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Genetics Notes
Website to visit
• http://learn.genetics.utah.edu/content/begi
n/traits/
• What is heredity?
• What is a trait?
Trait: a characteristic of an
organism
• Examples in peas:
Parent
generation:
Shows the
2 alleles
of the
gene for
this trait
F1
generatio
n: Shows
which is
dominant
2 alleles for Every Trait
• Organisms have 2 copies of each gene,
called alleles, for every trait
– One from mother
• (piece of DNA in the chromosomes you got from her)
– One from father
• ( piece of DNA in the 23 chromosomes you got from him)
http://learn.genetics.utah.edu/content/begin/traits/
http://wwwdelivery.superstock.com/WI/223/1538/PreviewComp/SuperStock_1538R-56651.jpg
Trait: a characteristic of an
organism
Mid-Digital Hair:
Tongue rolling.
Widow’s peak.
Earlobe attachment.
Hitchhiker’s thumb.
Mendel’s Law of Segregation
Reginald Punnett
• Each trait is defined by a pair of
Professor of Genetics at Cambridge
genes. Each parent can produce
two types of gametes: one allele
is “randomly separated” into each
gamete.
• A Punnett Square is a tool to
keep track of the alleles in the
gametes and work out the
possible combination in offspring
Even Pea plants have parents!
http://activity.ntsec.gov.tw/lifeworld/english/content/images/en_gene_c4c.jpg
P1 generation F1 generation F2 generation
Parent
generation
F1 generation
All
Heterozygous
F2 generation
¼ homozygous dominant,
2/4 heterozygous, ¼
homozygous recessive
All
Homozygous
http://library.thinkquest.org/17109/media/mendel2.gif
Dominant & Recessive Genes
• Dominant genes – capital letter.
Overpower recessive genes
• Recessive genes – lowercase letter.
are “masked” in a hybrid and only show up
in a purebred with both recessive genes.
Purebred vs. Hybrid
• Purebred = homozygous means there
are two alleles of the same type for a trait.
– TT (both tall genes)
– tt (both short genes)
• Hybrid= heterozygous means there are
two different alleles for a trait.
– Tt
Phenotype and Genotype
• Phenotype means the appearance of a
trait in an organism
– For example short/tall, wrinkled/smooth,
yellow/green are all phenotypes
• Genotype means the two alleles an
organism has for a trait.
– Examples:TT. Tt. tt
Websites for punnett square
problems:
• http://www.dnaftb.org/5/index.html “DNA
from the beginning
Steps to complete a Punnett
Square
Step #1: Read the problem to figure out the
phenotypes and genotypes of the parents
Problem: In pea plants, tall plants (T) are
dominant to short plants (t). Consider a genetic
cross of one short plant and one hybrid plant.
short
phenotype of parent #1: _____genotype
of parent #1: _____
tt
Tall
phenotype of parent #2: _____genotype
of parent #2: _____
Tt
• Step 2. draw a box with 4
squares
• Step 3. Write the genotype of
#1 parent across the top lining
up one gene above each
column below.
• Step 4: write the genotype of
the #2 parent along the side of
the square with one gene next
to each row
• Step #5: fill in the genotypes of
the offspring by putting one
gene from each box into the
squares.
• Step #6: analyze the genotype
and phenotype of the offspring
shown in the boxes.
t
TT
ttt
ttt
Analyze the results of the punnett
square
• What is the genotype and
phenotype of the following
POSSIBLE offspring?
• #1: tT tall
• #2 tT tall
• #3 tt short
• #4 tt short
• What percent of the offspring
are predicted to be tall? 50%
• What percent are predicted to
be purebred short? 50%
Tt
Tt
1
tt
2
tt
3
4
Monohybrid Crosses
• Involve one trait
whole allele may be
dominant or
recessive.
• Example two hybrid
pea plants where T:
tall and t: short.
• The punnett square
for this is:
• Mendel’s Law of Dominance: some
alleles are dominant and others
are recessive.
