Transcript File

Basics of Genetics
http://sps.k12.ar.us/massengale/genetics%20tutorial.htm
http://www.jic.bbsrc.ac.uk/germplas/pisum/zgs4f.htm
Transmission of characteristics from parents to
offspring = ___________________
heredity
The science that studies how those
Genetics
characteristics are passed on = _________
http://strongbrains.com/science/biology/default.htm
Gregor
Mendel
______________________________
•
•
•
•
•
Father of Genetics
Looked at one trait at a time
Made experimental crosses
Large sample size
Kept careful records
http://www.jic.bbsrc.ac.uk/germplas/pisum/zgs4f.htm
MENDEL’S PEA EXPERIMENTS
Peas are “self pollinating”
ie., egg and sperm come from same plant
Mendel’s experiments
Allowed him to
experiment and
observe offspring
produced from a
variety of known
genetic crosses
http://hus.yksd.com/distanceedcourses/YKSDbiology/lessons/FourthQuarter/Chapter11/11-1/images/MendelExperiment.gif
MENDEL’S EXPERIMENTS
P1 generation
____
(_________)
parental
F1
____
generation
(______=
offspring)
filial
F
2
___
generation
PATTERNS ARE THE KEY
Image modified from:
http://www.laskerfoundation.org/rprimers/gnn/timeline/1866.html
http://www.accessexcellence.org/AB/GG/mendel.html
Image modified from: http://www.newtonswindow.com/problem-solving.htm
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
genotype
Genetic makeup of organism = _________
phenotype
Appearance of organism = ____________
MENDEL’S MODEL
1.Alternative versions of genes account for
variations in inherited traits.
2.For each trait, an organism inherits TWO
alleles.
3.If the two alleles at a locus differ, one
determines the organism’s appearance;
the other has no effect.
4.The two alleles for a character separate
during gamete formation and end up in
different gametes.
Image modified from: http://www.newtonswindow.com/problem-solving.htm
1.Alternative versions of genes
account for variations in
inherited traits.
Trait =
____________
Observable characteristic
Ex: flower color, height, pod shape
From Biology; Miller and Levine; Pearson Prentice Hall publishing as Benjamin Cummings © 2005 Pearson Education Inc
___________
Allele = choices for a trait
Ex: blue eyes, green eyes, brown eyes)
http://sps.k12.ar.us/massengale/genetics%20tutorial.htm
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
2. For each trait, an organism inherits
TWO alleles.
Organisms with two identical alleles for a
PURE BREEDING
gene = HOMOZYGOUS
____________OR ______________
Organism with two different alleles for a
HETEROZYGOUS
HYBRID
gene = _______________OR
___________
3. If the two alleles at a locus differ,
one determines the organism’s
appearance; the other has no effect.
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
_________________
= allele that masks
DOMINANT
the presence of another allele
RECESSIVE
__________________
= An allele
that is hidden
4. The two alleles for a trait
separate during gamete formation
and end up in different gametes.
= MENDEL’S
LAW OF
SEGREGATION
Image modified from:
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif
Mendel’s Law of
Independent Assortment
http://fig.cox.miami.edu/~cmallery/150/mitosis/c13x9independent-assortment.jpg
Two or more pairs of alleles segregate independently
of one another during gamete formation.
_______________ is the likelihood
PROBABILITY
that a particular event will occur
EX:
If you close your eyes and pick a
disk, what is the probability you
will pick the white one?
It can be written as a:
Fraction ____
1/4
Percent ____
25%
Ratio ____
1:3
http://www.arborsci.com/CoolStuff/CoinFlip.jpg
COIN FLIP
capital
There are 2 possible
outcomes:
HEADS
TAILS
The chance the coin will land on either one is:
____
1/2
____
50%
____
1:1
Alleles segregate randomly just like a
coin flip. . . So can use probability to
predict outcomes of genetic crosses.
PROBABILITIES
Past outcomes DON’T affect future ones!
If last coin flip was heads… there is still a 50/50
chance the next flip will be heads too.
Probability works best in predicting a large
number of events.
