Heredity Probability and Punnett Squares

Probability = # times event is expected to happen 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 MM Mm mm

Monohybrid cross Mono = 1 Inheritance of 1 trait Cross can be: Homozygous-Homozygous Heterozygous-Heterozygous Heterozygous-Homozygous

Monohybrid cross T t TT Tt tt 2 heterozygous parents: Tt x Tt (F1) T=dominant tall t=recessive short Genotypic ratio: 1:2:1 ¼ (25%) = homozygous dominant ¼ (25%) = homozygous recessive ½ (50%) = heterozygous Phenotypic ratio: 3:1 ¾ (75%) = are tall ¼ (25%) = are short T 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 F1 generation: All offspring have same Genotype (RrYy) All have same Phenotype (round and yellow) 16:16 or 100% ry RY RrYy

Dihybrid cross R = dominant round r = recessive wrinkled Y = dominant yellow y = recessive green Cross 2 individuals from the F1 generation: RrYy x RrYy Analysis of Punnett Square: Genotypes Phenotypes RRYY- 1 round, yellow RRYy- 2 round, yellow RrYY- 2 round, yellow RrYy- 4 round, yellow RRyy- 1 round, green Rryy- 2 round, green rrYY- 1 wrinkled, yellow rrYy- 2 wrinkled, yellow rryy- 1 wrinkled, green 9 3 1 RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy

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 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 (ddBb). Make a dihybrid Punnett square to illustrate this cross. 1. How many dogs will be deaf? _____________________________ 2. How many dogs will be able to hear? _______________________ 3. How many dogs will have black tongues? ____________________ 4. How many dogs will have pink tongues? _____________________ 5. How many dogs will be deaf and have black tongues? _________ 6. How many dogs will be able to hear and have black tongues? ____ 7. How many dogs will be deaf and have pink tongues? ___________ 8. How many dogs will be able to hear and have pink tongues? _____