Transcript Advanced Genetics

Advanced Genetics
Pedigrees
Graphic representation of genetic inheritance
Pedigree Symbols
Unaffected
Male
Carrier
Male
Unaffected
Female
Carrier
Female
Heterozygous
Genotype
Affected
Male
Deceased
Male
Affected
Female
Deceased
Female
Pedigree Symbols
Mated Adults
Parents with children
Reading Pedigrees
Generation 1
Person 1
Carrier Male
Generation 2
Affected Male
Person 5
Generation 3
Affected Female
Person 3
Simple Recessive Heredity
• Must inherit 2 recessive alleles to display trait
(Homozygous)
– Example: rr, tt, ss, pp
• MOST genetic disorders are caused by
recessive alleles
2 Recessive Disorders
(1) Cystic fibrosis:
• A defective gene that causes the body to produce
unusually thick, sticky mucus that:
– Clogs the lungs & leads to life-threatening infections
– Obstructs the pancreas and stops the body from
breaking down food and absorbing nutrients.
• Treatment: medication, diet, & physical therapy
Genotypes
CC
Cc
cc
Phenotypes
NormalNo CF
Normal- no CF
but is a carrier of
the disease
Affectedhas CF
2 Recessive Disorders
(2) Phenylketonuria (PKU):
• Phenylalanine (amino acid) cannot be broken down and
builds up in the central nervous system causing mental
disability.
• Symptoms: delayed mental and social skills, seizures, skin
rashes, tremors, and unusual position of hands to some.
• Prevention: All babies blood tested at birth.
• Treatment: special diet
Genotypes
PP
Pp
pp
Phenotypes
Normal- No PKU
Normal- but is a
carrier of the
disease
Affected- has PKU
Simple Dominant Heredity
• Must inherit 1 dominant allele to display trait
– Example: RR, Rr
• Examples: tongue rolling, free earlobes,
hitchhiker’s thumb, widow’s peak, dimples,
almond shaped eyes, cleft chin, freckles.
Dominant Disorder
(1) Huntington’s disease:
• Results from genetically programmed loss of brain
cells, called neurons in certain areas of the brain.
• Onset is normally between ages 30-40
• Treatment: prescribe a number of medications to help
control emotional and movement problems, but no
treatment for actual loss of brain cells.
Genotypes
HH
Hh
hh
Phenotypes
Has
Huntington’s
Has Huntington’s
Normal- No
Huntington’s
Dominant Disorder
(1) Huntington’s disease:
• Behavior changes may occur before movement
problems.
– Examples: Hallucinations, irritability, moodiness, or
restlessness
• Abnormal and unusual movements
– Examples: Facial movements, quick, sudden or wild
jerking movements, slow, uncontrolled movements.
• Dementia that slowly gets worse
– Example: Disorientation or confusion, loss of judgment
and memory, personality changes and speech changes
Practice
• If a man with cystic fibrosis marries a female carrier,
what is the percentage chance that they will have
children with cystic fibrosis?
Man with cystic fibrosis:
What is his genotype?
____________
Female carrier:
What is her genotype?
________________
Inheritance patterns are often more
complex than predicted by simple
Mendelian genetics.
• Each character that Mendel studied is
controlled by a simple gene.
• Each gene has only two alleles, one of which is
completely dominant to the other.
• The heterozygous offspring always looked like
one of the parents because one allele was
dominant to the other.
When do we go beyond simple
Mendelian Genetics?
• When alleles are not completely dominant or
recessive
• When a gene has more than two alleles
• When a gene produces multiple phenotypes
Degrees of Dominance
• Alleles show different degrees of dominance
and recessiveness in relation to each other.
• In Mendel’s crosses we’ve seen Complete
Dominance
– BB (Brown) Bb (Brown) bb (Blue)
Incomplete Dominance
• Incomplete dominance: Inheritance pattern where
phenotypes of heterozygous individual is intermediate
(a blend) between the 2 homozygous individuals
producing a new trait.
•
•
•
•
Neither allele is dominant over the other
All capital letters because all dominant.
The letters can be the same or different
The third (inbetween) phenotype appears in the
heterozygous (hybrid) condition.
• Hint: Phenotype of offspring will look like a “blend” of parent’s
phenotypes.
Example
In carnations the color red (R) is incompletely dominant
over white (r). The hybrid color is pink. Give the
genotypic and phenotypic ratio from a cross between 2
pink flowers.
Rr X Rr
R
r
R
RR
Rr
r
Rr
rr
Genotypic = 1 RR : 2 Rr : 1 rr
Phenotypic = 1 red : 2 pink : 1 white
Practice
• In 4 o’clock flowers, when red flowers [R] and
blue flowers [r] are crossed, purple flowers are
created. Show the cross between two purple
flowers.
