DB

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.