• Mendel’s Law of Segregation: two
alleles are segregated from each
other so that each gamete carries
only a single copy of each gene.
• Mendel’s Law of Independent
Assortment: genes for different
traits can segregate independently
during the formation of gametes.
Dihybrid Crosses
Involve 2 traits:
Trait #1 Seed color
• Y:Yellow seed
• y: green seeds
Trait #2 seed shape
• R round seeds
• r wrinkled seeds
Dihybrid cross
• http://www.dnaftb.o
rg/5/problem.html
“Problem”
Incomplete dominance: The hybrid
shows a blending of alleles
4 o’clock flowers
• RR: red
• WW: white
• RW pink
Codominance: The hybrid has both
traits
• Example in chickens
– DD: dark colored feathers
– LL: light colored feathers
– DL: where the hybrid has both dark and light
speckled feathers.
Multiple Alleles: Genes that have
more then two alleles
Example:
Alleles that determine
blood type: A, B, O
Red blood cells
• In some ways, every person's blood is the same
they carry oxygen and nutrients to the body’s
cells
• But, when analyzed under a microscope, distinct
differences are visible.
• Blood can have 2 different markers (antigens)
on its surface
– Molecule “A” = Type A blood
– molecule “B”, = Type B blood
– Molecules “A & B”, = Type AB blood
– no molecules = Type O blood
The Rh protein
• The Rh factor genetic information is also
inherited from our parents, but it is inherited
independently of the ABO blood type alleles.
• There are 2 different alleles for the Rh factor
known as Rh+ and Rh-. Someone who is "Rh
positive" or "Rh+" has at least one Rh+ allele,
but could have two. Their genotype could be
either Rh+/Rh+ or Rh+/Rh-.
• Someone who Rh- has a genotype of Rh-/Rh-.
Rh factor Possible genotypes Rh+ Rh+/Rh+
Rh+/Rh- Rh- Rh-/Rh-
Molecules (antigens) on outside of red
blood cells
Type A
Type B
Type AB
Type O
Parent’s determine your blood type
• Your mother and father will both pass one
allele /genes for blood type to you.
• A and B are co-dominant
• O is recessive to both A and B
Genotypes for each blood type
What are the possible genotypes of the 4
blood types? A, B, AB, O
–Type A Blood
• AA
• AO
–Type B Blood
• BB
• BO
–Type AB Blood
• AB
–Type O Blood
• OO
2 different styles of notation
Donating Blood
• If two different blood types are mixed
together, the blood cells may begin to
clump together in the blood vessels,
causing a potentially fatal situation.
• Your body makes antibodies to attack
blood cells with molecules different then
your own.
Antibodies in your blood
• Type A blood has anti-B antibodies to
attack type B blood cells
• Type B blood has anti-A antibodies to
attack type A blood
• Type O blood has anti-A and anti-B
antibodies to attack type A and B blood.
• Type AB blood has no antibodies
Antibodies in blood plasma to
attack foreign blood
Type A
Type B
Type AB
Type O
Type A
Type B
Type AB
Type O
No marker molecules
Type A
Type B
Type AB
No
antibodies
Type O
Blood Donation
• Go to website:
http://www.givelife2.org/aboutblood/bloodt
ypes.asp
Almost 40% of the population has O+ blood
Out of 100 donors . . . . .
84 donors are
RH+
16 donors are
RH-
38 are O+
7 are O-
34 are A+
6 are A-
9 are B+
2 are B-
3 are AB+
1 is AB-
Source: AABB.ORG
Only about 7% of all people have Type O
negative blood
Type O negative blood is the preferred type
for accident victims and babies needing
exchange transfusions
There is always a need for Type O donors
because their blood may be transfused to a
person of any blood type in an emergency
Blood
Type
A
B
AB
O
Can donate
blood to
A, AB
B, AB
AB
O, A, B, AB
Can receive
blood from
A, O
B, O
AB, A, B, O
O
Universal Donor
• Type O blood has no molecules on the
outside of the red blood cells therefore
anti-A or anti-B antibodies will not attack if
they are in the blood of a recipient.
