BIOLOGY CHAPTER 12-4 Mutations

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BIOLOGY CHAPTER 12-4 Mutations
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CHAPTER 14 Human Heredity"MUTATIONS IN GENES"
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Mutation- change in DNA sequence that affects
genetic information.
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GENE MUTATIONS- a chemical change resulting from
a change in a single gene.EX Point Mutations
frameshift mutations
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The majority of gene mutations involve just one
nucleotide.
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POINT MUTATION- mutation that affects a single
nucleotide, usually by substituting one
nucleotide for another.
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These substitutions usually change one of the
amino acids in a protein.
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When a point mutation inserts or deletes a
nucleotide- a bigger change results.
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Genetic codes are read in groups of three bases
known as CODONS. If a nucleotide is inserted or
deleted the groupings are shifted for every
nucleotide that follows. These types of changes
are called
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FRAMESHIFT MUTATIONSbecause there is a shift in
the reading frame of the genetic message.
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Frameshift mutations affect every amino acid that
follows the point of the insertion or deletion.
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These mutations can alter a protein so that it is
unable to function normally.
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Figure 12-19 Substitution, Insertion, Deletion
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CHROMOSOMAL MUTATIONS- mutations that involve
changes in a whole chromosome.changes in the
number of chromosomes or in the structure of
chromosomes.
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Chromosomal mutations can even change the
locations of genes on chromosomes even the of
copies of some genes.
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.Deletion- the loss of all or part of a
chromosome.
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.Dulpication- (opposite of deletion) a segment of
a chromosome is repeated.
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.Inversion- when part of a chromosome becomes
oriented in the reverse of its usual direction.
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Translocation- when part of one chromosome breaks
off attaches to another NON-homologous
chromosome.
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In most cases non-homologous chromosomes
exchange segments so that 2 translocations occur
at the same time.
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page 308 Section Assessment 1-5 Write the
Questions!
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14-1 Human Heredity page 341Human traits are
inherited by the action if dominant and recessive
genes, but some traits are determined by more
complicated gene interactions.
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Diploid cell- has 2 sets of homologous
chromosomes...human diploid cells contain 46
chromosomes arranged in 23 pairs
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The 46 chromosomes contain 6 billion nucleotide
pairs of DNA.
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Nucleotide- a unit of nucleic acid that is made
up of a 5 carbon sugar, a phosphate group, and a
nitrogenous base
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Nucleic acids (RNA, DNA) store and transmit the
genetic information that is responsible for life
itself.
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EX In this textbook there are approximately 1500
letters on each page...In complete human DNA
sequence were written in the same size type of
this textbook, it would take a book of more than
4 million pages long to express how long the
sequence is
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According to Mendel, organisms inherit a single
copy of each gene from each parent.
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In Humans, gametes (reproductive cells) contain a
single copy of each gene.
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Gametes (sperm and eggs) are formed in
reproductive organs by the process of meiosis
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Each egg and sperm cell contain 23 chromosomes,
or the HAPLOID number of chromosomes.
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During fertilization, an egg and sperm unite and
a ZYGOTE (fertilized egg) is formed.
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The zygote contains 46 chromosomes (23 pairs) or
the DIPLOID number of chromosomes...the number
characteristic of the organism
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Of the 46 chromosomes found in a human diploid
cell...two are the sex chromosomes X and Y or X
and X.
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Females are 46 XX and males are 46 XYsee Punnett
Square on page 342
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The remaining 44 chromosomes are AUTOSOMES.
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Autosome- (autosomal chromosomes)a chromosome
that is NOT a sex chromosome. Autosomes are found
in the body cells
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Dominant and recessive traits can be inherited on
any of the 44 autosomes.
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Human genes carried on the sex chromosomes are
sex-linked.
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HUMAN TRAITS
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The phenotype of an organism is only partially
determined by its genotype.
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Some traits are influenced by environmental
factors such as nutrition and exercise.
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Improvements in infant and childhood nutrition in
the U.S. and Europe have greatly increase the
average height of these populations.
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Environmental influence is an important
consideration...HOWEVER, the environmental
influences on gene expression are not
inherited...only the genes are
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Genes that are denied proper environment in which
to reach full expression in one generation can,
in proper environment, achieve full potential in
a later generation.
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KARYOTYPE-set of photographs of chromosomes that
are grouped in order, in pairs.
