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