P020ADevelopmental Disabilities
Mrs. Elizabeth KeeleLecture 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
• 23 Pairs of Chromosomes• Diploid cells contain two
complete sets (2n) of chromosomes
• Total• 46• 1 - Maternal• 1 - Paternal
Sex Cells / Haploid Cells
• Only have 23 chromosomes• Sole representative• sperm / eggs called gametes
Karyotype
2 types of cells:
Somatic cells• Divide through
mitosis
Sex cells• 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.com/watch?v=cvlpmmvB_m4
• http://www.youtube.com/watch?v=zGVBAHAsjJM
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.com/watch?v=D1_-mQS_FZ0
• http://www.youtube.com/watch?v=zGVBAHAsjJM
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.
That’s a lot of diversity by this mechanism alone.
In humans, n = 23 and 223 = 6,000,0000.
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 Abnormalities:• Missing a
chromosome from a pair –monosomy
• Two chromosomes• trisomy
Chromosomal AbnormalitiesStructural 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=zwibgNGe4aY
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/mutationsanddisorders/possiblemutations
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 inheritance2. Autosomal Dominant Inheritance3. X-links Recessive inheritance4. X-Links Dominant inheritance
Punnett Squares
• Recessive genes–Blue eyes - b
• Dominant genes–Brown eyes – B
• BB = Brown• Bb = Brown• bb = blue
B BB BB BB
B BB BB
Punnett Squares
• Recessive genes–Blue eyes - b
• Dominant genes–Brown eyes – B
• BB = Brown• Bb = Brown• bb = blue
B bB BB Bb
B BB Bb
Punnett Squares
• Recessive genes–Blue eyes - b
• Dominant genes–Brown eyes – B
• BB = Brown• Bb = Brown• bb = blue
B bB 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