Genetics Vocabulary

Genetics Notes

Basic Concepts

• Trait: A distinct variant of a physical characteristic of an organism.
• Continuous Variation: Traits that show a range of values (e.g., height).
• Discontinuous Variation: Traits that have distinct, separate values (e.g., blood type).
• Hybridization: The process of crossing two different true-breeding varieties.

Mendelian Genetics

• Genes: Units of heredity that determine traits.
• Heterozygous: Having two different alleles for a trait.
• Law of Segregation: During gamete formation, allele pairs separate or segregate randomly, and each gamete has an equal chance of receiving either allele.
• Dominant: The allele that determines the phenotype in a heterozygote.
• Recessive: The allele that is masked in a heterozygote.
• Phenotype: The observable traits of an organism.
• Genotype: The genetic makeup of an organism (the specific alleles it possesses).
• Punnett Square: A diagram used to predict the genotypes and phenotypes of offspring in a genetic cross.

Advanced Genetic Crosses

• Pedigree: A family tree that describes the interrelationships of parents and children across generations; used to analyze human genetic traits.
• Dihybrid Crosses: A cross between individuals that are heterozygous for two traits.
• Law of Independent Assortment: Each pair of alleles segregates independently of other pairs of alleles during gamete formation. This law applies when genes for two characters are located on different chromosomes or when they are far apart on the same chromosome.

Patterns of Inheritance

• Complete Dominance: The dominant allele completely masks the effect of the recessive allele in heterozygous condition.
• Incomplete Dominance: The heterozygous phenotype is an intermediate between the two homozygous phenotypes. For example, if red and white flowers produce pink flowers.
• Co-dominance: Both alleles are expressed in the heterozygous phenotype. For example, human blood type AB where both A and B alleles are expressed.

Chromosomal Inheritance

• Polygenic Inheritance: An additive effect of two or more genes on a single phenotype. An example is skin color in humans.
• Pleiotropy: A single gene having multiple effects on an organism's phenotype. Example: Sickle cell anemia.
• Chromosomal Theory of Inheritance: Genes have specific positions (loci) on chromosomes, and it is the chromosomes that undergo segregation and independent assortment.
• Linkage: Genes located near each other on the same chromosome tend to be inherited together in genetic crosses; such genes are said to be linked.
• Wild Type: The phenotype most commonly observed in natural populations.
• Variants: Traits that differ from the wild type.
• Autosomes: Non-sex chromosomes.
• Allosomes: Sex chromosomes (e.g., X and Y chromosomes in humans).

Human Genetic Disorders

• Autosomal Dominant Disorder: A genetic disorder caused by a dominant allele on an autosome. Only one copy of the allele is needed for expression.
• Autosomal Recessive Disorder: A genetic disorder caused by a recessive allele on an autosome. Two copies of the allele are needed for expression.
• S(sex)-linked: Genes located on sex chromosomes exhibit unique inheritance patterns.
  • X-linked recessive: More males are affected than females since males only have one X chromosome. Affected fathers pass the trait to all daughters, but not to sons. Affected mothers pass the trait to both sons and daughters.
  • X-linked dominant: Affected fathers will pass the trait to all daughters. Affected mothers (if heterozygous) have a 50% chance of passing the trait to sons and daughters.