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Mendel/Punnett Square/Genotypes

Having a problem understanding Mendel's theory, would like help answering these scenario's. Have to write an report based on these questions please help

Assume that "S" represents the dominant trait of having long leaves,
and "s" represents the recessive short-leafed trait in a plant. In the
parental generation, you cross a homozygous long-leafed plant with a
homozygous short-leafed plant.

Draw a Punnett square illustrating this
cross, and give the genotypes and phenotypes of the F1 generation.

Using a Punnett square, show the genotypes and phenotypes of the F2
generation if the F1 plants in question 1 are self-fertilized.
In question 2, what is the probability that the F2 plants will have short
leaves?

You were thrilled to have a new baby sister, but excitement turned to
anxiety when she began to have digestive problems with persistent
vomiting. Doctors quickly learned that she had an autosomal
recessive disorder called galactosemia. Your sister lacked the enzyme
that breaks down the milk sugar galatose, so her pediatrician put her
on a special diet free of lactose and galactose. In a short time, your
sister was fine.
a. Neither of your parents is affected with galactosemia. If your
sister's genotype is gl/gl, what are your parents' genotypes?
b. You are not affected with galactosemia. What is your genotype or
possible genotypes?
c. Will your sister automatically pass on this disease to her children?
Why or why not?
4. The extra chromosome 21 that is found in persons with Down
syndrome is the cause of multiple developmental defects. What

Solution Preview

Question: Assume that "S" represents the dominant trait of having long leaves, and "s" represents the recessive short-leafed trait in a plant. In the parental generation, you cross a homozygous long-leafed plant with a homozygous short-leafed plant.

Draw a Punnett square illustrating this cross, and give the genotypes and phenotypes of the F1 generation.

Response: A homozygous condition means that both alleles are identical. Therefore, the homozygous long-leafed plant would have a genotype of SS since "S" is the allele for producing long-leafs. The homozygous short-leafed plant would have the genotype of ss.

Therefore, we can set up the cross as SS x ss. The SS parent can only produce one type of gamete: S. And, the ss parent can only produce one type of gamete: s. Therefore, the Punnett square is rather simple:

S S
s Ss Ss
s Ss Ss

All of the F1 progeny are identical and have the genotype of Ss. They have long leaves since the S allele is dominant to the s allele.

Question: Using a Punnett square, show the genotypes and phenotypes of the F2 generation if the F1 ...

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