Heredity
Mrs. Foles
2010-2011
Jag Mark 9/27/10
• Supply a definition for a mutation.
Include information on what can cause a
mutation, as well as, effects from a
mutation.
Jag Mark 9/28/10
• In humans, brown eyes (B) are dominant
over blue (b). A brown-eyed man marries
a blue-eyed woman and they have three
children, two of whom are brown-eyed
and one of whom is blue-eyed. Draw the
Punnett square that illustrates this
marriage. What is the man’s genotype?
What are the genotypes of the children?
Jag Mark 9/29/10
• In pea plants, yellow peas are dominant
over green peas. Use a Punnett square to
predict the phenotypic and genotypic
outcome (offspring) of a cross between a
plant heterozygous/hybrid for yellow (Yy)
peas and a plant homozygous/purebred
for green (yy) peas.
Jag Mark 9/30/10
• Mendel performed a genetic experiment by
crossing two pea plants that are heterozygous
for their purple flower color. The results of his
cross yielded 125 white pea plants and 375
purple pea plants.
• What is the ratio of white to purple pea plants?
• What is the ratio of purple pea plants to total
pea plants?
• Which color is the recessive trait?
Jag Mark 10/1/10
• What biological process produces sex
cells?
• How do sex cells differ from body cells?
• Explain why it is necessary to make sex
cells through a process separate from
mitosis.
Jag Mark 10/4/10
1. Physical appearance of
traits
2. Inherited combination of
alleles
3. Process that produces sex
cells
4. Process through which
bacteria reproduce
5. Mathematical chance an
event will occur
A.
B.
C.
D.
E.
Probability
Genotype
Binary Fission
Phenotype
Meiosis
Jag Mark 10/5/10
• Supply a definition for a genetic disorder.
• What can cause a genetic disorder?
• Are genetic disorders typically the result
of dominant or recessive genes?
• Give an example of a genetic disorder.
Jag Mark 10/6/10
• Here is a pedigree for
an inherited lung
disease. Provide the
genotypes of each of
the individuals
marked with lower
case letters.
Determine if they are
male or female.
Jag Mark 10/7/10
• Compare and contrast hybrid and
purebred organisms.
Jag Mark 10/8/10
1. Two forms of the same
gene
2. Each allele has its own
degree of influence
3. Structure of DNA
4. Process produces sex
cells
5. Mutation in these cells
can be passed down to
offspring
A.
B.
C.
D.
E.
F.
Meiosis
Double Helix
Alleles
Sex Cells
Body Cells
Incomplete
Dominance
Jag Mark 10/11/10
1. Keeps the cytoplasm
inside
2. Largest and most
visible organelle
3. Smallest and most
abundant organelle
4. Releases energy
5. Gives plants green
color
A. Chlorophyll
B. Ribosome
C. Nucleus
D. Mitochondria
E. Cell Membrane
Jag Mark 10/12/10
• One of Mendel’s experiments resulted in
705 plants with purple flowers and 224
plants with white flowers.
– What is the ratio of the purple-flowered
plants to all the offspring obtained from this
experiment?
– What is the ratio of the purple flowers to
white flowers?
Jag 10/13/10
• Compare and contrast selective breeding
and genetic engineering.
Jag 10/14/10
• Test Day!
• Clear Desk except for sheet of notebook
paper and a pencil.
Who do you look like?
• Heredity is the passing of traits from
parent to offspring.
• First person to notice the trend of heredity
was Gregor Mendel who studied pea
plants.
Why Studying Peas?
• Grow quickly and self pollinate
• Mendel studied only 1 trait at a time, but 7
total traits
– Example: height, seed shape, flower color
• Trait: is a distinct phenotypic characteristic
of an organism that may be inherited.
– Example: Eye color
Fun with Peas!
• Mendel made sure to study true-breeding
plants (which means that they produce the
same offspring type each time)
– Example: Tall always makes tall.
• Mendel cross-pollinated the true-breeding
plants to see what would happen.
How Did the New Pea Plants Look?
• The parent generation of one tall plant and
one short plant breed together made 100%
new tall plants in the F1 generation.
• He concluded that tall is a dominant trait
over short the recessive trait.
– Dominant: represented by a capital letter (T).
Masks the recessive allele
– Recessive: represented by a lower case letter (t).
Is masked by the dominant allele.
2nd Experiment
• Mendel cross pollinated two plant in the
F1 generation and found that about 75%
were tall and 25% were short.
What did this mean?
• Mendel determined that instructions for
these results must be found on genes.
• Each parent contributes a gene, two forms
of a gene make an allele.
• To test this theory, Mendel invented a
Punnett square.
Genotype/Phenotype
• Genotype: The
genetic makeup or
allelic makeup.
– Ex. (TT, Tt, tt)
• Phenotype is the
appearance of a trait.
– Ex. (tall, short)
• Two dominant alleles
is homozygous
dominant. (TT)
• One dominant allele
and one recessive
allele is heterozygous.
(Tt)
• Two recessive alleles
is homozygous
recessive. (tt)
Making a Punnett Square
• First, make a table
with 4 squares inside.
• Next, place the alleles
from the parents on
the top and the left
hand side of the big
square.
• How would Punnett
Squares look from the
P generation and the
F1 generation?
Practice
• Make a Punnett square to predict whether
or not a child will have dimples using a
parent that is homozygous recessive and
one that is heterozygous. (Dimples are
dominant.)
Incomplete Dominance
• When one trait is not completely dominant
over another. The result is a combined
phenotype.
– Ex. Snap dragons: Red Crossed with White
Codominance
• Occurs when both alleles for a gene are
expressed equally.
