Transcript File

Advanced Genetics Notes
Recessive Disorders (aa)
1.
•
Cystic Fibrosis – causes thick
mucus to build up in the lungs,
that could lead to a lung
infection. Also in the
digestive system, that could
prevent enzymes from
reaching the intestines to
break down food.
- 1 in 20 white americans are
unknowing carriers of the CF
gene.
2.
3.
4.
Albinism – Lack of pigment in the eyes, skin or
hair.
PKU – an absence of an enzyme that is
responsible for processing the amino acid,
phenalalanine. It is toxic if it builds up and
causes mental retardation.
Sickle Cell Anemia - crescent shaped red
blood cells
• Suppose Two individuals
heterozygous (Ss) for sickle
cell anemia marry. Show a
Punnett for the expected
genetic makeup of their
children. How many of their
children will suffer from sickle
cell anemia? How many will
be carriers?
S
s
S
s
SS
Ss
Ss
ss
Offspring with
sickle cell? 25%
Offspring that are
carriers? 50%
Dominant Disorder
1.
(AA or Aa)
Huntington’s Disease – a disease where
the nervous system degenerates
- it occurs later in life (40’s or 50’s)
- it only takes one copy of the defective
gene to produce the disease. Each child
of a parent has a 50/50 chance of getting
HD.
2.
Achondroplasia – it is a
disorder of bone growth, it
produces dwarfs under 4 feet
tall.
Pedigree
Pedigree: a genetic family tree that
shows the inheritance of a trait or a
disease.
How many females in the family? 5
How many members are affected? 3
What is the relationship between Kate & Donna?
Grandmother/granddaugther
If trait studied is cystic fibrosis (ff)
Give the genotype/phenotype for each person.
Carrier: carries the trait but is not
affected by it
Kate: Ff
Joe: Ff
Max: ff
Natalie: Ff
Ryan: Ff
Donna: ff
I
I-1
I-2
II
II-2
II-4
II-5
III
III-5
1.
2.
3.
4.
5.
How many generations are in this pedigree? 3
How many females are in the 2nd generation? 2
What is the genotype and phenotype of person II-2? ff/affected
What is the genotype and phenotype of person III-5? Ff/carrier
Complete a punnett square with II-4 & II-5?
Bob
Sue
This is a pedigree for Cystic Fibrosis.
1. Perform a cross between Bob and Sue. What is the
chance they will have a child with Cystic Fibrosis?
Co-Dominance
• Co-dominant alleles result in
the expression of both traits.
Example in Cattle:
RR – Red
WW - White
RW – Roan
(Cow has red and white hairs)
• Suppose a Roan colored Cow
was crossed with a white
colored bull. What would be
the expected offspring of a
cross to be?
R
W
RW
W
RW
W
WW
WW
Phenotypic percentages:
Red – 0%
White – 50%
Roan – 50%
Genotypic Percentages:
RR - 0% RW- 50% WW- 50%
Incomplete Dominance
• Incomplete Dominance –
blending of phenotypes
Example: Flowers red (R) and
white (R’) are both equally
dominant. When a
homozygous red (RR) and a
homozygous white (R’R’) are
crossed, the offspring are pink
(RR’).
Ex. Hair Texture (blending)
HH – curly hair
HH’ – wavy hair
H’H’-straight hair
R
What would be the expected
offspring of a cross between two pink
flowers?
R’
R
RR
RR’
R’
RR’
R’R’
Phenotypic percentages:
Red – 25%
White – 25%
Pink – 50%
Genotypic Percentages:
RR - 25% RR’- 50% R’R’- 25%
Traits that Follow Different Rules Continued…
• Polygenic Inheritance –
Traits are controlled by 2 or
more gene pairs. There is a
range of phenotypes.
Ex. Skin color, eye color, and
height
If height were controlled by
genes A, B, and C:
AABBCC – Tall
AaBbCc – Medium
aabbcc – Short
Polygenic traits will create a
bell shaped curve on a graph.
Range of
Height
# of
students
% of
students
120-129
130-139
140-149
150-159
160-169
170-179
180-189
190-200
X-axis = ranges of height
Y-axis = % of students
Practice
1. Black is dominant to white. Cross a
heterozygous with a white rabbit. What is the
probability of having white offspring.
2. Cross a red cow (RR) with a white cow (WW).
What is the phenotypes of the offspring? What
type of inheritance is this called?
