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Two copies of each autosomal gene affect
phenotype (physical).
• Mendel studied
autosomal gene traits,
like hair texture.
Autosome –
chromosome with genes
not related to sex of
organism (body cells)
Karyotype
The arrangement of all the chromosomes found in a cell.
Includes:
Autosomes: chromosome pairs 1-22
Sex Chromosomes: chromosome pair 23
Female =
XX
Male = X Y
23rd pair
Female sex
chromosomes
XX
FEMALE
“Autosomes”
MALE
Sex Chromosomes (they
determine male or female)
Who determines the sex of the
offspring?
Father – he can provide an X or
Y chromosome
Egg
X
X
XX
XX
X
X
Body Cell
X
XX
XX
XY
XY
X
XY
Body Cell
Y
Y
Sperm
1female:1male
– Carrier – has an allele for as trait or disease that is
not expressed.
– Carrier does not have disease symptoms but can
pass it on to offspring.
Dominant allele
disorders are rare.
Huntington’s disease is
an example of a disease
caused by a dominant
allele.
(dominant)
• Genes on sex chromosomes are called sex-linked genes.
.
– Y chromosome - male characteristics .
– X chromosome - genes affects many traits.
Males can pass on X or Y
Females only pass on X
Sex-linked disorder: Color Blindness
1. Genetic disorder found on the sex chromosome X
2. Known as a “sex-linked” because its found on chromosome 23
3.
Can’t distinguish between colors
4.
More boys, than girls, are color blind…..WHY?
Sex-linked disorder: Color Blindness
XC
XC
Color blind Dad and Normal mother produces….
Two normal sons
XC
XC XC XC XC
Y
XC Y
XC
XC
2 “carrier” daughters (NOT color blind)
XC Y
XC
XC XC XC XC
Normal Dad and Carrier mother
produces….
1 color blind son, 1 normal son
1 “carrier” daughter, 1 normal daughter
Y
XC Y
XC Y
What is the only way to get a color-blind daughter??
Sex-linked disorder: Hemophila
1. Recessive genetic disorder found on the sex chromosome X
2.
Disease in which blood doesn’t clot properly.
Sex-linked disorder: Hemophila
XH
XH
Affected dad and Normal Mother produces….
Two normal sons
Xh
XH Xh XH Xh
Y
XH Y
XH
2 “carrier” daughters
XH Y
Xh
Normal Father and Carrier Mother produces….
XH
XH XH XH Xh
1 color blind son, 1 normal son
1 “carrier” daughter, 1 normal daughter
Y
XH Y
Xh Y
What cross will ALWAYS yield you 100% affected sons?
• Males have an XY genotype.
– All of a male’s
sex-linked genes
are expressed.
– Males have no
second copies of
sex-linked genes
– Y chromosome is
much smaller
• Females have an XX genotype.
X chromosome inactivation -randomly “turns off”
one X chromosome.
Why are males more likely to than females to have genetic
disorders?
All sex-linked
genes are
expressed, even
recessive.
Females have a
backup X
chromosome.
• Some traits are neither totally dominant nor totally
recessive.
• Incomplete dominance - when neither gene is totally
dominant to the other
- Heterozygous phenotype is intermediate between the
two homozygous phenotypes
– Example: White flowers and red flowers produce
pink flowers
Sickle Cell Anemia
• Disease in which the body makes sickle-shaped red blood cells.
Sickle-shaped cells don’t move easily through your blood vessels.
They’re stiff and sticky and tend to form clumps and get stuck in the
blood vessels
•The disorder is found on chromosome
11. and is therefore not sex-linked.
• The Oxygen carrying hemoglobin can
not carry oxygen as efficiently and the
odd-shaped cells can easily clot and
break. Fatigue, pain, and organ failure
due to lack of oxygen supply are
common symptoms of sickle cell
anemia.
• It is common in the African community
Actual blood cells
Sickle Cell Anemia
Codominance Practice
•
Genes for blood cells:
• R = Round blood cells
• R’ = Sickle Cells
R
R’
Genotypes for blood cells
RR = normal blood
R
RR’ = some sickle cells, some
normal cells
R’R’ = has sickle cell anemia
R’
RR
RR’
RR’
R’R’
Complete the following crosses, Report the genotypes and phenotypes of the offspring
R = round blood cell
R’ = sickle cell
R R’ = carrier
Mixed Cells x Hybrid
---------- x ---------R’
R
Round Blood Cells x Hybrid
---------- x ---------EXPECTED
R
R
EXPECTED
R’ R’
R’ R
RESULTS
1 sickle cell anemia
--------------------------
R’
R’ R
R’ R
R R’ R
RR
2 mixed cells
-------------------------1 normal cells
--------------------------
R
RR
RR
R’
Sickle Cell Anemia x Pure Round
---------- x ----------
R’
R’ R’ R’
R
R’ R
R’
R’ R’
R’ R
EXPECTED
RESULTS
1 sickle cell anemia
--------------------------
2 mixed cells
-------------------------1 normal cells
--------------------------
RESULTS
2-------------------------mixed cells
2-------------------------normal cells
--------------------------
Round Blood Cells x Sickle
---------- x ----------
R’
R’
R’
R’ R’
R’ R’
R
R’ R
R’ R
EXPECTED
RESULTS
1-------------------------sickle cell anemia
2-------------------------mixed cells
1-------------------------normal cells
Incomplete dominance
Red
White
X
There is a third
color that exists in
the heterozygous
.
type. It’s a mixture
between the two
homozygous types.
