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1. What are the possible gametes from each of the following genotypes:

Remember, alleles (different forms of the same gene) always come in pairs in a diploid organism (e.g., you and me). Mendel determined that each allele pair segregated during the formation of gametes by meiosis; this means that each pair of alleles has to go into separate gametes.

• GG
• Gg
• GGRR
• GgRr
• GGRr
• GgRR
• GgRrXX

2. White flowers are recessive (r) to red flowers (R) in peas. You cross a homozygous white flower plant with a homozygous red flower plant. What color flowers will the offspring of this cross have?

4. Cystic fibrosis is a recessive disease in humans. If neither of your parents nor you have cystic fibrosis but your only brother does, what is the probability that the next child born will have cystic fibrosis?

6. Assuming complete dominance will occur, the offspring of the cross Aa x Aa will show a phenotypic ratio of _______.

• What are the genotypes of the father, mother and child? R = roll; r = non-roll, A = detached; a=attached
• What is the probability that a second child of theirs will have detached earlobes and won't be able to roll his/her tongue?

Genetic Problems Answers

1. What are the possible gametes from each of the following genotypes:
   Remember, alleles (different forms of the same gene) always come in pairs in a diploid organism (e.g., you and me). Mendel determined that each allele pair segregated during the formation of gametes by meiosis; this means that each pair of alleles has to go into separate gametes.
• GG
• G only
• Gg
• G or g
• GGRR
• GR only
• GgRr
• GR
• Gr
• gR
• gr
• GGRr
• GR
• Gr
• GgRR
• GR
• gR
• GgRrXX
• GRX
• GrX
• gRX
• grX
2. White flowers are recessive (r) to red flowers (R) in peas. You cross a homozygous white flower plant with a homozygous red flower plant. What color flowers will the offspring of this cross have?
   First you should determine the genotypes of the parents. The red-flower parent's genotype is RR and the white-flower parent's genotype is rr.
   
   Next you need to determine the types of gametes (egg or pollen) each parent can make. The red-flower plant can only make a gamete with a R allele in it. The white flower plant can only make a gamete with a r in it.

Now set up a Punnett square

All of your flower will be heterozygous (Rr) and red flowered!

3. Freckles are a dominant trait and non-freckles are recessive. Fred has freckles and Jane doesn't. What is the probability that their children will have freckles?
   
   First determine the genotypes of Fred and Jane. Can you determine the exact genotype of Fred, the freckled parent? Fred could be FF or Ff since freckles (F) is dominant! So given the information in the question you cannot determine the probability that your children will have freckles.
   
   If Fred, who had freckles, had a mother who did not have freckles and a father who did, now you could figure out what his genotype is as follows. His mother has the ff genotype and his father has the F? genotype. We don't need to worry about what the second allele is because we know that he passed the F allele to Fred - that is why he has freckles! And his mother passed the f allele to Fred, so Fred has an Ff genotype.
   
   Now what are the gametes?
   Fred --> F or f
   Jane --> f or f
   
   Set up the Punnett square

50% of the children would have freckles!

4. Cystic fibrosis is a recessive disease in humans. If neither of your parents nor you have cystic fibrosis but your only brother does, what is the probability that the next child born will have cystic fibrosis?
   
   Let X^C be normal allele and X^c represent cystic fibrosis.
   
   Your mother's genotype - X^cX^C and her gametes are either X^c or X^C
   Your father's genotype - X^CYand his gametes are either Y or X^C
   How did I figure out your parent's genotype?
   
   Set up the Punnett square

The probability is 25% or 0.25 or 1/4- they all say the same thing.

5. Tongue rolling is a dominant trait. Can a husband and wife who cannot roll their tongues produce a child who can roll his/her tongue?
   
   No. The husband and wife must both be homozygous recessive (rr) for non-tongue rolling and cannot produce a child that is either homozygous dominant (RR) or heterozygous (Rr).
   
   
   
   
   
6. Assuming complete dominance will occur, the offspring of the cross Aa x Aa will show a phenotypic ratio
   of _______.
   
   Set up the Punnett square

The phenotypic ratio will be 3:1 (dominant   phenotype: recessive phenotype)

7. At a gene location on a human chromosome, a dominant allele controls tongue-rolling ability. People who are homozygous for the recessive allele cannot roll their tongue. At a different gene locus, a dominant allele controls whether the earlobes will be attached or detached; attached is recessive. Suppose a tongue-rolling, detached ear lobed woman marries a man who has attached lopes and cannot roll his tongue. Their first child has the phenotype of the father. Given this outcome,

What is the genotypes of the father, mother and child? R = roll; r = non-roll, A = detached; a=attached
Father is rraa
Mother is RrAa
Child is rraa

What is the probability that a second child of theirs will have detached earlobes and won't be able to roll his/her tongue?
First figure out what the gametes of the parents will be:
Father = ra
Mother = RA or Ra or rA or ra

Set up a Punnett square

25%