Complex Patterns of Inheritance

COMPLEX PATTERNS OF

INHERITANCE

Patterns of inheritance that do NOT

follow Mendel’s law.

EQ: Which models are used to predict
and explain patterns of inheritance?

Review of Mendelian Genetics

• Mendel observed that traits were

either dominant or recessive

– The dominant allele masks the recessive

– Only 2 phenotypes are possible

– Round pea shape is dominant over

wrinkled pea shape
• RR & Rr = Round pea shapes
• rr = wrinkled pea shapes

Complex Patterns of Inheritance

• Complex patterns are modes of inheritance

that are neither dominant or recessive

• There are usually more than 2 phenotypes

possible

• Alleles may be represented by something

other than uppercase and lowercase letters

• There are 5 different types

1) Incomplete Dominance Inheritance

• The phenotype of the heterozygote is in

between those of the two homozygotes.

– It is an intermediate, and a third phenotype

appears when the heterozygote is present

– In heterozygotes, neither allele is completely

dominant.

• Examples:

– Feather colors in chicken
– Flower color in snapdragon

Example = Snapdragons

• R = red, R’ = white

– RR =
– R’R’ =
– RR’ =

–

•

R R

R’

R’

Red
White

Pink

RR’

RR’

RR’

RR’

Multiple Choice

The blending of two traits in which one is not completely dominant over the other is known as ---

• incomplete dominance

• codominance

Multiple Choice

The green fish offspring in this image is an example of ---

• Incomplete dominance

• Codominance

Dropdown

Snap dragon color is a incomplete dominant trait. A red flower (RR) is crossed with white flower (WW)? What color are flowers that are RW?

Select answer

Multiple Choice

A red flowered plant (RR) is crossed with a white flowered plant (WW). The gene for petal color in these plants expresses incomplete dominance. What percentage of the offspring will have pink (RW) flowers?

• 0%

• 25%

• 50%

• 100%

2) Codominant Inheritance

• The phenotypes of both alleles are

equally expressed in the
heterozygote

– The heterozygote shows BOTH alleles

• Examples:

– Sickle Cell disease
– Roan coloration in cattle & horses

Red

Horse

White

Horse

Roan

Horse

2) Codominant Inheritance

Example: Horses

• HR - Red in horses

• HW - White in horses

– HRHR =

– HWHW =

– HRHW =

HR HR

HW

HW

Red hair

White hair

Roan hair (Red &
white)

HRHW

HRHW

HRHW

HRHW

Multiple Choice

What type of inheritance pattern is shown here?

• Codominance

• Incomplete dominance

Multiple Choice

A calico cat shows both the traits for orange fur and black fur. What kind of allele expression is this?

• Incomplete dominance

• Codominance

Multiple Choice

Codominance occurs in calico cats, which allows for the Black and Tan colors to show. What percentage of the offspring represented in this P square will be calico (black and tan spotted)?

• 25%

• 50%

• 75%

• 100%

3) MULTIPLE ALLELE INHERITANCE

• Traits controlled by more than 2 alleles

• A diploid individual can only have 2

alleles of a trait.

– Example:

• Fur color in rabbits
• Blood type = 3 different alleles:

IA, IB, i

IA i

IA

IB

● 4 Possible phenotypes

(Type A, B, AB, O)

IAIA =

IAi =

IBIB =

IBi =

IAIB =

ii = Type O Blood

Type AB Blood
Type B Blood

Type B Blood

Type A Blood

Type A Blood
IAIA

IAIB

IBi

IAi

3) MULTIPLE ALLELES

Blood Type

Blood Type
That Can Be

Received

Type of
Antigens
Present

Type of

Antibodies
Produced

A ( IA )

A and O

A antigens

B antibodies

B ( IB )

B and O

B antigens

A antibodies

O ( i )

Universal Donor
Only O

No antigens
A and B
antibodies

AB ( IAIB )
Universal
Recipient

All types

A and B antigens

No antibodies

Multiple Select

A person with a Type A Phenotype would have what potential genotypes?

• I^AI^A

• I^Ai

• ii

• I^AI^B

Multiple Choice

A person with a Type AB Phenotype would have what potential genotypes?

• I^BI^B

• I^Bi

• ii

• I^AI^B

Multiple Choice

What is the Genotype for Homozygous "B" allele

• IᴬIᴮ

• Iᴮi

• IᴬIᴬ

• IᴮIᴮ

4) POLYGENIC INHERITANCE

• TRAITS ARE CONTROLLED BY 2 OR MORE

GENES

• Genes can be on the same chromosome or

on different chromosomes.