R
r
R
r
RR
Rr
Rr
rr
What percentage of the
offspring are homozygous?
50%
What percentage of the
offspring are purple?
50%
Codominance
• Codominance: Inheritance pattern where phenotypes of
both homozygous parents are produced in heterozygous
offspring so that both alleles are expressed equally.
• All capital letters because all dominant.
• The letters can be the same or different.
• Two dominant alleles are expressed at the same time so
both phenotypes are expressed.
• Hint: Phenotype of offspring will look like
”____ & _____”.
Example
In certain chickens black feathers are codominant with
white feathers.
A Black chicken (BB) is crossed with a White chicken
(WW) which results in Checkered chicken (BW)
offspring.
BB X WW
W
W
B
BW BW
B
BW BW
Example
Checkered color represents a codominant allele in chickens. What
phenotypes would be created when 2 checkered chickens are
crossed?
BW X BW
B
B
W
BB BW
W BW WW
Practice
• A farmer’s herd consist of black [B], white [W], and roan color.
Upon examination, it can be seen that the coat of a roan
horse consist of both black and white hairs. The farmer has
decided to cross two roan horses.
B
W
B
BB
W
BW WW
BW
What percentage of the offspring
is black?
25%
What percentage of the offspring
is roan?
50%
What percentage of the offspring
is white?
25%
Codominant Diseases
(1) Sickle Cell Anemia
• Hemoglobin protein, the protein that carries oxygen
in the blood, is mutated and causes the red blood
cells (normally round shaped) to be shaped like
bananas.
– Caused by a point mutation on DNA
• Mostly affects people of African ancestry, but also
occurs in other ethnic groups.
– 1 in 12 African Americans have sickle cell trait, which
means they carry a single gene for the disease, but do
not have the disease.
Genotypes
NN
NS
SS
Phenotypes
Normal- RBC
½ sickle RBC & ½
normal RBC
All sickled RBC
Normal Red Blood Cells and Sickle Cells
• When sickle-shaped
cells block small
blood vessels, less
blood can reach that
part of the body.
• Tissue that does not
receive a normal
blood flow
eventually becomes
damaged.
Malaria: A mosquito-borne disease of the blood.
• Potentially fatal blood disease caused by a parasite
that is transmitted to humans and animal hosts by
the mosquito.
• Human parasite digests the red blood cell’s
hemoglobin and changes the properties of the cell
it inhabits.
– This change causes the cell to stick to the walls of blood
vessels.
• Especially dangerous when the infected blood cells
stick to the capillaries in the brain, obstructing
blood flow, a condition called cerebral malaria.
Sickle Cell Anemia and Malaria
• Each year, malaria attacks about 400 million
people, two to three million of whom succumb
to the illness.
• Most malaria victims are children.
Practice
• A sickle cell anemic male marries a female
with half normal RBC and half sickled. What
percentage of their offspring would have
sickle cell?
Multiple Alleles
• Multiple alleles: The presences of more than 2
alleles for a trait.
• Remember: Each individual will only have two
alleles for a trait but there are several alleles to
choose from.
• Examples:
– Coat color in pigeons
– 3 alleles
– BA = ash, B= Blue, & b= brown
Multiple Alleles
• 2 or more alleles of the same gene that code for a single trait
• In humans, blood type is determined by 3 alleles – A, B, and O
BUT each human can only inherit 2 alleles
•Blood types are controlled by Multiple alleles.
1. Dominant – A and B (codominance)
Recessive – O
2. Blood type –
A = AA or AO
B = BB or BO
AB = AB
O = OO
Blood Typing Chart
Phenotypes
Genotypes
Blood Type A
IAIA or IAi
Blood Type B
IBIB or IBi
Blood Type AB
IAIB
Blood Type O
ii
Why is blood type important?
• Blood Transfusion
• Paternity/Maternity Testing
• Crime Scene Investigation
Practice
• A father has a Blood Type AB. The mother has
homozygous Blood Type A. Can the child have
Blood Type O?
Practice
• A man is accused of fathering 2 children. Child 1
is blood type O and Child 2 is blood type B. The
mother is heterozygous for blood type B. The
man is blood type AB. Could he father both
children?
Sex determination
• Human somatic cells = 46 chromosomes
(Diploid)
• Human gametes = 23 chromosomes (Haploid)
Sex determination
• Chromosomes # 1-22 pairs:
– Autosomes: Control things other than gender
• Chromosomes #23 pair:
– Sex chromosomes: control gender
Baby
XX
Mother
XY
Father
Sex-linked Inheritance
• Sex Linked Traits controlled by genes on the sex
chromosomes.
