Anatomy

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Anatomy Physiology I Unit Five Objective One
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The Characteristics and Functions of Meiosis
Production of gametes
Assures correct chromosome numbers in offspring
Creates new combinations of genes
Begins with a diploid sex cell ends with
non-identical haploid gametes
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Anatomy Physiology I Unit Five Objective Two
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Meiosis
Meiosis is the cell division process by which
gametes are produced
It occurs only in sex cells that are found in the
gonads
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Meiosis
The process goes through two meiotic divisions
meiosis I and meiosis II
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• A. What Is a Chromosome? A long, continuous
  strand of DNA, plus several types of associated
  proteins, and RNA.

• Heterochromatin DNA is tightly wound and composed
  of many repetitive sequences.
• Euchromatin DNA is more loosely wound is
  composed of many unique sequences. It encodes
  proteins.

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Meiosis
Homologous chromosomes pairs of similar
chromosomes
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Homologous Chromosomes Cont.

• In humans there are normally 23 pairs of
  homologous chromosomes
• Therefore, there are 46 diploid chromosomes in a
  normal human

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Meiosis
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Meiosis
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Meiosis
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Meiosis vs. Mitosis
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Anatomy Physiology I Unit Five Objective Three
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Genetics
Genetics the study of heredity
Heredity the passing of traits from one
generation to the next
Trait a physical or physiological
characteristic coded for by a gene
Gene a portion of a chromosome that codes for a
particular protein
Allele a form of a gene
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Genetics
Dominant allele an allele that masks the
effects of the other
Recessive allele an allele that can be masked
by a dominant allele
Locus the position of a gene on a chromosome
Codominance the two alleles at a locus are
equally expressed
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• Homologous chromosomes a pair of chromosomes,
  one each from the female male parent, that have
  identical structure and gene loci

Genetics
Mom (female)
Dad (male)
Dominant allele
Recessive allele
Homologous chromosomes
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Genetics
Genotype the set of genes an organism has
Homozygous alleles are the same type
Heterozygous alleles are different
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Genetics
Phenotype the expression of the genotype
Purebred having a homozygous genotype
Hybrid having a heterozygous genotype
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Karyotype is a chart of the chromosomes in a cell
or an organism arranged by size and centromere
position.
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Centromere Positions

• A. Telocentric centromere is located at tip.
• B. Acrocentric centromere is near one end.
• C. Submetacentric centromere divides chromosome
  into a long and short arm.
• D. Metacentric centromere is centrally
  located divides chromosome into two arms of
  approximately equal length.

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Anatomy Physiology I Unit Five Objective Four
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D
D
d
d
D
d
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D D


Dd Dd
Dd Dd
d d
Punnett Square
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D
D
d
d
d
D
D
D
D
d
d
d
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D d


DD Dd
Dd dd
D d
Complete Dominance
Monohybrid Cross
Genotypic Ratio 121
Phenotypic Ratio 31
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Complete Dominance
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D d


Dd dd
Dd dd
d d
Complete Dominance
Monohybrid Cross
Genotypic Ratio 22
Phenotypic Ratio 22
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A O
AB BO
AO OO
B O
Codominance
Genotypic Ratio 1111
Phenotypic Ratio 1111
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Anatomy Physiology I Unit Five Objective Five
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Autosomal vs. Sex Linked
Autosomes all chromosomes except for the ones
that determine sex
Sex chromosomes chromosomes that determine sex
Sex linked traits traits controlled by genes on
the sex chromosomes
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• X-Y System (presence of Y chromosome determines
  sex)

female is XX male is XY Ex. all mammals
SRY gene
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In X-Y system, male determines sex of offspring
(half his sperm contain X chromosome, while other
half contains Y chromosome)
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• Inheritance of Genes on Sex Chromosomes
• X-Linked traits are carried on the X
  chromosome and most are recessive
• Examples color blindness, hemophilia (disease
  where afflicted individuals lack a protein
  clotting factor that is essential in blood
  clotting)
• More common in females
• affected males are hemizygous (have only 1 set of
  X chromosomes, so they either have the trait or
  not), cannot be carriers
• Male inherits X-linked condition from carrier
  or affected mother
• Y-linked traits are very rare because Y has
  few genes

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(No Transcript)
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XB Xb
XBXb XbXb
XBY XbY
Xb Y
Sex Linked Cross
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• Hemophilia recessive X-linked trait
• Genotype Phenotype
• XHXH non-carrier female
• XHXh carrier female
• XhXh female with hemophilia
• XHY normal male
• XhY male with hemophilia

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What is the probability that a carrier female and
a normal male will have a son with hemophilia?
¼ or 25
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• Pedigree of several royal families with
  hemophilia. The mutant allele apparently arose
  in Queen Victoria, who was either a carrier or
  produced an oocyte that mutated to carry the
  allele.

