Download Document

Traits and
Inheritance
or: Why am I, the
I that I am?
Genes
• Gene – a set of instructions or an inherited
trait
Gene 1
– Ex. Gene 1 for eye color
Gene 2 for dimples, etc
– Each parent gives one set of
genes to the offspring
Gene 2
chromosome
• 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)
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 flowers
Yellow seeds
Tall plants
Allele
• Gene 1 has instructions for
eye color
• The alleles are brown and
blue
Gene 1 – blue eyes
Gene 1 - brown
eyes
Chromosome
from father
Chromosome
from mother
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)
• The appearance of an organism
• Mendel observed that pea
plant flowers could be purple
or white.
• What is your phenotype for eye color?
Phenotype
• Their phenotype was either 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)
brown
Which Allele is Dominant? __________
Bb
What is the genotype? _____________
brown
What is the phenotype? ____________
How is this useful?
Selective breeding
• Breed animals for the traits we want them
to have
non-shedding dogs
fat chickens
• 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
Homozygous or Heterozygous
Red (R) is dominant for red flowers,
and white (r) flowers are recessive.
How would you write:
RR
• Homozygous dominant ____
rr
• Homozygous recessive ______
Rr
• Heterozygous ______
Illustrates how
the parent’s
alleles might
combine in
offspring
Top of the square
Punnett
shows one
Squares 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
B
Bb
Bb
B
Bb
Bb
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
b
b
Bb
Bb
bb
bb
Genotype:
Bb
bb
Phenotype:
Brown eyes (50%)
Blue eyes (50%)