Universal Recipient
• Type AB blood produces no antibodies in it
therefore it will not attack any molecules
on blood that is mixed with it.
Blood Donation
• Go to website:
http://www.givelife2.org/aboutblood/bloodt
ypes.asp
O Rh Positive 37.4%
•
O Rh Negative 6.6%
A Rh Positive 35.7%
A Rh Negative 6.3%
B Rh Positive 8.5%
B Rh Negative 1.5%
AB Rh Positive 3.4%
AB Rh Negative.6%
• Helpful website:
http://learn.genetics.utah.edu/content/begi
n/traits/blood/
Problem #1: Show a punnett square
between a mother who is type O and a
father that is type AB.
O
O
A
A
B
B
O
O
AO
AO
BO
BO
What are the possible blood types of their children?
What are the ratio’s of these genotypes?
Sex chromosomes
• There are two chromosomes out of a persons 46 that
have been nicknamed the “x”chromosomes and the “y”
chromosome.
• These are “sex chromosomes” because they carry the
genes for sexual characteristics
–
–
–
–
Figure 1: Male human chromosomes.
X and Y chromosomes are indicated by
arrows.
Sexual organs
Body hair
Voice
Muscle mass
© Nature Reviews Genetics 2, 175-185
(March 2001).
• “x” chromosomes carry genes for female characteristics
• “y” chromosomes carry genes for male characteristics
Sex linked traits
• Some genes that affect both males and females
are found on the “x” sex chromosomes.
– For example the gene for color vision, blood clotting
(or hemophilia=not clotting)
• Because women have sex chromosomes XX
women have two copies of the gene and men
have one copy.
• For this reason x linked alleles are expressed in
males even if they are recessive.
• Notation in punnett squares the alleles are
written as a superscript above a Xh or Y
chromosome.
Sex linked problem
• In flies red eyes is
dominant to white
eyes
• A purebred red eyed
female is bred with a
white eyed male
Question: What color
are the male
offspring’s eyes?
Question: What color
are the female
offspring’s eyes?
Colorblindness
•
The term 'colour blindness' is misleading. People who can't see all colours
can still see things (other than colour) as clearly as people who are not
colour blind. The term means that a person can't see some colours, or sees
them differently from other people. Very few people who are colour blind are
blind to all colours. The usual colours that people have difficulty with are
greens, yellows, oranges and reds. Colour blindness is inherited, affecting
more boys than girls. Out of 20 boys, it is likely that one or two will have a
colour vision problem.
•
Color blindness test:
http://colorvisiontesting.com/ishihara.htm
• http://colorvisiontesting.com/online%20test.htm#
Test%20Card%20Number%203%20answer
•
For more info on seeing color:
http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Colour_blind
ness?OpenDocument
Can you see the numbers?
Using a pedigree
Hemophilia: The Royal Disease
• Queen Victoria of
England and her
family
http://www.sciencecases.org/hemo/hemo.asp
The royal pedigree
Questions from royal pedigree
• 1.a What is the probability that Alice of
Athlone’s other son was hemophilic?
– 50%
• 1.b What is the probability that her
daughter was a carrier?
– 50%
• 1.c What is the chance that both children
were normal?
– 50%
From royal pedigree
• 2. Would you predict that Juan Carlos was
normal, a carrier, or hemophilic?
– Normal, because neither his father nor mother
was a hemophiliac. Also males can’t be
carriers.
From royal pedigree
• 3. a. What was the probability that all 4 of Alix and
Nikolas II of Russia’s daughters were carriers?
– 50%
• 3.b If Alexis had lived and married a normal woman,
what are the chances that his daughter would be
hemophiliac?
– 0%
• 3.c What are the chances that Alexis daughters would be
carriers?
– 100%
• 3.d. What are the chances that his sons would be
hemophiliacs?
