Question:

Biology help please!?

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Two true breeding stocks of pea plants are crossed. One Parent has purplr, axial flowers and the other has white terminal flowers. All F1 individuals have red, axial flowers.

If 1,000 F2 offspring resulted from the cross how many of the following would you expect to have?

Purple, terminal flowers

A) 65 B) 565 C) 250 D) 190 E) 750

Purple Axial flowers

A) 65 B) 565 C) 250 D) 190 E) 750

White terminal flowers?

A) 65 B) 565 C) 250 D) 190 E)750

White axial flowers

A) 65 B) 565 C) 250 D) 190 E) 750

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  1. The question appears to be designed to throw a little curve at you where one locus has incomplete dominance (purple flowers).

    Purple is PP

    Red is PW

    White is WW

    Axial is AA

    Terminal is a

    Parental:  PPAA  x  WWaa

    F1:  PWAa

    F1 cross:  PWAa  x  PWAa

    F2:

    PPAA, purple, axial

    PWAA, red, axial

    PWAA, red, axial

    WWAA, white, axial

    PPAa, purple, axial

    PWAa, red, axial

    PWAa, red, axial

    WWAa white, axial

    PPAa, purple, axial

    PWAa, red, axial

    PWAa, red, axial

    WWAa, white, axial

    PPaa, purple, terminal

    PWaa, red, terminal

    PWaa, red, terminal

    WWaa, white, terminal

    The phenotypic ratios vary from the normally expected 9:3:3:1 ratio for a dihybrid cross due to the incomplete dominance situation and the normally 9 is divided into either purple or red flowers with axial and one of the 3's is divided into one purple terminal and two red, terminal:

    3 purple, axial

    6 red, axial

    3 white, axial

    1 purple, terminal

    2 red, terminal

    1 white, terminal

    So, first we need to find the total number of individuals divided by the number of phenotypes so we can find out the expected number of each:

    1000/16 = 62.5

    So, there should be approximately:

    3 x 62.5 = ~188 purple, axial

    6 x 62.5 = ~375 red, axial

    3 x 62.5 = ~188 white, axial

    1 x 62.5 = ~63 purple, terminal

    2 x 62.5 = ~125 red, terminal

    1 x 62.5 = ~63 white, terminal

    So, the answers are:

    purple, terminal flowers:  A

    purple, axial flowers:  D

    white, terminal flowers:  A

    white, axial flowers:  D


  2. Where did the RED flowers come from??
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