Lecture 8 Flashcards
(37 cards)
What is a genetic locus?
Where a gene lives on a chromosome (i.e., position of nucleotide, nucleotide sequence, or a gene on a chromosome)
What is polymorphism at the phenotypic level vs genotypic level?
Phenotypic level - observable variation in a population
Genotypic level - any DNA sequence or allele variation at a locus
What are alleles?
Alternate forms of a gene
__________ are the ultimate source of genetic variation in populations.
Mutations
What are the three types of substitution? Compare each of them.
- Synonymous (or silent, neutral):
—> GGG to GGA (resulting amino acid has not changed) - Nonsynonymous (or missense)
—> CGU to CAU (resulting amino acid has changed) - Nonsense substitution
—> UAC to UAA (stop codon)
—> translation stops early
—> shortened protein sequence
—> impacts healthy severely
Most mutations are ______ substitutions.
Synonymous
What is a wild type?
Most frequently observed variant
What is frequency dependent selection?
Compare insertions and deletions.
Insertions - moves reading frame to left
Deletions - moves reading frame to right; impacts all downstream amino acids
Which type of mutation has the greatest impact on health and evolutionary fitness?
Insertion + deletions (negative effect on fitness)
Which nucleotide(s) in a codon are less likely to be under the influence of natural selection? Why?
Third base (wobbly third)
• First and second base are conserved (not much variation)
• Third base has most amount of freedom (do not alter phenotype)
Sickle-cell anemia is the result of what type of mutation?
Non synonymous
What is mutation rate?
Rate of change in DNA sequence due to copying errors, external factors (UV radiation, X-rays)
Mutation rate is expressed as:
Number of mutations per nucleotide per generation
How do you calculate number of genome-wide point mutations you were born with?
(Mutation rate) x (number of nucleotides in genome) = total number of mutations)
What is nondisjunction?
Phenomenon where two chromosomes don’t separate properly
What are the consequences of nondisjunction?
Kleinfelter’s syndrome (XXY)
Down syndrome (trisomy 21)
Triple X syndrome (XXX)
What is heterozygote advantage? Give an example.
Heterozygote has higher fitness than either homozygote, resulting in higher than expected frequency of a deleterious recessive allele
Ex: sickle cell anemia
Sickle cell anemia is _______ and _______.
Deleterious; recessive
What causes sickle cell anemia?
Point mutation in hemoglobin polypeptide
Explain how sickle cell anemia is an example of heterozygote advantage.
If:
• SS = no sickle cell
—> more susceptible to plasmodium
—> no resistance to malaria
• Ss = some sickle cell
—> mostly asymptomatic
—> closer to homozygous dominant than recessive
—> resistant to malaria and sickle cell anemia
• ss = sickle cell anemia
—> better protected against plasmodium
—> resistant to malaria but not susceptible to sickle cell anemia
• 25% homozygous recessive - susceptible to sickle cell
• 25% homozygous dominant a susceptible to malaria
• 50% genotype with highest fitness (heterozygotes)
What are sources of new genetic variation? What are processes that maintain existing genetic variation in a population?
• Mutation
• Sexual reproduction
• Gene duplication
• Heterozygote advantage - does not create new variation; maintains exiting variation
Polymorphisms can be:
- Continuous - variation whose values can land anywhere on number line (e.g., height, mass, volume, speed, distance)
- Discrete - values land on integers (evenly spaced increments) (e.g., number of fingers on a hand, number of babies born to a woman)
What is mitosis? Explain the process.
DNA replication/cell division during growth and development (in multicellular organisms)
One diploid (2n) cell replicated chromosomes (4n) and divides once, resulting in two diploid (2n) daughter cells that are exact copies of original cell
