Genetic Terms and Concepts Notes

Definitions of Key Terms

Allele

• Different forms of a gene resulting from mutations, located at the same position on a chromosome.

Chromosome

• Structures composed of DNA and proteins carrying genetic information in the form of genes.

Centromere

• The region where two sister chromatids are joined together on a chromosome.

Cytokinesis

• The process in the final phase of cell division where the cytoplasm splits, leading to two daughter cells.

Diploid

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

Gametes

• Reproductive cells (sperm and egg) carrying half the genetic material of a parent.

Haploid

• A cell or organism with a single set of chromosomes, typically found in gametes.

Homologous Chromosomes

• Pairs of chromosomes from each parent that are similar in shape, size, and genetic content.

Interphase

• The cell cycle phase characterized by cell growth, DNA replication, and preparation for division.

M-phase

• The phase where mitosis or meiosis occurs, leading to the division of the nucleus and cytoplasm.

Meiosis

• Cell division resulting in four haploid cells with half the chromosome number.

Mitosis

• Cell division leading to two identical diploid daughter cells.

Nuclear DNA

• DNA found in the nucleus that codes for genetic information.

Plasmid

• A small circular DNA molecule found in bacteria, separate from chromosomal DNA.

S-phase

• The phase of interphase during which DNA is replicated.

Genetic Concepts

Sexual Reproduction

• Involves the fusion of two gametes producing genetically diverse offspring.

Asexual Reproduction

• Does not involve gametes; offspring are genetically identical to the parent.

Advantageous Mutation

• A mutation that enhances an organism's fitness.

Deleterious Mutation

• A mutation that negatively impacts an organism's survival or fitness.

Nonsense Mutation

• A mutation converting a codon into a stop codon, leading to a truncated protein.

Missense Mutation

• A mutation causing a change in one amino acid, possibly altering protein function.

Point Mutation

• A mutation affecting a single nucleotide in the DNA sequence.

Polyploidy

• A condition with more than two complete sets of chromosomes in an organism.

Recap of Genetic Mechanisms

Independent Assortment

• Phenomenon during meiosis where chromosomes segregate randomly into gametes, increasing genetic variation.

Tetrad

• Pair of homologous chromosomes during meiosis, facilitating genetic crossover.

Chiasmata

• Points of exchange where homologous chromosomes swap genetic material during meiosis.

Bivalent

• A pair of homologous chromosomes aligned during meiosis for genetic crossover.

Pedigree

• Diagram illustrating the inheritance of traits across generations.

Genetic Crosses and Inheritance Patterns

Monohybrid Cross

• A genetic cross focusing on a single trait.

Dihybrid Cross

• Examines the inheritance of two traits simultaneously.

Punnett Square

• Tool for predicting offspring genotypes and phenotypes.

Test Cross

• A cross to determine the genotype of an individual with a dominant phenotype using a homozygous recessive partner.

Mendel’s Laws

• Law of Segregation: Allele pairs separate during gamete formation.
• Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

Carrier

• An individual carrying one recessive allele but not expressing the trait.

Zygote

• The initial diploid cell formed after the fusion of sperm and egg.

Mutations and Chromosomal Abnormalities

Deletion Mutation

• Loss of a segment of a gene or chromosome, possibly leading to genetic disorders.

Inversion Mutation

• A chromosome segment is reversed end to end.

Translocation Mutation

• A segment from one chromosome moves to a different chromosome, potentially disrupting gene function.

Aneuploidy

• Abnormal number of chromosomes, either more or less than the diploid number leading to genetic disorders.

Germ-line Mutation

• Occurs in reproductive cells and can be passed to offspring.

Somatic Mutation

• Occurs in non-reproductive cells, not passed to the next generation.

Model Organisms and Genetic Research

Definition of a Model Organism

• A species widely studied to understand biological processes due to certain advantageous traits (e.g., durability, rapid reproduction).

Examples of Model Organisms

• Escherichia coli (bacteria)
• Drosophila melanogaster (fruit fly)
• Mus musculus (mouse)

Linkage Mapping

• Method for determining gene positions on a chromosome based on recombination frequency during meiosis.

Non-Recombinant Types

• Offspring with the same allele combination as their parents after meiosis, indicating no genetic recombination has occurred.