Traits and Inheritance

or: Why am I, the I that I am?

Genes• Gene – a set of instructions or an

inherited trait– Ex. Gene 1 for eye color Gene 2 for dimples, etc– Each parent gives one set of genes to the offspring

• Allele – different forms of a gene– Ex. Gene 1 may be for brown or blue eyes– one is dominant (CAPITAL letter) – one is recessive (lowercase letter)

Gene 2

Gene 1

chromosome

Dominant and

Recessive

Dominant alleles are more common and show up more frequently than recessive alleles.

Which traits in pea plants did Mendel observe as dominant?

Purple flowersYellow seedsTall plants

Allele

• Gene 1 has instructions for eye color

• The alleles are brown and blue

Gene 1 - brown eyes Chromosomefrom father

Chromosomefrom mother

Gene 1 – blue eyes

These two chromosomes make up a? Homologous pair

Genotype

• Both inherited alleles determine the genotype or an organism

• Genotype is written, using the two alleles (letters)

• If both inherited alleles are the same – homozygous– Both may be dominant (BB)– Both may be recessive (bb)

• If one allele is dominant and one recessive – heterozygous (Bb)

Phenotype

• Their phenotype was either purple or white.

• What is your phenotype for eye color?

• The appearance of an organism• Mendel observed that pea plant flowers could be purple

or white.

Example: Guinea Pigs!Guinea pigs have alleles which contain genes for fur color. Imagine a baby guinea which had the following alleles:

• The allele from mom is for Brown fur (B)• The allele from dad is for White fur (b)

Which Allele is Dominant? __________

What is the genotype? _____________

What is the phenotype? ____________

brownBb

brown

How is this useful? Selective breeding• Breed animals for the traits we want

them to have

• The genotypes of the parents can help us predict the phenotypes of the offspring– We can use the genotype to find the

probability of each phenotype

non-shedding dogsfat chickens

Homozygous or Heterozygous

Red (R) is dominant for red flowers, and white (r) flowers are recessive.

How would you write:• Homozygous dominant ____• Homozygous recessive ______• Heterozygous ______

rrRr

RR

Punnett

Squares

Illustrates how the parent’s alleles might combine in

offspring

Top of the square shows one

parent’s alleles for the trait

Side of the square shows

second parent’s alleles for the

trait

Each box shows how the alleles

might combine in potential offspring

Punnett Squares• What is the chance of a blue eyed

parent (bb) and a brown eyed parent (BB) producing brown eyed offspring?

B

B

bb

B B

B B

b b

b b

Genotype: Bb

Phenotype:Brown eyes (100%)Blue eyes (0 %)

Punnett Squares• What are the chances of a blue

eyed parent (bb) and a heterozygous Brown eyed parent (Bb) producing blue eyed offspring?

b

B

bb

B Bb b

b b

Genotype: Bbbb

Phenotype:Brown eyes (50%)Blue eyes (50%)

bb