Download Human Heredity Ch. 14

Human Heredity
• There are traits that are controlled by one
gene with 2 alleles. Often, one is
dominant and the other is recessive
• Example:
widow’s peaks and dimples.
Some traits are controlled by a gene with
multiple alleles – 3 or more for a single
trait.
For example: blood types and skin color in
humans.
• There are 44 chromosomes that we call
autosomal chromosomes.
• However, there are 2 chromosomes that
determine our sex and we call them sex
chromosomes.
• These 46 chromosomes all carrier genes
on them that determine our traits.
• Out of our 23 pairs of chromosomes, 1
pair is the sex chromosomes (X and Y).
•
Female = XX
•
Male = XY
• Question: What is the probability
that your parents will have a boy
or girl?
• XY (dad) x XX (mom)
X
X
XX
Y
XY
Phenotype:
50% boy
50% girl
X
Genotype:
XX
XY
50% XX
50% XY
Question?
If my parents have 5 boys in a row, what is
the chance they will have a girl the next
time?
50%
Human genes are inherited the same way
that Mendel discovered. Some traits are
controlled by one gene. Therefore, you can
study inheritance of traits through a
pedigree. A pedigree is a chart or “family
tree” that traits a specific trait.
Genetic counselors analyze these charts to
infer about genotypes of family member.
Dominant gene:
→affected individuals have at least one
affected parent
→the phenotype generally appears every
generation
Recessive gene:
→unaffected parents can have affected
offspring
→affected progeny are both male and
female
Sex-linked gene:
• Some traits are carried on the sex
chromosomes. Genes on the X or Y
chromosomes are sex-linked genes.
• These traits are passes on from parent to
child. Sex- linked genes can be recessive or
dominant.
• MALES are more likely to have a sex-linked
trait because they only have ONE X and Y. The
allele is USUALLY on the X chromosome.
• Ex. colorblindness, hemophilia, hairy ears,
muscular dystrophy
Are you colorblind?
What numbers do you see?
Carrier – person who has one recessive
allele and one dominant allele for a trait or
heterozygous for that trait (only women
can be carriers).
Example
Hemophiliac carrier XHXh
Colorblind carrier XBXb
• Carriers do not show that particular trait
phenotypically but have a chance to pass
the trait on to their child.
Carrier – half colored
Reading a Pedigree
Task 1: Genotyping a pedigree chart
Task 2:
Take out your pedigree sheet and some paper.
Lets do the first one together.
Do # 2.
Come see me to get your paper starred.
Sex linked Punnett Squares:
Question:
What is the probability that a carrier female and a
colorblind male will have a girl who is colorblind
(b = colorblind, B = normal)?
Xb
Y
Phenotype:
XB
XBXb
XBY
25% normal boy
25% colorblind boy
25% normal girl
Xb
25% colorblind girl
XbXb
XbY
Try this one on your own
Question:
What is the probability that a homozygous
(normal vision) female and a colorblind male will
have a girl who is colorblind (b = colorblind, B =
normal)?
Parents: XBXB x
Xb
X bY
Y
Phenotype:
XB
XBXb
XBY
XB
XBXb
XBY
50% normal girls
50% normal boys
?
Genetics Disorders and
Mutations
Mutations …
• are changes in the
genetic material
• can be good or bad
• can be on a single
gene or the whole
chromosome
Genetic Disorder –
abnormal condition that a person inherits
through genes or chromosomes.
They are caused by mutations or changes
in a person’s DNA.
Write down 3 disorders that have
affected someone you know.
Cystic Fibrosis
• Genetic disorder where the body produces abnormally thick mucus
in the lungs and intestines making respiration and digestion difficult
• caused by a mutation in a gene. The product of this gene is a
chloride ion channel important in creating sweat, digestive juices
and mucus.
• One in four babies are born with cystic fibrosis
• Most common among Northern European descent
Sickle Cell Anemia
•
•
•
•
Sickle cell is a genetic disorder that affects the
blood’s hemoglobin. Hemoglobin is the protein in
your blood that carries oxygen.
Sickle-cell anemia is caused by a point mutation in
protein chain of hemoglobin, replacing the amino
acid glutamic acid with the amino acid valine
The ‘sickle shape’ of the cell doesn’t allow the red
blood cell to carry very much oxygen.
Most common among African American descent
Famous People with Sickle Cell Disease
Miles Davis, jazz musician.
Paul Williams, singer (The Temptations)
Georgeanna Tillman, singer (The Marvelettes)
Tionne "T-Boz" Watkins, singer (TLC)
Hemophilia
•
•
•
Hemophilia is a genetic disorder in which a person’s
blood clots VERY slowly or not at all.
A person with hemophilia can bleed to death from a
paper cut or scrape.
This is sex-linked disorder on the X chromosome.
– Queen Elizabeth suffered from this disorder.
This man received a
vaccine. This is what having
hemophilia did to is body.
Down Syndrome
•
•
Down Syndrome is a genetic disorder that
occurs when an individual receives an extra
copy of a chromosome.
A mistake occurs during Meiosis I: the
chromosomes failed to separate correctly
(non-disjunction) therefore leaving an extra
copy of chromosome #21.
