Anatomy & Physiology I
Unit Five
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
Meiosis
Meiosis is the cell division process by
which gametes are produced
It occurs only in sex cells that are found
in the gonads
Meiosis
The process goes
through two meiotic
divisions – meiosis I
and meiosis II
Meiosis
Homologous chromosomes
Meiosis
Meiosis
Meiosis
Meiosis vs.
Mitosis
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
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
Genetics
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)
Recessive
allele
Dominant
allele
Homologous
chromosomes
Genetics
Genotype – the set of genes an
organism has
Homozygous – alleles are the same
type
Heterozygous – alleles are
different
Genetics
Phenotype – the expression of
the genotype
Purebred – having a homozygous
genotype
Hybrid – having a heterozygous
genotype
Genetics
Codominance – the two alleles at
a locus are equally expressed
Karyotype – a chart of the
chromosomes of an organism,
arranged in order by size and
structure
Genetics
D D
d
D
d
d
D
D
d
Dd
Dd
d
Dd
Dd
Punnett Square
D
D
d
D
D
d
D
d
d
D
d d
D
d
D
DD
Dd
d
Dd
dd
Monohybrid Cross
Genotypic Ratio – 1:2:1
Phenotypic Ratio – 3:1
Complete
Dominance
Complete
Dominance
d
D
d
Dd
dd
Complete
Dominance
d
Dd
Monohybrid Cross
Genotypic Ratio – 2:2
Phenotypic Ratio – 2:2
dd
A
O
B
AB
BO
O
AO
OO
Codominance
Genotypic Ratio – 1:1:1:1
Phenotypic Ratio – 1:1:1:1
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
XB
Xb
Xb
XBXb
XbXb
Y
XBY
XbY
Sex Linked Cross
Human Sex
Chromosomes
♀
♂
X X
X Y
Human Sex
Chromosomes
♀
♂
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
Mutations
Mutations involve:
- base pair substitutions
- base pair insertions or
deletions
- DNA segments
Mutations
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
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
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
Nondisjunction
Nondisjunction results in one
daughter cell with 24 chromosomes
and the other with 22 chromosomes
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
Disjunction
Nondisjunction
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
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
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
Genetic Disorders
These mutations can lead to a number of human
health disorders
Some of these abnormalities are inconvenient, while
others can be lethal
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
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
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
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
Genetic Disorders
Without treatment a child will usually die before age
two
Even with treatment most affected people die before
the age of fifty
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
Genetic Disorders
Approximately 8.5% of people of central and southern
African descent are carriers of the allele
Genetic Disorders
Phenylketonuria (PKU disease) is a disorder in
which the amino acid phenylalanine is not
metabolized due to the lack of an enzyme
Genetic Disorders
PKU disease is the result of a homozygous recessive
genotype that does not produce the enzyme that
converts phenylalanine into tyrosine
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
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
Genetic Disorders
The presence of an extra chromosome (trisomy) or
lack of one (monosomy) accounts for approximately
50% of all spontaneous abortions
Genetic Disorders
Only three autosomal trisomies are survivable:
* trisomy 13 – Patau syndrome
* trisomy 18 – Edward syndrome
* trisomy 21 – Down syndrome
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
Genetic Disorders
Karyotype of Down
syndrome (trisomy
21)
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
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
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
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)
Genetic Disorders
Triplo-X syndrome (XXX) results in a female
phenotype that is usually infertile and may exhibit
some intellectual impairment
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
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