• Most sex-linked traits are on the X-chromosomes.
How are Sex-Linked Traits inherited?
Fathers (XY)
can only pass
X-linked
disorders to
daughters
(XX)
Mothers (XX)
can pass Xlinked
disorders to
both sons (XY)
and daughters
(XX)
Types of Sex-Linked Traits
• X-linked traits are traits whose allele is carried on
the X chromosome.
– Most disorders are carried on the X chromosome, so
males are more likely to inherit them.
• Y-linked traits are traits whose allele is carried on
the Y chromosome.
– Most Y-linked mutations lead to sterility, and can not
be inherited.
Sex-linked Trait Examples
• Hemophilia: Your body cannot clot
blood
• Red-Green color blindness:
Cannot tell the difference
between red and green.
• Both examples are on the X
chromosomes and are recessive.
Hemophilia in the Royal Family
Colorblindness
• For sex-linked traits, you must write
genotypes like:
C
• XCXC : Normal color vision female
• XCXc : Normal color vision female
(carrier)
• XcXc : Color-blind female
• XCY : Normal color vision male
• XcY : Color-blind male
c
Hemophilia
• For sex-linked traits, you must write
genotypes like:
H
• XHXH : Normal clotting female
• XHXh : Normal clotting female
(carrier)
• XhXh :Hemophilic female
• XHY : Normal clotting male
• XhY : Hemophilic male
h
Practice
• A woman who is a carrier for hemophilia marries a
normal man. Show the possible results of this cross
and answer the following questions:
– A. What is the probability that this couple could have a son
with hemophilia?
– B. What is the probability that they could have a daughter
with hemophilia?
Sex-Linked Trait Facts
• Sex-linked traits occur more so in males than
females because:
• Males only need one “bad” gene on the X
chromosome.
• Females need two “bad” genes on both X
chromosomes.
Polygenic Inheritance
• Polygenic inheritance: Inheritance pattern of
a trait controlled by two or more genes; genes
may be on the same or different
chromosomes.
• Polygenic inheritance usually shows up as a
range of variation.
– ex: Hair color, eye color, height, and skin color.
Chromosomal Number
• Normal Somatic Cell = 46 chromosomes
• Scientists look at chromosome number
information by using a karyotype.
• A karyotype is a picture of an individual’s
chromosomes.
Detecting Genetic Disorders
Amniocentesis is used to detect genetic disorders by analyzing the
amniotic fluid that surrounds an embryo.
Female with Down’s syndrome
Chromosomal Number Mutations
• Sometimes cells have too many or too few
chromosomes:
• (1) Trisomy = 1 extra chromosome = 47
• (2) Monosomy = 1 less chromosome = 45
• Caused by nondisjunction during Meiosis
Down syndrome – (Trisomy 21) 47 chromosomes, extra
chromosome at pair #21
Down Syndrome
•
Autosomal chromosome disorder where there are three of
chromosome-21.
•
common physical traits: low muscle tone, small stature, an upward slant to
the eyes, and a single deep crease across the center of the palm.
•
Life expectancy increased from 25 in 1983 to 60 today.
•
Attend school, work, participate in decisions that affect them, and contribute
to society in many wonderful ways.
•
Experience mental processing delays, but the effect is usually mild to
moderate and is not indicative of the many strengths and talents that each
individual possesses.
Abnormal Chromosome # Disorders
Individuals can have the wrong number of sex
chromosomes
Females (no X chromosome)
- XO: Turner Syndrome
Physical Traits: Short Stature, premature
ovarian failure, webbed neck, and normal
overall intelligence.
Turner’s syndrome – only 45 chromosomes, missing a sex
chromosome (X)
Girls affected – short, slow growth, heart problems
Abnormal Chromosome # Disorders
Males (extra X chromosome)
-XXY: Klinefelter Syndrome
• puberty- make as much testosterone which can lead to a taller, less
muscular body, less facial and body hair, and broader hips than
other boys.
•
teens- may have larger breasts, weaker bones, and a lower energy
level than other boys.
•
adulthood- look similar to males without the condition, although
they are often taller. They are also more likely than other men to
have certain health problems,
such as autoimmune disorders, breast cancer, vein diseases,
osteoporosis, and
tooth decay.
Klinefelter’s syndrome – 47 chromosomes, extra X
chromosomes (XXY)
Boys affected – low testosterone levels, underdeveloped
muscles, sparse facial hair
• Having an extra set of chromosomes is fatal in animals,
but in plants it makes them larger and hardier.
Hardier