7.2 Complex Patterns of Inheritance - Weebly

7.2 Complex Patterns of Inheritance

KEY CONCEPT

Phenotype is affected by many different factors.


Phenotype can depend on interactions of alleles.

• Autosomal dominance

– Only need to inherit one copy of the disorder to be

affected

– Disease is dominant (DD or Dd)

– Homozygous dominant: early death, usually don’t survive to

reproduce

– Heterozygous: live into adulthood

– Healthy is recessive (dd)

– Ex: Familial hypercholesterolemia (also called FH) or

Huntington’s disease


Usually 50/50 chance of inheriting autosomal dominance

due to only 1 parent being affected


Autosomal Dominance Inheritance

• Ex:

• Paul has familial hypercholesterolemia and Stacy is healthy.

The two have 3 children, 2 boys, and a girl. After testing, the

middle child is the only healthy child.

Key

F = FH

f = healthy

disease disease

healthy healthy

Paul Stacy

Ff

Ff

Ffff

ff


Another example…

• Huntington’s disease is a dominant disorder found on

chromosome 4. Betty and Marcus met at a support clinic they

have been attending to help them cope with the knowledge of

their illness with Huntington’s disease. They would like to

know the risk of having a healthy child, now that Betty is

pregnant.

Key

H = Huntington’s disease

h = healthy

disease disease

disease healthy

Marcus Betty

Hh Hh

?


Incomplete Dominance• neither allele is completely dominant nor

completely recessive.

– Heterozygous phenotype is intermediate

between the two homozygous phenotypes

• Heterozygous is like a “blend”


Example: Cross a homozygous red carnation

flower (RR) with a homozygous white flower

(WW).

• List the

genotypes.

4RW

• List the

phenotypes.

4 Pink


Example: Cross one heterozygous pink (RW) 4

o’clock flower with a White flower (WW).

• List the

genotypes.

2RW, 2WW

• List the

phenotypes.

2 Pink, 2White


Codominance• Defined: When both alleles

are dominant and equally

expressed

• The colors do NOT blend

together, but are equally seen

• Ex: Cattle Coat

Red cow x White cow =

Roan Cow

• Ex: Human Blood types

Type A x Type B = Type AB


• Blood types are another example of codominance.

– The ABO blood types result from codominant alleles

– This blood group consists of 3 different alleles

• Dominant A allele

• Dominant B allele

• Recessive O allele

• A and B are equally

dominant


Ex: Cross Jason who is homozygous for

type A blood with Maria who is homozygous

for type B blood.

• List the genotypes.

4AB

• List the phenotypes.

4 type AB blood


Ex: Cross Mike who is heterozygous for type A

blood with Lisa who is heterozygous for type B

blood.

• List the genotypes.

1AB, 1Ao, 1Bo, 1oo

• List the phenotypes.

1 type AB blood

1 type A blood

1 type B blood

1 type o blood

• Probability of Heterozygous individual?

75%


Many genes may interact to produce one trait.

• Polygenic traits are

produced by two or

more genes.

Order of dominance:

brown > green > blue.


• An epistatic gene can interfere with other genes.

• This is like a “knock out” gene


The environment interacts with genotype.

• Height is an example of a

phenotype strongly affected

by the environment.

• The sex of sea turtles

depends on both genes

and the environment

• Phenotype is a combination

of genotype and

environment.

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