Comprehensive Genetics: Pedigrees, Inheritance, Meiosis, and Reproduction

Comprehensive practice flashcards focusing on core vocabulary from lectures on Mendelian genetics, non-Mendelian inheritance patterns, pedigree analysis, meiotic stages, and eukaryotic/prokaryotic reproductive life cycles.

Pedigree

A visual diagram used to read, trace, and infer genetic information, family relationships, inheritance patterns, and individual genotypes across generations.

Pedigree Key - Male

The standard pedigree chart symbol represented by an open or unshaded square.

Pedigree Key - Female

The standard pedigree chart symbol represented by an open or unshaded circle.

Pedigree Key - Affected Individual

A pedigree symbol (square or circle) that is completely shaded or filled in, indicating the presence of the condition or trait being tracked.

Pedigree Key - Deceased Individual

A pedigree symbol crossed through with a diagonal slash mark to indicate that the person has died.

Pedigree Key - Parents (First Generation)

Individuals indicated by Roman numeral $I$ connected by a horizontal mating line.

Pedigree Key - Offspring (Second Generation)

Individuals designated by Roman numeral $II$ connected vertically below the parental generation line.

Proband

The affected individual through whom a family with a genetic disorder is first brought to the attention of a geneticist or physician, denoted in a pedigree by an arrow.

Autosomal Dominant Inheritance

An inheritance pattern governed by two rules: if an offspring is affected, at least one parent must also be affected, and the trait cannot skip generations.

Autosomal Recessive Inheritance

An inheritance pattern governed by the rule that if both parents are affected, all offspring will be affected; the trait can skip generations through unaffected carriers.

Sex (X)-Linked Dominant Inheritance

An inheritance pattern where every affected offspring has at least one affected parent, cannot skip generations, affected fathers transmit the trait to all daughters, and affected sons must have an affected mother.

Female Bias in X-Linked Dominant Traits

A tendency (not an absolute rule) for X-linked dominant traits to affect females more frequently than males because females possess two X chromosomes.

Sex (X)-Linked Recessive Inheritance

An inheritance pattern where if both parents are affected, all offspring are affected; if a mother is affected, all sons are affected; and if a daughter is affected, her father must also be affected.

Male Bias in X-Linked Recessive Traits

A tendency (not an absolute rule) for X-linked recessive traits to appear predominantly in males because they possess only a single X chromosome.

Sex (Y)-Linked Inheritance

An inheritance pattern in which all sons of an affected father will have the trait, no sons of an unaffected father will have it, and no females ever exhibit it.

Mitochondrial Inheritance

A maternal inheritance pattern where all offspring of an affected mother will inherit the trait, while an unaffected mother produces no affected offspring.

Deduction in Pedigree Analysis

The analytical strategy of eliminating impossible modes of inheritance by finding broken inheritance rules before deciding on the most probable pattern.

Genotyping Homozygous Recessives

The initial step in pedigree genotyping where all individuals expressing the recessive phenotype are immediately assigned two recessive alleles ($aa$).

Assigning Dominant Phenotypes in Pedigrees

The step in pedigree genotyping where every individual expressing the dominant trait is initially recorded as possessing at least one dominant allele ($A\text{?}$).

Resolving Heterozygotes in Pedigrees

The pedigree genotyping step where parents and offspring of homozygous recessive individuals ($aa$) are determined to carry at least one recessive allele ($Aa$).

Non-Mendelian Genetics

Forms of genetic inheritance that violate Mendel's classical laws, exhibiting atypical phenotypic ratios or non-nuclear transmission.

Incomplete Dominance

A pattern where two alleles produce an intermediate blended phenotype in a heterozygote (such as pink flowers from red and white parents) rather than one being fully dominant.

Codominance

A pattern where two different alleles in a heterozygote are expressed simultaneously and distinctively without blending.

Pleiotropy

A genetic condition wherein a single gene exerts effects on multiple distinct physical traits.

MC1R Gene

A pleiotropic gene that influences both red hair pigmentation and the presence of freckles in humans.

Lethal Alleles

Alleles causing genotypes that are fatal during embryonic development, removing them from living offspring counts and modifying expected phenotypic ratios.

Yellow Mouse Cross ($A^Y A \times A^Y A$)

A genetic cross exhibiting a $2\text{ yellow} : 1\text{ brown}$ phenotypic ratio among survivors due to embryonic lethality in homozygous $A^Y A^Y$ individuals.

Polygenic Inheritance

The additive control of a single continuous trait (such as human height) by multiple independent genes, producing a normal distribution or bell curve.

Epistasis

A genetic phenomenon in which one gene masks or interferes with the phenotypic expression of a completely separate gene.

Dominant Epistasis

A type of epistasis wherein having at least one dominant allele at an epistatic locus masks the expression of another gene, yielding a $12:3:1$ phenotypic ratio.

