Genetics and Population Genetics Lecture Review

Comprehensive vocabulary flashcards covering classical Mendelian inheritance, linkage mapping, population genetics, evolutionary dynamics, and molecular evolution.

Blending theory

An old idea that offspring are an average of the parents, which fails because variation would dilute until everyone looked the same, and blended traits could never re-separate.

Spermist theory

An old idea proposing that a tiny preformed organism resides inside the sperm and is delivered to the egg.

Selfing

The process of fertilizing a plant with its own pollen, where male and female gametes originate from the same plant.

True-breeding (pure-breeding)

A strain that consistently produces the same phenotype when selfed because it is homozygous for that trait.

Particulate inheritance

Mendel's key insight that genes act as physical particles that come in pairs (diploid), separate into individual gametes (haploid), and do not blend.

Law of Segregation

Mendel's law stating that the two alleles of a gene separate during gamete formation, such that each gamete receives one allele with equal ($\frac{1}{2}$) probability.

Physical basis of segregation

The physical separation of homologous chromosomes during meiosis I.

Law of Independent Assortment

Mendel's law stating that alleles of different genes segregate into gametes independently of one another, which applies to genes located on different chromosomes or very far apart.

Physical basis of independent assortment

The independent alignment and separation of different homologous chromosome pairs during meiosis I.

Gene

The fundamental unit of heredity that carries genetic information from one generation to the next.

Allele

One of the alternative forms of a gene, defined by the specific DNA sequence at a given locus.

Locus

The physical position or place on a chromosome where a particular gene is located.

Genotype

The specific combination of alleles that an individual possesses for one or more genes.

Phenotype

The observable characteristics and traits of an organism, representing the outward manifestation of its genotype.

Gamete

A specialized haploid reproductive cell, such as an egg or a sperm cell.

Zygote

A diploid cell produced by the fusion of two haploid gametes (egg and sperm).

Test cross

A genetic cross between an individual of unknown genotype exhibiting a dominant phenotype and a homozygous recessive individual, used to reveal the unknown parent's gametes.

Product rule

A probability rule stating that the probability of two independent events both occurring (AND) is calculated by multiplying their individual probabilities.

Sum rule

A probability rule stating that the probability of either one of two mutually exclusive events occurring (OR) is calculated by adding their individual probabilities.

Walther Flemming

Scientist who stained chromatin and first described mitosis, demonstrating that chromosomes split and separate during somatic cell division.

Walter Sutton

Scientist who studied meiosis in grasshoppers ($11$ pairs plus an accessory sex chromosome) and proposed that chromosomes serve as the physical basis of Mendel's laws.

Thomas Hunt Morgan

Scientist who studied Drosophila, discovered a white-eyed mutant male, demonstrated that the white gene is X-linked, and investigated genetic linkage.

Reciprocal cross

A pair of genetic crosses where the phenotypes of the male and female parents are reversed, which yields differing phenotypic ratios between sexes for X-linked traits.

Linkage

The condition where genes located close together on the same chromosome tend to be inherited together, producing parental phenotypic classes more frequently than recombinant classes.

Parental (nonrecombinant) gametes

Gametes carrying the identical allele combinations present in the chromosomes inherited by an $F_1$ individual from its parents.

Recombinant gametes

Gametes possessing novel combinations of alleles produced as a result of crossing over between linked genes.

Crossing over

The physical exchange of chromosomal segments between non-sister chromatids of homologous chromosomes occurring during prophase I of meiosis.

Creighton & McClintock experiment

A landmark study in maize chromosome 9 featuring a physical knob and interchange, demonstrating that genetic recombination corresponds directly to physical crossing over.

Recombination frequency (RF)

A quantitative value calculated as the total number of recombinant progeny divided by the total progeny, multiplied by $100$.

Map unit (centiMorgan, cM)

A standard unit of relative genetic distance where $1\%$ recombinant progeny equals $1$ map unit.

Population genetics

The study of how genes and alleles are transmitted and how their frequencies change within a population over generations.

Evolution (population genetics definition)

Any change in allele or genotype frequencies within a population over time.

Gene pool

The complete set of all alleles present among the breeding individuals of a population.

Hardy-Weinberg equilibrium

A state in which observed genotype frequencies match expectations ($p^2$, $2pq$, $q^2$) derived from random mating, with allele and genotype frequencies remaining constant.

Genetic drift

Random fluctuations in allele frequencies that occur due to chance sampling of gametes, survival, and mating events in finite populations.

Fixation

The point at which a specific allele reaches a frequency of $100\%$ in a population, leading to the total loss of alternative alleles.

Population bottleneck

A sharp reduction in population size to a small number of surviving individuals, resulting in a dramatic loss of genetic variation.

Fitness

The relative reproductive success of a specific genotype within a particular environmental context.

Directional selection

Selection that consistently shifts an allele's frequency in one direction, encompassing positive selection and purifying selection.

Positive selection

A mode of natural selection where an advantageous allele confers higher fitness and consequently increases in frequency over time.

Purifying (negative) selection

A form of natural selection that eliminates harmful or deleterious alleles from a population.

Balancing selection

Natural selection that preserves multiple alleles and genetic diversity within a population, often via heterozygote advantage.

Haplotype

A specific combination of linked alleles situated along a single chromosome region.

Single nucleotide polymorphism (SNP)

A variation between haplotypes characterized by a difference in a single nucleotide position.

Linkage equilibrium

A state in which haplotype frequencies equal the product of individual allele frequencies, represented by $f(AB) = f(A) \times f(B)$.

Linkage disequilibrium (LD)

A state where observed haplotype frequencies deviate from random expectation, causing specific combinations of alleles to occur together more often than expected.

Selective sweep

The rapid rise in frequency of a favored allele that pulls its surrounding haplotype along, leaving a signature of reduced diversity and high-frequency long haplotypes.

Hitchhiking

The process by which neutral alleles increase in frequency solely because they are physically linked to an allele undergoing positive selection.

Neutral theory

The concept that the vast majority of genetic substitutions that become fixed in populations have no effect on fitness and spread via random genetic drift rather than natural selection.

Synonymous substitution

A nucleotide substitution within a coding sequence that alters a codon but does not change the specified amino acid.

Nonsynonymous substitution

A nucleotide substitution in a coding sequence that alters the codon to specify a different amino acid.

Conservative amino acid substitution

The replacement of an amino acid with another that possesses similar chemical properties, making the change more likely to be neutral.

Molecular clock

The hypothesis that neutral genetic substitutions accumulate at an approximately constant rate, making sequence divergence proportional to divergence time.

Unequal crossing over

A mechanism of gene duplication occurring when misaligned repetitive sequences during meiosis yield one chromosome with a gene duplication and one with a deletion.

Fetal hemoglobin

A specialized hemoglobin tetramer ($\alpha_2\gamma_2$) that exhibits higher oxygen affinity than adult hemoglobin ($\alpha_2\beta_2$), facilitating oxygen transfer from maternal blood to the fetus.