Genetics and Evolution – Core Concepts

A comprehensive set of question-and-answer flashcards covering fundamental genetics, Mendelian laws, molecular experiments, population genetics, mutations, and evolutionary theory.

What molecule carries the hereditary information that determines an organism’s traits?

DNA (deoxyribonucleic acid).

How are genes organized within the cell nucleus to ensure accurate transmission during division?

They are packaged into chromosomes.

What is the term for alternative versions of a gene found at the same locus?

Alleles.

Define genotype.

The genetic makeup (allele combination) of an individual.

Define phenotype.

The observable traits produced by the genotype and environment.

What are autosomes?

Chromosomes that determine most non-sex traits.

Which chromosomes determine an individual’s sex?

Sex chromosomes.

What term describes a pair of chromosomes, one from each parent, carrying similar genes?

Homologous chromosomes.

How many pairs of chromosomes do humans have?

23 pairs (46 total).

What is a dominant allele?

An allele that is expressed when present in one or two copies.

What is a recessive allele?

An allele expressed only when two copies are present.

Define homozygous genotype.

Having two identical alleles for a gene (AA or aa).

Define heterozygous genotype.

Having two different alleles for a gene (Aa).

What does hemizygous mean?

Possessing only one allele for a gene (e.g., genes on the X chromosome in males).

Who is considered the father of modern genetics?

Gregor Mendel.

In Mendel’s pea experiments, what generation is produced by crossing true-breeding parents?

The F1 (first filial) generation.

What is the F2 generation?

Offspring produced by self- or cross-pollinating F1 individuals.

State Mendel’s Law of Segregation.

Two alleles for a character separate during gamete formation, so each gamete receives only one allele.

State Mendel’s Law of Independent Assortment.

Alleles of different genes assort independently during gamete formation (if genes are on different chromosomes or far apart).

What is hybridization in genetics?

Crossing two true-breeding organisms with contrasting traits.

What tool predicts offspring genotypic and phenotypic ratios from a cross?

A Punnett square.

What genotype ratio results from crossing two heterozygotes (Aa × Aa) under complete dominance?

1 AA : 2 Aa : 1 aa.

What phenotype ratio is expected from the same heterozygote cross (complete dominance)?

3 dominant : 1 recessive.

Define monohybrid cross.

A cross tracking one trait (one gene).

Define dihybrid cross.

A cross tracking two traits (two genes).

Which experiment first suggested a 'transforming principle' in bacteria?

Griffith’s experiment (1928).

Which scientists identified DNA as the transforming substance?

Avery, MacLeod, and McCarty.

Which experiment using bacteriophages confirmed DNA is the genetic material?

The Hershey–Chase experiment (1952).

What five conditions define Hardy–Weinberg equilibrium?

1) Very large population, 2) No mutations, 3) Random mating, 4) No migration, 5) Equal reproductive success for all alleles.

Write the Hardy–Weinberg allele frequency equation.

p + q = 1.

Write the Hardy–Weinberg genotype frequency equation.

p² + 2pq + q² = 1.

In Hardy–Weinberg, what does 2pq represent?

Frequency of the heterozygous genotype.

Define gene pool.

All alleles present in a population.

What is a point mutation?

A single-nucleotide substitution in DNA.

Differentiate silent, missense, and nonsense mutations.

Silent: no amino-acid change; Missense: changes one amino acid; Nonsense: introduces a stop codon.

What is a frameshift mutation?

Insertion or deletion of nucleotides altering the reading frame.

Name two large-scale chromosomal mutations.

Deletion and duplication (also inversion, insertion, translocation).

What is genetic leakage?

Gene flow between different species producing hybrids.

Define genetic drift.

Random changes in allele frequencies, pronounced in small populations.

What is the founder effect?

Extreme genetic drift when a small group becomes reproductively isolated, leading to reduced genetic diversity.

Summarize Darwin’s theory of natural selection.

Individuals with heritable traits that increase fitness are more likely to survive and reproduce, passing those traits on.

What is differential reproduction in neo-Darwinism?

Favorable genetic changes are passed on more frequently, altering the gene pool over time.

Define inclusive fitness.

An organism’s success based on its own offspring plus the impact it has on the reproductive success of relatives.

What does the punctuated equilibrium model propose?

Species experience long periods of stasis interrupted by rapid evolutionary change.

Describe stabilizing selection.

Selects against extreme phenotypes, maintaining intermediate traits (e.g., human birth weight).

Describe directional selection.

Favors one extreme phenotype, shifting the population distribution (e.g., antibiotic-resistant bacteria).

Describe disruptive selection.

Favors both extreme phenotypes over the intermediate (e.g., beak sizes in Galápagos finches).

What is speciation?

Formation of a new species capable of fertile offspring.

Define divergent evolution.

Related species evolve different traits due to different environments.

Define parallel evolution.

Related species evolve similarly under similar selective pressures.

Define convergent evolution.

Unrelated lineages independently evolve similar traits (e.g., dolphins and fish).

What is complete dominance?

Heterozygote exhibits the same phenotype as the homozygous dominant.

What is incomplete dominance?

Heterozygote phenotype is intermediate between the two homozygotes (e.g., pink snapdragons).

What is codominance?

Both alleles are expressed equally in the phenotype (e.g., AB blood type).

During which meiotic process does the law of segregation occur?

Anaphase I, when homologous chromosomes separate.

Which meiotic event underlies the law of independent assortment?

Random alignment of homologous chromosome pairs in metaphase I.

What is a character in Mendelian terminology?

A heritable feature that varies among individuals (e.g., flower color).

What is a trait in Mendelian terminology?

A specific variant of a character (e.g., purple flowers).

Explain true breeding.

Organisms that, when self-crossed, produce offspring identical for the trait in question.

Why did Mendel use large sample sizes?

To obtain reliable ratios and minimize the effects of chance.

What does p² + 2pq represent in Hardy–Weinberg?

The frequency of the dominant phenotype in the population.

Name the three major steps of gene expression from DNA.

Replication, transcription, and translation.

How does chromosomal crossing over contribute to genetic diversity?

By exchanging genetic material between homologous chromosomes during meiosis.

What is fitness in an evolutionary context?

An individual’s genetic contribution to future generations.

What is a gene?

A DNA segment coding for a functional RNA or protein.