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See page 341figure 14-1
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THE INERITANCE OF HUMAN TRAITS
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Pedigree- a chart that shows the relationship
within a family
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Pedigree charts are most often used by
geneticists when tracking the inheritance of
genetic disorders,such as hemophila or
colorblindness.
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They are used to help parents understand the
probability of having a child with a genetic
disorder.
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Carriers are heterozygous for a trait and do not
exhibit the trait.
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Pedigree charts are based on observable traits-
phenotypes.
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Females who have one allele for the trait are
only carriers, while males who have one allele
for the trait express the trait.
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POLYGENIC- traits that are controlled by many
genes.
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HUMAN GENOME- our complete set of genetic
information.Page 344
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HUMAN BLOOD GROUPS
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Genes can have 2 contrasting forms (alleles..such
as short or tall)...some genes have more than 2
forms.
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MULTIPLE ALLELES- three or more alleles of the
same gene that code for a single trait
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In a diploid organism, only 2 of the alleles can
exist.
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ABO and Rh blood groups are examples of human
traits determined by multiple alleles.
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ABO BLOOD GROUPS....
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In 1900, Karl Landsteiner, and Austrian physician
discovered that human blood could be classified
into 4 general groups.
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Today we know these types as Landsteiner blood
groups.
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These four blood types are determined by the
presence or absence of certain chemical
substances in the blood.
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When certain blood types are mixed they
AGGLUTINATE or clump together.
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Red blood cells can carry 2 different antigens,
which he called A and B.
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ANTIGEN- molecules that can be recognized by the
immune system.
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The presence or absence of the A and B antigens
produces the four possible blood types
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A RBC's carry only the A antigen
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B RBC's carry only the B antigen
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AB RBC's carry the A and B antigen
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O RBC's do not carry either antigen
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Blood type information is very important in Blood
Transfusions...the wrong blood type can cause a
violent and even fatal reaction.
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The immune system does not recognize the antigen
and sees the blood as a foreign intruder.
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People who have AB blood can receive blood from
any of the four groups...UNIVERSAL RECIEPTIANT
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People who have type O blood can donate blood to
someone who has any of the 4 blood types but can
only receive type O blood..Type O UNIVERSAL
DONOR.
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The ABO blood groups are determined by a single
gene with 3 alleles
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See figure 14-4 pg 344
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IA and IB are codominant and i is recessive
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A person with IAIB produces both antigens making
their blood type AB.
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A person with IAIA or IAi produce only the A
antigen making them blood type A.
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IBIB or IBi produce only the B antigen making
them blood type B.
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Those who are homologous for the i allele (ii)
produce no antigen and are said to have blood
type O.
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Rh BLOOD GROUPS
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In addition to AB antigens there is another
antigen on RBC's...called the Rh antigen..so
named after the rhesus monkey in which the
antigen was first discovered.
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Lansteiner and Alexander Wiener discovered the Rh
factor.
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People who have the Rh antigen on their blood
cells are said to be Rh positive..those who do
not are said to be Rh negative.
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Simple dominance is displayed in the gene
expression of the Rh factor..
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Rh and Rh dominant positive
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Rh and Rh negative dominant positive
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Rh- and Rh- Rh negative
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RECESSIVE ALLELES
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Phenylketonuria (PKU)- people who lack the enzyme
that is needed to break down phenylalanine.an
amino acid found in milk and many other foods.
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Build up of phenylalanine in the tissues during
the child's first years of life and could cause
mental retardationcaused by a recessive allele
carried on chromosome 12.
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Tay-Sachs disease- caused by autosomal recessive
allelesfound mostly Jewish families of central
eastern European ancestary. This disease results
in nervous system break down and death in the
first few years of life.
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There is no treatment for this disease-
however-there is a test for this allele.
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DOMINANT ALLELES
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Remember that the effects of a dominant allele
are expressed even when the recessive allele is
present.therefore-if you have the dominant
allele for a genetic disorder- it will be
expressed.
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EX Dwarfism (Achondroplasiapronounced
ay-kahn-droh-PLAY-zhuh) Huntingtons Disease
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HUNTINGTON DISEASE
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This disease involves a slow and progressive
destruction of brain cells....a loss of muscle
control and mental function A person usually
dies 10-20 years after the first onset of the
symptoms....usually between the ages of 30-50
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This disease is caused by a dominant allele and
the symptoms do not show up until middle age.
