MonoHybrid Crosses

Genetics as it applies to evolution, molecular biology, and medical aspects.

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MonoHybrid Crosses

Post by Sarah<3 » Wed Nov 08, 2006 1:15 am

Hey Guys ^^
I'm looking for some help on a few questions from school.


1. A purple-flowered pea plant is crossed with a white-flowered pea plant.
All the F1 plants are crossed with each other. 401 of the F2 plants have purple flowers and 131 have white flowers. What are the genotypes of the parental and f1 generation plants. (this really confuses me)

2. In tomatoes, red fruit color is dominant to yellow. Suppose a tomato plant homozygous for red is crossed with on homozygous for yellow. Determine the appereance of

a) the f1
b) the f2
c) The offspring of the f1 bath to the orginal red parent
d) the offspring of a cross of the f1 back to the yellow parent
( i really dont understand c and d)

3. In guinea pigs, rough coat (R) is dominant over smooth coat (r). A rough-coated guinea pg is bred to a smooth on, giving 8 rough and 7 smooth progeny in the f1.

a) what are the genotypes of the parents and their offspring?
b) if one on the f1 animals is mated to its rough parent, what progeny would you expect?

I'm really confused with these.....oddly I find Dihybrid crosses alot more simple. I probbaly undertsand dihybrid because i learned it first. I know the basics and fully understand dihybrid but this monohybrid is stumping me. Thanks alot for your help guys.

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Post by r7iris » Wed Nov 08, 2006 1:38 am

1. if it is not a trick question, the genotype should be 1/4 of AA, 1/2 of Aa, 1/4 of aa and the parent are Aa x Aa..... since the ratio 3:1 is the result of heterozygous cross.

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Post by canalon » Wed Nov 08, 2006 2:49 am

2- Write the genotype of the f1 (a), it is homogeneous and do the punet squares with another f1 (that will be f2), and with each parent in turn, that would be the 2 back crosses.

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)

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