Human Genetic Variation Flashcards
WHAT CONTRIBUTES TO VARIATION
Both genes and the environment
SINGLE-GENE EXAMPLES:
- SLI
- Sickle-Celle Anemia
- Lactase Persistence
TRAITS INFLUENCED BY SINGLE GENES
- Controlled by one gene, making their expression more straightforward and less susceptible to environmental factors
- Follows standard patterns of Mendelian inheritance
SPECIFIC LANGUAGE IMPAIRMENT (SLI)
SLI caused by a dominant gene; most people with SLI will be heterozygotes
SLI in KE family caused by a single dominant allele of the FOXP2 gene: codes for a transcription factor that regulates gene expression in the brains of the fetus
SICKLE-CELL ANEMIA
Heterozygous individuals are protected against malaria
Example of balanced polymorphism
Heterozygous individuals = HbA HbS
Recessive individuals = HbS HbS
LACTASE PERSISTENCE
A genetic trait that allows people to digest lactose, the sugar in milk, into adulthood
Lactase persistence controlled by a single gene with two alleles
LACP = dominant (can digest lactose as an adult)
LACR = recessive (cannot digest lactose well as an adult)
Ability to digest milk evolved independently in European and African populations
CAUSES OF VARIATION WITHIN GROUPS:
- mutation and selection-mutation balance
GENETIC VARIATION WITHIN GROUPS: MUTATION
- Mutation can maintain deleterious genes at a low frequency
- If mutation rates introduce deleterious alleles at the same rate that selection removes them = selection-mutation balance
GENETIC VARIATION WITHIN GROUPS: BALANCED POLYMORPHISM
When heterozygotes have higher fitness than either homozygote
Both alleles can be maintained through selection (both persist in the population)
CAUSES OF VARIATION BETWEEN GROUPS:
- Selection
- Genetic Drift
CAUSES OF VARIATION BETWEEN GROUPS: SELECTION
Favors different genes in different environments
Can maintain variation among groups because humans live in different environments
CAUSES OF VARIATION BETWEEN GROUPS: GENETIC DRIFT
Causes random changes in gene frequencies once populations are isolated
Two populations can become distinct from each other through isolation
Strongest in smaller populations (founder effect)
COMMON (AND INCORRECT) BELEIFS ABOUT RACE
- Humans can be divided into distinct groups identifiable by a few externally visible traits, such as skin color
- Human races are natural, enduring, and distinct
- Members of races are genetically/biologically distinct
BIOLOGY AND RACE
‘Race’ is a cultural construct rather than a biological one (genetic/phenotypic similarities?)
Aren’t clear and consistent difference between races when looking at single genes or traits
Human groups weren’t separated long enough
for many biological differences to evolve (gene flow connects us all)
It takes a lot of genetic information about someone to be able to classify their race
HUMAN VARIATION
1) Genetic Variation - differences in genotype
2) Environmental Variation - due to habitat (e.g. food availability) climate, social interactions, influence of other species, culture, etc.
