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Oct 23, 2013 (3 years and 5 months ago)

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BIOLOGY 1

STANDARD 4.0

LESSON 4.6



PRINT OUT THIS LESSON BEFORE CONTINUING IN ORDER TO
FOLLOW THE DIRECTIONS AND COMPLETE THE ASSIGNMENT.

KEEP THESE PAGES IN YOUR NOTEBOOK



Genetics and Biotechnology

The student will investigate the concepts of geneti
cs and heredity,
different methods of reproduction, patterns of inheritance, and
genetic disorders; as well as, explore and evaluate the DNA
technologies from both a scientific and ethical perspective.


Lesson 9
-

Examine modes of inheritance involving sex
-
linkage

and interpreting pedigree charts




Proceed to the
Sex
-
Linked Genes Tutorial #1

for more information regarding
sex
-
linked traits.


Also visit
Sex
-
Linked Genes Tutorial #2

for genetic problem
illustrations of sex
-
linked traits

Sex
-
Linked Inheritance

(Courtesy: Prentice Hall Science Explorer, Cells and Heredity, 2000)



Some human traits occur more often

in one sex than the other.


The genes for
these traits are often carried on the sex chromosomes.


Genes on the X and Y
chromosomes are often called sex
-
linked genes because their alleles are passed
from parent to child on a sex chromosome.


Traits contro
lled by sex
-
linked genes
are called sex
-
linked traits.



Like other genes, sex
-
linked genes can have dominant and recessive alleles.


Recall that females have two X chromosomes, whereas males have one X
chromosome and one Y chromosome.


In females, a do
minate allele on one X
chromosome will mask a recessive allele on the other X chromosome.


The
situation is not the same in males, however.


In males there is no matching allele
on the Y chromosome to mask, or hide, the allele on the X chromosome.


As a
re
sult, any allele on the X chromosome
-

even a recessive allele
-

will produce
the trait in a male who inherits it.


Because males have only one X chromosome,
males are more likely than females to have a sex
-
linked trait that is controlled by
a recessive al
lele.




Sex Chromosomes and Linked Genes

A normal human cell (autosome) contains 46 chromosomes. 22 pairs of regular
chromosomes and one pair of sex chromosomes. These sex chromosomes are
designated by the letters
________

and
_________
. A human male cont
ains an

__________

and a
__________
, while the female contain two
___________
's.

During the reproductive process there is a fifty
-

fifty chance that a male or
female will be born. see below:












The X chromosome is the larger of the two. If the

Y chromosome is not present
the offspring will not develop male characteristics. In fact the offspring will be a
female suffering from
__________________ syndrome (XO)
.

If a male receives and extra X, it will become a male with
___________________________

syndrome
(
XXY
). If an organisms receives
additional chromosomes, other than the sex chromosomes, a variety of
abnormalities will occur. One example of this is
________________________
Syndrome
. Here an extra chromosome 21 is found, allowing the individual

to
develop an abnormal condition.

Certain other abnormal conditions may develop in offspring from certain genes
attached to the sex chromosome X. These are called sex
-
linked genes.
Examples of this are the bleeders disease called
_______________________

and
__________________________________
.

Hemophilia is called the bleeders disease. Here a person could bleed to death if
the bleeding is not stopped. People with this disease inherited it from their
parents. There is no cure for the disease, but an infect
ed person can receive the
chemical that is missing to complete the clotting process.

Phenotypes and Genotypes for blood clotting.

Phenotypes
(male)

Genotypes
(male)

Phenotypes
(female)

Genotypes
(female)

Normal

X
H
Y

Normal

X
H
X
H

Hemophiliac

X
h
Y

Carrier

X
H
X
h



Hemophiliac

X
h
X
h



1. What is a carrier?
________________________________________________________________

2. Is there such a person called a carrier male? _____________. Explain.
________________________

3. Mate a carrier female with a normal male
in the space below.


X

X

X

XX

XX

Y

XY

XY

a). What are the chances of these parents having normal sons?
_______________.

b). What are the chances of these parents having normal daughters?
___________________.

Colorblindness is inherited by the same proce
ss. Here the person infected with
the disease cannot distinguish red colors from green colors.

4. Mate a colorblind male with a normal female in the space below.


X

X

X

XX

XX

Y

XY

XY

a). What are the chances of these parents having normal sons?
_______
________.

b). What are the chances of these parents having normal daughters?
___________________

Please use the following links to study sex
-
linked traits

Color
blindness tutorial

Chromosomes carry genes


Use the following link to understand Pedigree Charts

Mendel's Laws apply to Huma
ns

After reading the first page, click on “animation” at the bottom of the screen.

Use the right arrow to scroll through the animation. When finished answer the

questions under

“problems” at the bottom of the page
.