Download File - Mr. Cramer

Mendel’s Laws of
Heredity
Why we look the way
we look...
What is genetics?
 Genetics is the study of heredity, how traits
are passed from parent to offspring
The father of Genetics

Gregor Mendel
• His most famous experiment
was done with pea plants.
• Was an Austrian Monk that
lived in the mid 1800s
Mendel observed that the
height of pea plants varied
 Mendel crossed different
size plants to see if he could
predict the height of the
offspring

Mendel’s cross between tall pea plants yielded all
tall pea plants. His cross between small pea plants
yielded all small pea plants.
X
=
X
=
Mendels’ cross between tall pea plants and small pea
plants yielded all tall pea plants.
x
=
Mendel then crossed these second generation tall pea
plants and ended up with 1 out 4 being small.
x
=
Lets Start heredity
These are my parents, who do I look like?
My dad?
My Mom?
What is heredity?
The
passing on of
characteristics (traits)
from parents to offspring
Genetics is the study of
heredity
Mendel used peas...
They
reproduce sexually
They have two distinct,
male and female, sex cells
Their traits are easy to
isolate
Mendel crossed them
Fertilization
- the uniting
of male and female
gametes
Cross - combining gametes
from parents with
different traits
Questions
What
What
What
What
What
What
did Mendel cross?
are traits?
are gametes?
is fertilization?
is heredity?
is genetics?
Rule of Unit Factors
Each
organism has two
alleles for each trait
–Alleles - different forms of
the same gene
–Genes - located on
chromosomes, they control
how an organism develops
Rule of Dominance
The
trait that is observed
in the offspring is the
dominant trait (uppercase)
The trait that disappears
in the offspring is the
recessive trait (lowercase)
Law of Segregation
A
parent randomly passes
only one allele for each
trait to each offspring
Questions...
How
many alleles are there
for each trait?
What is an allele?
How many alleles does a
parent pass on to each
offspring for each trait
Questions...
What
do we call the trait
that is observed?
What case (upper or lower)
is it written in?
What about the one that
disappears?
What case is it written in?
Phenotype & Genotype
Phenotype
- the way an
organism looks
– red hair or brown hair
genotype
- the gene
combination of an organism
– AA or Aa or aa
Heterozygous & Homozygous
Heterozygous
- if the two
alleles for a trait are
different (Aa)
Homozygous
- if the two
alleles for a trait are the
same (AA or aa)
Monohybrid
Monohybrid
Cross crossing parents who
differ in only one trait
(AA with aa)
Questions...
What
is the phenotype?
What is the genotype?
What is homozygous?
What is heterozygous?
What is monohybrid
crossing?
Let’s Practice –Take a look at the
genetics behind getting a widows peak
Dominant and Recessive Genes This is lily Widows Peak



A dominant gene will always Munster
mask a recessive gene.
A “widows peak” is dominant,
not having a widows peak is
recessive.
If one parent contributes a
gene for a widows peak, and the
other parent doesn’t, the offspring will have a widows peak.
Genetics
All organisms have two copies of each gene, one
contributed by the father, the other contributed by
the mother.
Homozygous - Two copies of the same gene
Heterozygous - Two different genes
Genetics
For the widows peak:
WW - has a widows peak
Ww - has a widows peak
ww - no widows peak
Homozygous dominant
Heterozygous
Homozygous recessive
Genetics
Since Herman has no widows peak, he must
be “ww”, since Lilly has a widows peak she
could be either “WW” or “Ww”
Definitely ww
Either Ww
or WW
Homozygous
recessive
Heterozygous
Homozygous
dominant
Genetics
We can use a “Punnet Square” to determine
what pairs of genes Lilly has
• A Punnet Square
begins with a box 2 x 2
Assume Lilly is heterozygous
Ww
Assume Herman is homoozygous
recessive
ww
• One gene is called an
“allele”
W
w
w
Ww
ww
w
Ww
ww
• One parents pair is
split into alleles on top,
the other along the side
• Each allele is crossed
with the other allele to
predict the traits of the
offspring
Genetics
Notice that when Lilly is crossed with
Herman, we would predict that half
the offspring would be “Ww”, the
other half would be “ww”
Half “Ww”, Heterozygous, and will have a
widows peak
Half “ww”, Homozygous, and
will not have a widows peak
W
w
w
Ww
ww
w
Ww
ww
Genetics
Another possibility is that Lilly might be
“WW”, homozygous dominant.
Assume Lilly is homozygous
dominant
WW
W
Assume Herman is homoozygous
ww
W
w
Ww Ww
w
Ww Ww
Notice that all the
offspring are
heterozygous and will
have a widows peak