The more flips. . . The closer results will be to
the expected 50:50 average.
MULTIPLICATION & ADDITION RULES
To determine the probability of two or more
independent events:
MULTIPLICATION RULE:
Multiply the probability of one event by
the probability of the other
What is the probability two coins tossed
simultaneously will both end up on heads?
½X½ =¼
http://www.arborsci.com/CoolStuff/CoinFlip.jpg
MULTIPLICATION RULE WORKS FOR
PREDICTING GENETIC CROSSES, TOO
Tt X Tt
What is the probability offspring will be tt ?
Each egg has a ½ chance of passing on t.
Each sperm has ½ chance of passing on t.
½X½ =¼
Punnett by Riedell
ADDITION RULE
To figure out the probability of an offspring
being heterozygous (Tt)
T can come from mom and t from dad OR
t can come from the mom and T from the dad
but not both (events are mutually exclusive)
1st probability
T from mom
t from dad
½X½ =¼
2nd probability
t from mom
T from dad
½X½ =¼
¼+¼=½
Punnett by Riedell
HOW CAN YOU TELL THE GENOTYPE?
Tall plant has two possible genotypes
___
TT OR ___
Tt
TEST CROSS
Make a ___________
with a _____________________
HOMOzygous recessive
t
t
T T
Tt Tt
Tt
Tt
t
T
Tt
t
tt
t
Tt
tt
Images from: BIOLOGY by Miller & Levine; Prentice Hall Publishing ©2006
GENES are more complicated
than Mendel thought
1. Environment influences gene
expression
2. Spectrum of dominance
3. Multiple allele traits
4. Polygenic traits
5. Gene Linkage
6. Mitochondrial & Chloroplast DNA
Environment influences Phenotype
“Nature vs Nurture”
• Siamese cats and Himalayan rabbits have dark
colored fur on their extremities
• Allele that controls pigment production is only
able to function at the lower temperatures of
those extremities.
Images from slide show by Tracy Nelson
Environment influences Phenotype
“Nature vs Nurture”
• Color of hydrangea flowers varies
depending on pH of soil
Images from: http://www.gardensablaze.com/Shrubs/ShrubsHydrangea.htm
GENES are more complicated
than MENDEL thought
Spectrum of DOMINANCE
COMPLETE DOMINANCE
____________________
____________________
INCOMPLETE DOMINANCE
CO-DOMINANCE
____________________
COMPLETE DOMINANCE
If two alleles are present
DOMINANT allele masks
the RECESSIVE allele
Recessive trait shows again
in F2 generation in
3:1 ratio
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html
INCOMPLETE DOMINANCE
Heterozygous
snapdragons
show a
blended
intermediate
trait
Image modified from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html
CO-DOMINANCE
BOTH traits are expressed at the same
time side by side in heterozygote
A ROAN HORSE has
both RED and WHITE
hair side by side
CO-DOMINANCE
Both traits are expressed together
(NO BLENDING) in heterozygote
Persons with an A allele
AND a B allele have
AB blood type
REMEMBER
• Membrane proteins
with sugars attached that help
cells “recognize self”
GLYCOPROTEINS
= ______________
• Type of sugars attached
gives cell its “Blood type”
• I is used for blood type alleles
http://www.mannanw.com/super-sugars.htm
BLOOD TYPES
Person with
IA IA OR IA i
genotype
has cells with a certain
glycoprotein “A”
on its surface
TYPE “A” BLOOD
BLOOD TYPES
Person with
IB IB OR IB i genotype
has cells with a different
glycoprotein “B”
on its surface
TYPE “B” BLOOD
BLOOD TYPES
Person with i i
genotype have
neither “A” nor “B”
glycoproteins on their
surface
TYPE “O” blood
Note: Cells have
other glycoproteins…
just not A or B
A and B are CO-DOMINANT
Person with IA IB
genotype has BOTH
“A” and “B”
glycoproteins on its
surface
TYPE “AB” Blood
BLOOD TYPE FREQUENCY
IN USA
A
B
AB
O
40%
10%
4%
46%
http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/newton/BldTyping.html
BLOOD TYPES
DONOR
BLOOD
YOU DON’T HAVE
ANYTHING I
DON’T HAVE!
