Download Sex- Linked Traits

Sex- Linked Traits,
and Human Genetics
NOTES ch14
Karyotype- Map of all of the chromosomes
in a cell
Karyotype
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Has 46 Chromosomes (23 pairs, Last pair is the sex
chromosomes XY : Male, XX: Female)
Enables scientists / doctor’s to view the chromosomes of
a person, plant or animal
Detection of abnormalities/ gender
Chromosomal defects
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What is a mutation?
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There are two types of mutations that can occur
in gamete cells:
1. Gene mutation: affect only one gene.
Examples: point and frameshift.
2. Chromosomal mutation: affect the number or
structure of chromosomes. Usually involves many,
many genes.
5 types of Chromosomal Mutations
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1. Deletion
2. Duplication
3. Inversion
4.Translocation
5. Non-disjunction
1.Deletion: Involves the loss of all or part
of a chromosome
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Examples: Cri du Chat syndrome, Angelman’s
syndrome, Prader-Willi syndrome, Miller-Dieker
syndrome
2.Duplication-Involves the production of
extra copies of parts of the chromosome
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Examples: Fragile X syndrome, Beckwith-Wiedeman
syndrome
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3.Inversion: Reverses the direction of parts of a
chromosome
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4.Translocation: When one part of a chromosome
breaks off and attaches to another chromosome.
Example: Edward’s syndrome
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5. Non-disjunction:
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Means “not coming apart”.
When homologous chromosomes fail to separate
properly during meiosis.
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Results in abnormal numbers of chromosomes.
Normal is two of each type of chromosome.
Trisomy means a person has an extra copy of a
chromosome.
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
TRACKING TRAITS AND GENETIC
DISORDERS
How
do we trace traits
or genetic diseases
through families?
Pedigrees!
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What is a pedigree?
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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 and/ or a generation.
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.
Symbols used : do not write
Royal disease
Human Traits
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Traits can be autosomal (on a chromosome other than
the sex chromosomes) or on the sex chromosomes.
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Almost all of human traits are polygenic.
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Human traits are also influenced by the environment.
Recessive Autosomal Disorders
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Inherited by recessive alleles.
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1. PKU- cannot process an amino acid
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2. Albinism
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3.Tay Sachs- lipid build up in brain caused by a single
nitrogen base change (A, C, T,G)
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4. Cystic Fibrosis – excessive mucous in lungs
Dominant Autosomal Disorders
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Caused by Dominant alleles
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Examples: 1. Achondroplasia – dwarfism
2. Huntington’s – mental deterioration
3. Hypercholesterolemia- heart disease due to
excessive cholesterol
4. Marfan’s syndrome- lanky, cardiovascular issues
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Codominant disorders
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Sickle cell disease/ anemia
Blood cells are abnormal or sickle-shaped
In a heterozygous individual, both normal and sickleshaped are present.