3. Cross a red flower (RR) with a white flower
(R’R’). What is the phenotype of the offspring?
What type of inheritance is this called?
Practice….again
1. Draw a Punnett square for Kate and Joe. What is the
chance they will have a child with the trait?
2. Draw a Punnett square for a black chicken (BB) and a
checkered chicken (BW). What are the possible
phenotypes?
3. Draw a Punnett square for two pink flowers (RR’). What
are the possible genotypes?
Human Karyotypes Exhibiting Various Abnormalities
• Karyotype – a picture/chart
of chromosome pairs.
• Aneuploidy – having an
abnormal number of
chromosomes.
Ex. Instead of having 46, you have
47 chromosomes.
• Trisomy – having 3 of a
chromosome instead of 2
• Monosomy – having 1 of a
chromosome instead of 2
How many chromosomes are there? 46
Is there an aneuploidy present? No
How does aneuploidy occur?
Nondisjunction: chromosomes fail to separate in Meiosis
Human Karyotypes Exhibiting Various Abnormalities
Down Syndrome Karyotype
How many chromosomes are there? 46
Is there an aneuploidy present? No
How many chromosomes are there? 47
What Chromosome pair has an extra
chromosome? 21
Is there an aneuploidy present? Yes
What is the sex of the individual? Female
Is this a trisomy? Yes
Down Syndrome
Down Syndrome Fact Sheet
• Down syndrome occurs when an individual has three, rather than two, copies of the 21st
chromosome. This additional genetic material alters the course of development and causes
the characteristics associated with Down syndrome.
• Down syndrome is the most commonly occurring chromosomal condition. One in every 733
babies is born with Down syndrome.
• There are more than 400,000 people living with Down syndrome in the United States.
• Down syndrome occurs in people of all races and economic levels.
• The incidence of births of children with Down syndrome increases with the age of the
mother. But due to higher fertility rates in younger women, 80% of children with Down
syndrome are born to women under 35 years of age.
• People with Down syndrome have an increased risk for certain medical conditions such as
congenital heart defects, respiratory and hearing problems, Alzheimer's disease, childhood
leukemia, and thyroid conditions. Many of these conditions are now treatable, so most people
with Down syndrome lead healthy lives.
• A few of the common physical traits of Down syndrome are low muscle tone, small stature,
an upward slant to the eyes, and a single deep crease across the center of the palm. Every
person with Down syndrome is a unique individual and may possess these characteristics to
different degrees or not at all.
• Life expectancy for people with Down syndrome has increased dramatically in recent
decades - from 25 in 1983 to 60 today.
• People with Down syndrome attend school, work, participate in decisions that affect them,
and contribute to society in many wonderful ways.
Human Karyotypes Exhibiting Various Abnormalities
Turner Syndrome Karyotype
How many chromosomes are there? 47
What Chromosome pair has an extra
chromosome? 23rd
Is there an aneuploidy present? Yes
What is the sex of the individual? Male
Is this a trisomy? Yes
How many chromosomes are there? 45
What Chromosome pair has an extra
chromosome? None
Is there an aneuploidy present? Yes
What is the sex of the individual? Female
Is this a trisomy? No, it is a monosomy
Klinefelter Syndrome
Turner Syndrome
Amniocentesis and Karyotyping
Amniocentesis is a procedure used to determine if a fetus has a genetic disorder. In this
procedure, a large needle is inserted into the abdomen of the mother and a sample of the
amniotic fluid is taken. The cells of the fetus can be analyzed for any genetic disorders. One
way to analyze the fetal cells is using a karyotype.
Sex Determination
• The sex of the child is
determined by the male.
Male = XY Female = XX
• Males can contribute an X
or Y to his offspring.
• Females always give an X
• Sex chromosomes are the
23rd pair
• Chromosomes 1-22 are
autosomes.
X
X
X
XX
XX
Y
XY
XY
Sex Linked Inheritance
• Sex Linked Traits – located
on the sex chromosomes
(usually the X)
Two of the most common human
traits found on the X chromosome
are:
1. Hemophilia – blood clotting
disorder (recessive)
2. Red-green Colorblindness –
difficulty telling the difference
between greens and reds.
