Heredity and environment

The Human Cell • The human body is comprised of over 200 different kinds of cells which are the smallest contained structures self-– Cell membrane: the outside layer of the cell – Cytop

2

3

4

5

6

7

The Human Cell

• The human body is comprised of over 200

different kinds of cells which are the smallest contained structures

self-– Cell membrane: the outside layer of the cell

– Cytoplasm: is comprised of specialized structures

– Mitochondria: are the powerhouses that process

nutrients and provide the cell’s energy

– Endoplasmic reticulum, Golgi apparatus, and

ribosomes: produce proteins

– Neucleus: The inner part of the cell

Chromosomes

• Rod shaped structures found in the center of

the nucleus of every cell in the body.

• Each sperm and each ovum contains 23

chromosomes.

• The chromosomes contain the DNA and genes.

• The fertilized egg (zygote) and all the body cells that develop from it (except the sperm cells and the ova) contain 46 chromosomes.

Chromosomes

• 22 of the pairs are called autosomes and are

numbered from largest to smallest

• The autosomes are not involved in

determining sex

• The 23rd pair are the sex chromosomes:

– XX in females

– XY in males

Karyotype

A photograph of a cell’s chromosomes arranged in pairs according to size

A Portion of a DNA Molecule

DNA Deoxyribonucleic Acid

Nucleotides are the building blocks of DNA

They contain 4 nitrogen-carbon-hydrogen

basis that bond to form specific pairs:

adenine can only pair with thymine cytosine can only pair with guanine

The combination of base pairs cannot vary

DNA What Can Vary:

1- Which side of the ladder each base comes from

2- The order in which the base pairs occur along the

ladder

3- The overall number of base pairs

These variations account for differences between

species.

All organisms use just these 4 bases, but with

different numbers and arrangements

DNA

There are 3.12 billion base pairs in human DNA

The DNA in each normal human being is about

99.9% the same as every other normal human

being

Only 1% accounts for the biological contribution to

all our individual differences in physical and

psychological characteristics

DNA Single Nucleotide Polymorphisms

(SNPs)

• A large portion of the 1% individual

difference takes the form of single

nucleotide polymorphisms

• SNPs (snips) are nucleotide variations that occur on average about every 1,250 base pairs

DNA

• They determine the nature of each cell in

the body and how it will function.

• At each level of the spiral or rungs of the

ladder are particular chemical pairs The arrangement of these pairs along the

DNA molecule determines which kind of proteins will be formed in the cell.

Genes

• The basic unit of genetic information

• They determine the nature and the function

of the cell

• The human genes (about 120,000) are

referred to as the human genome.

• A genome is the full set of genes in each cell of an organism

Proteins

Proteins are molecules that perform an array

of crucial functions in the human body:

Enzymes: break down and altar

biochemicals

Hemoglobin: binds with oxygen allowing it

to be transported to cells throughout the body

Collagen: in bones and connective tissues

Hormones: regulate physical growth

Genes and Protein Synthesis

• A nuclear enzyme attaches to a segment of DNA

causing nucleotide bonds to separate.

• Transcription occurs resulting in messenger RNA

22

23

24

25

1- Transcription: the transfer of information

from an DNA molecule into an RNA

(ribonucleic acid) molecule

2- Messenger RNA (mRNA): a type of RNA

synthesized from DNA; attaches to

ribosomes to specify the sequence of amino acids that form proteins

3- Translation: the transfer of information

from an RNA molecule into a Polypeptide,

in which language of the nucleic acids is

translated into that of amino acids

Celera Genomics The Human Genome Project

• In June 26, 2000, they both made an

announcement that the “correct alphabetical order of the 3.12 billion letters” of the

human genome had been mapped

• It will be many years before the incredibly complex functions of the genome in making and maintaining a living human being are fully understood

Scientific Breakthroughs

Greater insights into disease will be achievedCures may be found

Incurable diseases may be prevented

There will be new insights into the

evolutionary origins of humans

Controversial Issues

Will it be ethical for parents to have their

children screened prior to birth and decide not to have a child with a genome that is

Cell Division and Reproduction

When the cell is ready to divide and

Ultimately a new cell is formed

Meiosis

• Meiosis takes place in the testicles and ovaries.

• A diploid cell (having 2 copies of each

chromosome) undergoes a special form of cell

division to create haploid gametes (having 1 copy

of each chromosome).

