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Traits and Inheritance
or: Why am I, the I that I am?
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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
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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
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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
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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)
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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.
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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
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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
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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
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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
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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 %)
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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