Biology: Genetics

• Gregor Mendel is the "Father of Genetics".
• The principle of Independent Assortment states that the inheritance of one trait has no effect on the inheritance of another trait.
• Genetics is the study of how traits are passed from parent to offspring.
• Traits are determined by the genes on the chromosomes.
• A gene is a segment of DNA that determines a trait.
• Chromosomes come in homologous pairs, thus genes come in pairs.
• Homologous pairs - matching genes- one from female parent and one from male parent.
• Humans have 23 pairs of chromosomes, 46 in total.
• Alleles are different genes (possibilities) for the same trait.
• Gene that prevents the other gene from "showing" - dominant.
• Gene that does NOT "show" even though it is present - recessive.
• Both genes of a pair are the same - homozygous or purebred.
• One dominant and one recessive gene - heterozygous or hybrid.
• Combination of genes an organism has (actual gene makeup) - genotype.
• Phenotype is the physical appearance resulting from gene make-up.
• The Punnet Square is used to predict the possible gene makeup of offspring.
• Ratio Orders:

  Genotypic Ratio:

  homozygous dominant : heterozygous : homozygous recessive

  Phenotypic Ratio:

  dominant : recessive
• When one allele is not completely dominant over another (they blend) - incomplete dominance.
• When both alleles are expressed - codominance.
• Colorblindness is the inability to distinguish between certain colors.
• The most common type of color blindness is red-green color blindness.
• Hemophilia - blood won't clot.
• Pedigrees are graphic representations of how a trait is passed from parents to offspring.

  1. Circles are for females
  2. Squares are for males
  3. Horizontal lines connecting a male and a female represent a marriage
  4. Vertical line and brackets connect parent to offspring
  5. A shaded circle or square indicates a person has a trait
  6. A circle or square not shaded represents an individual who does not have the trait
  7. Partial shade indicates a carrier - someone who is heterozygous for the trait