Body images modified from:
http://www.new-fitness.com/images/body_shapes.jpg
See A blood cells as
DIFFERENT!
IMMUNE SYSTEM
ATTACKS!
BLOOD TYPES
DONOR
BLOOD
YOU DON’T HAVE
ANYTHING I
DON’T HAVE!
Body images modified from:
http://www.new-fitness.com/images/body_shapes.jpg
A and O see B cells
as DIFFERENT!
IMMUNE SYSTEM
ATTACKS!
BLOOD TYPES
DONOR
BLOOD
YOU’RE
LIKE ME!
Body images modified from:
http://www.new-fitness.com/images/body_shapes.jpg
A, B, and O see AB
cells as DIFFERENT!
IMMUNE SYSTEM
ATTACKS!
BLOOD TYPES
YOU DON’T HAVE
ANYTHING I
DON’T HAVE!
Body images modified from:
http://www.new-fitness.com/images/body_shapes.jpg
____
O can donate to
EVERY BLOOD TYPE
= _____________________
UNIVERSAL DONOR
NO A’s or B’s on surface to
recognize as “NOT SELF”
BLOOD TYPES
AB can RECEIVE FROM
______
EVERY BLOOD TYPE
UNIVERSAL RECIPIENT
= ________________________
Body image modified from:
http://www.new-fitness.com/images/body_shapes.jpg
ABO SYSTEM is NOT
THE ONLY ONE
+
Rh
Rh
OTHER BLOOD TYPES
NO PROBLEMS IF:
Rh+
MOM is _____
& BABY is _____
Rh+
Image modified from:
http://www.wsd1.org/lessonplans/images/Body.gif
MOM is _____
Rh+
& BABY is ____
Rh-
PROBLEM IF:
Can be a ___________
Mom is _____
Rh-
Baby is _____
Rh+
Image modified from:
http://www.wsd1.org/lessonplans/images/Body.gif
1st baby OK but few baby cells
entering mom’s bloodstream
put mom’s immune system on
alert for + cells.
Next + baby, mom’s immune
system can attack baby as it is
growing
= ERYTHROBLASTOSIS FETALIS
Mom given shot (RhoGAM) after
birth to prevent this
GENES are more complicated
than Mendel thought
MULTIPLE ALLELE TRAITS have
MORE THAN 2 allele choices
EX: blood type
A ___
B ___
O
Allele choices ___
GENES are more complicated
than MENDEL thought
POLYGENIC TRAITS are governed by the
cumulative effect of MORE THAN ONE GENE
Polygenic traits show a
whole range of
in-between phenotypes
EX: human height.
intelligence,
skin & eye color
http://www.bcps.org/offices/lis/models/life/images/grow.JPG
POLYGENIC traits are recognizable by their
expression as a gradation of small differences
(a continuous variation).
The results form a bell shaped curve.
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
Linked Genes
• Genes close together on same chromosome
are called linked genes
• Linked genes do not exhibit independent
assortment and they move together during
crossing over if they are very close
together on the chromosome.
http://anthro.palomar.edu/biobasis/bio_3.htm
Sex Linked Genes
Genes carried on the X chromosome are
called X-linked traits.
• Red-green colorblindness, hemophilia, an
Duchenne muscular dystropy are examples
of X-linked traits.
http://gizmodo.com/gadgets/peripherals/samsung-develops-lcd-for-colorblind-036306.php
X and y chromosomes
NON-HOMOLOGOUS partners
In mammals and flies, the Y chromosome is
very small and carries few genes
Some traits are sex limited, and expression
depends on the sex of the individual
Examples:
•Milk production in females
•Male pattern baldness
Y chromosome
Pedigrees are diagrams that show
how genes are passed on in families
over several generations
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005
Pedigrees can be used to predict future offspring
in families with genetic disorders
Drawing a pedigree chart
http://www.ikm.jmu.edu/Buttsjl/ISAT493/Hemophilia/hemophiliaeurope.html
MANY HUMAN GENES
HAVE BECOME KNOWN
THROUGH THE STUDY
OF GENETIC DISORDERS
DISORDERS result from
Many genetic ___________
changes in the DNA code so
NON-FUNCTIONING
_________________ proteins are
produced.
http://patentdocs.typepad.com/photos/uncategorized/2007/05/28/dna1.gif
A mutation in an allele that causes a protein to
be NON-FUNCTIONAL would appear
_______________
to the normal working allele.
