Transcript Sex-Linked Traits and Pedigrees

Sex-linked Traits
Sex determination
Sex chromosomes – determines the
sex of an individual
Y
X
Males have X and Y
Two kinds of gametes
Female have two X’s
Only one type of gamete
□ Autosomal Chromosomes
□ Sex Chromosomes
Which parents determines the sex of the offspring?
XY
male
X
XX
Y
X
Female
X
It is the male that determines the sex of
the offspring.
Sex Linked Traits
Traits controlled by genes located on
sex chromosomes (X or Y)
Most are X-linked
The X chromosome is larger and has more
genes
A Y has very few genes
Show inheritance pattern that differs
for autosomal traits.
Autosome-any chromosome besides X and Y
X-linked Inheritance
Males only have one copy of the X
chromosome (hemizygous), plus a Y
Female have two X chromosomes, and
may be homozygous or heterozygous for
a trait
X-linked genes are never passed from
father to son. The Y chromosome is the
only sex chromosome that passes from
father to son.
Females with one copy of the normal
gene and one copy of the mutated
gene are called carriers. They don’t
show the trait.
Males are never carriers – if they
have a mutated gene on the X
chromosome, it will be expressed
X-linked disorders
 Recessive
 Red-green color
blindness
 Hemophilia
 Duchenne muscular
dystrophy
 Ichthyosis
 Dominant
 Hypertrichosis
Red-green color blindness
Can not distinguish red from green.
Normal red-green
Red-green colorblind
What a red-green colorblind person would see
Normal
Red-green colorblind
Hemophilia
Pedigree Charts
I
II
III
Overview
I.
What is a pedigree?
a.
b.
II.
Constructing a pedigree
a.
b.
III.
Definition
Uses
Symbols
Connecting the symbols
Interpreting a pedigree
What is a Pedigree?
□ A pedigree is a chart of the genetic
history of family over several
generations.
□ Scientists or a genetic counselor would
find out about your family history and
make this chart to analyze.
Constructing a Pedigree
• Female
• Male
Connecting Pedigree Symbols
Examples of connected symbols:
□Married
Couple
□Siblings
Connecting Pedigree Symbols
Examples of connected symbols:
□Fraternal twins
□Identical twins
Example
What does a pedigree chart look like?
Symbols in a Pedigree Chart
□ Affected
□ Carrier
(autosomal or
sex linked)
□ ‘Normal’
•
Interpreting a Pedigree Chart
1. Determine if the pedigree chart shows an
autosomal or X-linked/sex-linked disease.
□ If most of the males in the pedigree are
affected the disorder is X-linked
□ If it is a 50/50 ratio between men and
women the disorder is autosomal.
Example of Pedigree Charts
□ Is it Autosomal or X-linked?
Answer
□ Autosomal
Interpreting a Pedigree Chart
2. Determine whether the disorder is
dominant or recessive.
□ If the disorder is dominant, one of the
parents must have the disorder.
□ If the disorder is recessive, neither
parent has to have the disorder
because they can be heterozygous.
Example of Pedigree Charts
□ Dominant or Recessive?
Answer
□ Dominant
Example of Pedigree Charts
Dominant or Recessive?
Answer
Recessive
Summary
Pedigrees are family trees that explain
your genetic history.
Pedigrees are used to find out the
probability of a child having a disorder
in a particular family.
To begin to interpret a pedigree,
determine if the disease or condition is
autosomal or X-linked and dominant or
recessive.
Pedigree Chart -Cystic Fibrosis
Hemophilia