Topic 4 Genetics
SL and HL
Topic 4.2: Meiosis
Mitosis Revision:
What is the purpose of mitosis?
In which stage does the cell spend most of it’s life?
Meiosis is the process that makes sex cells, the stages are similar to mitosis
Overview of process
Meiosis I
Meiosis II
Topic 4.1: Chromosomes, Genes, Alleles and Mutations
-Eukaryotic chromosomes are made up of DNA and protiens called histones.
A. Definitions
Gene – a heritable factor (sequence of DNA) controlling a specific
characteristic
Allele – a specific form of a gene, differing only slightly from a similar allele (
they are slightly different copies of the same gene)
Genome – whole of the genetic information of an organism
Gene pool – the total of the genes carried by the individual members of the
population.
B. Karyotyping
-A process in which chromosomes are arranged in pairs according to their
structure.
Steps:
1. A sample of cells are taken (usually through a process called
amniocentesis)
2. The chromosomes are isolated during prophase or metaphase
3. The chromosomes are stained
4. They are then arranged by size and banding
5. They are analyzed for problems
Picture of a normal human karyotype
Uses of Karyotyping:
-main use is to identify non-disjunctions and to provide a sample for genetic
testing.
C. Non-disjunction
Seperation of homologous (same) chromosomes (chromosomes consist of two
identical chromatides) is called disjunction.
Non-disjunction- failure of chromosomes to separate
-this can lead to missing or extra chromosomes
An example of non-disjunction
D. Gene Mutation
Gene mutation – a change in the base sequence of a gene.
Think of DNA as words, each word has a different meaning. What happens when you
change that meaning?
Example:
Real Example:
E. Sickle Cell Anemia
-A recessive genetic disorder in which the red blood cells have a sickle shape instead
of a biconcave shape.
View from the side:
-This can cause acute physical weakness and in some cases death.
This is caused by a base substitution mutation:
But having one copy the gene can also be an advantage:
Topic 3.3: Theoretical Genetics
A. Mendel’s 1st Law: law of segregation
-The separation of the pairs of parental factors, so that one factor is present in
each gamete.
B. Key Terms
Genotype- the alleles possessed by an organism
Phenotype- the characterists of an organism
Dominate allele – an allele which has the same effect on the phenotype
whether it is present in the homozygous or heterozygous state.
Recessive allele – an allele which only has an effect on the phenotype when
present in the homozygous state.
Codominate alleles – an allele which only has an effect on the phenotype when
present in heterozygous but a greater effect in homozygous individuals.
Locus- the particular position of a gene on homologous chromosomes.
Homozygous – having two identical alleles of a gene.
Heterozygous – having two different alleles of a gene.
Carrier – an individual that has a recessive allele of a gene that does not have
an effect on the phenotype.
Test cross – testing a suspected heterozygote by crossing with a known
homozygous recessive.
C. Punnett Squares
-
it is a method to determine the expected ratio of the offspring, given
certian parental phenotypes.
Ex. Mendel studied pea plants. He found that the “tall” allele is dominant
over the “short” allele. If he took a “pure breeding” (homozygous) tall plant
and breed it with a heterozygous tall plant, what would the expected ratios be?
D. Punnett Square Problems
1. Let's say that in seals, the gene for the length of the whiskers has two alleles. The
dominant allele (H) codes long whiskers & the recessive allele (h) codes for short
whiskers.
a) What percentage of offspring would be expected to have short whiskers from
the cross of two long-whiskered seals, one that is homozygous dominant and
one that is heterozygous?
b) If one parent seal is pure long-whiskered and the other is short-whiskered, what
percent of offspring would have short whiskers?
2. In purple people eaters (they don’t really exist), one-horn is dominant and no horns
is recessive. Draw a Punnet Square showing the cross of a purple people eater that is
heterozygous for horns with a purple people eater that does not have horns.
Summarize the genotypes & phenotypes of the possible offspring.
3. A green-leafed luboplant (I made this plant up) is crossed with a luboplant with
yellow-striped leaves. The cross produces 185 green-leafed luboplants. Summarize
the genotypes & phenotypes of the offspring that would be produced by crossing two
of the green-leafed luboplants obtained from the initial parent plants.
4. Mendel found that crossing wrinkle-seeded plants with pure round-seeded plants
produced only round-seeded plants. What genotypic & phenotypic ratios can be
expected from a cross of a wrinkle-seeded plant & a plant heterozygous for this trait
(seed appearance)?
E. Pedigree Charts
-A pedigree chart shows the inheritance of certain traits over several
generations.
Symbols used:
= normal male
= affected male or carrier male
= normal female
= Carrier female or affected female
= Carrier male
= Carrier female
Example:
Question: Jared has three siblings, 2 brothers and 1 sister. He has
three aunts on his mother’s side. His dad is an only child. Draw a pedigree
chart of Jareds family, going back to his grandparents.
