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Non-Mendalian Genetics
In a plant, long stems are dominant (L) to short stems (l). If a
homozygous dominant flower and a homozygous recessive plant are
crossed, what would be the phenotypic ratio of their offspring?
Science Fact of the Day
• The protein Titin or connectin is the largest
known protein with ~26,000 amino acids forming
the polypeptide chain. This protein is responsible
for muscle elasticity in the human body.
CO: I will predict possible genetic
outcomes using Non-Mendelian
inheritance and pedigrees.
LO: I will take notes and draw a
pedigree for a trait in a family.
Mendel’s principles form
the basis of the modern
science of genetics.
The inheritance of
biological characteristics is
determined by specific
segments of DNA called
Genes are passed from
parents to their offspring.
Today we’re going to talk about a
special case: sex-linked traits
• Remember: Each
person inherits an X
chromosome from
mom and either an X or
a Y from dad
• We use the letters X
and Y to represent
chromosomes (not
What do you think a “sex-linked”
trait is? Examples?
Sex-linked traits
• Are traits that are determined by either the Y
or X chromosome
– If they are determined by the Y chromosome
they are referred to as “Y-linked”
Y-linked disorders are very rare and often cause
infertility in men
– If they are determined by the X-chromosome
they are referred to as “X-linked”
X-linked dominant
• These conditions (such as vitamin D resistant
rickets) are rare and can affect both men and
– Men are more affected than women
– Both men and women can pass on the affected
chromosome to their children
In 18 words summarize these two diagrams.
X-linked recessive
• These disorders (such as hemophilia and color
blindness) more frequently affect men than
– Both men and women can pass these traits on to
their children (at different rates)
• An affected man/unaffected woman will have sons who
are unaffected and daughters who are carriers
• An affected woman/unaffected man will have a 50%
chance of passing the trait. If she passes on her affected
X chromosome, then her daughters will be carriers and
her sons will be affected
– This is why men are more likely to be color blind than women
How could you find out the
chances that you have hemophilia
running in your family?
Pedigree chart: a chart that shows relationships within a
Let’s practice
1. Pedigree Worksheet together
2. Flip knob—create your own pedigree chart
• A geneticist studying fruit flies hypothesizes that
short wings are a recessive trait coded for by a
single gene. Which observation is most likely to
have led her to form this hypothesis? Why?
1. Flies have wing lengths ranging from very long
to very short.
2. Flies with long wings are less likely to survive.
3. Flies with long wings can produce offspring
with short wings.
4. Flies with short wings prefer to mate with flies
with long wings.
Science Fact of the Day
CO: I will predict genetic outcomes
using non-Mendelian inheritance.
LO: I will write notes and create a
“baby” dominance with a partner
demonstrating both Mendelian and
Non-Mendelian inheritance.
Types of Inheritance
1. Mendelian: genetic traits are controlled by a
single gene
----- dominant or recessive; flower color
2. Sex-linked: genetic traits are controlled by the X
or Y chromosome
-----X-linked recessive; colorblindness
3. Co-dominance: both alleles contribute to the
phenotype equally (ex. Blood type)
4. Incomplete dominance: when the presence of
both alleles leads to a blending of traits (ex. Red
flower + white flower = pink flower)
5. Polygenic: when a trait is controlled by multiple
• When the genotype is heterozygous, then both
traits will show up equally
– Note: when writing we show this with two different
capital letters
Incomplete Dominance
• When the genotype
is heterozygous,
then the trait will
be a blend of the
two alleles
• Note: Sometimes, we
write this by using an
abbreviation of the trait
in a capital letter (C
=color) and the alleles as
a superscript (CR = red
flower) or subscript (CR).
• Sometimes, we just say
the heterozygous trait is
a blend.
Polygenic Inheritance
• Multiple genes control the inheritance of traits
Both genes and the environment
determine how traits are expressed in
a population
Rest of the Day
1. Practice by completing the Make a Face Lab
with a partner.
2. Remember, that you have homework for
1. Watch and take notes over the video “What is
Evolution?” by Stated Clearly. Come to class with
at least 3 questions over the video
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