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Genetics
Vocabulary
• Genetics
– The study of how hereditary
information is passed from parent to
offspring
• Gene
– Segment on DNA that codes for a
particular trait (hair color, height, eye
color etc.)
• Allele
– Different forms of a gene
– For every characteristic you inherit 2
alleles- one from each parent
– Examples:
• Eye color
B = Brown eyes
b = Blue eyes
• Freckles
F = Freckles
f = no freckles
• Dominant & Recessive Alleles
– Dominant Allele
• The allele that expresses (shows) itself in the
offspring
• Masks recessive alleles
• Represented by capital letters
– Recessive Allele
• The allele that does not express itself in the
offspring if the dominant allele is present
• Represented by lower case letters
• Homologous Chromosomes
– Are the same size & shape
– Contain the same genes
– One comes from dad, one from mom
• Genotype
– An organism’s genetic makeup
– Represents the exact alleles
– Example:
• B = brown eyes
• b = blue eyes
Genotype___________
Genotype___________
Genotype___________
• Phenotype
– An organism’s outward appearance
(what they look like)
– Example:
Phenotype___________
Phenotype___________
Phenotype___________
• Homozygous/Heterozygous
– Homozygous
• The 2 alleles coding for a trait are the same
• BB or bb
– Heterozygous
• The 2 alleles coding for a trait are different
• Bb
Gregor Mendel (1822-1884)
Mendel looked
at 7 traits in
pea plants
Punnett squares help us predict
the outcome of genetic crosses
1. In pea plants there are 2 alleles that code for
height. Tall (T) is dominant over short (t).
Show the cross of a female TT with a male tt.
What are the genotypes & phenotypes of the
offspring of this cross?
Genotypes___________________________
Phenotypes__________________________
2. In pea plants there are 2 alleles that code for
height. Tall (T) is dominant over short (t).
Show the cross of a female Tt with a male Tt.
What are the genotypes & phenotypes of the
offspring of this cross?
Genotypes___________________________
Phenotypes__________________________
3. In seals the gene for whisker length has 2
alleles. The dominant allele (W) codes for long
whiskers and the recessive allele (w) codes for
short whiskers. What percentage of offspring
would be expected to have short whiskers from
the cross of 2 long whiskered seals- one is
homozygous dominant and one is
heterozygous.
Lab: Probability & Inheritance
• Codominance
– 2 alleles are expressed at the same time
– Neither is dominant
• Example: coat color in cattle
White = WW
Red = RR
Roan =
• Show the cross of a red bull and a roan
cow
• What are the expected phenotypes of the
offspring?
• Example: feather color in chickens
Example: blood type in humans
• Incomplete Dominance
– The phenotype is a mix or intermediate of
the 2 alleles
• Example: 4 o’clock flower color
Red = RR
White = WW
Pink =
• Show the cross of 2 pink 4 o’clock flowers
• What are the expected genotypes &
phenotypes of the offspring?
• Example: human hair texture
Curly = CC
Straight = SS
Wavy =
• Show the cross of a curly haired woman
and wavy haired man
• Could they have a straight haired child?
• Multiple Alleles
– A particular trait has more than 2 alleles that
control it
– Each individual has 2 alleles for the trait
• Example: blood type in humans has 3 alleles
_______, _______ & ________
• Show the cross of a homozygous A blood
type woman (AA) and a heterozygous B
blood type man (BO)
• What are the expected blood types of the
offspring?
• Show the cross of a heterozygous A blood
type woman (AO) and a heterozygous B
blood type man (BO)
• Could the offspring have different blood
types from the parents?
• Polygenic Traits
– Traits that are produced by the interaction of
more than 1 gene
• Examples: skin color, height, hair color, eye
color
• Gene Linkage
– When different genes for different traits are
located close together on the same
chromosome
– These traits are often inherited together!
• Example: red hair & freckles
Sex determination
Is it a boy or girl?
• Humans have______chromosomes
– ______autosomes (chromosomes
responsible for all traits except gender)
– ______sex chromosomes (determine gender)
• XY = __________
• XX = __________
Who determines the sex of the
baby??__________
Karyotype machine analyses
chromosomes from cells
Karyotypes pair up homologous chromosomes
• Genetic disorders can involve
–Single genes
–Large sections of chromosomes
–Entire chromosomes
• Cystic Fibrosis
– Autosomal recessive trait
– Affects 1 in 2,000 babies
– Caused by a mutation in N Europe 300
years ago
– Lungs fill up with thick mucus
• Show the cross of 2 parents both
heterozygous for Cystic Fibrosis
• Could they have a child with CF?
• Show the cross of a mom with CF and a
homozygous normal dad
• Could they have a child with CF?
• Huntington’s Disease
– Autosomal dominant trait
– Symptoms begin when the person is 35-40
years old
– Severe neurological impairment
– Physical & mental abilities decline quickly
• Show the cross of a mom heterozygous for
Huntington’s Disease and a normal dad
• What is the chance their child will have
Huntington’s Disease?
• Show the cross of 2 parents both
heterozygous for Huntington’s Disease
• What’s the chance their child will have
Huntington’s?