Punnett Squares Questions
1. Some vampires have 4 fangs while others have only 2. 4 fangs is dominant over 2
fangs. A pure male vampire with 4 fangs mates with a female vampire with 2 fangs.
What will the phenotypes and genotypes of all the possible offspring be?
a. What are the 2 alleles for fangs?
b. Which is dominant?
2. Fruit flies can have a brown body or a yellow body. Having a brown body is
dominant. Bob the Brown fly mates with Yolanda the Yellow fly. If Bob is hybrid for
body color, what are the possible baby flies that could result?
a.
What are the 2 alleles for body color in flies?
b.
Which is dominant?
3. Piebald spotting is a condition found in humans in which there are patches of skin
that lack pigmentation. The condition results from the inability of pigment-producing
cells to migrate properly during development. Two adults with piebald spotting have
one child who has this trait and a second child with normal skin pigmentation.
a.
Is the piebald spotting trait dominant or recessive? What information
led you to this answer?
b.
What are the genotypes of the parents?
4. Galactosemia is a recessive human disease that is treatable by restricting lactose in
the diet. Susan Smithers and her husband are both heterozygous for the galactosemia
gene.
a. Susan is pregnant with twins. If she has fraternal (non-identical) twins,
what is the probability that both of the twins will have galactosemia?
b.
If the twins are identical, what is the probability that both will have
galactosemia?
F. Multiple Alleles
-Some genes have two or more alleles
-We say they have multiple alleles
Examples include: Blood groups, eye color, some flower color.
-This can result in codominance
codominace is when the different alleles express their traits at the same
time (neither one is dominate).
For example: Some flower colors are codominate. One allele gives a
red color, one allele gives a white color. Both alleles in a heterozygous
situtation will give a pink color.
G. ABO Blood Group and codominace.
-There are 4 different blood groups (phenotypes)
Blood group A , B, AB, and O
-There are 3 different alleles acting in this system (genotypes)
IA
IB i
Phenotype
Genotypes
(blood groups)
(Alleles present)
A
IAIA or IAi
B
IBIB or IBi
AB
IAIB
O
ii
Example: A homozygous mother with blood group A and a father with blood group
O are having a baby. What are the possible phenotypes and genotypes?
A baby is born with a blood group O. The father says that the baby cannot be his.
His blood group is A and he knows his genotype is IAIA. The mother says that he is
the father. She has a blood group B, with a genotype of IBi. Is the father or mother
right? Why?
Co-dominance Questions:
1. A cross between a blue blahblah bird & a white blahblah bird produces offspring
that are silver. The color of blahblah birds is determined by just two alleles.
a) What are the genotypes of the parent blahblah birds in the original cross?
b) What is/are the genotype(s) of the silver offspring?
c) What would be the phenotypic ratios of offspring produced by two silver blahblah
birds?
2. The color of fruit for plant "X" is determined by two alleles. When two plants
with orange fruits are crossed the following phenotypic ratios are present in the
offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit. What are the genotypes
of the parent orange-fruited plants?
H. Gender Determination
Gender refers to the sex of the organism.
In humans we are taking about the X and Y chromosome.
It is the Y chromosome that determines if it is a male or female.
-If 2 X chromosomes are present  female
-If a Y and X chromosome are present  male
What are the chances of having a male or female?
-Some genes are present on the X chromosome, but not on the Y chromosome.
Some of these genes have mutations which can cause genetic disorders.
Ex. Colorblindness, haemophilia
These disorders are an example of sex linkage:
Sex linkage- genes carried on the sex chromosomes, most often on the
X chromosome.
This presents certain problems.....
I. Sex-linked disorders
-these disorders are carried on a sex chromosome.
Ex. Colorblindness
Topic 3.4: Genetic Engineering and Other Aspects of Biotechnology
SL and HL
A. Genetic Screening, Genetic Fingerprinting, The Human Genome
Project
I. Gel Elecrophoresis
II. Restriction Enzymes
III. Polymerase Chain Reaction
VI. DNA Profiling (fingerprinting)
DNA Fingerprinting/DNA Profiling
DNA fingerprinting is a method of distinguishing one organism from another
using the pattern of bands that become visible when a sample of their DNA is
cut up with particular enzymes. The reason that this technique can distinguish
between people accurately enough to be used is that human DNA contains
large areas of highly repeated DNA sequences which are known not to be part
of any genes. These areas are unique to each person, and these sequences are
passed on to offspring. The result is a pattern of bands of DNA that have
moved through the gel according to their size, this process is called gel
electrophoresis. Each individual's pattern of band lengths is unique.
Practical Applications of DNA Finqerprintinq
1. Paternity and Maternity
2. Criminal Identification
3. Personal Identification
V. Genetic Screening
Genetic screening – testing an individual of the presence of absence of a gene
1. How it works:
2. Advantages:

