Notes on Genetics and Inheritance

Introduction to Inheritance, Genes, and Chromosomes

• Inheritance refers to the genetic transmission of traits from parents to offspring.
• Genes are sequences of DNA bases (A, T, G, C) located on chromosomes that encode traits.

Understanding Key Genetic Vocabulary

• Gene: A unit of heredity made up of DNA that specifies a trait.

• Chromosome: A structure within cells that contains DNA.

  • Humans typically have 23 pairs of chromosomes, inheriting one from each parent.

• Locus (plural: loci): The specific location of a gene on a chromosome.

Genetic Composition and Expression

• Each individual has two copies of most genes, inheriting one copy of each chromosome from each parent.
• Homologous chromosomes: Pairs of chromosomes carrying the same set of genes.
• Genotype: The genetic makeup of an individual (e.g., WW, Ww, ww).
• Phenotype: The observable physical expression or characteristics of a genotype (e.g., purple or white flowers).

Alleles and Traits

• Allele: A variant form of a gene that determines a specific trait.
  • Example: The flower color in pea plants can have alleles for purple or white.
• Dominant alleles: Alleles that express their traits in a heterozygote (e.g., purple is dominant over white).
• Recessive alleles: Alleles that do not express their traits unless in a homozygous condition (e.g., white flowers).

Mendel's Laws of Inheritance

• Law of Segregation: During gamete formation, alleles segregate independently into gametes. Each gamete receives one allele for each gene.
• Law of Independent Assortment: Alleles of different genes assort independently during gamete formation, unless the genes are linked.

Punnett Squares

• Monohybrid Cross: A genetic cross between individuals focusing on one character.
  • Example: Crossing WW (homozygous dominant) with ww (homozygous recessive) produces F1 generation (100% Ww).
• Dihybrid Cross: A cross examining two different traits simultaneously (e.g., flower color and seed shape).

Genetic Variations and Interaction

• Incomplete Dominance: A form of inheritance where the offspring's phenotype is a blend of the parents' traits (e.g., red and white flowers producing pink).
• Codominance: Where both alleles are fully expressed (e.g., AB blood type).
• Pleiotropy: A single gene affects multiple phenotypic traits (e.g., cystic fibrosis).
• Epistasis: Gene interactions where one gene masks or modifies the expression of another gene (e.g., Labrador coat color).

Sex-Linked Traits

• Sex-linked inheritance: Traits that are determined by genes located on sex chromosomes (X and Y).
  • Example: Genes for color blindness or hemophilia are found on the X chromosome, affecting mostly males.

Genetic Exchange in Prokaryotes

• Conjugation: A process where bacteria exchange genetic material through direct contact (via a sex pilus).
• Transformation: Bacteria uptake DNA from their environment, which can recombine with their own genetic material.

Summary of Key Concepts

• Phenotype can be influenced by genotype and environmental factors.

• Traits can show a blend of inheritance patterns including dominant, recessive, codominant, or incomplete dominance.

• Genetic studies often utilize Punnett squares to predict potential outcomes in offspring based on parental genotypes.

• Further Study may include looking at specific diseases linked to genetic mutations, such as Huntington’s Disease and its implications, as well as the role of gene expression in observable traits across diverse environmental contexts.