Transcript 11.3B Sex-linked Inheritance File

Ch.14-1
Non-Mendelian Inheritance II
Sex-linked Inheritance
POINT > Describe inheritance of genetic
disorders
POINT > Review inheritance of sex
chromosomes
POINT > Describe sex-linked traits
POINT > Use Punnett squares to predict
inheritance of sex-linked traits
POINT > Describe inheritance of genetic
disorders
Most genetic disorders are caused by recessive
alleles
Heterozygous individuals are called carriers
Carriers do not show symptoms of disorder, but
can pass on the disorder-causing allele to
offspring
POINT > Review inheritance of sex
chromosomes
Autosomal traits: Genes located on autosomes
(chromosomes #1-22)
Sex-linked traits: Genes located on sex
chromosomes (X and Y)
POINT > Review inheritance of sex
chromosomes
X
X
X
XX
XX
Y
XY
XY
WB CHECK:
Which statement is true?
a) dominant alleles cause most genetic diseases
b) genes located on autosomes cannot cause
diseases
c) autosomes are chromosomes #1-23
d) carriers of a disease do not have symptoms
e) autosomes can carry sex-linked traits
WB CHECK:
Which person could be a carrier?
a) XHXH
b) XhXH
c) CtCt
d) XtXt
POINT > Describe sex-linked traits
X-linked traits (sex-linked) are controlled by
genes found only on the X chromosome
Indicated with ‘X’ and single letter  XA
X-linked disorders affect both males &
females, but in different frequencies
POINT > Describe sex-linked traits
Y-linked genes are found only on the Y
chromosome
Indicated with ‘Y’ and single letter  YB
Affect only males
POINT > Describe sex-linked traits
Ex. Hemophilia: X-linked recessive disorder
Impairs the body’s ability to form blood clots
More on this later…
POINT > Describe sex-linked traits
Ex. Red-Green Color Blindness
X-linked recessive
Inability to distinguish
between red and green
hues
POINT > Describe sex-linked traits
Red-Green Color Blindness
X-Linked Recessive
XB – Normal allele
Xb – Color Blind allele
Y – No allele present
POINT > Describe sex-linked traits
Cross a man with normal vision with a female carrier
XB Xb x X B Y
XB
Xb
Genotypes
25% XB XB
XB
XB XB
XB Xb
25% XB Xb
25% XB Y
Y
XB Y
Xb Y
25% Xb Y
POINT > Describe sex-linked traits
XB Xb x X B Y
XB
XB
XB XB
Xb
XB Xb
Phenotypes
50% Normal
Female
25% Normal
Male
Y
XB
Y
Xb
Y
25% CB Male
WB CHECK:
Draw a Punnett square showing a cross
between a color blind male and a carrier
female.
What percentage of boys will be colorblind?
What percentage of girls will be color blind?
WB CHECK:
XB Xb x Xb Y
XB
Xb
Genotypes
25% XB Xb
Xb
XB Xb
Xb Xb
25% Xb Xb
25% XB Y
Y
XB Y
Xb Y
25% Xb Y
WB CHECK:
XB
Xb
x
Xb
Xb
Y
XB
Xb
XB Xb
Xb Xb
Phenotypes
25% Normal
Female
25% CB Female
25% Normal
Male
Y
XB Y
Xb Y
25%
CB Male
Homework:
Read pages 392-397
Assess #1-2 page 397
Dihybrid Crosses W.S.