RECESSIVE
Examples of __________________________
AUTOSOMAL RECESSIVE
GENETIC DISORDERS:
PHENYLKETONURIA
(PKU)
____________________
TAY-SACHS DISEASE
____________________
____________________
CYSTIC FIBROSIS
Phenylketonuria (PKU)
CAUSE:
Mutation in gene for an enzyme the breaks
down an amino acid called phenylalanine
MENTAL RETARDATION
Build up causes ________________________
http://biology.clc.uc.edu/courses/bio104/protein.htm
Phenylketonuria (PKU)
ALL babies are tested for PKU before they leave
the hospital.
Treatment:
Need a diet low in phenylalanine to extend life
and prevent mental retardation
Amino acid
If phenylalanine is an _____________,
what type of foods should PKU patients avoid?
PROTEINS !
__________________
THINK ABOUT IT
What does a can of
Diet Coke have to do
with human genetics?
LOOK AT THE WARNING LABEL !
NUTRASWEET is made with phenylalanine
______________
CYSTIC FIBROSIS
CAUSE:
• Loss of 3 DNA bases in a gene for the ion
channel protein that transports Cl- ions
• Salt balance is upset
• Causes a build up of thick mucous in lungs and
digestive organs
thick mucous
Image from: BIOLOGY by Miller and Levine; Prentice Hall Publishing ©2006
CYSTIC FIBROSIS
Leads to:
Respiratory and digestive complications,
increased susceptibility to infections;
“Salty skin” is a symptom
More common in Caucasians but can affect
all races.
30,000 people in U.S. have cystic fibrosis
1 in 31 people are carriers
CARRIER
Heteroygous individual
That carries one
recessive allele for a
genetic disorder
Doesn’t show the
disorder themselves,
but can pass it on to
offspring
http://www.biochem.arizona.edu/classes/bioc460/spring/rlm/RLM36.1.html
TAY-SACHS DISEASE
AUTOSOMAL RECESSIVE
___________________
CAUSE:
Mutation in gene for an enzyme the breaks down a kind
of lipid in the developing brain
As these lipids build up in brain infant suffers seizures,
blindness, loss of motor & mental function > > > leads
to early death.
Found more frequently in people with Jewish,
Mediterranean, or Middle Eastern ancestry
Image from: http://www.djsfoundation.org/images/Steeler%20pics%20Dylan.jpg
DISORDERS CAUSED
AUTOSOMAL CODOMINANT ALLELES
BY ____________________
SICKLE CELL DISEASE
____________________
CAUSE:
A changed to T
in gene for
HEMOGLOBIN
__________________
(protein in red blood cells
that carries oxygen in blood)
SICKLE CELL DISEASE
SYMPTOMS:
Red blood cells become sickle shaped under low
oxygen condition in persons with two sickle cell
alleles (ss)
Ss=Sickle cell trait Normally healthy, but can
suffer some sickle cell episodes
SICKLE CELL DISEASE
Circulatory problems
Cells stick in capillaries
Loss of blood cells (anemia)
Organ damage (brain, heart, spleen)
Can lead to DEATH
SICKLE CELL DISEASE
AFRICAN AMERICANS
More common in _________________
1 in 400 = have sickle cell disease
1 in 10 = carriers for allele
MEDITERRANEAN
Also affects persons of _______________
and _________________
MIDDLE EASTERN
descent
Why do so many African Americans
carry the sickle cell allele?
SICKLE CELL DISEASE
Many can trace their ancestry to west
MALARIA
central Africa where ___________,
a serious parasitic disease that
infects red blood cells is common.
