Heredity and Mendel

Heredity The passing of parents characteristics onto the offspring Genetics is the branch of biology that studies heredity

Gregor Mendel Considered the father of genetics Was an Austrian monk that used pea plants to study heredity Peas have easy traits to observe Pea plants can self pollinate so their genetic information can be controlled By carefully recording his data he made some great findings

Mendel Crossed Plants with different variations Mendel crossed a tall pea plant with a short pea plant to see what would happen x The result was that the offspring (first generation) were all tall However when crossed the second generation, 3 Tall, 1 Short

Mendel repeated these crosses for all the different variations He discovered that in the 2nd generation (F2)that the trait that had disappeared in the first generation (F1) reappeared again, always. Genetic generation abbreviations P1= parent generation F1= first generation F2=second generation

Mendel's findings Mendel concluded that each organism has 2 factors, which he called genes, that control each trait Alleles are different gene forms that determine the different form of the trait, one allele for a trait comes from the mother and the other from the father We use capital and lower case letters to represent alleles Genes can either be homozygous or heterozygous Homozygous has the same 2 alleles ie TT or tt Heterozygous has different alleles ie Tt GENES AND ALLELES ARE NOT THE SAME!!!

Mendel's findings Principle of Dominance = some alleles are dominant and will mask a recessive allele So TT or Tt will both be tall, whereas tt will be short Dominant genes are represented by upper case letters and recessive (non-dominant) by lower case TT= Tt= tt=

Genotype and Phenotype Genotype refers to the allele makeup of a gene Possibilities: Homozygous dominant (TT), Homozygous recessive (tt), or Heterozygous (Tt) Phenotype refers to the trait the is expressed by the organism or what it looks like Possibilities: Endless – it depends on the trait you are studying. IE Tall, short, pink, white, etc…

Mendel's findings Law of Segregation - alleles segregate when forming gametes

Mendel’s findings Law of Independent Assortment - alleles segregate independently of each other Summary of his findings

Monohybrid crosses illustrate Mendel's findings A monohybrid cross is one that looks at only one specific trait and how it segregates (predicts probabilities) Easy to do this using the punnett square method

Baby Steps Through Punnett Squares Determine the genotypes of the parents (usually given to you) Figure out possible gametes (Law of Segregation) Draw your Punnett square Put gametes on the outside of the square – mom on one side, dad on the other Determine possible offspring genotypes by filling in square (Law of Independent Assortment) Summarize your results – genotype and phenotype ratios Feel smart 

Let’s Try One! Spongebob Squarepants recently met Spongesusie Roundpants at a dance. Spongebob is heterozygous for his square shape and Spongesusie is round (square is dominant). If Spongebob and Spongesusie had children… What are the chances of a child with a square shape? What are the chances of a child with a round shape?

Dihybrid crosses Dihybrid crosses look at 2 different traits passed on from parents Ex: In peas, seed shape & seed color R = round Y = yellow r = wrinkled y = green

Dihybrid Crosses So RRYY X rryy (step 1) One Parent is RRYY (homozygous dominant) The other is rryy (homozygous recessive) So RRYY X rryy (step 1) Step 2: find all possible gamete combinations by using FOIL (First Outer Inner Last) There will always be 4 different combinations in dihybrid Crosses Possible gametes: RY RY RY RY x ry ry ry ry

Dihybrid crosses Step 3: Set up 4x4 punnett square Step 4: Put possible gametes from parents on top and side, then fill in squares for possible offspring (Step 5) Step 6: Summarize the results (Genotype and Phenotype)

Dihybrid crosses Now cross two F1 plants. RrYy x RrYy Possible gametes: RY Ry rY ry x RY Ry rY ry

Phenotypic Ratio for a Dihybrid Cross: For this cross, find the number of each - round yellow : round green : wrinkled yellow : wrinkled green 9/16 round yellow (R_Y_) 3/16 round green (R_yy) 3/16 wrinkled yellow (rrY_) 1/16 wrinkled green (rryy) Phenotypic Ratio = 9 : 3 : 3 : 1