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