Sex Linked Genes
The Xs and Ys of Genetics
X and Y
● Humans have ___ pairs of chromosomes. One of
those pairs are called the “sex chromosomes”.
● Sex chromosomes can either be __ chromosomes or
___ chromosomes.
Sex Linked Genes
• The ___ and ___ sex chromosomes carry the
genes that determine your gender
• Men have a combination of ___ and ___ sex
chromosomes.
• Women have two ___
chromosomes.
XY
XX
Before we move on,
• Draw a Punnett square
to show the probability
of having a boy in any
given pregnancy.
• Remember boys are XY
and girls are XX
Sex Linked
Genes
Genes that are carried by
either sex chromosome
(X or Y) are said to be
_______________
Males
• Men normally have
an X and a Y
combination of sex
chromosomes.
• Since only men
inherit the Y
chromosome, they
are the only ones
that inherit ______
_____________
Females
Females have 2 X
chromosomes
X Linked Traits
• Men and
Women can get
the X-linked
traits, Why?
Because they
both ______ X
chromosomes.
Sex inheritance patterns for male
and female children
X Chromosome Traits
• Men only have one X
chromosome
• Therefore genes on
that chromosome
are expressed in the
male phenotype,
even if it is a
___________ gene.
XAY dominant, shown
XaY recessive, shown
X-linked traits
X X
• In women, a recessive allele on the X
chromosome is often masked on their
phenotype.
• If the woman is heterozygous for the X-linked
disease she is said to be a ___________ . This
means she does not have the disease, but can
pass it to her children.
X-linked traits
• In humans, at least
_____ genes are
known to be X-linked.
• Genes for hemophilia,
red-green color
blindness, congenital
night blindness, and
Duchene muscular
dystrophy.
Hemophilia
• An X-linked
genetically inherited
recessive disease
• Can not clot their
blood
• Severe bleeding
from minor cuts
• Mostly in ________
Red-Green Color Blindness
• X-linked
• Cannot perceive the
difference between red and
green
• Most often afflicts males
Muscular Dystrophy (MD)
• Characterized by a gradual irreversible
wasting away of skeletal muscle.
• An X-linked trait most often passed on to sons
from their mothers.
• Begins to weaken the legs of boys by age 3
and gets worse every year.
• No cure and the individual afflicted with the
disease usually dies by age 30.
https://www.youtube.com/watch?v=Fw0CBMw0ios
Y-linked Traits
• The Y chromosome is small and therefore
does not contain many genes
• Y linked diseases are very rare
• Only passed from father to son.
• Example: Male infertility or retinitis pigmentosa
(causes progressive loss of sight.)
Hypertrichosis Pinnae.
• Hairy ears
• Can happen
later in life.
• Y-linked