UNDERSTANDING HEREDITY Part 2

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23 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

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UNDERSTANDING
HEREDITY

Part 2

MUTATIONS

Mutations


Genes code for proteins


Mistakes in genetic code cause mistakes in the
protein


Mutations are mistakes in genetic code


A point mutation involves one nitrogen base in a
codon


Some point mutations cause no difference in protein
produced


Others point mutations can cause a noticeable or
serious effect

Mutations, cont.

Types of Point Mutations:

1.
Substitution


one nucleotide is changed to another



Example:

CA
T

GCA CA
G

GCA

2.
Insertion


one nucleotide is inserted into a
sequence



Example:
CAT GCA CA
G

TGC A

3.
Deletion


one nucleotide is deleted from a
sequence



Example:

CA
T

GCA CAG CA

Mutations, cont.


Substitutions usually
affect only one amino
acid


Insertions or deletions
can result in a
frameshift

mutation


they shift the “reading
frame” of the bases


This can change every
amino acid that follows
the point of mutation


Mutations, cont.


Chromosomal
mutations


involve
changes in the number
or structure of
chromosomes


Some may change the
locations of genes on
chromosomes


Others may change
the number of copies
of a gene made


Mutations, cont.

Types of Chromosomal Mutations:

1.
Deletion


an entire gene is deleted

2.
Duplication


an extra copy of the gene is added

3.
Inversion


a segment of the chromosome is flipped
over

4.
Translocation


a portion of a chromosome breaks off
and reattaches to another chromosome

Mutations,cont
.


Many mutations are neutral


they have little/no effect
on the expression of genes or the function of proteins
for which they code


Some mutations can result in the production of
defective proteins that disrupt normal biological
activities


Harmful disruptions cause many genetic disorders


Beneficial disruptions can be the source of genetic
variation that allows certain members of a species to
be more successful in a changing environment

Mutations, cont.


Polyploidy


condition in which an organism has an
extra set of chromosomes


Occurs during meiosis when the chromosomes fail to
separate


Triploid
-

3N


Tetraploid
-

4N


In animals: polyploidy is deadly


In plants:


benefits


larger, stronger; source of seedless fruits


drawbacks


cannot be fertilized; have to purchase seed
to make more plants

GENETIC DISORDERS

Genetic Disorders


Genetic disorder


disease caused by an
abnormality in the organism’s DNA


Single
-
gene disorders are inherited in
Mendelian

patterns:

1.
Autosomal recessive disorders

2.
Autosomal dominant disorders

3.
Sex
-
linked patterns

Genetic Disorders, cont.

1.
Autosomal Recessive Disorders:


Most human genetic disorders are caused by recessive
alleles on autosomes


This means the individual must inherit two copies of the
recessive allele


Examples:


Sickle
-
cell Disease


red blood cells develop a rigid sickle
shape; blood cells clot and cause oxygen loss to body
cells


Cystic Fibrosis


thick mucus secretions in lung,
pancreas, liver and intestines


Tay
-
Sachs Disease


progressive degeneration of all
nerve cells starting about 6 months old with death by 4




Genetic Disorders, cont.

2. Autosomal Dominant Disorders:


Less common than recessive because they are often
lethal


In most cases, individuals with disorder live long enough
to reproduce


Keeps allele in population


Examples: Huntington’s Disease &
Marfan

Syndrome



Huntington’s Disease




degeneration of
nerves


affects
muscle
coordination


causes mental
and
emotional
decline


starts
in
mid
-
life


most
common cause of
death is
pneumonia;
second most common is
suicide



Marfan

Syndrome
-


affects
proper growth
of connective
tissue


individuals
are
unusually tall, with long
& thin
limbs/toes/fingers


disruption
of proper
heart function is most
serious complication


Genetic Disorders, cont.

3.
Sex
-
Linked Patterns


Females: XX Males: XY


Y chromosome contains the gene,
SRY
, that codes
for development of the testes


If testes form, other genes guide production of
testosterone and fetus develops into a male


If Y chromosome is absent or
SRY

gene does not
function correctly, fetus develops into a female

Genetic Disorders, cont.


Genes located on sex chromosomes are called sex
-
linked
genes


Many genes are found on the X chromosome, but not the
Y chromosome


Because there is not an alternate allele on the Y
chromosome, the allele on the X is the one expressed


Sex
-
linked = X
-
linked


Examples of X
-
linked disorders:


Color blindness


inability to see some, or all, colors in
the normal way


Hemophilia


blood disorder in which blood does not clot
properly (have low to no clotting factor in blood)


Pedigree Chart


Queen Victoria of
England (died 1901)


Died: 1945, no children

BIOTECHNOLOGY

Biotechnology


Biotechnology


use of living organisms to
improve the quality of human life


Biotechnology, cont.


Bacteria are the most
commonly used organisms in
biotechnology


This is because their DNA is
not surrounded by a nucleus
and is easier to manipulate


Also, manipulated bacteria
reproduce rapidly


Insulin, produced by
E.coli

bacteria, is the first protein
commercially manufactured
using this method



Biotechnology, cont.


Human DNA is 99.9% identical


The .1% difference is displayed in fingerprints, inherited
health conditions and appearance


Gel electrophoresis is a process used by scientists to
isolate and study specific proteins


This increases our understanding about how proteins
work and how we can utilize them to a better quality of life