Download X n Y

Sex influenced traits
• The gene is NOT on a
sex chromosome, but
SEX affects the
phenotype
• Ex-baldness-dominant in
males, recessive in
women
– If ‘B’ represents bald
and ‘b’ is hairy then
Men must be bb to keep
hair
Women can be Bb or bb
to keep hair
• Caused by a gene
that is located on a
SEX chromosome (X
or Y)
• Most SEX-linked
Traits are found on
the X chromosome
X-linked diseases
• Most are recessive
• Examples-hemophilia,
red-green colorblindness
• Males are more likely to
have these because they
cannot be carriers
• Why?
• Males are XY-if their ‘X’
has a bad gene, there is
nothing on the ‘Y’ to
dominate over it
How A Sex-linked trait is passed
Ex. Red-Green Colorblindness (x-recessive)
•
n
N
• XNXN=Normal
• XNXn=CARRIER, but
IS NOT colorblind
• XNY=Normal
• XnY=HAS red-green
colorblindess
Passing colorblindness
• Carrier mom XNXn
• Normal Dad XNY
XN
Xn
XN
XNXN
XNXn
Y
XNY
XnY
X-linked genes are on the X
chromosome
Autosomal genes-NOT on the X or
Y chromosomes
Other X-linked traits
• Orange and Black Alleles
are on the X chromosome
in cats
• White is on another
chromosome
• In every cell, only 1 X
chromosome is active
(other X is Barr Body)
• Result-some cells make
black fur, some orange
Multifactorial and polygenic traits
• Polygenic-more than
one pair of alleles
determines
phenotype- -eye
color
• Multifactorial-genes
AND environment
determine
phenotype –weight
and height
Epistasis
• Multiple alleles (more
than 2 involved)
• One allele causes the
other to act
differently)
• Example-E is brown
unless B is present