Nov 15 Chapter 9 Patterns of Inheritance (continued)

 

Carlos and Mollie Can Have a Perfectly Healthy Baby (or can they?)

Carlos and Mollie want to have children. However, they haven’t tried to start a family yet because they disagree on something important. Carlos wants Mollie to get tested to see if she is a carrier for cystic fibrosis (CF). Mollie doesn’t want to do it. People with CF have mutations in one or more genes. These mutated genes give faulty instructions for the production of proteins that help move salt in the body. One result is that the lungs become clogged with mucus, making it hard to breathe. Another result is that the body has a hard time digesting food. The disease can be painful and lead to an early death. Carlos had a brother with CF. He hated seeing his brother suffer so much. His parents struggled with the hardship and expense of caring for a sick child who never made it to adulthood. Carlos doesn’t want to repeat that experience in his own life. That’s why he had himself tested for CF. Unfortunately, he found out that he is a carrier. CF is a recessive disorder. That means his children will have the disease only if they inherit the mutated gene from both parents. Mollie can get tested to see if she carries the CF mutation. If she does, then when she gets pregnant they can have the fetus tested to make sure it does not have two CF genes and is therefore free of the disease. Mollie would prefer simply not knowing what the risks are. She figures that once a baby is in their arms, they will be glad they had it, no matter what. If you were Mollie or Carlos, what would you do?

 

<Cystic fibrosis (CF)>

-          Autosomal recessive

o       If both parents are carrier, the chance of their child getting CF is 25 %.

-          Most common fatal genetic disorder

-          Children with CF have difficulty breathing or digesting food.

-          Vulnerable to infections

-          The affected children may or may not make to the adulthood.

 

Carrier testing – Genetic testing to determine whether the person is a carrier of a

        recessive genetic disorder.

 

If Mollie turns out to be a carrier of the CF allele, what are their options?

 

-          They may decide not to get married.

-          They may decide not to have children.  They may want to adopt children instead.

-          They may decide to have fetus tested while Mollie is pregnant (Prenatal testing).

-          If the fetus has CF, they may decide to terminate pregnancy. 

-          They may consider in vitro fertilization.  Sperms and eggs are fertilized in a petri dish.  Obtained embryos can be tested for presence of the CF allele.  The embryos that do not carry the CF allele are implanted to mother’s uterus.  Very expensive procedure.  High failure rate.

 

Even if they try everything to avoid a child with CF, they may still be end up with a sick child.

 

Even if they have a child with CF, advancement of medical research may provide him/her a better quality of life.

 

 

Howard’s Health Is Up to Him (or is it?)

Howard will turn 50 soon, and it worries him. His grandfather died of a heart attack in his fifties, and so did his father and uncle. Several years ago, a doctor told Howard that he was at high risk for heart disease because of his family history. But the doctor said that Howard could improve his chances if he lost some weight, stopped smoking, and exercised. The doctor also told Howard to come back every year for a checkup. Howard hasn’t gone on a diet, and he hasn’t given up his cigarettes or taken up exercise. He also hasn’t been back to the doctor. He’s afraid of what the doctor might find. Howard can’t make up his mind. Sometimes he thinks he should try to take better care of his health. Other times, he thinks that he should just accept the fact that he won’t live much longer and should get as much fun out of life while he can. If you were Howard, what would you do?

 

Genes vs. environment (Nature vs. Nurture)

-          Most illness is caused by many factors.

-          While genes may play a role in many disorders, so do the conditions and circumstances of your life.

-          Very few disorders are triggered by a single gene.

-          Chances are that everyone has at least a handful of “problem” genes but they may never cause you trouble.

-          Genetic determinism is a misguided idea that everything is determined by genes. 

-          The idea is also the basis of ‘eugenetics’ that was prevalent during early 20th century. 

-          Eugenetics is the effort to control the genetic makeup of human populations, which created many controversial programs such as racial segregation, sterilization program and, in extreme case, racial elimination (holocaust, ethnic cleansing). 

-          Human characteristics, such as temperament, intelligence, social behavior and physical and artistic skill, are influenced by both genes and environment.

 

Genetic discrimination

-          The genetic information could easily be misused by employers and insurance companies.

-          An increasing number of insurance companies (health, life and disability insurances) are making genetic testing as prerequisite for joining the policy. 

-          They may force genetic testing even to those who do not wish to know their genetic status.  (Shouldn’t we have the right not to know our genetic status?)

-          These issues need to be solved at the government level.

 

Chapter 10 Molecular biology of the gene

Pre-chapter review

  1. ________ serves as genetic blueprints in living organisms.
  2. The process which the information in DNA is transferred to RNA is called ________.
  3. The process which the information in RNA is used to make polypeptides is called ________.
  4. Monomer units of nucleic acid are _______, which consists of nitrogenous base, sugar and ________ group.
  5. The four nitrogenous bases found in DNA are ________.
  6. The four nitrogenous bases found in RNA are ________.
  7. Double helix refers to the structure of ________.

 

In this chapter, you will learn gene structures and functions at the molecular level. Here are the headings:

  1. Mechanism of DNA replication
  2. Mechanism of gene expression
    1. Overview of gene expression
    2. Transcription
    3. RNA processing
    4. Translation
  3. Viruses

 

 

1. Mechanism of DNA replication

i) Structure of DNA

- Complementary base pairing

A only pairs with T

C only pairs with G

- The opposing strand is also ‘backwards’. (Fig 10.5B, p191)

 

 

- One strand of DNA serves as a template for the daughter strand being synthesized.

- DNA is always synthesized from the 5’ end to the 3’ end.  (5’ ® 3’)

 

ii) Steps of DNA replication

-          Origin of replication – double helix opens up to prepare for DNA synthesis.  (Fig 10.5A, C, p191)

-          DNA polymerase adds nucleotides to the 3’ end.

-          One daughter strand is synthesized in one continuous piece.

-          The other daughter strand first produces as short pieces.  They are then put together by DNA ligase.  (Fig 10.5C)

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