Genes, Populations,and the Environment

Biology Basics 3

BB3.1 Genes and the Environment Interact More than genomes affects traits and diseases

Environmental factors include • Prenatal environment• What we eat, breathe• Where we live

Multifactorial traits, affected by both genetics and environment

BB3.2 Genetics Affect Perception of and Response to Environment People’s senses react differently

Some people cannot taste a chemical called phenylthiocarbamide (PTC)

Genetic basis:• aa: Nontasters • AA or Aa: Tasters

Population Distribution of Tasting

Impact of Genetics on Food Choices

Two groups of tasters: tasters and supertasters

~25% of people are nontasters, ~50% are tasters, and ~25% are supertasters

May correlate with the aa, Aa, and AA genotypes

Supertasters can have > 10X taste buds as nontasters and have intense tastes

Supertasters High-sugar foods too sweet, coffee is bitter, and

hot peppers and spices more intense, unpleasant

Less likely to include certain foods and beverages in diet

BB3.3 Variations in Responses to Drugs and Medicines Range of reactions to drugs and medications,

may be genetically influenced Example: Rate metabolized affects dosage

Some capsules delay the release of the drug

Others drugs produced in variety of dosages

BB3.4 Relationship between Cancer and Environment Indirect and direct evidence that environment

plays important role in cancer

Some environmental factors implicated in cancer• Natural radiation • Occupational exposure to chemicals • Virus infections • Personal choices: exposure to UV, smoking, and

diet

Viral Infections: ~15% of Cancers

Viral infection alone is not enough to cause cancer, other factors involved

BB3.5 Genetics and Cancer Therapy

> 70% breast cancer cases: estrogen sensitive

Tamoxifen treats estrogen-sensitive cancer

In body, inactive form converted to endoxifen

Conversion of tamoxifen to endoxifen controlled by CYP2D6

Conversion of Tamoxifen to Endoxifen

CYP2D6 Gene

Several alleles, four phenotypes One phenotype group metabolizes tamoxifen

poorly, higher risk of recurrence

Genetics important in designing or specifying drug therapy

BB3.6 Behavior, Genes, and Environment

5-HTT gene controls nerve impulses in the brain

Variation may cause changes in stress-response behavior

Two alleles: one long and one short

Study of individuals ages 21–26 with ≥ 4 stress events, increased risk of depression for those with two copies of short allele

BB3.7 Environmental Factors, Genes, and Immune System Autoimmune diseases: third most common

form of disease in U.S.• 15–80 diseases, affect 5–8% of population• Include: diabetes, multiple sclerosis, and

rheumatoid arthritis• > 75% of affected are women

Distribution of Autoimmune Diseases

Autoimmune Diseases

Body’s immune system produces antibodies that attack specific cells and tissues

Almost all tissues and organs can be affected

ID environmental agents that might cause disorder

Both genetic and environmental factors involved in triggering disease

Autoimmune Diseases and Infections

BB3.8 Environment and Distribution and Frequency of a Genetic Disorder Populations and environment play a part in

genetics

Geneticists often look to environment for factors that may be responsible

In some cases, relationship between a gene and the environment is clearly established

In others cases, link is elusive and still unknown