Mendelian Genetics and Cytogenetics Review

Comprehensive vocabulary flashcards covering Mendelian principles, cell division, cytogenetics, sex linkage, non-Mendelian inheritance, and pedigree analysis.

Hybridization

Breeding between two individuals that have different characteristics.

Hybrids

The offspring that result from a cross between two individuals with different characteristics.

Self-fertilization

A breeding process where pollen and egg are derived from the same plant.

Cross-fertilization

A breeding process where pollen and egg are derived from two different plants.

Monohybrid Cross

A genetic cross in which a single characteristic is observed between two pure-bred parental strains with contrasting traits.

Gene

An inherited factor (region of DNA) that helps determine a characteristic.

Allele

One of two or more alternative forms of a gene.

Locus

A specific place on a chromosome occupied by an allele.

Genotype

The set of alleles possessed by an individual organism.

Homozygote

An individual organism possessing two of the same alleles at a locus.

Heterozygote

An individual organism possessing two different alleles at a locus.

Phenotype

The appearance or manifestation of a characteristic or trait.

Characteristic

An attribute or feature possessed by an organism, such as eye color or seed shape.

Principle of Segregation

Mendel's first law stating that each individual diploid organism possesses two alleles for any particular characteristic, which segregate when gametes are formed so that one allele goes into each gamete.

Concept of Dominance

The principle stating that when two different alleles are present in a genotype, only the trait encoded by the dominant allele is observed in the phenotype.

Punnett Square

A grid proposed by Reginald Punnett that enables prediction of the relative genotypic and phenotypic proportions of offspring from a genetic cross.

Probability

The likelihood of the occurrence of a particular event, calculated as the number of times an event occurs divided by the number of all possible outcomes.

Multiplication Rule

A rule of probability stating that the probability of two or more independent events taking place together is calculated by multiplying their independent probabilities.

Addition Rule

A rule of probability stating that the probability of any one of two or more mutually exclusive events taking place is calculated by adding their individual probabilities.

Testcross

A genetic cross used to test whether an individual with a dominant phenotype is homozygous or heterozygous by crossing it with a homozygous recessive individual.

Dihybrid Cross

A genetic cross in which two different characteristics are observed simultaneously.

Principle of Independent Assortment

Mendel's law stating that alleles at different loci separate independently of one another during gamete formation, applying to loci on different chromosomes.

Goodness of Fit Chi-Square Test

A statistical test used to evaluate the probability that the difference between observed and expected outcomes is due to chance, calculated using $\chi^2 = \sum \frac{(\text{observed} - \text{expected})^2}{\text{expected}}$

Null Hypothesis

A statistical hypothesis asserting that there is no real difference between observed ratios and expected ratios, and any deviation is due to chance.

Alternative Hypothesis

A statistical hypothesis asserting that there is a real, significant difference between observed ratios and expected ratios.

Degrees of Freedom

A statistical parameter calculated as $df = n - 1$, where $n$ represents the number of different expected observation categories or phenotypes.

Pedigree

A pictorial representation of a family history (family tree) outlining the inheritance of one or more characteristics across generations.

Proband

The first affected family member coming to the attention of a geneticist, from whom a pedigree is initiated.

Genome

The complete set of genetic instructions for an organism, composed of either RNA or DNA.

Transmission Genetics

The subdiscipline of genetics focusing on how an organism inherits and passes its genes to the next generation.

Molecular Genetics

The subdiscipline of genetics focusing on the chemical nature of the gene itself, including encoding, replication, and expression.

Population Genetics

The subdiscipline of genetics exploring the genetic composition of groups of individual members of the same species and how that composition changes over time.

Model Genetic Organisms

Organisms with specific characteristics—such as short generation times, numerous progeny, and ease of lab rearing—that make them useful for genetic analysis.

Diploid

Refers to cells or organisms possessing two sets of chromosomes organized as homologous pairs ($2n$).

Haploid

Refers to cells or organisms possessing a single set of chromosomes ($1n$).

Karyotype

The complete set of chromosomes possessed by an individual organism.

Autosomes

Paired non-sex chromosomes that have the same length and shape in both males and females.

Sex Chromosomes

A pair of chromosomes that differ in size or shape between sexes and determine the sex of an organism.

Centromere

The primary constricted region of a chromosome where sister chromatids are joined, kinetochores form, and spindle microtubules attach.

Telomeres

The stable ends or tips of a linear chromosome.

Origins of Replication

Specific sites on a chromosome where DNA synthesis begins.

