Wednesday, January 5, 2011 Objective: SWBAT predict offspring of parents using Punnett Squares Bellringer: What is the difference between a gene and an allele?

Review of Yesterday’s Vocabulary

HOMOZYGOUS organism with two identical alleles for the same trait (TT or tt)

HETEROZYGOUS organism with two different alleles for the same trait (Tt)

DOMINANT allele that is expressed when in the presence of a recessive allele (TT or Tt = tall)

RECESSIVE allele that is expressed only when homozygous (tt = short)

PHENOTYPE physical characteristics (Tall, Brown)

GENOTYPE the genetic makeup (TT, TtHh)

GENE = Height ALLELE = Tall, Short Gene is represented by the letter “t” Dominant = T Recessive = t Remember you need 2 copies of every gene!!!

How can we determine what the offspring are going to be?

PUNNETT SQUARES

Reginald C. Punnett Inventor of the Punnett Square

PUNNETT SQUARES chart showing the possible combination of alleles in a cross

Punnett Squares show the probability of getting a certain type of offspring

THE PARENTS GENOTYPES DAD = Tt (heterozygous) MOM = Tt (heterozygous) PHENOTYPES DAD = Tall MOM = Tall

PUNNETT SQUARES

THE OFFSPRING TT (homozygous dominant) Tt (heterozygous) tt (homozygous recessive) GENOTYPES 1TT:2Tt:1tt (1:2:1)

THE OFFSPRING TT (tall) Tt (tall) tt (short) PHENOTYPES 3 Tall :1 Short (3:1)

Practice Problems! Do the following problems on your notes paper.

Cross a homozygous dominant with a recessive (for height where T is dominant and tall). Find the genotype and the phenotype

Cross a heterozygote with a recessive (for height where T is dominant and tall). Find the genotype and the phenotype

Cross a heterozygote with another heterozygote (for skin color where Black is B, b = white). Find the genotype and the phenotype

Cross a heterozygote with another heterozygote (for nose size where big nose is N and small nose is n). Find the genotype and the phenotype

If we saw an organism that had round seeds (round is dominant), how could we figure out what its genotype is?

A cross between an unknown and a homozygous recessive Test Cross

Example of a Test Cross Unknown

Homework Bikini Bottom Genetics!