Genetics Review

Genetics

The branch of biology concerned with heredity, focusing on the inheritance of traits between parents and offspring.

Chromosome

Units of genetic material that allow for sorting during cell division and gamete formation, containing tightly packed DNA and proteins.

DNA Replication

The process by which a double-stranded DNA molecule is duplicated, resulting in two identical copies (sister chromatids) joined at the centromere.

Centromere

A constricted region on a chromosome, serving as the point where sister chromatids are joined, and where kinetochores attach.

Telomeres

The protective ends of chromosomes.

Kinetochore

A protein complex that forms at the centromere and allows chromosomes to attach to spindle fibers during cell division.

Sister Chromatids

Two identical copies of a chromosome created during S phase, joined together at the centromere.

Somatic Cells

Body cells, as opposed to gametes (sex cells).

Diploid (2n)

A cell or organism containing two complete sets of chromosomes, one from each parent.

Homologous Chromosomes

A pair of chromosomes (one maternal, one paternal) that are similar in length, centromere position, and carry the same genes at corresponding loci, though alleles may differ.

Haploid (n)

A cell or organism containing a single set of chromosomes, such as gametes after meiosis.

Loci

The specific physical location of a gene or other DNA sequence on a chromosome.

Allele

Different versions or forms of a gene.

Genotype

The specific combination of alleles inherited by an organism for a particular gene or set of genes.

Cell Division

The process by which a parent cell divides into two or more daughter cells, facilitating the passage of genetic material to offspring.

Asexual Reproduction

A form of reproduction in which a single organism produces offspring that are genetically identical to itself, common in unicellular species and bacteria.

Sexual Reproduction

A form of reproduction involving the combination of genetic material from two parent cells (gametes) to create genetically diverse offspring.

Eukaryotic Cell Cycle

The ordered sequence of events that a eukaryotic cell passes through, consisting of Interphase (G1, S, G2) and M phase (mitosis/meiosis and cytokinesis).

Interphase

The longest phase of the cell cycle, during which the cell grows, synthesizes proteins, and replicates its DNA in preparation for cell division, composed of G1, S, and G2 phases.

G0 Phase

A quiescent stage where cells are not actively preparing for division or are terminally differentiated.

G1 Phase

The first growth phase of interphase, where the cell grows and prepares for DNA synthesis; includes a restriction point.

S Phase

The synthesis phase of interphase, where the cell's genetic material (DNA) is replicated.

G2 Phase

The second growth phase of interphase, where the cell continues to grow and synthesizes proteins and organelles needed for division.

Mitosis

A type of cell division that produces two genetically identical diploid somatic (body) cells from a single parent cell; essential for multicellularity, growth, and repair.

Prophase (Mitosis)

The first phase of mitosis where chromatin condenses into visible chromosomes, centrosomes move apart, microtubules begin to form, and the nuclear membrane starts to dissolve.

Prometaphase (Mitosis)

The phase of mitosis where the nuclear membrane fully fragments, centrosomes are at opposite poles, and kinetochore microtubules attach to the kinetochores of sister chromatids.

Mitotic Spindle Apparatus

A protein structure in eukaryotic cells that segregates chromosomes during cell division, composed of microtubules organized by centrosomes (spindle poles).

Spindle Pole

A centrosome containing two centrioles in animal cells, which serves as a microtubule organizing center.

Metaphase (Mitosis)

The phase of mitosis where sister chromatids align along the metaphase plate (equatorial plane) of the cell.

Anaphase (Mitosis)

The phase of mitosis in which sister chromatids separate, become individual chromosomes, and are pulled towards opposite poles of the cell by shortening kinetochore microtubules, while polar microtubules elongate to push the poles apart.

Telophase (Mitosis)

The final phase of mitosis where chromosomes reach the poles and decondense, and nuclear membranes reform around the separated sets of chromosomes.

Cytokinesis

The process of physical cell division, where the cytoplasm divides to form two daughter cells (in animals, via a contractile ring and cleavage furrow; in plants, via a cell plate).

Meiosis

A specialized type of cell division that reduces the chromosome number by half (from diploid to haploid), creating four genetically distinct haploid gametes (sex cells); crucial for sexual reproduction and genetic diversity.

Chiasma (plural: chiasmata)

The X-shaped structure that forms at the site of crossing over between homologous chromosomes during Prophase I of meiosis.

Crossing Over

The exchange of genetic material between non-sister chromatids of homologous chromosomes during Prophase I of meiosis, leading to genetic recombination and diversity.

Independent Alignment of Homologs (Metaphase I)

The random orientation and segregation of homologous chromosome pairs at the metaphase plate during Meiosis I, contributing to genetic diversity and forming the basis for Mendel's Law of Independent Assortment.

Meiosis I (Reductional Division)

The first meiotic division, characterized by the separation of homologous chromosomes, which halves the chromosome number and results in two haploid cells with duplicated chromosomes.

Meiosis II (Mitotic Division)

The second meiotic division, during which sister chromatids separate (similar to mitosis), maintaining the chromosome number per cell and resulting in four haploid cells with unduplicated chromosomes.

Prophase I (Meiosis)

The initial and longest phase of meiosis, characterized by chromosome condensation, synapsis (pairing) of homologous chromosomes into tetrads, and crossing over at chiasmata.

Metaphase I (Meiosis)

The phase of meiosis I where homologous chromosome pairs (tetrads) align independently along the metaphase plate.

Gametes

Haploid reproductive cells (sperm or egg) formed through meiosis, each containing one member of each homologous chromosome pair.

Mendelian Genetics

The study of inheritance patterns that follow Gregor Mendel's two laws: the Law of Segregation and the Law of Independent Assortment.

Blending Hypothesis of Inheritance

An outdated hypothesis proposing that hereditary factors from parents blend together in offspring, leading to intermediate phenotypes and a lack of variation, which Mendel disproved.

True Breeding

An organism that, when self-fertilized, always produces offspring with the same phenotype as the parent for a particular trait; indicates homozygosity for the alleles controlling that trait.

Selfing (Self-Fertilization)

The process of pollination where an organism pollinates itself or is fertilized by its own gametes.

Monohybrid Cross

A genetic cross between two parents that differ in only one character, often involving individuals that are heterozygous for that single gene (e.g., F1 x F1).

Law of Segregation

Mendel's first law, stating that the two copies of a gene (alleles) segregate (separate) from each other during gamete formation, so each gamete receives only one allele.

Homozygous

Having two identical alleles for a particular gene (e.g., AA or aa).

Heterozygous

Having two different alleles for a particular gene (e.g., Aa).

Test Cross

A genetic cross between an individual with a dominant phenotype of unknown genotype and a homozygous recessive individual, used to determine the genotype of the dominant individual.

Law of Independent Assortment

Mendel's second law, stating that alleles of two or more different genes assort independently of each other during gamete formation, meaning their inheritance patterns are not linked.

Dihybrid Cross

A genetic cross involving two different characters, typically between individuals that are heterozygous for both genes (e.g., F1 x F1 for two traits).

Pedigree Analysis

The study of an inherited trait in a family tree to determine its pattern of inheritance.

Autosomal Recessive Trait

A trait or disorder located on a non-sex chromosome that only manifests when an individual inherits two copies of the recessive allele, often skipping generations and affecting males and females with equal frequency.

Autosomal Dominant Trait

A trait or disorder located on a non-sex chromosome that manifests when an individual inherits at least one copy of the dominant allele, typically appearing in every generation and affecting males and females with equal frequency.

Probability

The chance that a specific outcome will occur, expressed as a number between 0 (never) and 1 (always).

Random Sampling Error

The deviation between