Download Heredity

Heredity
• Heredity is the passing of traits from
parents (mom and dad) to offspring (you).
Traits
• Traits are characteristics that you inherited
from your parents.
• Think of a characteristic you have that looks
very much like one of your parents.
• Think of a characteristic you have that does
not look like either of you parents.
Gregor Mendel
• Let us read the book
on Mendel and his
work.
Gregor Mendel
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Gregor Mendel (1822-1884):
Born in 1822, poor, tutored other students
Loved plants and lived in Czech Republic
Educated in Vienna in math and science
Became a monk at 21
Studied pea plants and their characteristics by combining math and
botany
He ensured that plants got characteristics from only a single parent.
Controlled pollination
Short plants always yielded short plants.
Tall plants yielded 75% tall plants and 25% short plants.
In first cross breeding all plants were tall. Plant was tall because of tall
parents.
Tall plants dominated over short plants.
25% were tall pure, 50% were tall non-pure and 25% were short pure.
Recorded thousands of plants
Published his work but the work went unnoticed.
Gained so much weight he could not work on plants anymore.
Became abbot and stopped working with plants.
Work became known as Mendallian Laws of Inheritance.
Mendel’s Vocabulary
• Dominant trait: the
characteristic that expresses
itself over another. Example:
• Recessive trait: the
characteristic that recedes
into the background and
might express itself in later
generations. Example:
Mendel’s Ratios: Let us calculate them
Mendel’s Vocabulary
• Genes: A set of instructions
in the DNA that determines
an offspring’s characteristics.
In sexual reproduction, an
offspring receives one set of
genes from each parent.
• Alleles: The two forms of
genes, one from mom and
one from dad, are known as
alleles.
Mendel’s Vocabulary
• Genotype: The combination
of alleles in your body is your
genotype. The genotype
works behind the scenes.
• Phenotype: Your
appearance as a result of
your alleles is your
phenotype.
Punnett’s Vocabulary
• Dominant allele: Capital letter
• Recessive allele: lower case
letter
• Punnett Square: A square
with four boxes used to
predict the allele
combinations for offspring.
We will only use four.
Practice with Punnett Squares
• Take out your notes on Mendel and Punnett.
• Turn the paper to Punnett’s side.
• Let us choose a species and a trait for that species. We
must choose a dominant trait and a recessive trait. Do
not choose humans for species.
• Now, let us assume that a pure dominant parent will mate
with a pure recessive parent. Complete the first Punnett
square.
• Assume that two of the offspring from the first Punnett
square will mate (now do you see why we did not choose
humans?). Complete the second Punnett square.
• Excellent! We will now take our knowledge of heredity
and have some fun with aliens.
Heredity
• Heredity is the passing of traits from
parents (mom and dad) to offspring (you).
Traits
•Traits are characteristics that you inherited
from your parents.
Human Examples:
Pea Plant Examples:
Hair
Height
Nose
Pea color
Skin
Pea shape
Eyes
Flower Color
Dominant and Recessive
Traits / Alleles
•The dominant trait expresses itself over the
recessive trait. Traits are represented by
alleles. One allele from each parent.
Brown or Black hair is DOMINANT over blond or
red hair.
Capital “B”
for
dominant
allele
Lower case
“b” for
recessive
allele
Genes
•Genes are made up of DNA which are on
the chromosomes and found in every cell in
your body. Genes consist of two alleles.
Your genes determine your appearance and
internal make up.
Genotype versus Phenotype
Genotype: The genetic
(genes) make up of a
species. The two alleles
make up the genotype.
Example BB or Bb or bb
Phenotype: The
appearance of a species.
What you see is the
phenotype. Example: Red
hair, brown eyes, tall trees,
short trees.
BB
Tt
Bb
bb tt
TT