• An egg and a sperm fuse together to form a new diploid cell called zygote (a process called

fertilization)

33

Mitosis

• In the first step of mitosis, all chromosomes are

copied , so that instead of 2 copies, the cell briefly has 4 copies of each chromosome.

• Shortly afterwards, the cell divides in half,

resulting in two cells each has a complete copy of the genetic information.

• These cells grow larger and eventually undergo mitosis.

35

36

• Mitosis: each cell divides and duplicates

itself exactly

• Meiosis: How reproductive cells (ova and

sperm) are produced

• Results in gametes, cells that contain only

23 chromosomes

• In Males

Meiosis takes place in the

testes and involves 2

rounds of division

Results in 4 fertile sperm

cells

By puberty, males begin

producing many thousands

It occurs in a two-stage process

Results in one relatively big ovum and 2 small polar bodies that aren’t capable

of being fertilized

Mutation

A mutation is an alteration in the DNA that

typically occurs during mitosis and meiosis

In most cases mutation is maladaptive and the new cell simply dies or repairs and

eliminates the mutation

A small number of of mutations are viable –

the cell survives

Mutation

In mitotic cell division, if a viable mutation occurs

early in development, it will then be passed along

to all cells replicated.

In meiotic cell division, mutation only affects the

ensuing gametes and stops there, Unless a mutated gamete happens to be involved in producing

offspring – in which case the mutation can be

passed along to the next generation and beyond

Gregor Mendel (1800s)

individual only if the

other member of that

pair is also recessive

Phenotype

The traits that are expressed in the individual

Dominant Gene

One gene of a gene pair that will cause a

particular trait to be expressed

43

44

45

46

The child’s genotype for eye color would be Bb.

What actual eye color will the child display?

The allele for brown eyes is dominant (B)

The allele for blue eyes is recessive (b).

The dominant trait will be expressed as the

phenotype

Homozygous

Referring to the arrangement

in which the two alleles

for a simple dominant-

recessive trait are the

Referring to the arrangement

in which the two alleles for a simple dominant- recessive trait differ.

Heterozygous Individual (Eye Color)

Could be Bb, or bB The chance for having blue eyes is 25%

Incomplete Dominance

Where people with a single recessive gene for

a trait show some of the trait along with

other normal manifestations

Example:

Sickle-cell anemia

Sickle-Cell Anemia

• Occurs at its highest rate in individuals of black African ancestry.

• People with a single recessive gene for the trait

have a marked percentage of abnormal

“sickle-shaped” red blood cells that interfere with oxygen transport throughout the body.

• They also have normal (dominant) red blood

cells as well.

Sickle-Cell Anemia

• The sickle cells are resistant to malarial infection,

so those individuals with the trail would have

survived long enough to have children in areas of the world where mosquito-borne malaria is highly prevalent.

• Sickle-cell carriers experience pain in the joints,

blood clotting, swelling and infections under

conditions of oxygen shortage.

• It occurs when a person inherits both recessive

alleles

Codominance

Where neither the dominant nor recessive

allele is dominant and the resulting

phenotype is a blend of the two

Example:

If an individual gets an allele for each blood types A and B, the result is type AB blood type

Polygenic Inheritance

The overall system of interactions among

genes and gene pairs

More complex traits do not result from the

alleles of a single gene pair, but rather from

a combination of many gene pairs

In determining height, several gene pairs

combine to create people with taller or

shorter phenotype

Sex-Linked Disorders

• Involve the sex chromosome # 23

• Occur via dominant-recessive patterns

• A recessive gene on the X chromosome is more likely to be expressed as the

phenotype males because the Y

chromosome has no allele that might

contract the gene

Recessive disorders that affect 1 of 5,000 males

These interfere with normal blood clotting and

occur at different loci (the position on a

chromosome occupied by a particular gene) on the

X chromosome

Chromosomal Sex-Linked

Disorders

1- Fragile X Syndrome

Occurs in about 1 of 1,200 males and 1 of

2,500 females Results from a breakage of the tip of an X chromosome

2- Klinefelter Syndrome (XXY, XXXY, XXXXY)

Occurs in about 1 of 1,000 males It is caused

by an extra X chromosome

4- Supermale Syndrome (XYY, XYYY, XYYYY)

Occurs in about 1 0f 1,000 males The men tend to

be taller than average, with a greater incidence of acne and minor skeletal abnormalities.