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Anatomy Physiology I Unit Five Objective Six
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Human Sex Chromosomes
?
?
X
Y
X
X
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Human Sex Chromosomes
?
?
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(No Transcript)
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Anatomy Physiology I Unit Five Objective Seven
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Genes, Genetic Code Genetic Disease
Remember, genes are portions of DNA that code for
a particular protein
In order for the protein to be functional, the
DNA nitrogen base sequence must be correct
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Genes, Genetic Code Genetic Disease
Any variance of that sequence can cause the wrong
amino acid to be inserted into the polypeptide
which could result in - a non-functioning
protein - a protein that changes the
outcome of a process
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Anatomy Physiology I Unit Five Objective Seven
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Nondisjunction
Nondisjunction is the failure of chromosomes to
separate during anaphase I of meiosis
The normal separation, disjunction, produces
daughter cells with 23 chromosomes each
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Nondisjunction
Nondisjunction results in one daughter cell with
24 chromosomes and the other with 22 chromosomes
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Nondisjunction
Monosomy is the result of the fertilization of a
normal gamete and one that has only 22 chromosomes
Trisomy is the product of the fertilization of a
normal gamete and one that has 24 chromosomes
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Nondisjunction
Disjunction
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Chromosome Abnormalities

• 1. Polyploidy
• 2. Aneuploidy

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• 1. Polyploidy (many sets) extra full sets of
  chromosomes.
• animal polyploids spontaneously abort or die
  shortly after birth
• plant polyploids are relatively common
• Example wheat (tetraploid or hexaploid)
• Tetraploid has 4 copies of each chromosome in
  the cells
• Hexaploid has 6 copies of each chromosome in the
  cell

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• 2. Aneuploidy an extra (trisomy) or missing
  (monosomy) chromosome usually due to
  nondisjunction.
• Most aneuploids spontaneously abort in humans.

• Nondisjunction
• A chromosome pair fails to separate, either at
  the 1st or 2nd meiotic division.
• Results Sperm or oocyte have either 2 copies of
  a particular chromosome or none at all, rather
  than the normal 1 copy.
• If 1 of these abnormal gametes in a human is
  fertilized, the resulting zygote has either 45 or
  47 chromosomes instead of the normal 46.

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Aneuploidy Terminology

• Euploid has the normal chromosome number for
  the species in the cells
• Aneuploid has a missing or extra chromosome in
  the cells
• Extra genetic material is less dangerous than
  less genetic material

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Autosomal Aneuploidy Vs. Sex Chromosome
Aneuploidy

• Autosomal aneuploidy usually results in mental
  retardation because so many genes contribute to
  brain function
• Sex chromosome aneuploidy usually less severe
  than autosomal aneuploidy

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• Autosomal aneuploids
• trisomy 13
• trisomy 18
• trisomy 21 (Down syndrome)has 1 extra chromosome

• Sex chromosome aneuploids
• Turner syndrome XO female
• Triplo-X XXX female
• Klinefelter syndrome XXY male
• Jacobs syndrome XYY male

