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Genetics, Mutations, and Neoplasms

Genetics: The Foundation of Traits

  • Genes and DNA

    • Genes are composed of DNA.

    • DNA is a protein strand containing genetic information.

    • Genes determine physical characteristics, response mechanisms, and adaptive efforts.

  • Gene Expression and Punnett Squares

    • Punnett squares are used to visualize gene expression.

    • Genetic Vocabulary Review

      • Trait: A characteristic passed from one generation to another (e.g., eye color).

      • Allele: A different form of the same trait (e.g., various eye colors).

      • Homozygous Dominant Genotype: Represented by two capital letters (e.g., WW) as dominant traits are always written with capital letters.

      • Homozygous Recessive Genotype: Represented by two lowercase letters (e.g., ww) as recessive traits are written with lowercase letters.

      • Heterozygous Genotype: Represented by one capital and one lowercase letter (e.g., Ww) indicating different alleles.

    • Steps for Setting Up a Punnett Square

      1. Draw the Punnett square grid.

      2. Write the genotypes of the parents on the side and on top.

      3. Fill in the boxes to show possible offspring genotypes.

    • Example Problem 1: Seal Whisker Length

      • Scenario: In seals, long whiskers (dominant allele, W) and short whiskers (recessive allele, w).

      • Cross: Homozygous dominant long-whisker seal (WW) crossed with a heterozygous long-whisker seal (Ww).

      • Punnett Square Setup:

        • Parent 1 (Homozygous Dominant): WW

        • Parent 2 (Heterozygous): Ww

        • Possible offspring genotypes:

          • WW

          • Ww

          • WW

          • Ww

      • Phenotypic Probability: Since any presence of the dominant allele (capital W) results in long whiskers:

        • Probability of long whiskers: Four out of four ( rac{4}{4} , or 100
          \%).

        • Probability of short whiskers: Zero out of four ( rac{0}{4} , or 0
          \%).

    • Example Problem 2: Seal Whisker Length (Using Letter B)

      • Scenario: One parent seal is heterozygous long-whisker, and the other is short-whisker. Use letter 'b'.

      • Determining Dominance: A heterozygous genotype (Bb) always expresses the dominant trait. Therefore, long whiskers are dominant.

      • Parent Genotypes:

        • Heterozygous long-whisker parent: Bb

        • Short-whisker parent: Since short whiskers are recessive, the only way for the trait to be expressed is a homozygous recessive genotype, so bb (recessive traits are only expressed when two recessive alleles are present).

      • Punnett Square Setup:

        • Parent 1 (Heterozygous): Bb

        • Parent 2 (Homozygous Recessive): bb

        • Possible offspring genotypes:

          • Bb

          • Bb

          • bb

          • bb

      • Phenotypic Probability:

        • Probability of long whiskers (dominant trait due to B): Two out of four ( rac{2}{4} , or 50
          \%).

        • Probability of short whiskers (recessive trait due to bb): Two out of four ( rac{2}{4} , or 50
          \%).

    • Summary: A heterozygous genotype (Bb, Ww, etc.) always indicates the dominant trait is expressed.

Advanced Genetics and Mutations

  • Genetic Similarities and Differences

    • Human genetics are similar to primates, but gene expression differs.

  • Human Genome Project

    • A massive genetic mapping initiative.

    • Identified several genetic mutations linked to cancers and birth defects, aiding early diagnosis and detection.

  • Gene Structure

    • Genes consist of hundreds to thousands of nucleotides.

    • Humans have 46 chromosomes:

      • 22 paired sets of autosomes.

      • Sex chromosomes: XX for female, XY for male.

  • Karyotype and Phenotype

    • Karyotype: The complete set of chromosomes in a species (not fully defined in transcript, implies the unique set of an individual).

    • Phenotype: The physical expression of genes (how traits are physically observed).

    • Note: Not all genes are expressed.

  • Types of Traits

    • Alleles: Single genes with variants (as discussed in Punnett squares).

    • Polygenetic Traits: Determined by sets of multiple genes.

    • Homozygous: Identical alleles on a chromosome (e.g., AA or aa).

    • Heterozygous: Different alleles on a chromosome (e.g., Aa).

    • Dominant Traits: Usually the ones that are expressed.

  • Epigenomes

    • Definition: Collections of chemical changes to DNA and proteins that regulate gene expression.

    • Mechanism: Interact with DNA, alter gene expression, and react to different environments.

    • Inheritance: Changes can be passed on.

    • Role: Influence hypersensitivities and allergies, alter genetic risk factors, affect the expression of mutations (whether a mutation is