Genetics Probability and Punnet Squares

ObjectivesBy the end of class you will know: 1. How to indicate the difference

between dominant and recessive alleles

2. The definitions of heterozygous and homozygous

3. The definitions of genotype and phenotype

• Gene:

• Found on a chromosome in a specific location called a locus

• Allele:

• Example: the gene for pea height has two alleles: Tall or Short

Vocabulary

A dominant allele will always mask a recessive allele.

Vocabulary• Dominant: Alleles that are always expressed.

A CAPITAL LETTER used to show a dominant allele• Example: Tongue Rolling

• Tongue Rolling: Dominant • Non-Tongue Rolling: Recessive

When a person has both alleles, Tongue Rolling and Non-Tongue Rolling, the person will always be a ____________________________

Vocabulary• Recessive: Alleles that are only expressed

when paired with another recessive allele. A lowercase letter represents the recessive allele.• Example: Hitchhiker’s thumb

• Straight thumb = Dominant• Hitch-hiker’s thumb = Recessive

When a person has both recessive alleles, the person will have a _____________________ thumb.

VocabularyAll organisms have two copies of each

gene, one contributed by the father, the other contributed by the mother.

• Homozygous: • Example:• Heterozygous:

• Example:

Two different alleles are present (heterozygous) for pea shape, round and wrinkled. Round is dominant and wrinkled is recessive.

• Using the letter R/r to show pea shape. How would this be written?

• Genotype:

• Describing an organism in terms of the individual’s genes• Example: Pea Shape - Wrinkled (R) or Non-

wrinkled (r) • Genotype Possibilities:

RR – wrinkled pea

Rr – wrinkled pea Heterozygous

rr – non-wrinkled

Vocabulary

• Phenotype:

• Example: Pea Shape (Wrinkled or Non-Wrinkled)• Phenotype Possibilities

• Wrinkled • Round

** Use the genotypes to determine the phenotypes

Vocabulary

Genetics and Probability

• The likelihood that a particular event will occur is called probability.

Example: Consider flipping a coinLanding: Heads UP or Tails UPThe probability of landing heads?

The probability of landing 3 heads in a row?

Penny Flipping Lab