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Genetic Disorders
Several genetic disorders are sex linked and
found predominantly in men, but can also be
present in women
The shorter Y chromosome means there is only one
allele that determines these traits
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Genetic Disorders
Male pattern baldness and color blindness are two
examples that are inconvenient, but non-life
threatening
Hemophilia, a condition in which the blood does
not clot correctly, can be deadly
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Genetic Disorders
Remember Any variance of the DNA base sequence
can cause the wrong amino acid to be inserted
into the polypeptide which could result in - a
non-functioning protein - a protein that
changes the outcome of a process
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Genetic Disorders
These mutations can lead to a number of human
health disorders
Some of these abnormalities are inconvenient,
while others can be lethal
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Genetic Disorders
Albinism is a condition in which the body does
not produce the pigment melanin
The phenotypic results are white hair, pale skin
and pink colored eyes
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Genetic Disorders
Albinism is the result of a homozygous recessive
genotype that produces a nonfunctional tyrosinase
enzyme
Melanin is synthesized from tyrosine by way of
the enzyme tyrosinase
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Genetic Disorders
Sickle cell disease is a condition in which red
blood cells are deformed due to the substitution
of one amino acid in a hemoglobin chain
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Genetic Disorders
The deformation of the RBCs inhibits the binding
of oxygen, causing anemia
The deformation also causes the sickled RBCs to
be sticky and agglutinate
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Genetic Disorders
Without treatment a child will usually die before
age two
Even with treatment most affected people die
before the age of fifty
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Genetic Disorders
The substitution of one amino acid is caused by a
recessive allele
Sickle cell is the result of a homozygous
recessive genotype that produces the malformed
hemoglobin
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Genetic Disorders
Approximately 8.5 of people of central and
southern African descent are carriers of the
allele
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Genetic Disorders
Phenylketonuria (PKU disease) is a disorder in
which the amino acid phenylalanine is not
metabolized due to the lack of an enzyme
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Genetic Disorders
PKU disease is the result of a homozygous
recessive genotype that does not produce the
enzyme that converts phenylalanine into tyrosine
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Genetic Disorders
Phenylalanine accumulates in the blood and acts
as a neurotoxin, causing brain damage and
retardation
Required tests on newborns now identify those
affected, which will be put on a low
phenylalanine diet
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Genetic Disorders
Remember Nondisjunction in gametes causes a
change in chromosome numbers that affects the
development of an embryo
Approximately 90 of nondisjunction events are
maternal in origin
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Genetic Disorders
The presence of an extra chromosome (trisomy) or
lack of one (monosomy) accounts for approximately
50 of all spontaneous abortions
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Genetic Disorders
Only three autosomal trisomies are survivable
trisomy 13 Patau syndrome trisomy 18
Edward syndrome trisomy 21 Down syndrome
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Genetic Disorders
Most fetuses with Patau or Edward syndrome will
die before birth
The few that are born are severely deformed and
usually die within their first year
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Genetic Disorders
Karyotype of Down syndrome (trisomy 21)
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Genetic Disorders
Down syndrome is the most survivable of the
trisomies, but approximately 75 die before birth
and 20 of those born will die before the age of
ten
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Genetic Disorders
Down syndrome effects short stature a
flat face with almond shaped eyes
enlarged protruding tongue broad hands with
short fingers varying degrees of mental
retardation
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Genetic Disorders
Of those that survive past the age of ten, life
expectancy has been extended to sixty years
However, after the age of forty many develop
early onset Alzheimer disease
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Genetic Disorders
Nondisjunction also occurs with the sex
chromosomes trisomy 23 Klinefelter
syndrome (XXY) trisomy 23
Triplo-X syndrome (XXX)
monosomy 23 Turner
syndrome (XO)
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Genetic Disorders
Triplo-X syndrome (XXX) results in a female
phenotype that is usually infertile and may
exhibit some intellectual impairment
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Genetic Disorders
Klinefelter syndrome (XXY) results in a sterile
male phenotype that is of normal intelligence and
upon the onset of puberty exhibits unusually long
arms, sparse body hair, undeveloped testes and
enlarged breasts
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Genetic Disorders
Turner syndrome (XO) results in a sterile female
phenotype that fails to develop secondary sex
characteristics at puberty and is usually short
in stature
Approximately 97 of all (XO) fetuses die before
birth
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Anatomy Physiology I Unit Five Objective Eight
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Mutations
A mutation is any change in the DNA of an organism
Mutations occur due to - pathogen infection
- exposure to radiation - introduction of
chemicals - nondisjunction
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Mutations
Mutations involve - base pair substitutions
- base pair insertions or deletions - DNA
segments
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Mutations
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• 3. Deletion part of a chromosome is missing.

4. Duplication part of a chromosome is present
twice.
5. Inversion part of a chromosome is reversed.
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• 6. Translocation nonhomologous chromosomes
  exchange parts (reciprocal translocation) or
  combine (Robertsonian translocation).
• Certain viruses, drugs, and radiation can cause
  translocations, but we often do not know how they
  arise.