Recessive Epistasis

A type of epistasis where homozygous recessive alleles at one locus mask the phenotype at a second locus, producing a $9:3:4$ ratio (e.g., $9/16$ agouti, $3/16$ black, $4/16$ albino mice).

Complementary Genes

A form of epistasis where recessive alleles of different genes produce the identical phenotype, requiring both genes to carry a dominant allele for the trait to be expressed.

Bombay Blood Phenotype

A condition caused by homozygous recessive alleles ($hh$) failing to form the H-antigen precursor, which masks the expression of ABO blood group alleles and makes the individual test as type O.

Sex Linkage

The pattern of inheritance and expression of genes carried specifically on the sex chromosomes, resulting in different frequencies between sexes.

Maternal Effects

An inheritance phenomenon in which an offspring's phenotype is determined solely by the nuclear genotype of its mother rather than its own genotype (e.g., snail shell coiling).

Chloroplast Inheritance

A cytoplasmic non-Mendelian inheritance mechanism where chloroplast DNA is inherited exclusively through maternal cytoplasm, as observed in Four O'clock (Mirabilis) plant leaf coloration.

Organellar Heterogeneity

The absence of a mitotic-like partitioning mechanism for organellar DNA, resulting in daughter cells having varying mixtures of non-identical mitochondria or chloroplasts.

Twin Studies

Studies comparing identical twins sharing identical genetic makeup to determine whether phenotypic differences result from environmental factors ('nature vs. nurture').

Complete Penetrance

A condition in which $100\%$ of individuals with a given genotype express the corresponding phenotype.

Incomplete Penetrance

A condition in which less than $100\%$ of individuals carrying a specific genotype exhibit the associated phenotype.

Gregor Mendel (1866)

The Austrian monk and 'Father of Genetics' who discovered Mendelian inheritance by proposing that inheritance in pea plants is governed by the pairing of invisible factors (chromosomes).

Frederick Griffith (1928)

The scientist who demonstrated through bacterial transformation experiments that DNA carries genetic information.

Telomere

The repetitive nucleotide structure located at the ends of a chromosome that protects it from degradation.

Centromere

The constricted chromosomal region that links sister chromatids together and serves as an attachment site for spindle fibers.

Chromosome Short Arm (p)

The shorter arm of a eukaryotic chromosome extending from the centromere, conventionally designated by the letter 'p'.

Chromosome Long Arm (q)

The longer arm of a eukaryotic chromosome extending from the centromere, conventionally designated by the letter 'q'.

Sister Chromatids

Identical copies of a single replicated chromosome joined together at a common centromere.

Nucleotide

The monomer building block of nucleic acids, consisting of a nitrogenous base, a sugar, and a phosphate group.

Codon

A sequence of three nucleotides on DNA or RNA that codes for a specific amino acid.

Chromosome

A single, continuous strand of organized DNA containing multiple genes.

Homologous Chromosomes

Pairs of maternal and paternal chromosomes having the same genes at the same loci, but possibly different alleles.

Genome

The complete set of genetic material and instructional DNA contained within an organism.

Gene

The basic physical and functional unit of inheritance, defined as a specific locus on a chromosome.

Allele

A specific variant or alternative form of a gene located at a given chromosomal locus.

Trait

A physical, anatomical, or physiological characteristic of an organism resulting from genes, alleles, and environmental interaction.

Law of Dominance

Mendel's principle stating that some alleles are dominant and will mask the presence of recessive alleles in a heterozygote.

Dominant Allele

An allele that is always phenotypically expressed whenever it is present in an individual.

Recessive Allele

An allele that is phenotypically expressed only in the absence of a dominant allele.

Genotype

The specific underlying genetic makeup or allelic composition of an organism (e.g., $Dd$ or $pp$).

Phenotype

The observable physical characteristics or expressed traits of an organism (e.g., purple flowers or dwarfism).

Homozygous Dominant

A genotype possessing two identical dominant alleles for a given gene locus (e.g., $DD$).

Heterozygous

A genotype possessing one dominant and one recessive allele for a gene locus (e.g., $Dd$).

Homozygous Recessive

A genotype possessing two identical recessive alleles for a gene locus (e.g., $dd$).

Achondroplasia

An autosomal dominant form of dwarfism where affected individuals possess the heterozygous genotype ($Dd$).

True-Breeding Plants

Organisms homozygous for a trait ($PP$ or $pp$) that consistently produce offspring with the same phenotype when self-pollinated.

Law of Segregation

Mendel's law stating that only one of the two gene copies present in an organism is distributed to each gamete during meiosis.

$F_1$ Generation Monohybrid Cross

A cross between homozygous dominant ($PP$) and homozygous recessive ($pp$) parents that produces $100\%$ heterozygous ($Pp$) purple offspring.

