1.2 Genes: Answers and Questions1.2 Genes: Answers and Questions

The Nucleus: control centre of the cellThe Nucleus: control centre of the cell• The nucleus contains the master set of instructions that determines:

• what each cell will become• how it will function• how long it will live before being replaced

• These instructions are carried in chromosomes

Chromosome – a thread-like structure made mostly of DNA, found in the nucleus of a cell

ChromosomesChromosomes

• Every species has a specific number of chromosomes• Chromosomes come in pairs (one from each of the parent)• Humans have 46 chromosomes (23 from the mother’s egg and 23 from the father’s sperm)

The DNA CodeThe DNA Code

DNA (deoxyribonucleic acid) – material found in the cell nucleus that contains genetic information[Dee-OXy RYE-bo-NEW-clee-ik]

Gene – a segment of DNA that controls protein production

• Each chromosome consists of a single molecule of DNA

• DNA is divided into segments called genes

Why is DNA important?Why is DNA important?

• DNA controls many of your features (hair, eye colour)• Lifestyle choices also play a role in how your body functions and looks

Genes Direct Protein ProductionGenes Direct Protein Production

The DNA CodeThe DNA Code

• In 1953 scientists James Watson and Francis Crick created a model of DNA (the twisted ladder design is sometimes called a “double helix”).

DNA Screening – testing for the presence of genetic disorders

DNA ScreeningDNA Screening

DNA ScreeningDNA Screeningkaryotype - micrograph of the chromosomes in a person’s cells

• individual chromosomes from the karyotype can be mapped and then be examined for any irregularities

Karyotype

Down SyndromeDown Syndrome

• can be detected in a fetus through amniocentesis• technicians look at chromosome 21• positive test = 3 chromosomes (instead of the usual pair)• the extra chromosome leads to overproduction of certain proteins which result in physical and development disabilities

PKUPKU

• babies are tested after birth by examining a blood sample• if uncorrected, it can lead to severe brain damage• treatment includes following a diet low in natural protein• testing is inexpensive compared to the costs of treating PKU if not detected early

Huntington DiseaseHuntington Disease

• affects nerve cells• symptoms include loss of muscular control & brain function• normally appear in a person’s 40’s and worsen for about 15 years before the disease causes death• individuals have a 50% chance of having the gene if one of the parents have it• someone who has the gene will develop the disease

Control HD

Issues Related to DNA ScreeningIssues Related to DNA Screening• DNA testing can reveal genetic disorders (such as Down Syndrome, PKU, Huntington Disease) and can help determine how susceptible a person might be to ailments such as cancers and heart disease.• The controversy related to genetic testing revolves around a variety of social issues.

Ethics of Genetic ScreeningEthics of Genetic ScreeningAGAINST TESTING

• may lead to needless emotional pain (if there is no cure, nothing can be done)• the testing is expensive (will not save lives)

IN FAVOUR OF TESTING

• results (positive or negative) reduce the stress of uncertainty• might change a person’s life decisions

Ethics of Drug ResearchEthics of Drug ResearchExample:• Drug company develops an effective drug in lab condition• Carries out clinical trials on humans (very risky and expensive)• Tries to recover the cost by putting high price on drug• Ex. the annual cost of taking Kuvan (PKU drug) may be as high as US $200,000

• What do you think?

Ethics of Drug ResearchEthics of Drug Research A company discovered a very expensive cure for cancer.

• Does the company own the cure and has the right to sell it?

• Does the company have an ethical obligation to make life-saving cures available to everyone?

Section 1.2 ReviewSection 1.2 Review

Concepts to be reviewed:• genetic material in the nucleus: DNA, chromosomes, and

genes

• the structure of DNA

• DNA screening and related issues

• various genetic diseases

• ethics of genetic screening

HomeworkHomework

• Complete Activity 1.2 0n p 21.• Work in groups of five• Complete question 1-6.