• Colorblindness
– Sex linked trait
– Person can’t distinguish between red &
green
– More common in boys
• Show the cross of a mom who carries the
trait for color blindness and a normal dad
• What is the chance their son/daughter will
be color blind?
• Show the cross of a carrier mom and a
colorblind dad
• What’s the chance their son/daughter will
be colorblind?
Bioethics Case Study
• James & Carol, CF child
• Angela, Huntington’s Disease
Lab: Investigating inherited human
traits
• Some diseases arise because a big
section of a chromosome is missing or
there’s an extra copy of a chromosome
• Chromatid
– Half of a doubled chromosome
• Centromere
– Holds the 2 chromatids together
• Non-disjunction
– When the 2 chromatids fail to separate
during meiosis
– Leads to an abnormal number of
chromosomes in the offspring
• Wolf-Hirschhorn Syndrome
– Chromosome #4 has a deletion
• Jacobsen Syndrome
– Chromosome #11 has a deletion
• Down’s Syndrome
– Duplication of chromosome 21
• Edward’s Syndrome
– Duplication of chromosome 18
• Charcot Marie tooth disease
– Duplication of a piece of chromosome 17
• Can we test for chromosomal disorders
before birth?
• Yes! With Amniocentesis
Lab: chromosome study
Happy Earth Day (April 22)
Do your part to take care of the Earth!!
Review of DNA structure
(from earlier unit on biochemistry)
Nucleic acids
• Contains C, H, O, N and P (phosphorus)
• 2 types: DNA & RNA
• DNA= Deoxyribonucleic acid
– Hereditary material which makes up
chromosomes in the nucleus,
mitochondria & chloroplast
– Double Helix
Watson & Crick
determined DNA structure
1962 Nobel Prize
Structure of DNA
• Twists into a double helix
• 2 long chains of alternating sugar &
phosphates
• Nitrogenous bases attached to the
sugars (like rungs on a ladder)
– Adenine bonds to Thymine
– Guanine bonds to Cytosine
• Nucleotide
– Building block of a nucleic acid
– Made up of sugar, phosphate &
nitrogenous base
*New information*
Nucleotide sequence on DNA strand
G–A–T–T–A–C–A
__- __- __ -__ -__- __- __
Nucleotide sequence on
complementary DNA strand
Nucleotide sequence on DNA strand
A–T–C–A–T–G–G
__- __- __ -__ -__- __- __
Nucleotide sequence on
complementary DNA strand
Nucleotide sequence on DNA strand
C–A–C–T–G–C–C
__- __- __ -__ -__- __- __
Nucleotide sequence on
complementary DNA strand
• How similar are human DNA
& chimp DNA?
• What is the first thing a cell needs to do to
prepare itself for division?_____________
• What do you need to make a copy of
something?_________________________
• Each strand of the DNA double helix serves
as the ______________for copying itself
Steps of DNA replication
(with a lot of help from enzymes!)
1. The DNA double helix ______________
2. Free (unattached) nitrogen bases floating
around in the cell match up with the
exposed strand of DNA
•
•
T pairs up with ________
C pairs up with ________
3. 2 new, identical strands of DNA are
formed!!!!
video
• As with everyone, enzymes can make
mistakes too
• Sometimes the wrong base is added, a
base is left out or an extra base is added
• These errors in DNA replication are called
__________________
Mutations can be bad, good
or have no effect at all
• Bad mutations:
– Cause an organism to no longer function
properly
• Good mutations:
– Provide a source of genetic variation that may
make an organism better suited for its
environment
• Mutations that have no effect:
– Doesn’t affect the functioning of the organism
• How do we make use of all the genetic
information stored in our DNA?
• How do we get from the sequence of
bases in our DNA to the expression of
our traits?
This is howMemorize this sequence!!!
__________
↓
__________
↓
__________
↓
__________
video
RNA differs from DNA
DNA
# of strands?
Located inside
or outside
nucleus?
Nitrogenous
base pairs are:
RNA
dna vs rna
```
DNA
mRNA
tRNA
Protein part
(Amino acid)
(Look at tRNA &
use codon chart)
A-T-G-G-C-T-T-A-T G-A-T-T-A-C-A-T-T
Normal DNA
Mutation
```
DNA
mRNA
tRNA
Protein part
(Amino
acid)
(Look at tRNA &
use codon chart)
T-G-C-G-T-G-C-C-A T-G-C-A-T-G-C-C-A
• (CBS/AP) A sickle cell trait will keep Pittsburgh
Steelers safety Ryan Clark out of Sunday's AFC
Wild Card game in Denver. The trait makes it
dangerous for the 32-year-old to play in the high
altitudes at Denver's Mile High Stadium.
Lab: How can a mutation in DNA
affect an organism?
