Genetics and Inheritance Terminology

Chromosomes and DNA

  • Chromosomes contain segments of DNA that code for proteins.

    • Genes: Segments within DNA that code for proteins.

    • Locus: The specific location of a gene on the chromosome.

    • Alleles: Different forms of a gene.

Inheritance and Alleles

  • Humans are diploid, meaning they inherit two alleles for every trait, one from each parent.

    • These two alleles are located on homologous chromosomes.

    • Homologous chromosomes independently assort during metaphase I of meiosis.

    • Resulting gametes may have different combinations of alleles compared to the parents.

    • Fertilization leads to a zygote that can have a unique combination of alleles from both parents.

Objectives of the Lab

  • Investigate how parental alleles separate into gametes.

  • Understand how gametes combine during fertilization to form unique offspring.

  • Learn to use a Punnett Square to predict inheritance patterns in eukaryotic organisms.

Key Terminology Related to Inheritance

  • Genotype: The genetic makeup represented by alleles. Typically denoted by a pair of letters (e.g., Aa, BB).

  • Dominant Allele: Masks the expression of a recessive allele; represented by a capital letter (e.g., A).

  • Recessive Allele: Only expressed when both alleles are recessive, represented by a lowercase letter (e.g., a).

  • Homozygous: Both alleles are the same. Example: AA or aa.

  • Heterozygous: The alleles are different. Example: Aa.

  • Phenotype: The expressed trait or observable characteristics resulting from the genotype.

    • Examples: Freckles, blue eyes, blood type, and diseases like Hemophilia or Cystic Fibrosis.

Other Patterns of Inheritance

  • Incomplete Dominance: Neither allele is dominant; heterozygous individuals show intermediate traits.

  • Codominance: Both alleles are fully expressed; heterozygous individuals show traits of both parents.

  • Multiple Alleles: More than two possible alleles exist for a trait, but individuals inherit only two.

  • X-linked Traits: The allele for the trait is located on the X chromosome and may not have a corresponding allele on the Y chromosome.

Karyotype- pictorial view of 46 chromosomes

Non disjunction- result or failure of non homologous chromosomes to par or separate properly in meiosis