Chromosomal Sex-linked

Disorders

5- Turner’s Syndrome (XO)

Occurs in about 1 of 10,000 females One of the X chromosomes is either missing or

inactive These women have immature

female appearance, do not develop

secondary sex characteristics, and lack

internal reproductive organs

Genetic Autosomnal Disorders

1- Angelman’s syndrome

Occurs in about 1 of 10,000 to 15,000 people It is

determined by a set of mutated genes on

chromosome 15.

2- Cystic Fibrosis

A recessive disorder that occurs in about 1 of 2,5000 people of white European ancestry Related to a

mutated gene on chromosome 17 Characterized

by excessive secretion of the mucus in the body.

Genetic Autosomal Disorders

3- Huntington Disease

A dominant disorder that occurs in about 1 of

10,000 people A dominant gene on

chromosome 4 is responsible

It causes degeneration of neurons producing dementia, and random jerking movements

5- Prader Willi Syndrome

A recessive disorder that occurs in 1 of

10,000 to 15,000 people It is determined by

a set of mutated genes on chromosome 15

Genetic Autosomnal Disorders

6- Sickle-Cell Anemia

Occurs in about 1 of 12 U.S blacks The defective

gene on chromosome 11 is responsible.

7- Tay-sachs Disease

A recessive disorder that occurs in about 1 of 5,000

people of European Ashkenazi Jewish ancestry

Defective gene on chromosome 15 is

responsible.

Chromosomal Autosomal

Disorders

Down Syndrome

Occurs in about 1 in 1,000 live births An

extra chromosome is attached to the 21 st

pair Risk increases with maternal age

Pregnancies of women over age 35 accounts for 20% of Down syndrome birth

Genetics and Environment

Sandra Scarr

• Active genotype-environment effects

• Passive genotype-environment effects

• Evocative genotype-environment effects

67

68

69

Genetic Counseling

• Can help couples obtain valuable

information about the parents’ genetic

makeup

• It can help potential parents to evaluate

genetic risk factors in childbearing and

enable them to make intelligent decisions

• It includes analysis of parental medical

records and family histories to construct a family pedigree

(e.g club feet)

Diseases that run in

families

Inability to thrive

Genetic or chromosomal abnormality

Infertility Mother/father’s age Stillbirths

Ethnic background Exposure to toxic agents Cancer

74

75

Genetic Engineering

• Alteration of Human Genes

• 1- Gene Therapy

• 2- Germ-line Genetic Alterations

Germ-line Genetic Intervention

• 3- Genetic Enhancement

• When the genes arrive at the site of the

defective genes, they produce chemicals

that can treat the problem

2-Germ-line Genetic Alteration

• Can correct problems for unborn individuals and

future generations.

• It targets the genes in the reproductive cells – the egg

and the sperm that combine the DNA to conceive a new human.

• Scientist might detect defective cells soon after

conception, removing them from the mother and

placing them in a test-tube culture.

• Gene therapy could be employed to correct the defects

in the cells.

• The result could be cloning Parents could some day

customize their children.

3-Genetic Enhancement

• Non therapeutic genetic alteration

• An attempt to enhance an already healthy genetic makeup by inserting a gene for

improvement (e.g height, intelligence, eye color)

What Do You Think?

Genetic Engineering Gene Therapy Germ-Line Genetic

Alterations Genetic enhancement

Cloning

• Producing genetic replicas of

the organism

Stop and Discuss

• In the light of scriptural truth, how ethical are these issues?

Stages of Prenatal Period

1- Germinal Stage (fertilization to 2 weeks)

Blastocyst

Cell Division

Specialized Cells

2- Embryonic Stage

(2 weeks to 8 weeks)

• 1-Ectoderm (outer layer)

Skin, teeth, hair, sense organs, brain, spinal cord

• 2-Endoderm (inner layer)

Digestive system, pancreas, respiratory

system

• 3-Mesoderm (in between both)

Muscles, bones, blood, circulatory system

86

Sociocultural Influences

Paul Blates (87, 88)

• Normative Age-Graded Influence

The biological and social changes (e.g aging, entering school, marriage)

• Normative History-Graded Influence

Historical events (e.g wars, depression)

• Nonnormative Influences

Individual environmental factors (e.g

divorce, unemployment)