Transcript Day 5 Sex Link Traits PPT

Non-Mendelian: Sex- Linked Traits
A.Determining Sex
1. Humans have a diploid number of 46
chromosomes or 23 pairs
2. 22 of the pairs are autosomes, they are the same
for males and females
3. The 23rd pair of chromosomes differ in males and
females
 The are the sex chromosomes and are indicated
by X and Y
XY = male
XX = female
• Males determine the baby’s sex
because only men give the Y
chromosome
IX.Sex- Linked Traits
B.Inheriting sex linked traits
1.Genes located on the sex chromosomes
are called sex- linked traits
2.Because the Y chromosome is small it carries
few genes, including the male determinant
sex gene.
IX.Sex- Linked Traits
B.Inheriting sex linked traits
3. Males who receive a
recessive allele on the
X chromosomes will
express the recessive
phenotype because he
cannot inherit on the Y
chromosome.
o There is no dominant
allele to overpower
the recessive gene
4.Males have a higher
percent chance of
expressing the recessive
trait
IX.Sex- Linked Traits
C.Examples in Humans
1. Hemophilia
 Causes a problem with
blood clotting
 Caused by a recessive
allele on the X
chromosomes
 Males: 1/10,000
 Need one recessive allele
from carrier mom
 Females: 1/10,000,000
 Need two recessive
alleles; one from mom and
one from dad
A woman who is heterozygous (a carrier) for
hemophilia marries a normal man:
 Queen Victoria of England was a carrier of the gene for hemophilia. She
passed the harmful allele to 4 sons and 2 daughters. Her son Leopold
had the disease and died at age 30, while her daughters were only
carriers. As a result of marrying into other European royal families, the
princesses Alice and Beatrice spread hemophilia to Russia, Germany,
and Spain. By the early 20th century, ten of Victoria's descendents had
hemophilia. All of them were men, as expected.
IX.Sex- Linked Traits
C.Examples in Humans
1.Red-Green Color
Blindness
People who have
red-green color
blindness cannot
differentiate
between the two
colors.
Caused by a
recessive allele on
the X chromosomes
Are you colorblind?
Colorblindness
The allele that
controls
colorblindness is
found on the X
chromosome and is
recessive .
What genotype must
a female have to be
diagnosed as
colorblind?
Sample problem
A colorblind man marries a woman who is not colorblind.
Assuming there is no colorblindness in the woman’s ancestry,
what will most likely be the genotype and phenotypes of their
sons and daughters? Show your work
a. Key: XX= female XY= male
C= normal c’= colorblind
a. Parents:
Xc’Y
c. Genotype Ratio:
1:2
1:2
XCY
XCXc’
d. Phenotype Ratio:
1:2 female carriers
1:2 normal males
XCXC
Feb 5th Do all 5 steps!
1. Cross a heterozygous B blood
type with an AB blood type.
2. A colorblind woman has children
with a normal sighted man. What
are the chances their children will
have normal sight?