Download Genetics – the study of how traits are passed from parents to offspring.

Mendelian
Genetics
Chapter 8
I. Patterns of Inheritance
Male
Female
+
Genetics is the study of
how traits are passed
from parents to
offspring.
These traits are the characteristics that make an organism what it
is. Traits can be for:
legs
wings
proteins
tongues
hair color, to name a few…
The study of genetics started
with an Austrian monk
named Gregor Mendel
(1822-1884).
Mendel is known as the
Father of Genetics.
Mendel used pea plants to study how traits are inherited.
He observed the traits of tallness and color of sweet pea
plants. He fertilized the flowers of the peas to produce
offspring with different traits. From this, he made up the
basic laws of genetics, called Mendelian traits.
•Some of the peas were
purebred, or have the same
genetic traits from both their
parents.
Some of the traits in
peas that Mendel
studied
•Some were hybrids (also called
heterozygous), or crossbreeds
(organisms that receive different
forms of a genetic trait from
each parent).
Mendel hypothesized that each trait is controlled by a distinct
“factor.” These factors are now known as genes, or segments
of DNA that carry the code for a specific trait; genes are dark
bands found on the chromosome, or rod-shaped structures
found inside the nucleus of a cell.
Cell
-
Nucleus
- Chromosome - DNA Strand - Gene Code
Most organisms have two copies of every gene, one from
each parent.
Ex. Humans have 46 chromosomes: 23 from each parent (sperm
and egg)
Some other
organisms’
chromosome
counts compared
to humans.
The different forms of the pair of genes are known as alleles.
One from
mom and one
from dad.
Difference between a
pair of alleles and just
any two genes on a
pair of chromosomes.
DOMINANT GENES
•If an organism has two different alleles for a trait, say height, only one
is expressed, or visible. This is known as the dominant gene.
Which color is dominant in
this family?
•Symbols for dominant genes are always capitalized (ex. D, B, T, R).
Examples of dominant traits in humans.
Recessive Genes
•The recessive gene is a weaker gene that does NOT show even
though they are present unless there is no dominant gene present.
Here the recessive
genes are only
expressed 1 out of 4
times. 3 out of 4
times, the dominant
gene hides it.
•Symbols for recessive genes are always lowercased (ex. d, b, t, r).
Examples of recessive traits in humans.
Here’s an example:
- alleles for height
T = the allele for tallness
t = the allele for shortness
If an organism was Tt or TT, then the
dominant allele would be expressed and
the recessive allele would not. The
organism would be tall.
If the organism was tt, then the recessive alleles would be
expressed and the organism would be short.
II. Principles of Inheritance
If an organism is either TT or tt (the same case letter), then
that individual is homozygous (homo- means “the same”)
- homozygous dominant = HH, BB, TT (Pure Dominant)
- homozygous recessive = tt, rr, hh, bb (Pure Recessive)
- Many pets and domesticated animals are bred for their homozygous traits.
If an organism is Tt (different case letters), then that
individual is called heterozygous (hetero- means “different”)
Also called: Hybrid, Carrier, Crossbreed)
Some animals bred for…
…their heterozygous traits.
What is the difference between
Genotype and Phenotype?
Phenotype (“pheno” means “physical”)
A. This term refers to a physical trait that can be
seen. (Blue eyes or Type A blood, would be
examples.)
Genotype (“geno” means “genetic”)
A. This term refers to an organism’s genetic
(DNA) make-up for a trait. (Such as BB, Bb, and
bb.)
The examples TT, Tt, or tt are known as an individual’s genotype,
or the actual genetic makeup of an organism; type of genes. ex
- Aa, AA, aa
If the genotype were TT or Tt, for example, then their outward
appearance would be tall. This is known as phenotype, or the way
an offspring appears or looks; a physical description.
tall
blonde
albino
freckles
If the genotype were tt, then their phenotype would be
short. Get it?!
Short plants
Actor, Warwick Davis
Mendel’s discoveries of inheritance were lost until
1903.
Then, Walter S. Sutton outlined the chromosome theory of heredity.
Sutton observed stained cells through a microscope
and witnessed chromosomes for the first time.
Stop.
Gregor Mendel’s studies produced three major laws known as
Mendel’s Laws.
1. The Law of
Segregation
- gene pairs
separate when gametes
(sperm & egg) form
- half the
gametes contain one
gene, half the other
2. The Law of Independent Assortment
- gene pairs segregate into gametes randomly and
independently of each other
3. The Law of Dominance
- the dominant allele is
expressed and the recessive allele
can be hidden
Offspring are all red. Red
is dominant over white.
Dominance
Complete Dominance
A. The dominant allele has information and it is
expressed, even if there is only one copy.
Geneticists call this “100%
penetrance”.
Incomplete Dominance
A. Information from both alleles is expressed in
the cell. Neither phenotype is completely
penetrant, therefore the
heterozygous phenotype appears “blended”.
(Red + White = Pink)
Dominance continued…
Codominance
A. Both alleles are
expressed in the cell. They
are both equally present in
terms of phenotype, i.e.
black and white coats
in animals, AB blood type in
humans.
III. Genetics and Predictions
Mother’s Alleles Go Here
Punnett Square – grid work to determine probabilities
for each pregnancy, mating, crossing, or pairing. Each
new mating requires a NEW Punnett Square.
