Human Populations Exam 1

What is a gene?

A region of DNA that codes for messenger RNA (which encodes a protein) or for a functional RNA molecule

What is the genetic code?

The set of rules by which the sequence of nucleotides in mRNA is translated into the amino acid sequence of a protein

What determines protein function?

The three-dimensional structure of a protein

What are the main levels of protein structure?

Primary (amino acid sequence), secondary (α-helices and β-sheets), tertiary (3D folding), and quaternary (multi-subunit complexes)

What are non-coding RNA products?

RNA molecules that are not translated into proteins but have functions on their own (e.g., rRNA, tRNA, miRNA, ribozymes)

What are chromosomes?

Highly compacted structures of DNA and proteins that contain genes and other DNA elements

Define ploidy

The number of sets of chromosomes in a cell (e.g., haploid = 1 set, diploid = 2 sets, polyploid = multiple sets)

What is a genome?

The complete set of genetic material in an organism, including all of its genes and non-coding DNA

What percent of the genome is composed of genes?

Only a small percentage (around 1–2% in humans)

What are the two methods of transposition?

cut-and-paste (transposon excises and reinserts elsewhere)
Copy-and-paste (transposon makes a copy that inserts elsewhere)

What is a mutation?

A change in the DNA sequence relative to a reference or ancestral sequence

Why are mutations important?

They are the ultimate source of genetic variation, drive evolution, leave records of evolutionary history, and can cause genetic disorders

What causes mutations?

DNA replication errors, meiotic errors, environmental mutagens, or transposable elements

Can mutations occur in both somatic and germline cells?

Yes. Somatic mutations affect only the individual, while germline mutations are heritable

Are DNA replication errors fixed?

Most are corrected by proofreading and repair, but some escape correction and persist

How many mutations enter the human population yearly?

About 9.5 billion new mutations (≈68 new mutations per child × 140 million births per year)

What is a substitution mutation?

A single nucleotide is replaced with another, which may alter a protein’s amino acid sequence (e.g., mc1r gene in beach mice)

What are insertion/deletion (INDEL) mutations?

Mutations where one or more nucleotides are inserted or deleted from the DNA sequence, potentially disrupting gene function

How can mutations occur in non-coding regions?

They can alter regulatory elements (e.g., promoters, enhancers, introns), affecting gene expression without changing protein coding sequence

What do gene duplications generate?

New copies of existing genes, which can evolve new functions (example: antifreeze proteins in Antarctic icefish)

What is a chromosomal inversion?

A mutation where a chromosome segment is flipped in orientation.

• Paracentric inversion: does not include the centromere

• Pericentric inversion: includes the centromere

What is a translocation?

A mutation where segments of DNA are swapped between different chromosomes

What is a chromosomal fusion?

A mutation where two separate chromosomes join together into one

What are the largest-scale mutations?

Whole chromosome duplications/deletions (aneuploidy) and whole genome duplications (polyploidy)

What is a locus?

A specific physical location of a gene (or genetic marker) on a chromosome

What is an allele?

A variant form of a gene found at a locus

What is a genotype?

The combination of alleles present in an individual at one or more loci

What is a phenotype?

The observable characteristics of an individual (e.g., color, size, shape) determined by genotype + environment

What is a haplotype?

The combination of alleles at multiple loci on the same chromosome in one individual

What is the mechanism of inheritance at the chromosomal level?

Chromosomal segregation during meiosis + recombination (crossing over) leads to inheritance patterns

What is Mendel’s Law of Segregation?

During meiosis, the two alleles for a gene separate so each gamete gets only one allele

What was Mendel’s pea flower color experiment?

He crossed purple and white flowered peas to study inheritance

What was the result and conclusion of Mendel’s pea experiment?

Traits are inherited in predictable ratios (3:1 in F2); inheritance is determined by discrete units (alleles), not blending

What is genetic linkage?

The tendency of alleles close together on the same chromosome to be inherited together

What is crossing over during meiosis?

The exchange of DNA segments between homologous chromosomes, creating new allele combinations (recombinants)

Who were T.H. Morgan and Alfred “Hot Dog” Sturtevant?

Geneticists who used Drosophila melanogaster (fruit flies) to demonstrate genetic linkage and map genes

What was the hypothesis of Morgan & Sturtevant’s experiment?

• H1: Genes for body color (b) and wing shape (vg) assort independently

• H2: They are inherited together as a single unit (linked)

What was the result of Morgan & Sturtevant’s experiment?

Offspring ratios did not match independent assortment → instead showed linkage with some recombinants

What was the conclusion of the experiment?

The b and vg loci are on the same chromosome but separated by a measurable genetic distance; recombination frequency reflects physical distance between loci

What determines the strength of genetic linkage?

Physical proximity of loci: close together → strong linkage (inherited together). Far apart → weak linkage (more recombination)

What is a recombination rate?

The average number of crossovers in a chromosomal region per generation

What are recombination hotspots?

Specific regions in genomes (like in humans) where crossing over occurs more frequently

Why does the amount of shared DNA among siblings vary?

Recombination is probabilistic → different crossover events shuffle alleles differently in each meiosis

What is a selective sweep?

When a beneficial allele increases in frequency, nearby linked loci also increase in frequency due to reduced recombination

What is genetic hitchhiking?

The rise in frequency of alleles near a beneficial mutation because they are linked to it

Why does recombination matter for evolution?

It creates new allele combinations each generation, increasing genetic diversity for natural selection to act on

Why are siblings genetically different despite having the same parents?

Independent assortment of chromosomes + recombination during meiosis remix alleles each generation

What is a gamete?

A haploid reproductive cell (sperm/egg) that carries one allele for each locus

What is the difference between haploid and diploid?

Haploid = 1 set of chromosomes (gametes). Diploid = 2 sets of chromosomes (somatic cells, parents)

How do recombination rates vary across species?

They differ massively; some species have high rates, others low, affecting how genetic variation is generated

What is a double (or multiple) crossover?

More than one recombination event between loci in a single meiosis, leading to complex recombinant haplotypes