Genetics

• Genetics: science that studies how genes are transmitted from one generation to the next
• gene: a segment of DNA that controls a hereditary trait
• Chromosome: a long chain of genes
• traits: the characteristics of an organism
• alleles: different versions of a gene that produce distinguishable traits in offspring
• two alleles must appear for a trait to appear in offspring
• gregor mendel: father of genetics and founder of law of dominance and recession, principle of segregation, principle of independent assortment
• P generation: parental generation
• F1 generation: first generation of offspring
• F2 generation: second generation of offspring
• hybrids: the offspring of parents with different traits
• some alleles (capitalized) are dominant over other alleles (lowercase + recessive)
• a dominant allele can cover up a recessive allele
• dominant allele: if the dominant allele is present, the dominant trait will show up in the offspring
• recessive allele: the trait will show up in the offspring only if no dominant trait is present
• principle of segregation: offspring carries the dwarf trait and hides it, having it reappear in the next generation
• principle of segregation: every individual carries two alleles for each trait, and these two alleles separate/segregate during the formation of gametes
• homozygous: two alleles are the same
• heterozygous: two alleles are different
• the combination of alleles received by the offspring may be either homozygous or heterozygous
• phenotype: a physical characteristic of an organism
• genotype: the genetic makeup of an organism
• recombination: when the egg and sperm unite during fertilization
• a punnett square: diagram showing the allele combinations that might result from the genetic cross of two parents
• Monohybrid crosses use punnet squares consisting of 4 boxes
• Dihybrid crosses use Punnett squares consisting of 16 boxes
• Principle of Independent Assortment states that when gametes are formed, the alleles of a gene for one trait segregate independently of the alleles of a gene for another trait
• exception 1: some alleles are neither dominant nor recessive
• exception 2: the majority of genes have more than two alleles
• exception 3: some traits are controlled by more than one gene
• incomplete dominance or nondominance: some traits are not controlled by dominant and recessive alleles
• incomplete dominance: nondominant and nonrecessive alleles blend together in the offspring
• codominance: neither allele is dominant or recessive, nor do the alleles blend together. the alleles contribute to the phenotype, so both dominant alleles are present
• A and B alleles are codominant and O is recessive