$F_2$ Generation Monohybrid Cross

A cross between two heterozygous monohybrids ($Pp \times Pp$) that yields a $3:1$ phenotypic ratio ($3\text{ purple} : 1\text{ white}$) and a $1:2:1$ genotypic ratio.

Law of Independent Assortment

Mendel's law stating that the segregation of alleles for one gene occurs completely independently of the segregation of alleles for another gene.

FOIL Method (Gamete Finding)

A mnemonic method (First, Outside, Inside, Last) used to determine all four possible gamete combinations from a dihybrid genotype ($RrYy$).

Dihybrid Cross Phenotypic Ratio

The classical $9:3:3:1$ phenotypic ratio resulting from a cross between two individuals heterozygous for two unlinked traits ($RrYy \times RrYy$).

Dihybrid Cross Product Rule Shortcut

Calculating the probability of a multi-gene genotype by multiplying independent monohybrid probabilities (e.g., $\frac{1}{4} \times \frac{1}{4} = \frac{1}{16}$ for $rryy$).

Huntington's Disease

An autosomal dominant neurodegenerative disorder characterized by enlargement of frontal horns of lateral ventricles, symptom onset between ages $30\text{--}50$, and death within $15\text{--}20$ years.

GEDmatch

An open genetic database that pulls data from consumer testing services (like 23andMe and AncestryDNA) used by investigators to identify the Golden State Killer via relatives' DNA.

Meiosis

A specialized cell division process that halves the chromosome number ($2N \rightarrow 1N$) to produce four genetically diverse haploid daughter cells.

Pre-Meiotic Interphase

The cell cycle preparation phase consisting of G1, S phase (during which chromosomes duplicate), and G2 prior to meiosis.

Meiosis I

The reductional division stage of meiosis ($2N \rightarrow 1N$) characterized by homologous chromosome pairing, crossing over, and independent assortment.

Synaptonemal Complex

A protein structure that forms between homologous chromosomes during Prophase I to hold them tightly together for crossing over.

Recombination (Crossing Over)

The exchange of genetic material between non-sister chromatids of homologous chromosomes during Prophase I to increase genetic diversity.

Chiasma

The X-shaped anatomical site where homologous non-sister chromatids remain in contact and crossover after the synaptonemal complex dissolves.

Metaphase I

The stage of Meiosis I where homologous pairs (tetrads) align randomly along the equatorial metaphase plate.

Independent Assortment Gamete Combinations ($2^n$)

The mathematical calculation of possible gamete combinations based on homologous pair alignment; in humans with $23$ pairs, it yields $2^{23} = 8{,}388{,}608$ unique combinations.

Anaphase I

The meiotic stage where homologous chromosomes separate and move toward opposite poles while sister chromatids remain attached at their centromeres.

Telophase I

The stage ending Meiosis I where chromosomes decondense and new nuclei form around newly haploid ($n=2$ in model diagrams) sets of chromosomes.

Meiosis II

The equational division stage of meiosis, practically identical to mitosis, which separates sister chromatids in haploid cells without further DNA replication.

Anaphase II

The phase of Meiosis II during which sister chromatids finally separate and move to opposite spindle poles.

Spermatogenesis

The process of male gamete production in the testes that generates four functional haploid sperm from one diploid primary spermatocyte.

Oogenesis

The process of female gamete formation in ovaries that yields one functional haploid ovum (egg) and three non-functional polar bodies from a primary oocyte.

Gene Linkage

The phenomenon where genes located physically close together on the same chromosome are unlikely to be separated by recombination and fail to assort independently.

Nondisjunction

The failure of homologous chromosomes to separate in Anaphase I or sister chromatids in Anaphase II, producing gametes with abnormal numbers ($n+1$ or $n-1$).

Pseudoautosomal Region

A small homologous segment shared between X and Y chromosomes that pairs and undergoes crossing over during male meiosis.

Asexual Reproduction

A mode of reproduction involving one parent that yields genetically identical offspring without gamete fusion.

Binary Fission

A type of asexual cell division in prokaryotes where a single cell splits into two identical daughter cells.

Sexual Reproduction

A reproductive mechanism involving two parents that combines genetic material via meiosis and fertilization to produce genetically varied offspring.

Bacterial Conjugation

A horizontal DNA transfer process in prokaryotes where a mobile plasmid is transferred from a donor bacterium to a recipient bacterium through a pilus, relaxosome, and transferosome.

Allosomes

Chromosomes that determine the biological sex of an organism (the sex chromosomes, such as X and Y in humans).

Autosomes

Chromosomes that do not determine biological sex (pairs 1 through 22 in humans).

Haploid ($1N$)

A cell or organism possessing only one single copy of each chromosome.

Diploid ($2N$)

A cell or organism possessing two homologous copies of each chromosome, one maternal and one paternal in origin.

Fertilization

The fusion of haploid male and female gametes (sperm and egg) to produce a single diploid zygote.