Define polygenic inheritance 10.3.1

Defining polygenic inheritance
• A characteristic which is controlled by one or
more gene.
• “Multi-factorial” inheritance
– Mendel
• Multi-gene inheritance
Polygenic conditions
• Skin color
• Obesity
• Cancer
• Diabetes
Things that can affect polygenic
• Environment
– Ex. A person who tans may have darker skin.
Polygenic Inheritance
• Explains how genes can continuously vary
• Examples of this are a person’s height, blood
type, and skin color
Polygenic inheritance differentiates skin color
Polygenic inheritance affects blood type
Genotype and phenotype
• Genotype: The entire set of alleles in an
organism. Usually written with letters
• Phenotype: Alleles that include all
characteristics based on the genotype.
• Ex: tall
– TT
– Tt/ Tall
• Co dominant Alleles: A
pair of alleles that are
both affect the
phenotype when present
in a heterozygote.
• Example: red flower +
white flower= pink flower
• To write co dominance
the main letter should
relate to the gene and the
suffix to the allele
*draw on board
having two
different alleles
for the same gene
Pedigree Chart
• Pedigree Chart: Pedigree charts are used to
record blood lines in families. They can be
used to figure the probability of an offspring
and the donor of certain diseases.
: affected male
: affected female
: male
: female
• Autosomal Dominant
– You only need to get the abnormal gene from one
parent in order for you to inherit the disease.
• Autosomal Recessive
– Two copies of an abnormal gene must be present
in order for the disease or trait to develop.
• Sex-linked Dominance
– A single abnormal gene on the X chromosome can
cause a sex-linked dominant disease.
• Sex-linked Recessive
– An abnormal gene on both X chromosomes causes a
sex-linked recessive disease
Disease and Pedigree
• Color Blindness: A
condition that is caused
by genetic factors.
• Is determined by a carrier
of the recessive trait
• Females have two
chromosomes, so to have
color blindness she would
need two recessive
• The male has only one X
chromosome and just
needs one recessive allele
to be affected.
Pedigree Bingo!
• 1. Obtain a blank pedigree chart, and an orange, yellow, red, and blue
colored pencil.
• 2. Color in the circles for the Grandmother. Make them a variety of your
• 3. Then do the same for the Grandfather using different colors.
• 4. Next, close your eyes and randomly pick a colored pencil. Choose 3
examples from Grandmother and 3 examples from Grandfather.
• 5. Color in these circles for their first child, a daughter. Then complete
these steps again for the rest of their children.
• 6.Next, look at the son and his partner. Make the partner have all 6 circles
• 7. Randomly pick colors from the Son and his partner. Because his partner
has all red, 3 circles will be red, and 3 circles will randomly be chosen from
the father.
• 8. Do this for all 3 children.
• 9. Analyze the results.
– Red = high risk of heart disease
– Orange = medium risk of heart disease
– yellow= low risk of heart disease
– Negative risk of heart disease
Works cited
• Http://

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