Father’s Alleles Go Here
Example:
If a mother is Pure Dominant for Brown Eyes (BB) and a
father is Hybrid for brown eyes (Bb), the Punnett Square can
help you find the possible eye color of the offspring
B
b
B
BB
Bb
B
BB
Bb
Mom’s
Alleles
Dad’s
Alleles
The offspring has
a 50% chance of
being Pure
Dominant, a 50%
chance of being
hybrid, and a 0%
chance of being
recessive.
Sex-Linked Traits – attaches to an X chromosome; female is
usually a carrier only (she will possibly pass on bad trait, but will not get it
herself); the reason is that she has 2 “X” chromosomes and one is probably
normal. The male only has one “X” chromosome, so he is usually affected
with the condition.
Examples:
Male:
XY
Color Blindness
Hemophilia
Duchenne muscular dystrophy
Female:
XX
Example #1:
Example #2:
A normal mother and a father
with color blindness have a child.
What are the chances that the
child will have color blindness?
A carrier mother and a father
with color blindness have a child.
What are the chances that the
child will have color blindness?
Xc
X
c
XX
X
X Xc
Y
Xc
Y
XY
Xc Xc Xc Xc Y
XY
X X Xc X Y
There is no chance that a child
will have color blindness.
There is a 50% chance that a
child will have color blindness.
One process scientists use to locate genes is called cytogenetic mapping. After
breaking open nuclei, scientists fix the chromosomes on a slide, and then stain
the chromosomes to see the bands. A complete set of banded chromosomes is
also called a karyotype. The banding pattern is unique for each chromosome
and allow to pair the chromosomes together and identify abnormalities.
XX – Karyotype Female (normal)
XY – Karyotype male (normal)
Bellwork: Punnett Square Problems
1. A pure dominant father and a pure recessive mother
have a child. What are the chances of the baby having
blonde hair? ( Hair color : B=dominant, b= recessive)
2. A heterozygous black rabbit and a white rabbit cross.
What percentage of the offspring will be black?
3. A homozygous brown dog mates with a heterozygous
brown dog. What are the chances of the offspring being
homozygous?
4. A pure recessive white flower crosses with a pure
dominant red flower. How many off spring will be
homozygous?
5. Two tall parents produce a short offspring. How can you
explain this? Show your work.
Down syndrome:
Causes cognitive
impairments
and developmental delays
ranging from mild to
serious. Effects one in
every 800 infants.
Symptoms include:
• Flattened facial features
• Protruding tongue
• Small head
• Upward slanting eyes
• Unusually shaped ears
• Poor muscle tone
• Broad, short hands
• Single crease in the palm
• Relatively short fingers
• Excessive flexibility
Genetic
Disorder
caused by
“Trisomy 21”
Actor Chris
Burke from
“Life Goes
On”
XXX – Multi X Female
Around one woman in
1,000 has three or more
X-chromosomes. Most
47, XXX women are
normal but some may
have mild cognitive
delays. With each extra X
the impairments
increase. For instance, a
woman with 49, XXXXX
will have severe
disabilities.
Caused by trisomy
(or greater) of the X
chromosome
XXY – Klinefelter’s Syndrome
• XXY – male with extra X chromosome
• Extreme or non-apparent depending on the person
• Can have affects on sex characteristics
For example:
–
–
–
–
–
–
–
Enlarged breasts
Wide hips
Voice not breaking
Narrow shoulders
Long arms or legs
testicular atrophy
infertility
•
•
•
•
•
•
•
XYY – “super male”
Male with extra Y chromosome
More physically active
Delayed mental maturation
Learning Difficulties
More aggressive
Lower IQ
ADD or ADHD
XO – Turner’s syndrome
• Turners Syndrome: a genetic defect in women in which there is only one
X chromosome instead of the usual two.
• Affected women are infertile. They have female external genitalia but no
ovaries and therefore no menstrual.
• Characteristically they are short in stature and have variable
developmental defects which may include webbing of the neck.
Actress Geri Jewell
fro “Facts of Life”
Tay-Sachs disease
• progressive destruction of nerve cells in the brain and spinal
cord.
• Infants appear normal until the age of 3 to 6 months
• lose motor skills such as turning over, sitting, and crawling
• develop seizures
• vision and hearing loss
• mental retardation
• Paralysis
• Rarely live beyond 5 years
“floppy” child –
muscle hypotonia
Prader-Willi
7 genes are deleted from
chromosome #15
• mild cognitive delays
• crossed eyes
• small hands and feet
• growth delay
• short stature
• become extremely obese
due to incorrigible eating.
Patau's syndrome (Trisomy-13)
• tiny head
• abnormal limbic system
• tiny eyes
• one cerebral hemisphere
• a single eye
Stillborn term infant with Patau's syndrome.
The baby has no eyes, no nose opening, and
an elongated bulb hanging from forehead.
Cri Du Chat Syndrome “Cat’s Cry”
• deletion of part of chromosome 5
• 1 in 50,000 live births.
• distinctive facial features
• shortened lifespan
• Cognitive delays
William's Syndrome
• deletion of a part of chromosome 7
• Causes difference in the protein Elastin
• Elf-like features: wide smile, large ears
• Disorders with circulatory system
• Affinity to music
William's Syndrome is a rare genetic defect, affecting approx. 1/20,000 births
Ethical Issues with Gene Research
Behavioral Genetics
Your genes determine
how you will behave.
Forensics
DNA can prove
innocence or
guilt in many
criminal cases.
Genetic Engineering
Food, crops, animals,
HUMANS?
Gene Testing
Can determine
if a fetus has
genetic
disorders
Gene therapy
is a technique for
correcting
defective genes
Cloning
?
Genetic
Discrimination
?
Stem cell research
Regeneration
?
?