AGRI-376 Genetics - Comprehensive Vocabulary Flashcards :

Vocabulary flashcards covering chromosome structure, cell division, Mendelian transmission genetics, molecular and population genetics, and modifications of Mendelian ratios.

Reductional Division

The first meiotic division (Meiosis I) in which homologous chromosome pairs separate, reducing the chromosome number from diploid ($2n$) to haploid ($n$).

Equational Division

The second meiotic division (Meiosis II) in which sister chromatids separate into individual monads.

Synapsis

The pairing of homologous chromosomes during Prophase I of meiosis to form a tetrad.

Leptonema

The initial substage of meiotic Prophase I in which chromatin condenses into visible, thin chromosome threads.

Zygonema

The substage of meiotic Prophase I in which homologous chromosomes align and begin pairing through synapsis.

Pachynema

The substage of meiotic Prophase I in which chromosomes shorten and thicken, tetrads become fully formed, and crossing over occurs.

Diplonema

The substage of meiotic Prophase I in which synapsed homologous chromosomes pull apart slightly, revealing chiasmata where exchange took place.

Diakinesis

The final substage of meiotic Prophase I where non-sister chromatids detach, nucleoli and the nuclear envelope break down, and spindle fibers attach to kinetochores.

Spermatozoa

Mature male gametes produced through the complete process of spermatogenesis.

Oogenesis

The process of female gamete formation progressing from oogonium through primary and secondary oocytes, polar bodies, ootid, and mature ovum.

Monohybrid Cross

A genetic cross between parental individuals that differ in contrasting traits for a single character.

Selfing

The process of self-fertilization in an organism.

$P_1$ Generation

The original parental generation involved in a formal genetic cross.

$F_1$ Generation

The first filial generation resulting directly from crossing the $P_1$ generation.

$F_2$ Generation

The second filial generation produced by selfing or intercrossing individuals from the $F_1$ generation.

Phenotype

The observable physical appearance or functional trait of an organism resulting from its genetic makeup.

Genotype

The specific allelic composition or combination of genes present in an individual (e.g., $DD$, $Dd$, or $dd$).

Allele

An alternative form or variant of a single gene.

Homozygous

Having two identical alleles for a specific gene in an individual.

Heterozygous

Having two different alleles for a specific gene in an individual.

Principle of Segregation

Mendel's postulate stating that during gamete formation, paired unit factors (alleles) separate randomly so that each gamete receives one or the other with equal likelihood.

Principle of Independent Assortment

Mendel's postulate stating that during gamete formation, segregating pairs of unit factors (genes) assort independently of one another.

Testcross

A genetic cross between an individual expressing a dominant phenotype (unknown genotype) and a homozygous recessive individual.

Product Law

A probability rule stating that the combined probability of two or more independent events occurring simultaneously is equal to the product of their individual probabilities.

Nucleosome

A basic unit of chromatin structure consisting of a histone octamer complexed with 147 base pairs of DNA, forming a $6\,\text{nm} \times 11\,\text{nm}$ flat disc structure.

Solenoid

A coiled $30\,\text{nm}$ diameter chromatin structure formed by the interaction of nucleosomes with $H1$ histone proteins.

$G_1/S$ Checkpoint

A cell cycle control point that monitors cell size and DNA integrity prior to entering the S phase.

$G_2/M$ Checkpoint

A cell cycle control point that checks for DNA damage and verifies the completion of DNA replication before mitosis.

$M$ Checkpoint

A cell cycle control point that monitors spindle formation and proper attachment of spindle fibers to kinetochores.

Genetics

The branch of biology concerned with the study of inheritance, gene function, and variation across organisms.

Theory of Epigenesis

The historical concept proposed by William Harvey stating that an organism develops progressively from an egg rather than existing fully formed.

Preformation

The disproved historical belief that an individual exists preformed as a miniature human inside a gamete.

Central Dogma of Molecular Genetics

The core framework defining the directional flow of genetic information from DNA to RNA to protein.

Transmission Genetics

The subfield of genetics that analyzes patterns and rules of inheritance of traits passed between generations.

Cytogenetics

The subfield of genetics focused on the structural study of chromosomes as carriers of genetic material.

Molecular Genetics

The subfield of genetics dealing with the molecular structure, expression, regulation, and modification of genetic material.

Population Genetics

The subfield of genetics that investigates allele frequency distribution and genetic change in groups of organisms over generations.

Karyotype

A standardized visual array displaying an individual's paired chromosomes organized by size and structure.

Wild-type

The most commonly occurring phenotype or allele found in a natural population.

Incomplete Dominance

An inheritance condition in which neither allele is completely dominant, yielding an intermediate heterozygous phenotype.

Codominance

An inheritance pattern in which two alleles of a single gene produce distinct, fully detectable gene products simultaneously in a heterozygote.

Lethal Allele

A mutant allele in an essential gene that causes mortality in affected individuals.

Epistasis

A gene interaction in which the allele combination of one gene locus masks or alters the phenotypic expression of a second gene locus.

X-linkage

The mode of inheritance for genes physically located on the X chromosome.

Sex-influenced Trait

A hereditary trait whose phenotypic expression for a given genotype differs depending on the sex of the individual.

Position Effect

A change in the expression of a gene resulting from a alteration in its relative physical location on a chromosome.

Temperature Effect

An environmental modification where ambient temperature affects enzyme performance and alters phenotypic outcome.