• Doctor’s use tools like amniocentesis and
karyotypes to help detect most diseases.
?
What is a karyotype?
• Picture of your
chromosomes
• Arranged from largest
to smallest
• quickly identify
chromosomal
changes
Diagnosis the karyotypes in the back of
the room at your table.
Make sure to include:
• Case number
• Boy or girl
• Number of chromosomes
• Normal or abnormal
(if abnormal, what is the problem?)
4 Types of Genetic Disorders
1. Single gene
– Change in the DNA sequence
– More than 6000 known disorders
– Autosomal or sex linked
– 1 in 200 births
Examples:
cystic fibrosis, sickle cell anemia, Marfan
syndrome, Huntington’s disease
Types of Genetic Disorders
2. Multi-factoral
– combination of environmental factors and
mutations in multiple genes
– more complicated
Examples:
heart disease, high blood pressure,
Alzheimer’s disease, arthritis, diabetes,
cancer, and obesity
Types of Genetic Disorders
3. Chromosomal
– abnormalities in chromosome structure as
missing or extra copies or gross breaks and
rejoining
Example:
Down Syndrome
Types of Genetic Disorders
4. Mitochondrial
– rare type of genetic disorder
– caused by mutations in the non-chromosomal
DNA of mitochondria
Here are some genetics disorders,
some you have heard about and
some you haven’t.
Turners Syndrome
1 in 5,000 births
45 chromosomes
X only
#23 Monosomy
Nondisjunction
Turners Syndrome
96-98% do not survive to birth
No menstruation
No breast development
No hips
Broad shoulders and neck
Cri-Du-Chat Syndrome
1 in 216,000 births
46 chromosomes
XY or XX
#5 Deletion of lower
arm
Cri-Du-Chat Syndrome
Moon-shaped face
Heart disease
Mentally retarded
Malformed larynx
Normal lifespan
Aniridia-Wilms Tumor
Syndrome
1 in 50,000,000 births
46 chromosomes
XY or XX
#11 Deletion of upper arm
Aniridia-Wilms Tumor Syndrome
Mentally retarded
Growth retarded
Blindness
Tumors on kidneys
Short lifespan
Thirteen Q Deletion
Syndrome
1 in 500,000 births
46 chromosomes
XY or XX
#13 Deletion of lower arm
Thirteen Q Deletion Syndrome
Mentally retarded
Deformed face
No thumbs
Heart disease
Short lifespan
Prader-Willi Syndrome
1 in 5,000,000 births
46 chromosomes
XY=97%
XX=3%
#15 Deletion of lower arm
Prader-Willi Syndrome
Small bird-like head
Mentally retarded
Respiratory problems
Obesity
Short lifespan
Eighteen Q Deletion
Syndrome
1 in 10,000,000 births
46 chromosomes
XY or XX
#18 Deletion of lower arm
Eighteen Q Deletion Syndrome
Mentally retarded
Heart disease
Abnormal hands and feet
Large eyes
Large ears
Normal lifespan
Cat-Eye Syndrome
1 in 1,000,000 births
46 chromosomes
XY or XX
#22 Deletion of bottom
arm
Cat-Eye Syndrome
Fused fingers and toes
Mentally retarded
Small jaw
Heart problems
Normal lifespan
Four-Ring Syndrome
1 in 10,000,000 births
46 chromosomes
XY or XX
#4 Inversion
Four-Ring Syndrome
Cleft palate
Club feet
Testes don’t descend
Short lifespan
Down
Syndrome
1 in 31,000 births
46 chromosomes
XY=97%
XX=3%
#14/21 Translocation
Down Syndrome
Trisomy
1 in 1,250 births
47 chromosomes
XY or XX
#21 Trisomy
Nondisjunction
Down Syndrome
Short, broad hands
Stubby fingers
Rough skin
Impotency in males
Mentally retarded
Small round face
Protruding tongue
Short lifespan
Patau’s Trisomy
Syndrome
1 in 14,000 births
47 chromosomes
XY or XX
#13 Trisomy
Nondisjunction
Patau’s Trisomy Syndrome
Small head
Small or missing eyes
Heart defects
Extra fingers
Abnormal genitalia
Mentally retarded
Cleft palate
Most die a few weeks after birth
Edward’s Trisomy
Syndrome
1 in 4,400 births
47 chromosomes
XX=80%
XY=20%
#18 Trisomy
Nondisjunction
Edward’s Trisomy Syndrome
Small head
Mentally retarded
Internal organ abnormalities
90% die before 5 months of age
Jacob’s Syndrome
1 in 1,800 births
47 chromosomes
XYY only
#23 Trisomy
Nondisjunction
Jacob’s Syndrome
Normal physically
Normal mentally
Increase in testosterone
More aggressive
Normal lifespan
?
Klinefelter Syndrome
1 in 1,100 births
47 chromosomes
XXY only
#23 Trisomy
Nondisjunction
Klinefelter Syndrome
Scarce beard
Longer fingers and arms
Sterile
Delicate skin
Low mental ability
Normal lifespan
Triple X Syndrome
1 in 2,500 births
47 chromosomes
XXX only
#23 Trisomy
Nondisjunction
Triple X Syndrome
Normally physically
Normal mentally
Fertile