P020A
Developmental Disabilities
Mrs. Elizabeth Keele
Lecture 2
Course Content #7
• Describe the 2 types of mental
retardation that are determined at
the time of conception:
–Chromosomal abnormalities
–Gene determined disorders
Cells • Humans are
made up of cells
Cells
•
•
•
•
Cell
Nucleus
Chromatin
Chromosomes
What is a chromosome?
• Thread like structures
• Inside nucleus of each
cell
What is a chromosome?
• Thread like structures
• Composed of
– Protein
– Deoxyribonucleic acid
(DNA)
– Makes up your genes
Somatic Cells /
Diploid cells
Sex Cells / Haploid Cells
• 23 Pairs of Chromosomes
• Diploid cells contain two
complete sets (2n) of
chromosomes
• Total
• 46
• 1 - Maternal
• 1 - Paternal
• Only have 23 chromosomes
• Sole representative
• sperm / eggs called gametes
Karyotype
2 types of cells:
Somatic cells
Sex cells
• Divide through
mitosis
• Divide through
meiosis
Course Content #9
• Differentiate between meiosis &
mitosis and describe the stages of
meiosis and mitosis
Cell division
Mitosis
• Equal cell division
• Cell duplicates
• Divides one time
• Result
– 2 - Daughter cell
– Identical to mother cell
Meiosis
• Reduction division
• Divides 2 times
• Results
– 4- daughter cells
– Haploid cells (1/2 #
chromosomes)
Mitosis
• Interphase
–Preparatory
–Centrioles
doubles
Mitosis
• Prophase
–Chromosomes
double
Mitosis
• Prometaphase
– Nucleus dissolves
– Polar centrioles
– Microtubules
attach
Mitosis
• Metaphase
–Chromosome
align
Mitosis
• Anaphase
–Chromosomes
separate
Mitosis
• Telophase
–Cell division
begins
Mitosis
• Cytokinesis
–Two daughter
cells
–Identical
• http://www.youtube.co
m/watch?v=cvlpmmvB_
m4
• http://www.youtube.co
m/watch?v=zGVBAHAsj
JM
Cell division
Mitosis
• Equal cell division
• Cell duplicates
• Divides once
• Result
– 2 - Daughter cell
– Identical to mother cell
Meiosis
• Reduction division
• 2 divisions
• Results
– 4- daughter cells
– Haploid cells (1/2 #
chromosomes)
Meiosis
• http://www.youtube.co
m/watch?v=D1_mQS_FZ0
• http://www.youtube.co
m/watch?v=zGVBAHAsj
JM
Meiosis
• Sexual
reproduction
– Form Haploids
• Gamete
– Sperm & eggs
• Reduce the
number of
Chromosomes
Meiosis does two things.
• One diploid cells
produces four
haploid cells.
Why do we need meiosis?
• Reduce #
chromosome
•½
2nd purpose of meiosis
• Genetic diversity
• Accomplished
through
– independent
assortment
– crossing-over
The Stages of Meiosis:
• aka: Reduction Division
Meiosis I : Separates
Homologous Chromosomes
• Interphase
–Each of the
chromosomes replicate
Prophase I
• Chromosome match up with their homologous
pair
• Fasten together (synapsis)
– tetrad
• Crossing over can occur.
– exchange of segments
Metaphase I
• The chromosomes line up at
the equator attached by their
centromeres to spindle fibers
from centrioles.
– Still in homologous pairs
Anaphase I
• spindle move
chromosomes toward the
poles
Telophase I
• End 1st division
• cytoplasm divides
– two daughter cells.
Meiosis II :
2nd division
• Proceeds similar to mitosis
• THERE IS NO INTERPHASE II !
Prophase II
• Spindle
• Move toward equator
Metaphase II
• The chromosomes are positioned
on the metaphase plate in a
mitosis-like fashion
Anaphase II
• Centromeres separate
• Move toward opposite poles
– individual chromosomes
Telophase II and Cytokinesis
• Nuclei form at opposite poles of the cell
and cytokinesis occurs
• After completion of cytokinesis there are
four daughter cells
– All are haploid (n)
One Way Meiosis Makes Lots of
Different Sex Cells (Gametes) –
Independent Assortment
Independent assortment produces 2n distinct
gametes, where n = the number of unique
chromosomes.
In humans, n = 23 and 223 = 6,000,0000.
That’s a lot of diversity by this mechanism alone.
Meiosis – division error
Chromosome pair
Meiosis error - fertilization
• Often occurs
with the 21st
pair
• Trisomic zygote
• Downs
Syndrome
Course Content #14
• Explain how the presence or
absence of a Y chromosome
determines the sex of an
individual.
23 chromosomes
• 22
– Autosomes
• Same male to
female
• Same loci
• Same function
•1
– Sex chromosome
What is a chromosome?
• In cell nucleus
• DNA thread coiled
around proteins
– Histones
• Chromosome
constriction point
– Centromere
How many chromosomes do people
have?
• 23 pairs
• total of 46.
• 22 autosomes
– look the same in both males
and females.
•
1 pair sex chromosomes
– #23
– differ between males and
females.
• Females
– XX
• Males
– one X and one Y
Can changes in the number of
chromosomes affect health and
development?
• Normally
– 23 pairs of chromosomes
– Total 46 chromosomes in
each cell
• Change the # of
chromosomes 
problems with
– growth,
– development,
– function of the body’s
systems.
Chromosomal Abnormalities
Numerical
• Two chromosomes
Abnormalities:
• trisomy
• Missing a
chromosome from
a pair
–monosomy
Chromosomal Abnormalities
Structural Abnormalities:
• Deletions:
– A portion of the
chromosome is
missing or deleted.
