Genetics and Inheritance The Scientific Study of Genes and the Inheritance of Traits
Gregor Mendel (1860) = “Father of Genetics” Experimented with pea plants Used self-fertilization (asexual reproduction) and cross-fertilization methods (sexual reproduction) chose simple traits to follow (flower color, height, seed color, seed texture etc.)
Key Terms To Know: Trait = any characteristic that can be passed from parents to their offspring Gene = genetic material on a chromosome that contains the instructions for creating a particular trait Allele = one of several varieties of a gene, an alternate form of the same gene for a given trait example: A or a (same letter, different case) Locus = the location on a chromosome where a gene is located
Monohybrid Crosses Monohybrid Cross = a cross involving only a single allele responsible for a trait; each parent contributes information for the trait (ex. Aa X AA)
Trait Characteristics Dominant trait = the trait that gets expressed in a monohybrid cross where the mode of inheritance is Complete Dominance; shown by a capital letter : A Recessive trait = the trait that is hidden in a monohybrid cross where the mode of inheritance is Complete Dominance; shown by a lower case letter : a
Allele Pairing Homozygous = the two alleles for a trait that an organism has are identical ex: Homozygous Dominant = AA, Homozygous Recessive = aa Heterozygous = the two alleles coding for a trait are different ex: Aa
Genotype vs. Phenotype Genotype = the actual genetic information, all the alleles that an organism possesses (the actual letters) Phenotype = physical appearance based on alleles
Mendel’s First Law of Heredity Law of DominanceLaw of Dominance: When a trait is Completely Dominant over another trait, then that dominant allele controls the gene pair. In the heterozygous form (Aa) the dominant trait only gets expressed. The recessive allele gets hidden.
Mendel’s Second Law of Heredity Law of SegregationLaw of Segregation: Pairs of alleles separate during the formation of the gametes (sex cells) during Meiosis I. Therefore each gamete will contain one allele for each gene.
Mendels Third Law Of Heredity Law of Independent AssortmentLaw of Independent Assortment : Gene pairs separate into the gametes both independently and randomly of each other. The rules of probability are used to describe how the different chromosomes and their alleles from parents assemble into gametes and ultimately into offspring.
PUNNETT SQUARES Used to track a trait from parents to offspring. Shows possible ratios for offspring outcomes. P Generation = Parents F 1 Generation = Offspring from the cross of the parents F 2 Generation = Offspring produced from crosses among the F 1 F = filial, refers to sons and daughters
Punnett Square Rules 1. Make a key; show dominant and recessive alleles 2. Properly label parents genotypes, place them on the outside of the punnett square 3. Correctly perform the cross 4. Interpret the results; determine ratios
Test Crosses –Suppose we have two Tall pea plants T= tall t = short
What are the possible genotypes for each plant? tt For A Short Plant TT OR Tt For a Tall Plant
Test Cross: cross the tall plant (TT or Tt) with a short one (tt) If any recessive phenotypes show up in the next generation, the unknown genotype MUST be Heterozygous Homozygous tall x short TT x tt Heterozygous Tall x short Tt x tt