Watch a video about
sickle cell and malaria
Images from: http://en.wikipedia.org/wiki/Malaria
AT MOLECULAR LEVEL Sickle cell allele is
CODOMINANT
ss- has abnormal hemoglobin; unhealthy
SS-has normal hemoglobin and can be
infected with malaria
Ss-makes both normal and abnormal
hemoglobin; resistant to malaria infection
Sickle cell disease is a trade off for malaria
resistance
GENETIC LINK TO DISEASE
• Many human genetic disorders may be the small
“price we pay” for mutations that provide
protection from otherwise lethal diseases
• Persons heterozygous for cystic fibrosis are
resistant to typhoid
• Changes in Vitamin D receptors confer resistance
to tuberculosis, but result in greater
susceptibility to osteoporosis
CLOSER LOOK AT RELATIONSHIP
BETWEEN DOMINANCE AND PHENOTYPE
REVEALS AN INTRIGUING FACT:
DOMINANCE ?
CODOMINANCE?
INCOMPLETE DOMINANCE ?
Depends on how you look at it!
Image from: http://www.djsfoundation.org/images/Steeler%20pics%20Dylan.jpg
TAY-SACHS DISEASE
Human genetic disorder in which brain cells are
unable to metabolize certain lipids because
a crucial enzyme does not work properly.
As these lipids build up in brain infant suffers seizures, blindness,
loss of motor & mental function > > > leads to early death.
At ORGANISMAL LEVEL acts as a recessive trait.
Child with two copies of Tay-Sachs allele (tt-homozygous) has the
disorder. Child with Tt or TT does not (COMPLETE DOMINANCE)
At BIOCHEMICAL LEVEL- Tt individual has enzyme activity level
in between the TT and tt person (INCOMPLETE DOMINANCE ?)
At the MOLECULAR LEVEL – Tt individual makes equal number of
normal and dysfunctional enzyme molecules (CODOMINANT ?)
HUNTINGTON’S DISEASE
AUTOSOMAL DOMINANT
______________________
CAUSE:
CAG repeats at end of gene
Extra 40-100 ______________
on chromosome 4
more repeats . . . the more __________
severe
The _____________
the symptoms.
http://www.healthsystem.virginia.edu/internet/huntdisease/images/cag.gif
HUNTINGTON’S DISEASE
Huntington’s brain
Begins in middle age
Causes progressive loss
of muscle control and
mental function
1 in 10,000 people in U.S.
have Huntington’s disease
Normal brain
http://www.scielo.br/img/revistas/bjmbr/v39n8/html/6233i01.htm
A person with
Huntington’s disease
50% chance of
has a _____
passing the disorder on to
their offspring.
Problem:
Symptoms of disorder usually don’t show
until ____________
MIDDLE AGE . . .
so you don’t know you have it until
________
AFTER you have had children.
ACHONDROPLASIA
(One kind of Dwarfism)
AUTOSOMAL DOMINANT
CAUSE: ___________________________
gene
1 in 25,000 births
DD = lethal
Dd = dwarf phenotype
dd= = normal height
200,000 “little people” worldwide
One of oldest known disorders – seen in Egyptian art
ACHONDROPLASIA
(One kind of Dwarfism)
Normal size head and
torso; short arms and legs
Problem with way cartilage
changes to bone as bones
grow
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2006
KARYOTYPE is a picture of
A __________
an organism’s chromosomes
SEX DETERMINATION
XX = female
Xy = male
•
•
•
•
Karyotype can show:
Sex of baby
Missing or extra chromosomes
Major deletions or translocations
Can’t see individual gene changes
http://content.answers.com/main/content/wp/en/1/11/Down_Syndrome_Karyotype.png
http://content.answers.com/main/content/wp/en/thumb/f/f3/220px-Down_syndrome_translocation.png
• Some traits result from nonnuclear
inheritance
– Chloroplasts and mitochondria randomly
assorted to gametes and daughter cells; thus
traits determined by chloroplast and
mitochondrial DNA do not follow simple
Mendelian rules.
– In animals, mitochondrial DNA is transmitted
by the egg and not by sperm (so the mother
determines the offspring’s traits)