Genetics the study of heredity

Gregor Mendel “Father of Genetics” Heredity -the transfer of characteristics from parents to offspring through their genes Gregor Mendel -used garden peas to study heredity

Mendel’s Experiments cross fertilization: Mendel crossed two parent plants with opposite traits (purple x white). This was the Parental generation (P). The First generation (F1) were identical (purple). self fertilization: Mendel allowed the purple flowers from the First generation (F1) to self-pollinate. Self pollination produced the Second generation (F2). Muskopf, Shannan

Mendel’s Conclusions The F1 generation all showed the purple trait (called the dominant trait) In the F2 generation the (white) trait reappears in ¼ of the flowers (called the recessive trait) Each flower has two alleles that determine the appearance The alleles are represented by letters (uppercase letter represents the dominant allele; lowercase letter represents the recessive allele) P is dominant and represents purple p is recessive and represents white The Dominant Is Expressed No Matter What Need 2 Copies Of The Recessive Allele In Order To Be Expressed PP = purple flower Pp = purple flower pp = white flower

Alleles –homozygous: organisms that have 2 identical alleles for a trait (could be two capital or two lowercase letters) PP pp –heterozygous: organisms that have 2 different alleles for a trait ex: Pp (the dominant allele P is expressed so this flower would be purple)

Genotype: letters used for the alleles –ex: PP, Pp, pp Phenotype: what an organisms looks like –ex: purple, white

Punnett square A Punnett square is used to show the possible allele combinations in the offspring of 2 parents. Monohybrid cross = cross involving only 1 trait The four boxes represent the four possible offspring

A plant heterozygous with green peas (Gg) is crossed with a plant that has yellow peas (g). Step 1: Choose a letter for the alleles (green is dominant; yellow is recessive) G : green peag: yellow pea Step 2: Write the genotypes of the parents heterozygous plant with green peas : Gg plant with yellow peas: gg parents: Gg x gg Example of a Monohybrid Cross

G g g g g g gg Gg g g g g g g g g g g g g gg Gg Step 3: Set up the punnett square with one parent on each side Step 4: Fill out the punnett square middle G g g g g g

Step 5: Look at the four boxes from Step 5 and determine the genotypes of the four offspring –Genotypic ratio: 2 Gg: 2 gg Step 6: Look at the genotypes in Step 6 and determine the phenotypes; –Green (G) is dominant over yellow (g), plants that have G in their offspring have green peas –Phenotypic ratio: 2 green: 2 yellow

Practice-Monohybrid Crosses Cross an individual with blue eyes with an individual with homozygous brown eyes. Brown eyes (B) is dominant to blue eyes (b). Phenotypes: Genotypes: B B b b

Cross an individual with blue eyes with an individual with homozygous brown eyes. Brown eyes (B) is dominant to blue eyes (b). Phenotypes: All Brown Eyes Genotypes: All Bb B B b Bb Bb

Practice-Monohybrid Crosses A child is diagnosed with a recessive genetic disease. Neither parent has the disease. What are the genotypes of the parents? Phenotypes: Genotypes: N ? ? nn N

A child is diagnosed with a recessive genetic disease. Neither parent has the disease. What are the genotypes of the parents? Genotypes of the parents are Nn N n n Nn nn N NN nn

Incomplete Dominance = Blending In snapdragons, there is not a dominant allele. The flower color can be red, pink, or white. A heterozygous flower (Rr) will a blending of red and white (pink). Muskopf, Shannan. Online Images. The Biology Corner. 20 April

Codominance: the recessive & dominant traits appear together (both are dominant, no recessive allele) –Ex: Cross a red cow with a white cow. What will the offspring be? R R W W

–phenotype: all red and white speckled –genotype: all RW W RW RW R R Muskopf, Shannan. Online Images. The Biology Corner. 20 April chromosomes.htmlhttp:// chromosomes.html

Polygenic Traits: “many genes” act together resulting in a range of phenotypes –Ex: skin, hair, eye color Skin color is a polygenic trait because it shows a range of colors. There is not a dominant and recessive color. Farabee, M.J. “Skin Pigmentation.” Online Image. Online Biology Book. 5 May

Multiple Alleles: genes that have more than two alleles –There are four blood types (phenotypes): A, B, AB, and O –Blood type is controlled by three alleles: A, B, and O –Each individual only inherits two alleles (one from each parent). –A and B are codominant –O is recessive, two O alleles result in type O Blood Blood Types Possible Genotypes Dominant A AA or AO Dominant B BB or BO Codominant AB AB Recessive O OO

Practice: Cross a Type AB with a Type O. AB x OO A B O AO BO 1. Set up punnett square with one parent on each side 2. Fill out the punnett square middle What are the possible blood types of the four offspring? GenotypeBlood Type 2 AO2 Type A 2 BO2 Type B

A woman heterozygous for Type A blood marries and a man with Type AB blood. Show the cross and the possible offspring. 1. Write the genotypes of the parents: woman heterozygous for Type A: AO man with Type AB: AB 2. Set up punnett square with one parent on each side and fill in the middle. Practice A O A AA AO B AB BO Blood types of possible offspring: AA: Type A blood AO: Type A blood AB: Type AB blood BO: Type B blood

If a Type O individual marries a Type B individual can they have offspring with Type O blood? What type of blood can the offspring have? Practice B ? O O Blood types of possible offspring: AA: Type A blood AO: Type A blood AB: Type AB blood BO: Type B blood

If a Type O individual marries a Type B individual can they have offspring with Type O blood? What type of blood can the offspring have? B O O BO OO Yes, they can have a child with type O or type B blood.

If 2 individuals with Type AB blood marry, what percentage of their offspring will have Type AB blood? A B A B Practice

50% of their offspring could be Type AB A B A AA AB B AB BB If 2 individuals with Type AB blood marry, what percentage of their offspring will have Type AB blood?

Review of Terms AlleleA form of a gene HomozygousBoth Alleles are the Same HeterozygousAlleles are Different Homozygous DominantAA Homozygous Recessiveaa Heterozygous Aa Genotypic Ratio2 PP : 2 pp Phenotypic Ratio2 Purple : 2 White