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 Pea plants self pollinate usually 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, ¼ were short

Mendel repeated these crosses for all the different variations He discovered that in the 2 nd 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 1. Mendel concluded that each organism has 2 factors called genes that control each trait Alleles are different gene forms that determine the different form of the trait For example the gene for height has an allele for tall and another for small Typically we use upper and lower case letters to identify these T=tall allele and t=short allele Genes can either be homozygous or heterozygous Homozygous has the same 2 alleles ie TT or tt Heterozygous has different alleles ie Tt

Mendel's findings 2. 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=

Mendel's findings Noticed that alleles segregate when forming gametes Also noticed alleles segregate independently of each other – called Independent Assortment

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

Determining Genotype and Phenotype Genotype refers to the allele makeup of a gene For example the genotype of the punnett square is ¼ TT, ½ Tt, and ¼ tt This gives a genotypic ratio of 1:2:1 Phenotype refers to the trait the is expressed by the organism or what it looks like Since both TT and Tt are tall, the phenotype of the punnett square is ¾ tall and ¼ short The phenotypic ratio is 3:1

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

Dihybrid Crosses One Parent is RRYY (homozygous dominant) The other is rryy (homozygous recessive) So RRYY X rryy Step 1: 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

Dihybrid crosses Step 2: Set up 4x4 punnett square and put possible gametes from parents on top and side, then fill in squares for possible offspring All offspring are heterozygous for both seed shape and seed color - RrYy, what is their phenotype and genotype?

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