Chapter 13: Mutation and Genetic Variation

BIOL 1020 Rebecca Riggs

What is a genotype?

the genetic makeup of a cell or organism

What is a phenotype?

the observable characteristics resulting from the genotype

What are small-scale mutations?

point mutations, insertions, deletions, and movement of transposable elements

What are chromosomal mutations?

mutations involving large regions of one or more chromosomes

How do mutations occur?

randomly or induced by mutagens; most DNA damage is repaired

What are alleles?

different forms of a gene corresponding to different DNA sequences

What does homozygous mean?

having two copies of the same allele for a gene

What does heterozygous mean?

having two different alleles for a gene

What are polymorphisms?

genetic differences among individuals in a population

What can polymorphisms do?

be harmful, beneficial, or neutral in effect

What is the difference between homozygous and heterozygous?

homozygous: same alleles; heterozygous: different alleles

What is a mutation?

any heritable change in genetic material.

What makes a mutation heritable?

it is passed on through cell division (not RNA)

What are the effects of mutations?

harmful, beneficial, or neutral

What gene causes Huntington’s disease when mutated?

the HTT gene

What is a neutral polymorphism example?

TAS2R38 taste receptor gene

What are the PAV and AVI alleles related to?

bitter taste perception (tasters vs. non-tasters)

What defines a beneficial mutation?

one that improves survival or reproduction

What causes lactase persistence?

mutations in enhancer elements that increase lactase gene transcription

When is lactase normally turned off?

after weaning

How can a mutation’s effect be altered?

by the environment or other gene expression

What mutation causes sickle-cell disease?

a single base-pair change in the hemoglobin gene

What are the advantages of sickle-cell heterozygotes?

resistance to malaria

How do mutations occur?

spontaneously and randomly

What affects mutation rates?

genome size and hotspots

Which sex has higher mutation rates?

males

What affects the human DNA replication error rate?

hotspots and sex-based differences

What are somatic mutations?

mutations in nonreproductive cells

What are germ-line mutations?

mutations in reproductive cells that can be inherited

How do mutations lead to cancer?

accumulated mutations in somatic cells cause malignancy

What forms from early mutations in colon cancer?

polyps

How can mutations be inherited?

if they occur in germ cells of a parent

What can personal genomes tell us?

mutations already carried and risk for diseases

What causes mutations?

unrepaired errors during DNA replication

What are small-scale mutations?

single base-pair or frameshift mutations

What are large-scale mutations?

chromosome-level mutations

What is a point mutation?

a change in a single nucelotide

What is a silent mutation?

a mutation that doesn’t change the amino acid sequence

What is a missense (nonsynonymous) mutation?

a change that alters the amino acid sequence

What is an example of a nonsynonymous mutation?

the beta-hemoglobin S or C allele mutation

What is a nonsense mutation?

one that introduces a premature stop codon

What happens in insertions or deletions?

the reading frame can change (frameshift)

What causes cystic fibrosis?

deletion of one amino acid leading to misfolded protein

What is a frameshift mutation?

addition or deletion of one or two bases changing the reading frame

What is the difference with three-base insertions/deletions?

they maintain the frame but add/remove an amino acid

What are transposable elements?

DNA segments that can move within the genome

Who discovered transposable elements?

Barbra McClintock

What did McClintock discover in corn?

yellow kernels caused by a jumping transposable element disrupting pigment genes

What caused purple speckles in corn?

the element jumping out, restoring gene function