Genetics and Cellular Reproduction

Vocabulary practice flashcards covering meiosis, chromosomal inheritance, Mendelian genetics, non-Mendelian traits, and genetic disorders.

Meiosis

The eukaryotic form of sexual reproduction occurring in gametes that produces genetically diverse haploid ($n$) daughter cells from a diploid ($2n$) parent cell.

Gametes

Specialized reproductive cells produced through meiosis; specifically sperm produced in the testes in males and eggs produced in the ovaries in females.

Haploid ($n$)

The chromosome condition of a cell containing only $1$ copy of each chromosome ($23$ chromosomes in humans), characteristic of gametes.

Diploid ($2n$)

The chromosome condition of a cell containing $2$ copies of each chromosome ($46$ chromosomes in humans), characteristic of parent and somatic cells.

Eukaryotic Cell Cycle

The process of growth and division for eukaryotic cells that allows for the production of new cells, consisting of Interphase, Meiosis 1, and Meiosis 2.

Interphase

The cell preparation phase and longest phase of the cell cycle, divided into Gap 1 ($G_1$), Synthesis ($S$), and Gap 2 ($G_2$). It does not occur between Meiosis 1 and Meiosis 2.

Gap 1 ($G_1$)

The stage of Interphase characterized by cell growth and general organelle replication.

Synthesis ($S$)

The stage of Interphase during which DNA replication occurs to produce exact chromosome copies.

Gap 2 ($G_2$)

The stage of Interphase focused on division-specific organelle preparation and final cell division prep.

Homologous Chromosomes

Chromosomes that carry alleles for the same traits in the identical gene order and location.

Tetrad

A pair of homologous chromosomes aligned closely together during Prophase 1 of meiosis.

Crossing Over

The exchange of alleles for the same traits between homologous chromosomes during Prophase 1, generating recombinant chromatids.

Metaphase 1

The stage of Meiosis 1 where homologous chromosome pairs (tetrads) line up along the middle (equator) of the cell.

Anaphase 1

The stage of Meiosis 1 where homologous chromosome pairs separate and duplicated chromosomes move toward opposite poles of the cell.

Anaphase 2

The stage of Meiosis 2 where duplicated chromosomes separate at the centromere, pulling sister chromatids (unduplicated chromosomes) to opposite sides.

Karyotype

A genetic tool and visual display representing the chromosome number and physical appearance within a cell nucleus ($46$ chromosomes or $23$ pairs in a normal human).

Autosomes

Non-sex chromosomes (chromosome pairs $1$ through $22$, or chromosomes $1$ through $44$ in humans) that carry traits with no gender bias.

Sex Chromosomes

The pair of chromosomes responsible for determining biological sex in humans ($XX$ for females and $XY$ for males).

Nondisjunction

The failure of homologous chromosome pairs or sister chromatids to separate properly during meiosis, resulting in gametes with abnormal chromosome numbers.

Amniocentesis

A prenatal diagnostic procedure that samples amniotic fluid to provide definitive testing for chromosomal number mutations.

Down Syndrome (Trisomy 21)

A chromosomal condition caused by nondisjunction resulting in an extra third copy of chromosome $21$.

Turner Syndrome

A chromosomal condition denoted by the absence of a second sex chromosome, leaving the individual with a single X chromosome ($XO$) and a female genetic sex.

Klinefelter's Syndrome

A chromosomal condition characterized by the presence of an extra X chromosome in males, yielding an $XXY$ genotype.

Gene

A portion of a DNA molecule that serves as the basic unit of heredity by coding for specific proteins.

Gene Expression

The appearance in a phenotype of a characteristic or effect attributed to the activation and protein production of a particular gene.

Epigenetics

Heritable changes in organisms caused by the modification of gene expression rather than alteration of the underlying genetic code itself.

Genotype

The two-allele genetic makeup that represents the specific gene combination possessed for a trait (e.g., $BB$, $Bb$, or $bb$).

