How can principles of Mendelian genetics be used to predict phenotypes of F1 and F2 generations?
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If you assume that a single gene controls a trait and that there are two alleles, one from each parent, you can use Mendelian genetics to determine the probability of genotype and phenotype of the offspring by using Punnett squares. For example if wrinkled peas are recessive and smooth peas are dominant you may assign a big letter for the dominant trait and a small letter for a recessive trait

P - Dominant - smooth

p - Recessive - wrinkled

Assume that each plant has two alleles.  You can have the following combinations

PP, Pp, pP, pp

In situations of complete dominance, the dominant trait will always show if there is at least one big P allele.  The phenotypes are as follows:

Genotype

Phenotype

PP - Homozygous

Smooth Peas

Pp - Heterozygous

Smooth Peas

pP - Heterozygous

Smooth Peas

pp - Homozygous

Wrinkled Peas

If we know the genotype of the parents we can use a Punnett square to determine the probability for the genotype and and phenotype of the offspring as follows

crossing PP x PP gives us the following:

 

P

P

P

PP

PP

P

PP

PP

100% of the offspring will be homozygous and will have a genotype of PP and a phenotype of smooth.

crossing Pp and Pp gives the following:

 

P

p

P

PP

Pp

p

pP

pp

25% off the offspring would be homozygous dominant and smooth.

50% would be heterozygous dominant and smooth.

25% would be homozygous recessive and wrinkled.

Hope this helps.

by Level 3 User (8.5k points)

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