MENDELIAN GENETICS Gregory Mendel: Heredity: Cross: X P1 Generation: F1 Generation: F2 Generation: Gametes: Dominant: Recessive: Genotype: Phenotype: Law of Dominance: Genes: Alleles: Law of Segregation: Homozygous: Heterozygous: GAMETE FORMATION Parents and Possible Gametes: 1. Bb Bb 2. bb BB Sperm Eggs Sperm Eggs
How to Make a Punnet Square Step 1: How do I know what letter I am supposed to use for each allele? Step 2: Step 5: Step 6: Step 3: Step 4: The number of purebred dominant (AA) compared to hybrid (Aa) compared to purebred recessive (aa) is called the: The number of that APPEAR dominant compared to the number that APPEAR recessive is called the: SAMPLE PROBLEM: A. Cross a plant with pure purple flowers with a white flowered plant (purple is dominant): 1. 4. 2. 3. 5. 6. B. Cross a homozygous yellow seed plant with a homozygous green seed plant (yellow is dominant). C. Cross two heterozygous yellow seed plants.
Probability Notes Probability: Formula: Rule of Addition Rule of Multiplication You Try: Solve the following probability problems and say which rule you used (Show all work) What are the chances of having a boy? What are the chances of having a boy or a girl? RULE What are the chances of having a boy and a girl? RULE What is the Probability of flipping 3 heads in a row? RULE What is the probability of rolling a 6 on a die? What is the probability of rolling a 6 or a 5 on a dice cube? RULE What is the probability of rolling a 6 and a 5? RULE What is the probability of pulling out the Queen of Hearts out of a deck of cards? What is the probability of pulling hearts as the suit? In which case do you have a greater probability: Pulling out a Queen of Hearts of pulling out a card with the heart on it? What is probability of pulling the queen of hearts and having the next card be a heart suit?
TEST CROSSES Pure Breed Hybrid What do you do if you don t know the genotype of a dominant parent? A dominant trait can be either or You have to do a test to determine what type of dominance the unknown parent has. How is it tested? ***If any offspring show the recessive trait, the dominant parent HAD to be Sample Test Cross A. A black mouse is mated with a brown mouse (black is dominate to brown). They have 10 black offspring. What is the genotype of the black mouse? B. Several black mice of the same genotype are mated and produce 29 black and 9 white offspring. What are the genotypes of the parents?
Law of Independent Assortment: Dihybrid Cross: Number of traits? Number of Alleles? Use the FOIL method from math to determine the Gametes First Outer---Inner--Last In mice, black (B) is dominant over tan and short tails (S) is dominant over long tails. Homozygous tan / Heterozygous short X Heterozygous black / Homozygous long 1. Identify Dominant and Recessive Alleles: 2. P1 Phenotypes: x 3. P1 Genotype: & 4. Gametes (Foil): x 5. Dihybrid Punnet 6. Possible Phenotypes D/D D/R R/D R/R 7. Phenotype Ratio Solving Dihybrid with Probability and Two Separate Monohybrid Crosses Multiple the Probabilities!!!!
Exceptions to Mendel s Laws Exceptions to the Law of Dominance: It is not always true that one allele is always dominant and fully expressed over the recessive allele Incomplete Dominance Seen in: Flowers can be white, pink, or red. (Red is dominant) R= red r= white Cross a red flower with a white flower. RR= Red x White Rr= x rr= Genotypic Ratio: Phenotypic Ratio: Anytime you are doing a cross that involves blood cells you use the letter I to represent blood Codominance Example: Sickle Cell Anemia in Humans N=Normal S=Sickle Cell (heterozygous = carrier) Cross a Normal person with a carrier. Seen in: I N I N = Normal X Carrier I N I S = X S S I I = Genotypic Ratio: Phenotypic Ratio: Multiple Alleles Codominance Alleles I A & I B Phen otype Genotype A B AB O Recessive Allele i Type O x Type AB Genotypic Ratio: Phenotypic Ratio: Three alleles control blood type: I A I B i
Exceptions to the Law of Independent Assortment: Many Genes are located n the same chromosome and therefore can have an affect on each other. Gene Linkage: Crossing over: Unlinked Genes Step 1: Step 2: Linked Genes Step 3: Result: Result:
Exception to the Law of Segregation: It is not always true that each gene has at least 2 alleles. The X and Y-chromosomes are different. Female: Male: Sex Linked (X & Y): Autosomal: Common Sex Linked Traits: X-Chromosome: & Why do more males inherit these recessive disorders than females? When doing X-linked crosses, the sex of the individual needs to be taken into account, but the rules for dominance and recessive still apply Color Blindness Phenotype Normal Female Carrier Female Colorblind Female Normal Male Colorblind Male N = Normal n = color blind Genotype Cross a colorblind male & carrier female What is the probability of having a colorblind boy? What is the probability of having a colorblind girl?
POLYGENIC TRAITS: Examples: SEX LIMITED: Examples: So Why do men have nipples then? SEX INFLUENCED: Examples: Why do men some men go bald? Why do women grow facial hair as they age? EPISTASIS: Examples: So why do labs have different coats? EPIGENETICS: Examples: So why do some rabbits change color in the winter?
Pedigree: family tree drawn with standard genetic symbols, used to study human heredity Affected or Not? Unshaded means they are not affected with the trait/disorder What about carrier? Use the people with the trait to figure out who carries the gene and who is unaffected by the trait. Completely shaded means they have the trait/disorder AA aa Aa Recessive or Dominant Trait? If dominant, every affected individual will have a parent with the disorder If recessive, an affected individual can have normal parents Sex-linked or Autosomal? Autosomal= seen equally in males and females Sex-linked= usually only seen in males If it is sex-linked remember to use the X s and that their Y can t have an allele.
Practice Dominant or Recessive? Autosomal or Sex Linked? Fill in the Genotypes Complete shading Dominant or Recessive? Autosomal or Sex Linked? Fill in the Genotypes Complete shading Dominant or Recessive? Autosomal or Sex Linked? Fill in the Genotypes Complete shading