Phenotype

The observable outward physical expression or trait resulting from an organism's genotype.

Homozygous (Purebred)

Having two identical alleles for a particular gene (such as $AA$ or $aa$).

Heterozygous (Hybrid)

Having two different alleles for a particular gene (such as $Aa$).

Rule of Dominance

The Mendelian principle stating that one allele can conceal or mask the phenotypic expression of another allele when both are present.

Dominant Allele

An allele that is always expressed in the phenotype when at least one copy is present, represented by a capital letter.

Recessive Allele

An allele whose phenotypic effect is masked in the presence of a dominant allele and is only expressed when homozygous, represented by a lowercase letter.

Carrier

A heterozygous individual ($Aa$) who carries a recessive allele without displaying the associated phenotype or disease.

Punnett Square

A diagrammatic grid used to calculate the mathematical probabilities of potential genotypic and phenotypic outcomes resulting from a genetic cross.

Monohybrid Cross

A genetic breeding experiment tracking the inheritance of a single trait between two parent organisms.

Dihybrid Cross

A genetic cross examining the simultaneous inheritance of two distinct traits, typically producing a $9:3:3:1$ phenotypic ratio when both parents are heterozygous.

Pedigree

A chart depicting the lineage and occurrence of phenotypic traits across several generations of a family.

Pedigree Symbols

Standard genealogical notations where squares represent males, circles represent females, fully shaded shapes represent affected individuals, and half-shaded shapes represent carriers.

Autosomal Recessive Inheritance

A pattern of inheritance for traits on autosomes that often skip generations, affect males and females equally, and require two mutant alleles ($aa$) for expression.

Autosomal Dominant Inheritance

A pattern of inheritance for traits on autosomes that appear in every generation, affect both sexes equally, and require only one dominant allele ($AA$ or $Aa$) to express the phenotype.

Sex-Linked Recessive Inheritance

An inheritance pattern located on the X chromosome that skips generations, affects males disproportionately, and cannot be passed directly from an affected father to his sons.

Cystic Fibrosis

An autosomal recessive disorder caused by a CFTR protein mutation that blocks chloride ion passage, leading to thick, sticky mucus buildup and chronic lung infections.

Sickle Cell Anemia

An autosomal recessive disorder caused by a point mutation in the hemoglobin gene resulting in deformed, sickle-shaped red blood cells.

Sickle Cell Trait

The heterozygous genotype ($Aa$) for sickle hemoglobin that provides an evolutionary survival advantage against malaria without causing sickle cell disease.

Huntington's Disease

An autosomal dominant disorder ($AA$ or $Aa$) with middle-age onset caused by a defective gene leading to progressive nerve cell breakdown in the brain.

Hemophilia

A sex-linked recessive disorder characterized by a mutation that impairs the production of functional blood clotting factor protein.

Red-Green Colorblindness

A sex-linked recessive genetic mutation that impairs the function of red- and green-light-sensitive cone cells in the retina.

Incomplete Dominance

A non-Mendelian inheritance pattern where the dominant allele does not completely mask the recessive allele, producing a blended intermediate heterozygous phenotype (e.g., pink snapdragons).

Codominance

A non-Mendelian inheritance pattern where two distinct alleles are both fully dominant and expressed simultaneously and equally in heterozygotes (e.g., roan cattle).

Multiple Alleles

An inheritance condition in which three or more alternative forms of a gene exist in the population, though an individual carries only two (e.g., human ABO blood groups $I^A$, $I^B$, and $i$).

Polygenic Inheritance

A pattern of inheritance where a single phenotypic trait is controlled by the additive effects of two or more distinct genes, resulting in continuous variation (e.g., skin color, height).

Rh Factor

A distinct surface protein on red blood cells first identified in Rhesus monkeys that classifies blood as either Rh positive ($Rh+$) or Rh negative ($Rh-$).