Page 200 - Science Course 3 (Book 1)

Mo5-L2b: What are the Patterns of Inheritance?

Polygenic Inheritance Human blood type is an example of multiple alleles,
or a gene that has more than two alleles.
an inheritance pattern in which multiple genes
determine the phenotype of a trait. The I and I alleles are codominant to each other,
B
A
but both are dominant to the i allele.
Skin Pigmentation
| A | B i
| | | | | i
A
A B
A A
X
| A A AB A
aabbc AABBCC
B
B B
B A
(very light) (very light) | | | | | i
| B
AB B B
X i| A i| B ii
i
AaBbCc AaBbCc A B O

Human ABO Blood Type
Let’s Begin Phenotype Possible Genotype

A
A A
Type A | | | or I i
Other Patterns of Inheritance
B
B B
Type B | | | or I i
When an offspring’s phenotype is a combination of
its parents’ phenotypes, it is called incomplete Type O ii
dominance.
A B
Type AB | |

When the allele for a trait is on an X or Y
chromosome, it is called a sex-linked trait.

In fruit flies, the allele for eye color is on only the X
chromosome, not on the Y chromosome,

X w X
When both alleles can be independently observed in
a phenotype, it is called codominance X X w X X
w
w
X w

Codominance
X Y XY
w
Y
Yellow Red
rr RR

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