– Ex. Blood Type
Probability
• Probability is the mathematical likelihood
that something is the case or will happen
• May expressed as a fraction or as a
percent.
– Ex. Flipping a coin
• ½ chance of coin landing on heads and ½ chance of
coin landing on tails
• 50% chance of coin landing on heads and 50%
chance of coin landing on tails
Why we are all so different?
• Because of sexual reproduction!! Which is
when a man’s sperm cell joins with a woman’s
egg cell. These cells are called sex cells or
gametes.
• Sex cells only contain half of a normal body
cell’s chromosomes.
• Therefore sex cells must be made by a process
other than mitosis.
• When two sex cells combine they form a
zygote.
Meiosis
• Sex cells are made from meiosis!!!!!
• Meiosis is basically mitosis twice without
replication after the initial mitosis. The
result is four cells with half the genetic
information as the original cell. These
new cells are called haploid cells.
• Each body cell has 46 chromosomes. Each
sex cell has 23 chromosomes.
• Homologous Chromosomes: pairs of
chromosomes
Meiosis
Are you a boy or a girl?
• Sex Chromosomes determine your sex.
• Males have one X sex chromosome and one Y
sex chromosome. (XY)
• Females have two X sex chromosomes. (XX)
Karyotype
• Map of chromosomes
• Is this a male or
female?
• How can you tell?
Probability
• What is the probability of
– Having a girl?
– Having two girls in a row?
– Having three girls in a row?
• What is the probability of having a boy
after having three girls in a row?
• First Draw a Punnett Square!!!
Genetics in Action
• Selective Breeding: involves crossing of
organisms with desired traits to maximize
their potential
• Ex. Flowers, fruits, vegetables, animals (cows)
– Benefits of genetic engineering: recombinant
DNA used to make bacteria produce insulin.
Genetic Engineering
• Faster form of selective breeding, where
genetic information is changed in an
organism.
• Removing one piece of DNA and inserting
a more desired piece of DNA.
Genes in Action
• Purebred: Organism
results from crossing
two organisms with
similar traits
– Advantages:
• Predictable
– Disadvantages:
• Undesirable traits get
passed on
• Lack of genetic variation
(problems if disease occurs)
– Example:
• TT x TT = TT
• Labrodor dogs
• Hybrid: Organism
produced from crossing
two organisms with
different traits.
– Advantages:
• Variety
• Maximize desirable traits
– Disadvantages:
• Unpredictable
– Example:
• TT x tt = Tt
• Tomato plants
Genetics in Action
• Pedigree: a tool used to trace a particular trait
throughout a families generations
• □ squares=males
• Ο circles=females
• Vertical lines connect children to their parents
• Solid squares or circles indicate the presence of
the trait
• Half-filled squares or circles indicates that the
person is a carrier for a particular trait.
Pedigree
Reproduction
• Asexual reproduction:
– Requires only 1 parent
– Does not involve sex
cell production
– Occurs in bacteria,
archea, as well as
some fungi and plants
• Binary fission: bacteria
• Budding: sponge
• Sexual reproduction
– Requires two parents
– Involves fertilization of
two gametes (sex cells)
produced from meiosis
When Genetics Goes Wrong
• Genetic disorders: are disorders caused
by abnormalities in the DNA as the result
of mutations or errors during meiosis.
– Most are congenital (born with)
– Most are due to recessive genes; therefore
both parents must be a carrier to affect the
child.
• Genetic disorders: Cystic Fibrosis,
Trisomy 21 (Down’s Syndrome), Sickle
Cell Anemia
Trisomy 21
• Individuals with
Down’s Syndrome
have an extra
chromosome 21 due to
problems in meiosis.
• Symptoms: retarded,
smaller head and body,
slanted eyes due to
folds in skin.
• Risks increase after
mother is 35.
Trisomy 21
Cystic Fibrosis
• Occurs in 1 in 2,500 (common among Caucasian)
• CF is a "multi-system" disease, meaning that it
affects many body organs. (Mostly the lungs and the
digestive system.)
• Normally, mucus is watery. It keeps the linings of
certain organs moist and prevents them from drying
out or getting infected. In CF, an abnormal gene on
chromosome 7 causes mucus to become thick and
sticky.
• The mucus builds up in your lungs and blocks the
airways. This makes it easy for bacteria to grow and
leads to repeated serious lung infections. These
infections can cause serious damage to the lungs.
Cystic Fibrosis
• The thick, sticky mucus can also block in the
pancreas. As a result, digestive enzymes that are
produced by the pancreas cannot reach your small
intestine or help break down food. The intestines do
not absorb fats and proteins fully.
• As a result:
– Nutrients leave your body unused, and lead to
malnutrition.
– Stools become bulky.
– Lack vitamins A, D, E, and K.
– May lead to intestinal gas, a swollen belly, and
pain or discomfort.
Cystic Fibrosis
• Both parents must be
a carrier for the child
to have cystic fibrosis.
• The average survival
is now more than 30
years and have a
greater than 80%
chance of living into
their late forties
Sickle-Cell Anemia
• Normal RBCs
– Are donut shaped
with the centers
partially scooped out
and are soft and
flexible
– Pass easily through
blood vessels
– Live about 120 days
• Sickle RBCs
– Are Stiff, sticky, and
distorted in shape
– have difficulty
passing through
small blood vessels
leading to possible
death of tissue
– Live about 16 days
Sickle-Cell Anemia
Genetic counselors
• Genetic counselors can aid people who want
to have children, but are afraid of passing a
disease on to their children.