Describe the gene and protein defects in phenylketonuria (PKU). How are these defects connected to disease symptoms?

Answer the following questions for autosomal conditions such as PKU.

If both parents are heterozygous carriers of a mutant allele, what is the chance that their first child will be homozygous recessive for the mutation?

Answer the following questions for autosomal conditions such as PKU.

Parents who are each heterozygous carriers for a recessive mutant allele have a child who does not have the condition. What is the chance this child is a heterozygous carrier of the condition?

Answer the following questions for autosomal conditions such as PKU.

If the first child of parents who are both heterozygous carriers of a recessive mutant allele is homozygous recessive, what is the chance the second child of the couple will be homozygous recessive? What is the chance the second child will be a heterozygous carrier of the recessive mutation?

Homocystinuria is a rare autosomal recessive condition on the RUSP list of conditions screened by newborn genetic testing. The condition results from a mutation that blocks the degradation of the amino acid methionine. The absence of a critical enzyme causes the buildup of the compound homocysteine, which is one of the intermediate compounds in the methionine breakdown pathway. Homocystinuria causes mental impairment, heart problems, seizures, eye abnormalities, and a number of other symptoms that shorten life if not treated. The condition is treated by a specialized diet that is low in methionine and by the ingestion of several supplements.

Why do you think eating a low-methionine diet is critical to controlling homocystinuria?

Homocystinuria is a rare autosomal recessive condition on the RUSP list of conditions screened by newborn genetic testing. The condition results from a mutation that blocks the degradation of the amino acid methionine. The absence of a critical enzyme causes the buildup of the compound homocysteine, which is one of the intermediate compounds in the methionine breakdown pathway. Homocystinuria causes mental impairment, heart problems, seizures, eye abnormalities, and a number of other symptoms that shorten life if not treated. The condition is treated by a specialized diet that is low in methionine and by the ingestion of several supplements.

The low-methionine diet must be maintained throughout life to manage homocystinuria. Why do you think this is the case?

A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.

Draw a pedigree of this family, including the woman, the man, their siblings, parents, and grandparents.

A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.

On the pedigree, write the genotypes (GG, Gg, or gg) for each person who has been tested or for whom you can deduce a genotype. If a genotype cannot be determined completely, list the alleles you know or deduce must be present.

A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.

Explain why you are able to assign genotypes to the man's parents despite their not being tested.

If a man and a woman are each heterozygous carriers of a mutation causing a disease on the RUSP list, what do you think are the three or four most important factors they should consider in their decision making about having children?

Suppose a man and a woman are each heterozygous carriers of a mutation causing a fatal hereditary disease not on the RUSP list. Prenatal genetic testing can identify the genotype of a fetus with regard to this disease and can identify fetuses with the disease. What do you think are the three or four most important factors this couple should consider in their decision making about having children?

If you were to look up Gaucher disease on the OMIM website, you would see that there are three major types, designated Type I (OMIM 230800), Type II (OMIM 230900), and Type III (OMIM 231000). All three types are mutations of the gene for acid-β-glucosidase, encoded on chromosome 1. Different mutations of this gene produce the three types of Gaucher disease that differ somewhat in their symptoms and disease severity.

For each mutation, speculate about whether the acid-β-glucosidase enzyme is merely reduced in function or whether its production is eliminated, and explain why.

If you were to look up Gaucher disease on the OMIM website, you would see that there are three major types, designated Type I (OMIM 230800), Type II (OMIM 230900), and Type III (OMIM 231000). All three types are mutations of the gene for acid-β-glucosidase, encoded on chromosome 1. Different mutations of this gene produce the three types of Gaucher disease that differ somewhat in their symptoms and disease severity.

Thinking about the production or function of the acid-β-glucosidase enzyme, why do you suppose different mutations of this gene produce differences in symptoms and disease severity?

Some proteins are composed of two or more polypeptides. Suppose the DNA template strand sequence 3′-TACGTAGGCTAACGGAGTAAGCTAACT-5′ produces a polypeptide that joins in pairs to form a functional protein. What is the amino acid sequence of the polypeptide produced from this sequence?

Some proteins are composed of two or more polypeptides. Suppose the DNA template strand sequence 3′-TACGTAGGCTAACGGAGTAAGCTAACT-5′ produces a polypeptide that joins in pairs to form a functional protein.

What term is used to identify a functional protein like this one formed when two identical polypeptides join together?

In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.

Describe how the codon for phenylalanine was identified.

In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.

What was the result of studies of synthetic mRNAs composed exclusively of cytosine?

In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.

What result was obtained for synthetic mRNAs containing AG repeats, that is, AGAGAGAG...?

In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.

Predict the results of experiments examining GCUA repeats.

Several lines of experimental evidence pointed to a triplet genetic code. Identify three pieces of information that supported the triplet hypothesis of genetic code structure.

Outline the events that occur during initiation of translation in E. coli.

A portion of a DNA template strand has the base sequence

5′-...ACGCGATGCGTGATGTATAGAGCT...-3′

Identify the sequence and polarity of the mRNA transcribed from this fragmentary template-strand sequence.

A portion of a DNA template strand has the base sequence

5′-...ACGCGATGCGTGATGTATAGAGCT...-3′

Assume the mRNA is written in the correct reading frame. Determine the amino acid sequence encoded by this fragment. Identify the N- and C-terminal directions of the polypeptide.

A portion of a DNA template strand has the base sequence

5′-...ACGCGATGCGTGATGTATAGAGCT...-3′

Which is the third amino acid added to the polypeptide chain?

Describe three features of tRNA molecules that lead to their correct charging by tRNA synthetase enzymes.

Identify the amino acid carried by tRNAs with the following anticodon sequences.

5′-UAG-3′

Identify the amino acid carried by tRNAs with the following anticodon sequences.

5′-AAA-3′

Identify the amino acid carried by tRNAs with the following anticodon sequences.

5′-CUC-3′

Identify the amino acid carried by tRNAs with the following anticodon sequences.

5′-AUG-3′

Identify the amino acid carried by tRNAs with the following anticodon sequences.

5′-GAU-3′