• Phenotypes usually show a continuous

range or variability.

- Example: Height = A, B, and C all contribute to

height

A

a

C c

B

b

•Tallest = AABBCC

•Shortest = aabbcc

•In between = AaBbCc

•Polygenic traits include: skin color, body weight, eye

color, hair color, and height

• Sex determination

–
If females have the XX combination then all eggs
will contain an X chromosome

–
If males contain the XY combination then the sperm
will contain either the X or the Y chromosome.

*Therefore, the male always determines the sex of the

offspring*

•If he passes the X chromosome the result will be a female
offspring.

•If he passes the Y chromosome the result will be male
offspring

5)Sex-Linked Inheritance

• Discovered by Thomas Hunt Morgan

while studying fruit flies.

– Noticed most flies have red eyes

– Discovered a male with white eyes and

decided to mate him with a red eyed
female

• Morgan’s Experiment

– All the offspring (F1) had red eyes and

the male and female ratio was 50:50

– Then he crossed a male and a female

from the F1 generation

• In the F2 generation

–75% had red eyes, and 25% had white eyes

–50% were male and 50% were female

–ALL of the white eyed flies were MALE.

–

• Sex-linked trait = a trait that is carried on the

X chromosome. (XHXh or XhY)

• It is most commonly expressed in males

• Sex-linked traits in humans include:

• Hemophilia
• Duchenne Muscular Dystrophy
• Red/Green Color Blindness

ARE YOU COLOR BLIND?

Sex-linked Traits are found on the Sex Chromosomes

​

​

Sex-Linked Traits

Dropdown

X and Y are ​​

Select answer

chromosomes. Females are ​

Select answer

and males are ​

Select answer

.

​Sex-linked Traits are shown as a Superscript on the X or Y.

Sex-Linked Traits

Multiple Choice

In fruit flies, eye color is a sex-linked trait.  Red (R) is dominant to white (r).

Which genotype shows a female fly with white eyes?

• $$X^{R^{ }}X^r$$

• $$X^RX^R$$

• $$X^rX^r$$

Multiple Choice

Which genotype shows a male with white eyes?

R = Red, r= white

• $$X^rY$$

• $$X^RY$$

Match

Match the following. H= no hemophilia, h = hemophilia

• Male without hemophilia

• Female with hemophilia

• Female Carrier

• Male with hemophilia

• Female who is NOT a carrier

X^HY

X^hX^h

X^H X^h

X^hY

X^HX^H

• X^HY

• X^hX^h

• X^H X^h

• X^hY

• X^HX^H

​ 1. Write out XX or XY

2. Add in trait to the X only

3. Fill out punnett square as normal.

How to show Punnett Square

Multiple Choice

Which of the following genotypes belongs in the red box in the Punnett square?

• X^BX^b

• X^bX^b

• X^bY

• X^BY

Multiple Choice

The following punnett square depicts the x-linked cross of a female who carries hemophilia with a man showing no symptoms. Fill in the genootype represented by the blank box in the punnett square.

• X^H X^H

• X^h X^H

• X^H Y

• X^h Y

Draw

Show punnett square for X^rX^r crossed with X^RY

Multiple Choice

Hemophilia is a recessive x-linked disorder.
Which genotype represents a female who is a carrier for hemophilia?

• X^HX^h

• X^hX^h

• X^HX^H

• X^hY

Draw

Hemophilia (h) is recessive. Draw a punnett square for X^hX^h with X^HY

Dropdown

What is the likelihood of this cross have a child that is colorblind?

Select answer

Multiple Choice

What is the chance that a daughter will be colorblind?

• 100%

• 50%

• 25%

• 0%

Multiple Choice

What chance will a boy will be colorblind?

• 100%

• 50%

• 25%

• 0%

Multiple Choice

Who is more likely to have an X-linked trait?

• Males

• Females

• Both males and females

Dropdown

​

Select answer

are more likely to have an x-linked trait because males have only ​

Select answer

X chromosome. Females can be ​

Select answer

of an X-linked trait because they can be ​

Select answer

for the trait since they have ​

Select answer

X's.

Vocabulary

• codominance

• incomplete dominance

• multiple alleles

• genotype

• phenotype

• sex-linked inheritance

Poll

Rate how well you understand this topic.