allows treatment of some genetic diseases before harmful effects
develop

harmful genes could be found and eliminated or replaced to
eliminate a genetic disease

suffering of an individual who would have had a genetic disease is
prevented

parents with the same harmful recessive mutation can choose other
partners or not reproduce

screened embryos can be discarded/aborted
3. Disadvantages:

diagnosis is of little use if no treatment is available

does not show how serious the effect of a gene will be as this
varies between individuals

diagnosis in fetuses may encourage more abortions

might make parents only accept a "perfect" fetus

may cause depression in individuals who find out that they have a
harmful gene

difficulties in obtaining jobs / insurance / partners
VI. Human Genome Project
-is an international cooperatuve venture established to sequence the complete
human genome
Background Information:
Begun formally in 1990, the U.S. Human Genome Project was a 13-year effort
coordinated by the U.S. Department of Energy and the National Institutes of Health.
The project originally was planned to last 15 years, but rapid technological advances
accelerated the completion date to 2003. Project goals were to
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
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identify all the approximately 20,000-25,000 genes in human DNA,
determine the sequences of the 3 billion chemical base pairs that make up
human DNA,
store this information in databases,
improve tools for data analysis,
transfer related technologies to the private sector, and
address the ethical, legal, and social issues (ELSI) that may arise from the
project.
To help achieve these goals, researchers also studied the genetic makeup of several
nonhuman organisms. These include the common human gut bacterium Escherichia
coli, the fruit fly, and the laboratory mouse.
A unique aspect of the U.S. Human Genome Project is that it was the first large
scientific undertaking to address potential ELSI implications arising from project
data.
Another important feature of the project was the federal government's long-standing
dedication to the transfer of technology to the private sector. By licensing
technologies to private companies and awarding grants for innovative research, the
project catalyzed the multibillion-dollar U.S. biotechnology industry and fostered the
development of new medical applications.
Benefits of the human genome project:

may lead to an understanding of genetic/inherited
diseases/conditions

may lead to the production of gene probes to detect carriers of
genetic diseases

may lead to the production of pharmaceuticals based on DNA
sequences

study of similarities/differences between human race/population

find location of genes / produce a complete gene map

study of human origins / migration / relationships with other species
Issues involved with the Human Genome Project (and Biotechnology in General):
Fairness in the use of genetic information by insurers, employers, courts, schools, adoption agencies,
and the military, among others.
Privacy and confidentiality of genetic information.
Reproductive issues including adequate informed consent for complex and potentially controversial
procedures, use of genetic information in reproductive decision making, and reproductive rights.
Conceptual and philosophical implications regarding human responsibility, free will vs genetic
determinism, and concepts of health and disease.
B. Genetic Engineering
i.
Gene transfer involving plasmids
Examples:
Bt Corn- contains a chemical normally found in bacteria that is toxic to insects
Frost resistant strawberries- contains a gene found in artic fish that prevents the
strawberry from getting frost
Possible benefits
benefits include more specific (less random) breeding than with traditional
methods
faster than traditional methods
some characteristics from other species are unlikely in the gene pool /
selective breeding cannot produce desired phenotype
increased productivity of food production / less land required for
production
less use of chemicals (e.g. pesticides)
food production possible in extreme conditions
less expensive drug preparation (e.g. pharmaceuticals in milk)
human insulin engineered so no allergic reactions
may cure genetic diseases
Possible harmful effects
some gene transfers are regarded as potentially harmful to
organism (especially animals)
release of genetically engineered organisms in the environment
can spread and compete with the naturally occurring varieties
some of the engineered genes could also cross species barriers
technological solution when less invasive methods may
bring similar benefits
reduces genetic variation/biodiversity
ii.
Gene Therapy
The example below illustrates how gene therapy can work for children who
has SCID. SCID (severe combined immunodefiency) results in a person who
does not have a functioning immune system. The cause is one defective
enzyme called ADA.
C. Cloning
A clone is a group of genetically identical organisms or a group of cells
artificially derived from a single parent cell.
Dolly the clone:
Ethical Issues:
Arguments against cloning
reduces the value / dignity of the individual / causes psychological
problems
high miscarriage rates / cloned individuals are likely to have
developmental
disorders/health problems / cloned individuals may show premature aging
costly process and money could be better spent on other types of
healthcare
cloning may be done for inappropriate motives/replace lost loved
one/perfect race etc.
Arguments for cloning
identical twins are formed by cloning so it is a natural process
cloned embryos can be tested for genetic disease / genetic screening
increased chance of children for infertile couples
cloning research may lead to spin-offs for other research areas such as
cancer/transplant research/regeneration research