Population Genetics and Mendelian Genetics

Population Genetics

  • Key Concepts and Definitions:
    • Allele Frequency:
      • Definition: The proportion of a specific allele among all alleles for a given gene in a population.
      • Example: If a gene has alleles A and a, and the population has 70 A alleles and 30 a alleles, the allele frequency of A is 0.7 and a is 0.3.
    • Gene Flow:
      • Definition: The transfer of genetic variability from one population to another due to migration of individuals or gametes (e.g., pollen).
      • Example: Pollen from one flower population fertilizes flowers in another population, introducing new alleles.
    • Genetic Equilibrium:
      • Definition: A state in which allele frequencies in a population remain constant over time under certain conditions (Hardy-Weinberg Principle).
      • Implication: In the absence of evolutionary influences, allele frequencies will not change.
    • Genetic Drift:
      • Definition: Random fluctuations in allele frequencies due to chance events, often having more significant effects in smaller populations.
      • Example: A natural disaster wipes out a portion of a population, leading to a change in allele frequency.
    • Bottleneck Effect:
      • Definition: A form of genetic drift that occurs when a population's size is significantly reduced for at least one generation.
      • Example: A severe drought reduces the population of a species, resulting in a loss of genetic diversity.
    • Founder Effect:
      • Definition: Genetic differences that arise when a new population is established by a small number of individuals from a larger population.
      • Example: A small group of individuals colonizing a new island may have different allele frequencies compared to the mainland population.

Study Guide for ADVANCED GENETICS

Mendelian Genetics

  • Gregor Mendel’s Principles:
    • Principle of Heredity:
      • Definition: Traits are inherited through discrete units known as genes, which are passed from parents to offspring.
    • Principle of Segregation:
      • Definition: During the formation of gametes, the two alleles responsible for a trait segregate from each other.
      • Example: In a heterozygous plant (Aa), the alleles A and a separate during gamete formation, resulting in gametes carrying either A or a.
    • Principle of Independent Assortment:
      • Definition: Genes for different traits can segregate independently during the formation of gametes.
      • Example: The inheritance of seed shape (round vs wrinkled) does not influence the inheritance of seed color (yellow vs green).

Tracking Traits

  • Definitions and Examples:
    • Purebred vs. Hybrid:
      • Purebred: Organisms that are genetically uniform for a particular trait (e.g., AA or aa).
      • Hybrid: Offspring resulting from the cross of two different purebred varieties (e.g., Aa).
    • Punnett Square vs. Pedigree:
      • Punnett Square: A diagram used to predict the genetic makeup of offspring from a cross between two individuals.
      • Pedigree: A chart that shows the inheritance of traits in a family over generations.
    • Simple Dominance:
      • Definition: A pattern of inheritance where one allele masks the effect of another allele (dominant vs. recessive).
    • Incomplete Dominance:
      • Definition: A situation where one allele is not completely dominant over another allele, resulting in a blended phenotype.
      • Example: A red flower crossed with a white flower results in pink flowers.
    • Codominance:
      • Definition: A scenario where both alleles in a heterozygote are fully expressed.
      • Example: A flower with both red and white patches.
    • Multiple Alleles:
      • Definition: The presence of more than two alleles for a genetic trait within a population.
      • Example: Blood types in humans (A, B, AB, O).
    • Polygenic Inheritance:
      • Definition: A mode of inheritance where multiple genes contribute to a single trait.
      • Example: Human skin color determined by several genes.
    • Sex-Linked Traits:
      • Definition: Traits that are associated with genes located on sex chromosomes (X or Y).
      • Example: Color blindness is often linked to genes on the X chromosome.
    • Carriers:
      • Definition: Individuals who carry one copy of a recessive allele for a trait but do not display the trait themselves.

Gene Expression

  • Main Factors Controlling Gene Expression:
    • DNA:
      • Components affecting gene expression:
      • Promoters: Regions of DNA that initiate transcription of a gene.
      • Enhancers: DNA sequences that increase the likelihood of transcription when bound by specific proteins.
      • Silencers (Repressors): DNA elements that inhibit gene transcription when proteins bind to them.
      • Regulatory Proteins: Proteins that interact with specific sequences of DNA to modulate gene expression.
      • Introns: Non-coding segments of RNA that are removed during RNA processing.
      • Exons: Coding segments of RNA that are expressed and remain in the mature mRNA.
    • Environment:
      • Examples of environmental factors influencing gene expression:
      • Hormone-activated changes (e.g., hormonal influence on growth).
      • Light exposure affecting flower coloration.
      • Temperature variations impacting phenotype (e.g., fur color in Siamese cats).
      • Chemical exposure that can alter gene expression.

Cell Differentiation

  • Concepts to Know:
    • Cell Differentiation:
      • Definition: The process by which a less specialized cell becomes a more specialized cell type.
    • Homeotic Genes:
      • Definition: Genes that regulate the development of anatomical structures in various organisms.
      • Role: Determine the identity of body parts during embryonic development.
    • Stem Cells:
      • Definition: Undifferentiated cells that have the potential to develop into different cell types.
      • Role: Contribute to growth, development, and tissue repair.