#### Transcript Genetics Powerpoint - Liberty Union High School District

MENDELIAN GENETICS Gregor Mendel? “Father of Genetics” Heredity the study of how traits are passed from parent to offspring Mendel CROSSED pea plants Cross = breed 2 different individuals Tracking Generations P1 Generation = parent F1 Generation = 1st offspring F2 Generation = 2nd offspring Dominant: always expressed – TT = tall – Tt = tall Recessive: expressed when not with a dominant – tt = short GENOTYPE: genetic makeup of genes – TT – Tt – tt PHENOTYPE: physical expression of genes – Tall pea plant – Short pea plant You can see phenotype, not genotype Law of Dominance: • Some alleles are dominant, others are recessive – an organism with at least one dominant allele will display the effect of the dominant allele – dominant = uppercase – recessive = lowercase Example: Straight thumb is dominant to hitchhiker thumb T = straight thumb t = hitchhikers thumb Straight thumb = TT Straight thumb = Tt Hitchhikers thumb = tt * Must have 2 recessive alleles for a recessive trait to “show” Traits are determined by the genes gene = segment of DNA that determines a trait allele – different genes (possibilities) for the same trait Law of Segregation: 2 alleles that code for a trait separate during gamete formation (meiosis) • Both genes are the same – homozygous AA – homozygous dominant aa – homozygous recessive • 1 dominant 1 recessive gene - heterozygous Aa – heterozygous AA – Black Aa – Black bb – White Gamete Formation 1) Bb X Bb B B b b #2) bb x BB b bB B B How to Make a Punnett Square 1. Parent genotypes 2. Parent phenotypes 3. Segregate set up Punnett square 4. Fill Offspring genotypes 5. Genotype Ratio 6. Phenotype Ratio Sample Problems A. PP x pp B. YY x yy C. Yy x Yy Probability Notes Probability is the likelihood of a particular event or offspring …given as percent (25%), ratio (1:4), or fraction (¼) Mendel’s Laws follow the same probability as flipping a coin or rolling dice Formula: # of one kind of possible outcome total # all possible outcomes Rule of Addition • Chance an event can occur in 2 or more different ways • Use when the word OR is used • ADD separate probabilities Example: What’s the probability of rolling a 1 or 6? 1/6 + 1/6 = 2/6 Rule of Multiplication • Chances 2 more independent events can occur together • Use when the word AND is used Example: If you roll 2 dice, what’s the probability of rolling a 1 and 6? 1/6 x 1/6 = 1/36 • Multiply separate probabilities You Try: Work on the problems on your notes handout Show work Answers • Boy ½ • Boy or girl Addition ½ + ½ = 1 • Boy and girl Multiplication ½ x ½ = ¼ • 3 heads in row Multiplication ½ x ½ x ½ = 1/8 • Rolling a 6 on a die 1/6 • Rolling a 6 or a 5 on a die Addition 1/6 + 1/6 = 2/6 • Rolling a 6 and a 5 Multiplication 1/6 x 1/6 = 1/12 • Pulling out Queen of Hearts 1/52 • Pulling hearts as the suit ¼ • Queen Hearts of heart as suit heart as suit • Pulling Queen and Heart Multiplication 1/52 x ¼ = 1/208 Class Practice If you toss a penny into the air, what’s the probability that it will land heads up? What’s the probability of rolling a 6 with one die? What’s the probability of pulling the ace of hearts out of a deck of 52 cards? What’s the probability of pulling any ace from a deck of cards? RULE? A bag of beans contains 100 white beans and 100 red beans. What is the probability of reaching into the bag and pulling out a white bean? What’s the probability of tossing 2 coins and having them both land heads up? RULE? What’s the probability of rolling a pair of dice and getting snake eyes (double 1s)? Rule? What’s the probability of rolling a pair of dice and getting any doubles at all? Rule? What’s the probability that a woman’s first child will be a baby girl? What’s the probability a family with 3 kids will have 3 daughters? RULE? Testcross Purebred – Describes a homozygous trait – Purebred dominant = AA – Purebred recessive = aa – “homozygous” Hybrid – Describes a heterozygous trait – Aa – “heterozygous What do you do if you don’t know the genotype of the dominant parent? TESTCROSS! Dominant parents can be homozygous dominant or heterozygous AA or Aa You have to do a TEST to determine the type of dominance HOW? Breed mystery dominant parent to a homozygous recessive parent If any offspring show the recessive trait, the dominant parent HAD to be heterozygous Sample A black mouse is mated with a brown mouse (black is dominant to brown). They have 10 black offspring. What is the genotype of the black mouse? Several black mice of the same genotype are mated and produce 29 black and 9 brown offspring. What are the genotypes of the parents? Start by thinking of different possibilities! BB x BB BB x Bb or Bb x BB Bb x Bb Then do a backwards cross [called backcross]