Heredity • The study of how traits are passed from parents to offspring • Perceptions have evolved over time • Incomplete Dominance • Co-Dominance • Mendelian Genetics
Gregor Johann Mendel (1822 - 1884) • The father of modern genetics • Published one paper in 1866 that went unnoticed for 40 years • Proposed heredity was controlled by paired factors that segregate with gamete production and rejoin at fertilization
Genes: • Everyone has DNA in their cells and DNA contains instructions for building a person. • Each physical characteristic (or Trait) an organism possesses is controlled by one or more genes. • Offspring look like parents because they inherit the same genes that the parent has.
Alleles: Alternate forms of Genes • Every Labrador dog has genes for fur, but the genes sometimes have slight variations ie, COLOR. • Variations of genes are called alleles. • In the blending example with the flowers, the red and white alleles were equal, and both were expressed equally in the offspring. • In the case of Labrador fur, the alleles are NOT equal. This is an example of DOMINANCE.
Dominant & Recessive Genes • Dominant alleles are always expressed in an offspring, and will mask any other allele present in the offsprings’ cells. In Labradors, black fur is dominant. • Alleles which are masked in this way are called Recessive alleles. Chocolate fur is recessive. A Labrador can only have chocolate fur if there are NO alleles for black fur in its DNA. Dominant Recessive
Dominant Alleles are always expressed in the Phenotype. Does this mean that they are always passed on to the offspring as well? NO! If a parent has both a dominant and a recessive allele for a trait, there is an equal chance of passing either allele on.
The Law of Segregation • Every individual has 2 alleles for every gene.
The Law of Segregation • These allele pairs separate when gametes are formed….
The Law of Segregation • …and 1 of each randomly combine to create the offspring's genotype.
Dominant & Recessive Genes = Genotype = Homozygous Recessive Phenotype = Chocolate
Dominant & Recessive Genes = Genotype = Homozygous Dominant Phenotype = Black
Dominant & Recessive Genes = Genotype = Heterozygous Phenotype = Black
Generations + P-generation (Parents) F1-generation (First Filial) + F2-generation (Second Filial)
The Summary So Far: • The physical characteristics (traits) of individuals are controlled by genes • Different forms of the same gene are called alleles. • The physical appearance of an organism (that you can observe) is called the Phenotype. The alleles that that individual carries (invisibly) in its’ DNA is its’ Genotype. • Some alleles can overpower others, and are called Dominant. These alleles are always expressed in the phenotype of the offspring. • Alleles that are masked by Dominant alleles are called Recessive. An individual can only show a recessive phenotype if it has NO Dominant alleles.
Monohybrid Crosses • Example: Determining the Presence of the allele for Anthocyanin • STEP 1: Assign the dominant and recessive alleles names = A = a
Monohybrid Crosses • STEP 2: Find out the genotype of each parent • In this lab, we starting with both heterozygous F1 plants + Aa x Aa
Monohybrid Crosses • STEP 3: Build a Punnett Square to determine all the possible gametes each parent can produce.
Monohybrid Crosses • STEP 3: Build a Punnett Square to determine all the possible gametes each parent can produce. a A A a
Monohybrid Crosses • STEP 4: Determine the possible allele combinations A a A AA Aa a Aa aa
Monohybrid Crosses • STEP 5: Determine the possible phenotypes of the F2 generation a A A AA Aa a Aa aa
STEP 1 Dihybrid Crosses = G = A = a = g
STEP 2 (These are also F1 plants) Dihybrid Crosses AaGg x AaGg
STEP 3 Dihybrid Crosses A A A a a a G G G g g g A AG a aG G Ag g ag
STEP 4 Dihybrid Crosses AG Ag aG ag AG AAGg AaGG AAGG AaGg AaGg Aagg Ag AAgg AAGg aG AaGG AaGg aaGG aaGg ag aaGg aagg AaGg Aagg
STEP 5 Dihybrid Crosses AG Ag aG ag AG AAGG AAGg AaGG AaGg AAGg AaGg Aagg Ag AAgg aG AaGG AaGg aaGG aaGg ag AaGg Aagg aaGg aagg
Dihybrid Crosses AAGG, AAGg, AaGG, AaGg= = 9/16 plants AAgg, Aagg= = 3/16 plants aaGG, aaGg= = 3/16 plants = 1/16 plants aagg =