– 0%
websites
• What makes you rhyming presentation:
http://www.amnh.org/ology/genetics#features/youYou/yo
uyou.php?TB_iframe=true&height=350&width=600
• What do you know about genetics quiz and answers:
http://www.amnh.org/ology/genetics#features/whatdoyou
know_genetics/?TB_iframe=true&height=400&width=60
0
• Cloning sheep explanation
http://www.amnh.org/ology/index.php?channel=genetics
#features/cloning/?TB_iframe=true&height=450&width=6
00
Karyotypes
Using Karyotypes To Diagnose Genetic Disorders
http://learn.genetics.utah.edu/content/chromosomes/diagnose/
A picture of a person’s
chromosomes organized into
homologous pairs
Chromosomes organized
into a karyotype
Chromosomes as seen
through a microscope
• Where does a person get their 46 chromosomes?
– 23 from mom
– 23 from dad
• What is the type of cell division in which a persons
46 chromosomes are divided to produce sex cells
with only 23 chromosomes?
– MEIOSIS!
How to make a karyotype
1.
During Mitosis chromosomes are spread out
within a cell and can all be seen.
Chromosomes in metaphase are stained to
produce a banding pattern of light and dark
regions.
2.
–
3.
4.
The dye stains regions of chromosomes that are rich in
the base pairs Adenine (A) and Thymine (T) producing a
dark band. Thin bands contain hundreds of genes.
The are photographed
They are organized into homologous pairs.
Male vs. Female
Female: “X” “X” sex chromosomes
Male: “X” & “Y” sex chromosomes
Typical Human’s have 46 total chromosomes.
“XX” female / “XY” male
• The “x” chromosome is larger
than the “y” chromosomes
• “x” chromosomes have
genes resulting in female
reproductive systems and
other genes that do not have
to do with gender like genes
to see color.
• “y” chromosome is smaller
has fewer genes and they
code for male reproductive
organs.
Image:
http://www.biotechnologyonline.gov.au/images/contentpages/karyotype.jpg
Chromosomal Disorders
• Trisomy: having three copies of a
chromosome. The most common is
Down’s Syndrome
• Nondisjunction: when chromosomes fail to
separate properly in meiosis forming
gametes with too many or too few
chromosomes.
•
Website showing nondisjunction:
http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htm
2 ways nondisjunction can
occur
http://warunee.chs.ac.th/c15x11nondisjunction.jpg
Steven
Lisa
Sarah
Mark
Kevin
Lisa “A” Typical Female
Lisa
All chromosomes match
Sex chromosomes “x” “x”
look identical.
Steven “B” Male
Trisomy 21 Down’s Syndrome
• 22 pairs of chromosomes match
• Male: Sex chromosomes “X” “Y”
• 3 chromosomes at #21
Kevin “C” Male
Trisomy 18
•sex chromosomes “x” & “y”
• 3 chromosomes at #18
Mark “D” Typical Male
22 pairs of chromosomes
match
Sex chromosomes “X” “Y”
look different.
Sarah “E” Female
Trisomy 21 Down’s Syndrome
Sarah
• All chromosomes match
• Sex chromosomes “x” “x”
• 3 chromosomes at #21
• A genetic disorder is a disease that
is caused by an abnormality in an
individual's DNA. Abnormalities can range
from a small mutation in a single gene to
the addition or subtraction of an entire
chromosome or set of chromosomes.
(http://learn.genetics.utah.edu/content/disorders/whataregd/)
Disorders
• Most disorders are due to changes within
one chromosome not a change to an entire
chromosome.
– Cystic fibrosis (thick mucus in respiratory system)
– Sickle Cell disease (malformed red blood cells that get stuck in capillaries)
– Lou Gehrig’s disease/ALS (loss of muscle control)
• Due to a change in entire chromosome
–
–
–
–
–
–
Down’s Syndrome /trisomy 21
Edward’s Syndrome Trisomy 18
Patau syndrome Trisomy 13
Klinefelters syndrome XXY
Turner’s Syndrome XO
XYY
Genetic Engineering
1. Combining genes from different organisms
2. Genetically modified (GM), Genetically
modified organisms (GMO’s), genetically
engineered, transgenic