Hemophilia
XH = Normal
Xh = hemophilia
Female
Genotype
XH XH =
Female
Male
Phenotype Genotype
XH Xh =
Normal
Normal,
carrier
Xh Xh =
hemophilia
Male
Phenotype
XH Y =
Normal
Xh Y =
hemophilia
Cross: Female Carrier x Normal Male
Parental Cross:
XH Xh
XH
x
XH y
Xh
XH
XH XH
XH X h
y
XH y
Xh y
Hemophilia – 25%
Normal – 75%
XH XH: 25%
XH Xh: 25%
XH y: 25%
XH y: 25%
Hemophilia
Pedigree
Are there more males
or females with
hemophilia?
Why?
Red-Green Colorblindness
Can you see the
green 15?
What is the genotype of
a male that is colorblind?
Use “R”
Xr Y
What is the genotype of
a female that is colorblind?
Xr Xr
PRACTICE -Do a punnett square for the following
individuals:
1. XHXh
•
Xhy
2. XHXH • Xhy
3. Colorblind woman with a normal male
4. Homozygous dominant brown rabbit with a white
rabbit.
5. Red cow (RR) with a white cow (WW)
Warm Up
1. Cross a carrier female with a hemophiliac
male. What is the chance their child will
have hemophilia?
2. Cross a normal male with a carrier female.
What is the chance their child will have
hemophilia?
3. Cross a red flower (RR) with a white flower
(R’R’). What is the phenotype of the
offspring?
Multiple Alleles
Multiple alleles  genes exist
in more than 2 allele forms.
•Combinations of any 2 of
these alleles can produce
different phenotypes
Example in humans – ABO
blood groups
(4 blood groups controlled by 3
alleles)
• IA and IB are codominant, “i”
is recessive.
•Each person has 2 of these 3
alleles
Genotypes
Phenotypes
IA IA or IA i
A
IBIB, or IB i
ii
B
O
IA IB
AB
Cross a heterozygous type A female and a type
AB male. What are the possible phenotypes
and genotypes for their offspring.
Parent Cross IA i x IA IB
IA
i
IA
IA IA
IA i
IB
IA IB
IB i
Blood Types
• Charles Drew: discovered blood
types of people differ, created the
first blood bank.
Blood Type
Antigens
Antibodies
A
A
B
B
B
A
• Antigens: markers on the surface
of red cell that determine type.
AB
A and B
None
O
none
A or B
• Antibodies – fight against blood
not your type
•Universal Donor is O blood type
because it has no antigens on its
surface.
• If type of A antigens come in contact
with anti A antibodies, the blood will
clump. The clumping called agglutination,
can cause serious problems, even death.
Two reasons to know your blood type:
•Universal Recipient is AB blood type 1. In case of emergency, you need
blood
because they have no antibodies
2. To donate
that would attack foreign blood.
Complete Dominance
Inheritance Pattern
Incomplete
Dominance
TT – dominant
Tt – dominant
tt - recessive
What makes it
different
Symbols used in
Punnett Square
Example
Phenotypes BLEND
RR - red
R’R’ - white
RR’ – pink
Red & white flowers
make pink
Both Phenotypes
show up
RR - red
WW - white
RW – roan
Roan cattle
Checkered chicken
Polygeneic
Inheritance
Many genes code for
one trait – gives a
wide variety
RrAAttBb
Human skin color,
height, hair color
Multiple Alleles
2+ versions of a gene,
but only receive 2
IAIA IAi – A blood
IBIB IBi – B blood
IAIB - AB blood
ii – O blood
Blood Typing
Sex-Linked
Recessive gene found
on the ‘X’
chromosome
XHXH – normal female
XHXh - carrier female
XhXh – affected female
XHy – normal male
Xhy – affected male
Hemophilia
Colorblindness
Co-dominance
1. A man who has hemophilia has children with a normal female.
What is the chance their child will have hemophilia?
2. Cross a true breeding tall plant with a true breeding short plant.
What are the genotypes of the offspring?
3. A man with AB blood crosses with a female with heterozygous B.
What are the possible phenotypes of their offspring?
4. A cross between a BB (black) and B’B’ (white) goose will give you
BB’ (gray) offspring. Cross 2 gray geese and what are the possible
phenotypes?
5. A red cow (RR) crosses with a white cow (WW), what are the
possible phenotypes of their offspring?
6. If two parens are heterozygous for rounds seeds. What are the
chances they will have round offspring?