Karyotype – A diagram that shows homologous chromosome pairs

Key Terminology

  • Karyotype: Diagram showing homologous chromosome pairs.

  • Phenotype: The physical traits expressed by an organism.

  • Linked Genes: Genes that are likely inherited together due to their physical proximity on a chromosome.

  • Law of Independent Assortment: Chromosomes line up randomly during metaphase, allowing varying combinations of chromosomes to be passed on to offspring.

  • Chromosome: Condensed form of genetic material.

  • Multiple Alleles: More than two versions of a gene, beyond just dominant and recessive.

  • Sex Chromosomes: Chromosomes that determine the biological sex of an organism.

  • Homozygous: A genotype with identical alleles inherited from both parents.

  • Sex-linked: Traits associated with genes located on the X chromosome.

  • Epistasis: Occurs when one gene interferes with the expression of another gene.

  • Codominance: Heterozygous genotype where both alleles are fully expressed.

  • Law of Dominance: Some alleles overshadow others in expression.

  • Protein: A macromolecule that performs various functions in the body including expression of traits.

  • Allele: A specific version of a gene.

  • Heterozygous: A genotype with different alleles inherited from parents.

  • Autosomes: Chromosomes 1-44 in humans that do not determine sex.

  • Law of Segregation: Each gamete receives only one allele from each homologous pair at the end of meiosis.

  • Carrier: An individual with a gene for a trait or disease who does not exhibit it.

  • Incomplete Dominance: Heterozygous genotype creates a blended phenotype.

  • Gene: A segment of DNA coding for a specific protein.

  • Recessive Allele: Expressed only in the homozygous state.

  • Genotype: The genetic constitution of an organism.

  • Dominant Allele: An allele that expresses its trait in the presence of another allele.

  • Agglutinogens: Antigens on red blood cells that determine blood type.

  • Rh Factor: Determines positive or negative blood type; presence indicates positive.

  • Genetic Recombination: The exchange of genetic material between homologous chromosomes during meiosis.

Mutation Overview

  • Definition: Any change in the DNA sequence of a gene.

  • Causes of Mutations:

    • Mistakes during: DNA replication, mitosis, meiosis, or protein synthesis.

    • Mutagens: Chemicals (e.g., nitrous oxide, hydroxylamine) and physical agents (e.g., UV radiation, gamma rays) that induce mutations.

    • Viruses: Can also cause mutations.

  • Types of Mutations:

    • Gene Mutations: Changes in the DNA sequence during replication.

    • Chromosome Mutations: Changes in the structure or number of chromosomes.

Types of Gene Mutations

  • Point Mutations: Replacement of one nucleotide with another (e.g., ATTACC to AATACC).

  • Frameshift Mutations: Addition or deletion of nucleotides, affecting the entire reading frame (e.g., ATTACC to ATACC (deletion); ATTACC to ACTTACC (insertion)).

  • Substitutions: One nucleotide replaces another, affecting downstream codons.

Types of Chromosome Mutations

  • Deletion: Loss of a chromosome segment.

  • Duplication: A segment of DNA is repeated.

  • Inversion: A segment breaks off and attaches in reverse order.

  • Translocation: A segment from one chromosome moves to a non-homologous chromosome.

  • Nondisjunction: Failure of homologous chromosomes to separate during meiosis, resulting in gametes with abnormal chromosome numbers.

Genetic Disorders

Types of Genetic Disorders

  • Based on Genes:

    • Autosomal Recessive Disorders: Require two recessive alleles for expression; carriers do not show symptoms.

    • Autosomal Dominant Disorders: Require at least one dominant allele; generally less common.

    • Sex-Linked Disorders: Caused by alleles on the X chromosome.

Chromosome Disorders

  • Autosomal Chromosome Disorders: Often due to non-disjunction.

  • Sex Chromosome Disorders: Result from non-disjunction of sex chromosomes.

Pedigree Analysis

  • Definition: Chart used to trace traits through generations.

  • Similar to Family Tree: Highlights inheritance patterns including disorders in family lines.

  • Symbols:

    • Squares represent males, circles represent females.

    • Filled shapes indicate presence of traits or disorders; hollow shapes indicate absence.

Inheritance Patterns

  • Autosomal Recessive: Rare in families; equally likely in males and females; may skip generations.

  • Sex-Linked Recessive: Less common; affects males more often than females.