Download Show the cross between a white eyed male and

Journal
Chromosomal Theory of
Inheritance: simply
states that
chromosomes are
carriers of genetic
information (Walter
Sutton)
Human Chromosomes (Karyotype)
Humans have 22 pairs
of autosomes, 1 pair
of sex chromosomes
Fruit flies have 3 pairs
of autosomes, 1 pair
of sex chromosomes
What is the sex
of this person?
Female eggs = XX
Male sperm = XY
Possible offspring are
shown in square:
50% male
50% female
What happens when an allele is
located on the X chromosome?
Males only get ONE !
These are a few
of the known
alleles located on
the X
chromosome
Disorders that
are recessive are
masked in
females by the
other X
chromosome.
Sex Linked Genes
•Genes located on the X
chromosome are inherited with
that X.
•When doing crosses you must
include the sex chromosomes in
your cross.
•Use superscript letters for the
allele.
Example: In fruit flies, eye color is a sex
linked trait. Red is dominant to white.
FRUIT FLY CHROMOSOMES
Females
XRXR
XRXr
XrXr
Males
XR Y
Xr Y
Drosophila melanogaster
Figure 12.6
Thomas Morgan
used crosses
with fruit flies.
Why do you
think he used
them?
Figure 12.1
What is an autosome?
Show the cross between a white eyed male and a red
eyed female: XrY x XRXR
Show the cross between a red eyed male and a white
eyed female:
Figure 12.2
Human Sex Linked Disorders
1. Colorblindness
2. Muscular Dystrophy
3. Hemophilia
4. Fragile X Syndrome
COLORBLINDNESS
More Tests
Muscular Dystrophy
• characterized by the wasting away of muscles
• life expectancy: ~20 yrs
• females can be carriers for the disease, where
they pass the disease to their sons only
Show the cross of a female who is a carrier and a
normal male:
Fragile X Syndrome
• caused by triplet repeats in a gene on the X chromosome
• causes mental retardation
• named because the X chromosome had an odd appearance - the
tip of the chromosome seemed to be attached only by a small
thread
• the number of repeats of the gene determines the severity of the
disease
Figure 12Aa
Hemophilia
• also known as "bleeder's disease", blood does not clot properly
• disease was present in the royal family, starting with Queen Victoria
Show the cross between a female with hemophilia and a normal
man:
Pedigree Key
• Squares represent males
• Circles are used for females
• A horizontal line from male to female
represents mates that have produced
offspring
• The offspring are listed below their
parents from oldest to youngest
• A fully shaded individual posses the trait
being studied
– If the condition being studied is a
monogenic recessive condition (rr), then
those shaded gray have the genotype rr
– If the condition being studied is dominant
condition (Rr or RR), then those that are
unshaded have the genotype rr
• A line through a symbol indicated that
the person is deceased
How to analyze
a pedigree
Figure 12.5
Identify all of the CARRIERS