Pink
• Color blindness is a
problem in which red or
green look like shades
of gray or other colors.
• The gene is carried on
the X chromosome and
is a recessive trait.
XCXC = normal female
XCXc = female, normal vision
(carrier)
XCY = normal vision male
XcY = color blind male
XC
XC
Y
Xc
XCXC
XCXc
XCY
XcY
• Codominant - alleles will both be completely expressed.
– Codominant
alleles are
neither
dominant nor
recessive.
– The ABO blood
types result
from
codominant
alleles.
Example – red and white flower produce a
flower with BOTH colors
• Many genes have more than two alleles.
1. Blood Type
4 different blood types
• there are _________________________
Blood Type
Genes
Blood Type A
A A or A O
Blood Type B
B B or B O
Blood Type AB
AB
Blood Type O
OO
Which blood types are compatible for transfusion??
Yes or No ?
O
B
A
AB
B
Yes
A
No
AB
Yes
A
No
Yes
O
AB
A
A
B
AB
AB
B
AB
A
A
B
AA
AB
A
O
B
AB
BO
O
AO
OO
A
B
AB
B
O
AO
BO
O
AO
BO
AB
BB
O
O
A
AO
AO
A
AA
O
OO
OO
O
AO
A
O
AO
OO
Blood type statistics…
• If there are 100 people in the room:
39 will be O+
7 will be O34 will be A+
6 will be A9 will be B+
2 will be B3 will be AB+
and only 1 in 200 will be ABNote: The + and – is the presence (or absence) of a third
antigen (Rh).
• Polygenic traits
are produced
by two or more
genes.
Order of dominance:
brown > green > blue.
• Epistatic gene - can interfere with the
expression of all other genes.
Mice have 5
genes that
control fur
color.
2 genes for
general color
1 for shading
1 for spots
1 epistatic
gene for color
that overrrules
all other genes
• Phenotype is a combination
of genotype and
environment.
• The sex of sea turtles
depends on both genes
and the environment.
Warm eggs develop into
females
• Height is an example of a
phenotype strongly affected
by the environmental factors
such as early nutrition and
health care.
Gene linkage was explained through fruit flies.
• Morgan found that linked traits are on the
same chromosome. Traits can be inherited
as a group.
• Chromosomes, not genes, assort
independently during meiosis.
Wild type
Mutant
• Linked genes are not inherited together
every time.
• Chromosomes exchange homologous genes during
meiosis.
Linkage maps – map of location of genes on a chromosome.
• The closer together two genes are, the more likely
they will be inherited together.
• Cross-over frequencies are related to distances
between genes.
• Cross-over frequencies can be converted into map units.
– gene A and gene B cross over 6.0
percent of the time
– gene B and gene C
cross over 12.5 percent
of the time
– gene A and gene C cross over 18.5 percent of the
time
Human genetics follows the patterns seen in other organisms.
• The basic principles of genetics are the
same in all sexually reproducing organisms.
– Inheritance of many human
traits is complex.
– Single-gene traits are
important in understanding
human genetics.
Females can carry sex-linked genetic disorders.
• Males (XY) express all of their sex linked genes.
• Expression of the disorder depends on which parent carries
the allele and the sex of the child.
X chromosome carries about 1100 genes while the Y carries about 250
Pedigree - chart for tracing genes in a family.
• Phenotypes are used to infer genotypes on a pedigree.
• Autosomal genes show different patterns on a pedigree
than sex-linked genes.
Widow’s peak: W = widow’s peak
w = non widow’s peak
• If the phenotype is more common in males,
the gene is likely sex-linked.
Colorblindness: M = normal vision m = colorblindness
Several methods help map human chromosomes.
• Karyotype - a picture of all chromosomes in a cell.
XY
FEMALE
“Autosomes”
MALE
Sex Chromosomes (they
determine male or female)
Amniocentesis
A medical technique used to collect the chromosomes of a developing
fetus. It is done by inserting a needle into the womb and gathering
cells in the amniotic fluid.
• Karyotypes can show changes in chromosomes.
– deletion of part of a chromosome or loss of a
chromosome
– large changes in chromosomes
– extra chromosomes or duplication of part of a
chromosome