Download Sex- Linked Traits

Sex- Linked Traits,
Multiple Alleles and
Human Genetics
ch14
Review Question
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Which parent determines the sex of an offspring?
________________
How?
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Sex linked traits… what are they?
 those
traits that are controlled by genes
on the X or Y chromosomes.
 The Y
chromosome is much smaller than
the X chromosome and only contains
fewer genes. Most sex-linked traits are on
the X chromosome.
Question:
Why
is a male more
likely to inherit a sexlinked genetic
disorder?
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A male can inherit a recessive trait if the gene for the
trait is present on his X chromosome, because Y
chromosome cannot hide the trait.
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A female must have the recessive trait on both X
chromosomes for that trait to show
Previous Knowledge :
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What are some sex-linked genetic disorders that you
already know?
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Duchenne Muscular Dystrophy
SCID- severe combined immune deficiency disorder
Colorblindess
Hemophilia
* Klinefelter’s Syndrome and *Turner’s syndrome caused
by chromosome abnormalities of the sex chromosomes
but, the genes are not located on the X chromosome.
Punnett Squares with Sex-Linked Traits
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In humans, hemophilia is a sex-linked trait. Having hemophilia
is recessive (Xh) to being normal (XH).The heterozygous
female is called a carrier. Cross a carrier female with a
normal male.
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__ XHXh __ X __ XHY ___
What are the phenotypic ratios?
XH
X
H
Y
Xh
Multiple Alleles
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Multiple Alleles: when more than two different alleles
exist for the same trait.
(Remember: each individual will only have two alleles for
a trait but there are several alleles to choose from.)
Example:
In humans, blood type has multiple alleles. IA and IB are
codominant and i (type O blood) is recessive.
Blood Types

Blood Type
Type of Antigen
Possible Genotypes
Type A
A antigen
IA IA ,IA i
Type B
B antigen
IB I B, IB i
Type AB
A and B antigens
IA I B
Type O
No antigens
ii
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Complete Sample problems on Worksheet With Blood
type lab!
Polygenic Inheritance
the inheritance pattern is controlled by
two or more genes each with two alleles.
 Example:
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eye color is the result of polygenic inheritance.
At present, three gene pairs controlling human eye color
are known

Polygenic inheritance usually shows up as a
range of variation such has height, skin color
or hair color.
 The
results of an average population will
result in a bell-shaped curve.
TRACKING TRAITS AND GENETIC
DISORDERS
WHAT
CAN WE USE
TO DO THIS?
Pedigrees!

What is a pedigree?

A chart that shows relationships within a family that is
used to show inheritance of traits.
INTERPRETING AND DRAWING PEDIGREES
1. squares represent males, circles represent females
2. shaded shapes represent those family members having
the trait being traced (or disease)
3. un-shaded shapes represent family members not
affected by trait or disease.
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4.½ shaded square or circle indicates a carrier
(heterozygous) individual.
5.Horizontal line connecting circle to square indicates a
marriage.
6.Vertical line with a bracket connecting circles or
squares to a marriage line indicates siblings (oldest child
first)
7. Roman numerals or capital letters indicate
generations.
8. The oldest children are placed on left, and youngest are
on the right.
9. Each horizontal line represents a generation.
Symbols used : do not write
Royal disease