Heredity Probability and Punnett Squares Probability Likelihood that
Heredity Probability and Punnett Squares
Probability • Likelihood that a specific event will occur Probability = # times event is expected to happen # opportunities for event to happen • Decimal, %, fraction or ratio • Remember: The more trials you perform – the more likely you are to reach the expected probability
Punnett Squares • You can predict & compare genetic variations that will result in offspring by performing a cross using a punnett square M m M MM Mm mm
Monohybrid cross • Mono = 1 • Inheritance of 1 trait • Cross can be: – Homozygous-Homozygous – Heterozygous-Heterozygous – Heterozygous-Homozygous
Monohybrid cross • 2 heterozygous parents: Tt x Tt (F 1) – T=dominant tall – t=recessive short • Genotypic ratio: 1: 2: 1 • Phenotypic ratio: 3: 1 – ¼ (25%) = homozygous dominant – ¼ (25%) = homozygous recessive – ½ (50%) = heterozygous – ¾ (75%) = are tall – ¼ (25%) = are short T TT Tt tt
Dihybrid Cross • Di = 2 • Inheritance of 2 traits
Dihybrid cross R = dominant round r = recessive wrinkled Y = dominant yellow y = recessive green • P generation: rryy x RRYY • F 1 generation: All offspring have same Genotype (Rr. Yy) All have same Phenotype (round and yellow) 16: 16 or 100% ry ry RY Rr. Yy Rr. Yy
Dihybrid cross R = dominant round Y = dominant yellow r = recessive wrinkled y = recessive green • Cross 2 individuals from the F 1 generation: Rr. Yy x Rr. Yy RY Ry r. Y ry RY RRYy Rr. YY Rr. Yy Ry RRYy RRyy Rr. Yy Rryy r. Y Rr. Yy rr. YY rr. Yy ry Rr. Yy Rryy rr. Yy rryy Analysis of Punnett Square: Genotypes RRYY- 1 RRYy- 2 9 Rr. YY- 2 Rr. Yy- 4 RRyy- 1 3 Rryy- 2 rr. YY- 1 3 rr. Yy- 2 rryy- 1 1 Phenotypes round, yellow round, green wrinkled, yellow wrinkled, green
1. How many guinea pigs will have black fur? _________ 2. How many guinea pigs will have brown fur? ________ 3. How many guinea pigs will have short fur? _________ 4. How many guinea pigs will have long fur? _________ 5. How many guinea pigs will have black short fur? ______ 6. How many guinea pigs will have black long fur? _______ 7. How many guinea pigs will have brown short fur? ______ 8. How many guinea pigs will have brown long fur? ______
In dogs, there is a hereditary deafness caused by a recessive gene, “d. ” A kennel owner has a male dog that she wants to use for breeding purposes. The dog also has a black tongue which he inherited from his mother, a Chow. The dog’s genotype is DDbb. (DD because he is not deaf; bb because the black tongue is recessive. ) Suppose the dog mates with a dog who is deaf, but is heterozygous for the pink tongue (dd. Bb). Make a dihybrid Punnett square to illustrate this cross. 1. 2. 3. 4. 5. 6. 7. 8. How How many many dogs dogs will will be deaf? _______________ be able to hear? ____________ have black tongues? __________ have pink tongues? ___________ be deaf and have black tongues? _____ be able to hear and have black tongues? ____ be deaf and have pink tongues? ______ be able to hear and have pink tongues? _____
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