• Duplications:
– A portion of the
chromosome is
duplicated
• Translocations:
– A portion of one
chromosome is
transferred to
another
• Inversions:
– A portion of the
chromosome has
broken off
Trisomy
• Extra chromosome
• Down syndrome
– three copies of
chromosome 21
– total of 47
chromosomes per
cell
Monosomy
• Monosomy
– loss of one chromosome
in cells,
• Turner syndrome is a
condition
– Female
– only one copy of the X
chromosome
– total =45 chromosomes
Course Content #10
• Explain the process by which humans
inherit 23 chromosomes from each
parent to create a total compliment of
46 chromosomes (23 pairs).
• Meiosis
• Haploid / gamete
cells due to
reduction have
– ? Chromosomes
– 23
• Each chromosome is
the sole
representative of the
original 23 pairs
During fertilization…
• sperm + egg = Zygote
• 23 + 23 = 46
Course Content #13
• Explain the relationship between
the following nitrogenous bases in
forming an individuals genetic
code:
– Adenine
– Thymine
– Guanine
– Cytosine
Course Content #12
• Define and explain the relationship
between DNA & RNA
• http://www.youtube.com/watch?v=zw
ibgNGe4aY
DNA
• Deoxyribonucleic Acid
• Carrier genetic code
• 4 nitrogenous bases
–
–
–
–
Adenine
Guanine
Cytosine
Thymine
RNA
• RNA
– interprets the
code
–Messenger
• DNA 
• RNA 
– Out of nucleus
– Cytoplasm
– + ribosome (factory)
•
•
•
•
•
•
Amino Acids (20)
Proteins 
Living cells 
Tissues 
Organs 
Living organism
Course Content #11
• Describe the role & function of
– Operator genes
– Structural genes
– Regulator genes
What is a gene?
• Functional unit of
heredity.
• Made up of DNA
What is a chromosome
• DNA and histone
proteins are
packaged into
structures called
chromosomes.
How many chromosomes do people
have?
• 23 pairs
• 46 total
What are proteins and what do they
do?
• Large, complex
molecules
• Made up of smaller
units called amino acids
• There are 20 different
types of amino acids
that can be combined
to make a protein.
Can genes be turned on and off in
cells?
• Yes
• Gene regulation.
types of genes
• Structural gene
– Determines the type of
protein to be synthesized
• Operator
– Turns protein synthesis on
and off in structural gene
• Regulator
– Suppresses or activated
operator and structural
genes
What kind of gene mutations are
possible?
• Altered DNA
sequence
• http://ghr.nlm.nih.gov/
handbook/mutationsan
ddisorders/possiblemut
ations
What is a gene?
• Most basic unit of
heredity
• Particular nucleic
acid sequence
within DNA
molecule
• Carriers of
biochemical
information to the
cell instructing it
what kinds of
protein it will
produce
Course Content #8
• Identify the trait carry elements of
heredity
Course Content #16
• Differentiate between autosomal
dominant inheritance and
autosomal recessive inheritance
Gregor Mendel
• 1822 -1884
• Austrian Monk
• Experimented with
pea plants
• Identified 4 basic
patterns of
inheritance
Mendelian Patterns of Inheritance
1. Autosomal Recessive inheritance
2. Autosomal Dominant Inheritance
3. X-links Recessive inheritance
4. X-Links Dominant inheritance
Punnett Squares
• Recessive genes
– Blue eyes - b
• Dominant genes
– Brown eyes – B
• BB = Brown
• Bb = Brown
• bb = blue
B
B
B
BB
BB
B
BB
BB
Punnett Squares
• Recessive genes
– Blue eyes - b
• Dominant genes
– Brown eyes – B
• BB = Brown
• Bb = Brown
• bb = blue
B
b
B
BB
Bb
B
BB
Bb
Punnett Squares
• Recessive genes
– Blue eyes - b
• Dominant genes
– Brown eyes – B
• BB = Brown
• Bb = Brown
• bb = blue
B
b
B
BB
Bb
b
Bb
bb
Punnett Squares
• Recessive genes
– Blue eyes - b
• Dominant genes
– Brown eyes – B
• BB = Brown
• Bb = Brown
• bb = blue
B
B
B
BB
BB
b
BB
BB
Autosomal Recessive Inheritance
An autosomal recessive disorder means
two copies of an abnormal gene must
be present in order for the disease or
trait to develop.
-ex: Tay Sachs, PKU, Galactosemia
Autosomal Recessive
Autosomal Recessive
Autosomal Dominant Inheritance
-refers to inheritance of a dominant mutant gene
carried on an autosome
-has one good gene, but not enough to make body
work or grow correctly
-person will be affected
-mutated gene dominates the correct gene copy
-ex: Neurofibromatosis, Tuberous Sclerosis
Autosomal Dominant
Autosomal Dominant
X-linked Recessive Inheritance
-refers to inheritance of mutated gene carried
on X chromosome
-mutations on X chromosome are most
commonly recessive
-since females have two X, can be a carrier, but
not generally affected
Ex: Lesch-Nyhan, one type of Fragile X
X-linked Recessive
X-linked Recessive
X-linked Recessive Inheritance
(con’t)
-in male offspring: 1:2 chance of being
affected; males can’t be carriers
-in females: 1:2 chance of being a carrier,
generally unaffected;
X-linked Dominant Inheritance
-refers to inheritance of a mutant gene carried
on an X chromosome
-not enough, or no, correct gene product to
work or grow properly
-person is affected
-mutated gene copy dominates the correct gene
copy
-ex: Muscular Dystrophy
X-linked Dominant
X-linked Dominant