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(Extra Information)
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In 1993 the gene for HD was located on
chromosome 4 and isolated. The DNA sequence for
the gene was determined...this allows researchers
to see how the disease works and how to fix it.
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Tests are available to see if you have this
disease...Would you want to know whether or not
you carry this allele?
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(Extra Information)The frequency of this disease
is higher in South Africa than in any other part
of the world...All affected persons in South
Africa were directly or indirectly descended from
a Dutchman who settled there in 1658
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FOUNDER EFFECT- the phenomenon of one or a few
individuals with a genetic abnormality causing
the establishment of a new population...most
likely to occur in regions that are remote and
have a relatively small total population
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CODOMINANT ALLELES
Sickle Cell AnemiaCharacterized by bent
twisted shape of red blood cells (RBCS).
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The rigid shape causes the RBCs to get stuck in
the capillaries (The narrowest blood cells in
the body) Blood stops moving through vessels
damaging cells tissues beyond the blockage.
Sickle Cell disease produces physical weakness,
damage to the brain, heart, spleen.
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The normal allele for the hemoglobin gene differs
from the sickle cell gene very little.just one
DNA base is changed! (Hemoglobin- the protein
that carries oxygen in the blood) Sickle Cell
Anemia has a relationship to Malaria.
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Malaria is a serious parasitic disease that
infects RBCs. People who are heterozygous for
the Sickle Cell allele are usually healthy. They
are also resistant to malariasee page 348Low O2
levels cause some RBCs to become sickle
shapedthen the body destroys the sickled cells
therefore gets rid of the Malaria parasite at the
same time.
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Being heterozygous for Sickle Cell Anemia is
considered partly beneficial in parts of the
world where malaria is a major health
threat. CYSTIC FIBROSIS (CF) A common fatal
disease caused by a recessive allele on
chromosome 7. Children with CF have serious
digestive problems.
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Children with CF produce a thick, heavy mucus
that clogs their lungs and breathing passageways.
Only about ½ of the children born with cystic
fibrosis survive into their 20s. CF involves a
very small genetic changeusually caused by the
deletion of 3 bases in the middle of a sequence
for a proteinFigure 14-8 page 347
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14-2 HUMAN CHROMOSOMES Sex Linked Gene- a gene
located on the X or Y chromosome. Most are
located on the X chromosome which is larger than
the Y chromosome.
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COLORBLINDNESS Three human genes associated with
color vision are located on the X chromosome. In
males a defect in any one of these three genes
produces colorblindness. Colorblindness is rare
in females. WHY?
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Males have just ONE X chromosome. This means that
all X-linked alleles are expressed in males,
even if the allele is recessive. In order for the
recessive allele to be expressed in females,
there must be 2 copies of the alleleone on each
of the 2 X chromosomes.
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Hemophilia is another example of sex-linked
disorders. People with hemophilia lack a protein
for normal clotting of the blood. They can bleed
to death from minor cuts may suffer internal
bleeding from bumps bruises. Hemophilia can be
treated with injections of normal clotting
proteins.
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The process that separates chromosomes during
meiosis usually works correctlybut every now and
then something goes wrong. NONDISJUNCTION- error
in meiosis in which homologous chromosomes fail
to separate.
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If nondisjunction occurs, abnormal s of
chromosomes may end up in the sex cellsand a
disorder of chromosome s may result. DOWN
SYNDROME- TRISOMY 21Three copies of chromosome
21 results. See page 353 Figure 14-16
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In the US, one baby in 800 is born with Down
Syndrome. Down Syndrome produces mild to severe
mental retardation. It also causes the person to
be susceptible to many diseases and causes a
higher frequency of some birth defects.
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SEX CHROMOSOME DISORDERS Turners Syndrome- A
disorder where a female inherits only ONE X
chromosomeGenotype XO Women with Turner
Syndrome are sterile because their sex organs do
not develop at puberty.
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Klinefelters Syndrome- A disorder in which
males inherit an extra copy of the X chromosome.
Genotype XXY They have even found people who are
XXXY XXXXY! .
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There are NO reported incidences of babies
being born without an X chromosome! This
indicates that the X chromosome contains genes
that are vital for normal development. This also
points to the role of the y chromosome.
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The Y chromosome contains a sex determining
region that is necessary to produce males in
development. If this region of the Y chromosome
is absent.the embryo develops as a female! TEST
CH 12-4 CH 14-1 14-2