Kinetochore

A protein complex that assembles at the centromere during mitosis and meiosis to attach spindle microtubules.

Metacentric Chromosome

A chromosome with its centromere located in the middle, resulting in two arms of equal length.

Submetacentric Chromosome

A chromosome with its centromere positioned between the middle and one end.

Acrocentric Chromosome

A chromosome with its centromere positioned close to one end.

Telocentric Chromosome

A chromosome with its centromere located at the very end.

Mitosis

Process of nuclear and cell division resulting in two daughter cells that are genetically identical to the parent cell.

Meiosis

Process of cell division consisting of two divisions that produces four daughter cells, each containing half the chromosome number of the parent cell and genetically distinct.

Synapsis

The close pairing association of homologous chromosomes occurring during prophase I of meiosis to form tetrads.

Chiasmata

Specific locations on homologous chromosomes where crossing over occurs between non-sister chromatids.

Aneuploidy

A change in the number of individual chromosomes, leading to an abnormal chromosome count.

Nondisjunction

The failure of homologous chromosomes or sister chromatids to separate properly during meiosis or mitosis.

Nullisomy

A form of aneuploidy involving the loss of both members of a homologous pair of chromosomes, represented as $2n - 2$.

Monosomy

A form of aneuploidy involving the loss of a single chromosome, represented as $2n - 1$.

Trisomy

A form of aneuploidy involving the gain of a single chromosome, represented as $2n + 1$.

Tetrasomy

A form of aneuploidy involving the gain of two homologous chromosomes, represented as $2n + 2$.

Heterogametic Sex

The gender that produces two different types of gametes with respect to sex chromosomes.

Homogametic Sex

The gender that produces gametes that are all uniform with respect to sex chromosomes.

Hemizygous

Possessing only a single copy of an allele or locus, such as males for X-linked genes.

Genic Sex-Determining System

A sex determination system where sex is specified by genotypes at one or more loci without distinct sex chromosomes.

SRY Gene

The primary Sex-determining Region Y gene in mammals located on the Y chromosome that causes gonads to develop into testes.

Klinefelter Syndrome

A human condition resulting from an $XXY$ (or $XXYY$, $XXXY$) chromosomal phenotype, characterized by male traits, tall stature, small testes, and reduced hair.

Turner Syndrome

A human condition in females resulting from an $XO$ chromosomal phenotype, characterized by short stature, low hairline, broad chest, and neck folds.

Sex-Linked Characteristics

Traits determined by genes located on the sex chromosomes (X or Y).

Dosage Compensation

Mechanisms that equalize the amount of protein expressed by X-linked genes in males and females.

Barr Body

An inactivated, highly condensed X chromosome observed in female mammalian cells.

Lyon Hypothesis

The proposal that one X chromosome is randomly inactivated in each cell of female mammals during embryonic development.

Epistasis

A gene interaction in which one gene masks or suppresses the phenotypic effect of a gene at a different locus.

Recessive Epistasis

A gene interaction where two recessive alleles at one locus mask the expression of alleles at a second locus, yielding a $9 : 3 : 4$ ratio in an $F_2$ dihybrid cross.

Dominant Epistasis

A gene interaction where a single dominant allele at one locus suppresses the phenotypic expression of alleles at another locus, yielding a $12 : 3 : 1$ ratio in an $F_2$ cross.

Duplicate Recessive Epistasis

A gene interaction where recessive alleles at either of two loci mask the dominant phenotype, yielding a $9 : 7$ ratio in an $F_2$ cross.

Cytoplasmic Inheritance

Inheritance of characteristics encoded by genes in organelle DNA (mitochondria or chloroplasts), which are passed exclusively from the maternal parent.

Genetic Maternal Effect

An inheritance pattern where the phenotype of the offspring is determined by the nuclear genotype of the mother, regardless of the offspring's own genotype.

Genomic Imprinting

An epigenetic phenomenon in which expression of a gene is differentially affected depending on whether it is inherited from the male or female parent.

Complete Dominance

A dominance relationship in which the phenotype of the heterozygote is identical to the phenotype of one of the homozygotes.

Incomplete Dominance

A dominance relationship in which the phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes.

Codominance

A dominance relationship in which the phenotype of the heterozygote simultaneously exhibits the phenotypes of both homozygotes.

Penetrance

The percentage of individuals possessing a particular genotype that express the expected phenotype.

Expressivity

The degree or extent to which a trait is expressed phenotypically in an individual possessing a given genotype.