Monsanto- company that produces
GM plants
• Many of Monsanto's agricultural seed products are
genetically modified for resistance to herbicides, such as
glyphosate, which Monsanto sells under the brand,
"Roundup" – Monsanto calls these seeds "Roundup
Ready". Monsanto's introduction of this system (planting
glyphosate-resistant seed and then applying glyphosate
once plants emerged) provided farmers with an
opportunity to dramatically increase the yield from a
given plot of land, since this allowed them to plant rows
closer together.[60] Without it, farmers had to plant rows
far enough apart to control post-emergent weeds with
mechanical tillage.[60] Farmers have widely adopted the
technology – for example over 90% of maize (Mon 832),
soybean (MON-Ø4Ø32-6), cotton, sugar beet, and
canola planted in the United States are glyphosateresistant
• As recently as a decade ago, farms in the Midwest were commonly
marred - at least as a farmer would view it - by unruly patches of
milkweed amid the neat rows of emerging corn or soybeans.
Not anymore. Fields are now planted with genetically modified corn
and soybeans resistant to the herbicide Roundup, allowing farmers
to spray the chemical to eradicate weeds, including milkweed.
And while that sounds like good news for the farmers, a growing
number of scientists fear it is imperiling the monarch butterfly, whose
spectacular migrations make it one of the most beloved of insects "the Bambi of the insect world," as an entomologist once put it.
Monarchs lay their eggs on milkweed, and their larvae eat it. While
the evidence is still preliminary and disputed, experts like Chip
Taylor say the growing use of genetically modified crops is
threatening the orange-and-black butterfly by depriving it of habitat.
"This milkweed has disappeared from at least 100 million acres of
these row crops," said Dr. Taylor, an insect ecologist at the
University of Kansas and director of the research and conservation
program Monarch Watch. "Your milkweed is virtually gone."
Video: Jimmy’s GM food fight
youtube 58 min
Environmental factors
(both inside & outside the organism)
influence gene expression
• Male pattern baldness
– Influenced by testosterone
• Color in Himalayan Rabbits, Siamese cats
– Influenced by temperature
• Siamese cats have a form of albinism resulting from a
mutation carried genetically on the C-locus-- the same
locus that also houses the gene for complete albinism.
Temperature-sensitive albino cats have a mutated form
of tyrosinase, the enzyme resposible for producing
melanin, the pigment involved in darkened fur.
• Instead of tyrosinase and melanain completely absent,
as in animals with true albinism, Siamese cats and other
pointed cat breeds have a form of tyrosinas that is able
to operate only at below-average body temperatures.
Because of this, only the coolest parts of the body-- the
feet, tail, and face-- receive properly-processed levels of
melanin.
• Selective breeding (artificial selection)
• Genetic engineering (recombinant DNA
technology)
• Cloning
• Selective Breeding (artificial selection)
– 2 individuals with desirable characteristics
are bred with the purpose of increasing those
desirable characteristics in the offspring
– Breeders work with the variation that exists
in nature
– Examples:
• Does selective breeding involve
chance?____
• Genetic Engineering (recombinant DNA
technology)
– Favorable genes from one organism are
recombined with other pieces of DNA in
another organism
– The genetic makeup of various plant &
animals is changed!
– Examples:
BT corn
• These mice are glowing because
scientists inserted a gene found in certain
bioluminescent jellyfish into their DNA.
That gene is a recipe for a protein that
glows green when hit by blue or ultraviolet
light. The protein is present throughout
their bodies. As a result, their skin, eyes
and organs give off an eerie light. Only
their fur does not glow.
• Biogeneticists in this field have spoken about glowing
trees that light up highways, agricultural crops that glow
when they need watering, and even bioluminescent
methods of detecting dodgy meats and other foods. Yet
the real controversy arose when they began speaking
about bioluminescent pets.
• GloFish sparks debate
Pet stores in the United States have been under the
spotlight since 2004 over the sale of genetically-modified
fish that glow in the dark. Sold under the name GloFish,
these creatures carry a lofty claim to fame: they are the
nation’s first officially sanctioned genetically-modified
pet, and scientists say that they won’t be the last.
• The GloFish is a zebra danio that is made to glow red by
the insertion of a gene found in sea coral. Naturally black
and white, the new GloFish has gone from curiosity to a
focal point in the debate over biotechnology.
– How does genetic engineering work?
• Enzymes are used to cut desirable DNA and
use it to replace a less desirable section of
DNA
• Bacteria cells aid the process
• Cloning: 5 steps
– A body cell is taken from the individual to be
cloned (Individual A)
– The nucleus from a donor egg is removed
(Individual B)
– The body cell from Individual A gets
combined with Individual B’s empty egg
forming a zygote that has the exact same
DNA as Individual A
– This zygote is implanted into the uterus of a
surrogate mother (Individual C)
– A clone of Individual A is born!
Dolly
Dolly was born on 5 July 1996 to three mothers (one provided the egg, another the DNA
and a third carried the cloned embryo to term).[
• Dolly Parton
How can we tell if clones
are really clones???
• Electrophoresis/ DNA fingerprinting
• What is electrophoresis??
– A method used to separate & analyze DNA
fragments based on size
• How does electrophoresis work??
– video
biodiversity state lab
• Simulated lab
• A 13 year project, completed in 2003, to
identify all the approximately 20,00030,000 genes in human DNA
• The project determined the sequences
of all 3 million base pairs in human
DNA
• These efforts can hopefully lead to
revolutionary new ways to diagnose,
treat, and someday prevent diseases
Practice questions: genetics