1/17 X-linked Traits

Incomplete Dominance:

• Incomplete Dominance is a

__________ or a blend of alleles
producing a 3rd phenotype.

• Neither allele is completely
dominant over the other.

Codominance: Co-operate

•Both alleles are equally
________.
•Both will be expressed in the
phenotype.
•Creates a “speckled” phenotype
with both equally showing.
(speckled chicken)

Multiple Choice

this image is an example of

• codominance
• dominance
• incomplete dominance

Multiple Choice

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

• 25

• 50

• 75

• 100

Multiple Choice

A long-haired female rabbit and a short-haired male rabbit produced this offspring with a medium-length coat:

• Incomplete dominance

• Codominance

• Complete dominance

Multiple Choice

this image is an example of

• codominance
• dominance
• incomplete dominance

Multiple Choice

This is an example of ---

• Incomplete dominance

• Codominance

Multiple Choice

A woman with curly hair and a man with straight hair produced a child with wavy hair:

• Incomplete dominance

• Codominance

• Complete dominance

Turn to
this page
Sex-Linked
Traits

Turn and talk: What do you notice
about the two sets of chromosomes?

Sex Linked Genes

• The X and Y sex chromosomes carry the genes

that determine your gender

• Men have a combination of X and Y sex

chromosomes.

• Women have two X
chromosomes.

XY
XX

Sex-linked traits

Also referred to as “x-linked traits”.

Most x-linked traits are controlled
by genes on the X chromosome

Sex inheritance patterns for male

and female children

X Linked Traits

• Men and Women

can get the
X-linked traits,
Why?

Because they
both inherit X
chromosomes.

X Linked Traits

• Males cannot

be carriers of
the X-linked
traits they only
have one X.

Females are
the only X
chromosome
carriers.

X-linked Recessive Inheritance

► These traits tend to show up in males more

than females. Why?

► Males cannot be carriers of the X trait.

They either have it or they don’t. Only
Female are X-Chromosome carriers.

X-linked Recessive Inheritance

► X-linked recessive traits are traits resulting from

a recessive allele on the X chromosome.

► Uppercase and lowercase superscripts are

used to represent dominant and recessive
alleles as shown below.

XA = dominant

Xa = recessive

► Sons can only receive a Y chromosome from

their father and inherit their X chromosome from
their mother.

Back to Regular
Mendel Genetic Rules

X Chromosome Traits

• Men only have one

X chromosome

• Therefore genes

on that
chromosome are
expressed in the
male phenotype.
(Example
colorblindness).

XAY dominant, shown
XaY recessive,
shown

XA XA dominant, shown
XA Xa dominant masks the recessive, shown
Xa Xa recessive, not shown

Turn and Talk: What would the
results of the Punnett Square be?

X-linked Recessive Inheritance-

Colorblindness

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

Hotspot

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

Multiple Choice

Colorblindness is a recessive X-linked disorder.

Which genotype represents a male with normal vision?

• X^N Y^N

• Xⁿ Yⁿ

• X^N Y

• Xⁿ Y

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

If a female express a recessive sex-linked trait, then all of her ______ _______ offspring will show the trait as well.

• biologically male

• biologically female

Multiple Choice

Which genotype shows a male with white eyes?

R = Red, r= white

• $$X^rY$$

• $$X^RY$$

Multiple Choice

What are the female chromosomes?

• XX

• XY

Poll

Rate how well you understand this topic.

• Need more practice

Answer the remaining questions front
and back