Heredity, GeneticsPunnett Squares & Probability Mr. Miller
Lets find out if the two pigeons onthe left produce offspring that havethe traits of the pigeon on the right
To do this we must understand how to use a Punnet SquareWhat is a Punnet Square?• A chart that allows us to determine the different genotypes that offspring can inherit from their parents
Lets see how to use it• First we must get the genotype of each parentExample:T: allele for tallnesst: allele for shortness tt – mothers genotype Tt – fathers genotype
Now lets set up the Punnet Square T tt T t t tt T t t t
What are the number of genotypes for the traits the offspring can inherit?•The offspring caninherit two sets ofgenes that will T tproduce a tallphenotype•The offspring can t Tt ttinherit two sets ofgenes that will t Tt ttproduce a shortphenotype
Now lets talk about probabilityWhat is probability?Probability is the chance that an event will occurHow do you find the probability of an event?You must know:• the number of specific events• the number of possible events
Lets find the probability the child will be tallHow many T tgenotypes willproduce a talloffspring? 2 t Tt ttWhat are numberof possiblegenotypes? 4 t Tt tt
Now lets find the probability! Probability =Number of specific event 2 1Number of possible events 4 2The probability of having a tall offspring is ½, 1:2, or 50%
Now try this one Determine the types of genes an offspring can inherit from parents that Z z have the following genotypes: Z Z Z ZzZz - father’s genotypeZz - mother’s genotype z Zz zzZ: gene for gray feathersz: allele for white feathers
Now lets look at the possible genotypes and the phenotypes that will be expressed There is a single possibility of inheriting a homozygous (pure) Z z dominant genotype which will produce a phenotype with grey Z Z Z Zz feathers There are two possibilities of z Zz zz inheriting heterozygous (hybrid) genotypes which will produce a phenotype with grey feathers
Now lets look at the possible genotypes and the phenotypes that will be expressed There is a single possibility of inheriting a homozygous (pure) Z z Z Z Z Zz recessive genotype which will produce a phenotype with white feathers z Zz zz So two grey birds can produce a pigeon with white feathers!
Now lets find the probability Z z Lets find the ZZ Zz Z probability the offspring will have z Zz zz grey feathers.number of specific events 3number of possible events =4
Now lets find the probability Z z Lets find the ZZ Zz Z probability the offspring will have z Zz zz white feathers.number of specific events 1number of possible events =4
Vocabulary• Probability: A number that describes how likely it is that an event will occur.• Punnett Square: A chart that shows all the possible combination of alleles that can result from a genetic cross.
Vocabulary• Phenotype: An organism’s physical appearance, or visible traits.• Genotype: An organism’s genetic makeup or allele combination.• Homozygous: An organism that has two identical alleles for a trait.
Vocabulary• Heterozygous: An organism that has different alleles for a trait.• Codominance: When alleles are neither dominant nor recessive. As a result, both alleles are expressed in the offspring.