heterozygous filial 1

    #2 Tom is known by his dominant phenotype but not his genotype so it is written for the known and a space for the unknown as: S_
    The Queen is known as homozygous recessive: ss
    S_ x ss
    If SS x ss then all Ss
    if Ss x ss then 1:1
    However there were 6Ss : 2ss not a perfect 1:1 ratio but definitely not 100% Ss.
    This tells you the Tom was heterozygous and that the data pool was to small to reflect more than chance variation from the expected ratio.

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