Modern Genetics
Genetic Patterns
Each chromosome pair may contain as many as
2,000 traits. Chromosome 1, the largest human
Chromosome, contains between 2000 and 2100 traits.
These genes carry the information or code to
produce proteins. It is estimated that the 23 pairs of
human chromosomes contain 20,000 to 25,000 genes.
Each of these genes are a result of the processes of
meiosis and fertilization.
Five theories that resulted from Mendel’s work:
1. Law of Segregation-every organism contains
a pair of alleles for any particular trait and that this
Organism can pass a randomly selected copy of one
Of these alleles to its offspring.(meiosis)
The offspring then receives its own pair of alleles for
that trait by inheriting homologous chromosomes
from its parents. (recombination)
2. Law of Independent Assortment- genes located
On different chromosomes or nonhomologous
Chromosomes will be inherited independently and
Randomly. This allows for diversity and variety.
Roughly 8 million combinations exist.
3. Gene linkage-genes for different traits that are found
on the same chromosome are linked and will be
inherited together. This is the reason why freckles and
Red hair are frequently found inherited together.
4. Sex linked-genes for traits found on the X
Chromosome will be inherited if the X chromosome
Is passed to an offspring.
5. Law of Dominance-each allele can be classified as
Dominant or recessive. If a dominant allele is inherited it will always be seen in the phenotype of the
organism, masking the recessive allele. For the
recessive allele to be seen the organism must
inherit both recessive alleles.
Remember how this process works:
Within the nucleus there are homologous
chromosomes-chromosomes carrying alleles for the
same trait. One allele came from the female-the
Other from the male.
Because they carry the code
For the same trait they are
Called homologous
Chromosomes.
During interphase, the chromosomes replicate, making
2 of each homologous chromosomes.
The process continues through each of the phases
Of meiosis.
During prophase the chromosomes are very
Close together. They may exchange some
Codes that are on the chromatids. This changes
The code for those traits that are linked by a
Gene producing a different combination of
Alleles.
Crossing over:
Increases the
Diversity of
Species.
Remember, genes are segments or specific codes
of DNA. These codes are a result of a specific pattern
of nitrogen bases. If the pattern is changed in any
way the code changes, in both DNA and RNA.
CCGTATGGC
GGCATACCG
DNA code
C C G U A U G G C - RNA code
CCGTATGGC
GCCATAGCG
MUTATED DNA CODE
C G G U A U C G C – MUTATED RNA CODE
These changes in the pattern are called mutations –
sometimes good, but most of the times harmful.
Mutations are harmful because the code is changed
and the function related to that code is also changed.
If the code is for protein synthesis through the RNA
Molecule, then the protein/enzymes will not form
Or function correctly.
If the code is altered where there is a dominant
recessive allele and the dominant allele is not
affected then the cell will continue to function
properly.
Mutations in somatic cells are not inherited.
Mutations in gametes are inherited
Mutations can occur in several different ways:
*these changes in the pattern are results of:
Viruses, chemicals, radiation
** in most cases the body can heal these changes.
1. deletion-loss of all or part of the code=loss of trait
2. insertion- segment is repeated
Chain becomes longer=domino effect
3. Cross over: genetic material from one chromatid
Is exchanged with the genetic material from its
Homologous chromatid (as seen earlier in this PPt)
Few diseases result from this. Rather a greater
variety or diversity is observed.
4. Translocation: similar to cross over but occurs
on nonhomologous chromosomes. This means
that 2 translocations occur simultaneously
because 2 nonhomologous chromosomes are
involved.
This type of mutation is usually not observed
(phenotypically) in a heterozygous individual, but
will affect meiosis.
Nondisjunction: occurs during meiosis. Chromatin
Fail to separate.
One less chromatid
To be inherited
Normal gamete formation
One extra chromatid
In gamete
Some disorders/diseases caused by these mutations:
Deletion – Cri-du-chat, DeGeorge Syndrome
Insertion – Fragile X
Huntingtons disease
Translocation – Philadelphia gene – leukemia
Nondisjunction – Down Syndrome
Turner Syndrome
Kleinfelter Syndrome
Sex determination: Diploid cells contain two different
Types of chromosomes-alleles. Those chromosomes
Controlling body traits are called autosomes 22 pairs.
But one pair of chromosomes control the gender
of a species, called sex chromosomes. Specifically
these alleles are found on the 23rd pair and have the
combination of XX and XY.
There is a 50/50 chance of inheriting the X and Y
Chromosome.
Female = XX
Mother gives X to son
Male = XY
Father gives Y to son
Sex linked disorders/traits are those found on the
X chromosomes.
Men: will be affected by the disorder if they have
Inherited the affected X
:will pass the affected X to their daughters.
Women: can be carriers of the disorder if they have
Inherited only one affected X or affected if they have
Inherited both X chromosomes.
:will pass the affected X to their sons.
Genetic Engineering: term used to describe the use of
specific techniques to move genetic material from
one organism to another organism. One small piece
of DNA from a cell is removed and added to the
DNA of another cell. The new DNA that results from
This process is call recombinant DNA. This
recombinant DNA will continue to produce the
polypeptide product that it was originally coded for
giving the organism a new polypeptide.
This techniques improves the functions of the
Cells/organism.
This can only work because the DNA is the same for
all organisms.
A couple of facts to remember:
a. DNA is the same for all organisms-only the pattern
changes.
b. Bacteria is often used as the ‘carrier’ molecule.
It is called a plasmid. Think of ‘plaster’. Once this
bacteria is injected into the recipient, the recipient’s
cells will use the code to produce the needed protein.
c. Restriction enzymes are used to cut the DNA
molecule apart.
Insulin, growth hormone, interferon
Some uses of recombinant DNA
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Better Crops (drought & heat
resistance)
Recombinant Vaccines (ie.
Hepatitis B)
Prevention and cure of sickle
cell anemia
Prevention and cure of cystic
fibrosis
Production of clotting factors
Production of insulin
Production of recombinant
pharmaceuticals
Plants that produce their own
insecticides
Cloning: an identical copy of an organism. Two
organisms have the exact DNA code.
identical twins are a natural form of cloning
mitosis
Why clone? All DNA will be inheritable.
1. Maintain supply of diseased lab animals for
testing.
2. Grow stem cells
3. Protect endangered species
4. Produce high quality livestock/plants for food
5. Produce drug carrying animals.
Negatives:
1. Loss of diversity
2. Moral issues