Transcript Heredity and Environment

Genetics and Prenatal
Development
• The Beginning of Life
• Conception
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The Human Cell
• The human body is comprised of over 200
different kinds of cells which are the smallest selfcontained structures
– 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
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The Nucleus
• Chromosomes
• Genes
• Deoxyribonucleic acid (DNA)
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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.
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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
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Karyotype
A photograph of a cell’s chromosomes
arranged in pairs according to size
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A Portion of a DNA Molecule
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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
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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
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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
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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
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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.
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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.
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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
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Genes and Protein Synthesis
• A nuclear enzyme attaches to a segment of DNA
causing nucleotide bonds to separate.
• Transcription occurs resulting in messenger RNA
(mRNA).
• Transfer RNA (tRNA) initiates translation into
amino acid.
• Ribosomes move along the RNA bonding amino
acids into polypeptide chains which make
proteins.
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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.
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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.
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Scientific Breakthroughs
Greater insights into disease will be achieved
Cures may be found
Incurable diseases may be prevented
There will be new insights into the
evolutionary origins of humans
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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
merely undesirable ?
What about employers not hiring people with
bad genomes and insurance companies
refusing to insure them?
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Cell Division and Reproduction
When the cell is ready to divide and
reproduce:
the DNA staircase unwinds and the two
long chains separate
each chain attracts new biochemical
material from the cell to synthesize a new
and complementary chain
Ultimately a new cell is formed
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Terms
• Gametes:
Sex cells (ovum or sperm)
• Diploid cells:
Cells having 2 copies of each chromosome
• Haploid gametes:
Gametes having 1 copy of each chromosome
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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)
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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.
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• 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
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• 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
of sperm cells on an
ongoing basis, and they
continue to do so through
out their life span
• In Females
Meiosis begins in the ovaries
before birth and partly
completes all of the
roughly 400,000 ova a
woman will ever have.
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
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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
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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.
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Gregor Mendel (1800s)
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Genotype
The genetic makeup of a
given individual
Recessive Gene
The gene pair that
determines a trait in an
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
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Alleles
A pair of genes, found on corresponding
chromosomes, that affect the same trait
The child might inherit an allele for brown eyes (B)
from the father and an allele for blue eyes (b) from
the mother
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
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Homozygous
Referring to the arrangement
in which the two alleles
for a simple dominantrecessive trait are the
same.
Homozygous Individual
(Eye Color)
Could be BB or bb
Heterozygous
Referring to the arrangement
in which the two alleles
for a simple dominantrecessive trait differ.
Heterozygous Individual
(Eye Color)
Could be Bb, or bB
The chance for having blue
eyes is 25%
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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
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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 “sickleshaped” red blood cells that interfere with oxygen
transport throughout the body.
• They also have normal (dominant) red blood
cells as well.
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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
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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
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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.
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Inherited Disorders
• Sex-Linked Disorders
– Genetic Disorders
– Chromosomal Disorders
• Autosomal Disorders
– Genetic Disorders
– Chromosomal Disorders
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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.
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Genetic Sex-Linked Disorders
1- Color Blindness
Genetic X-linked recessive disorder. Occurs in 1 of
10 males
2- Hemophilia A and B
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.
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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
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Chromosomal Sex-linked
Disorders
3- Superfemale Syndrome (XXX, XXXX, XXXXX)
Occurs in about 1 of 1,000 females. Women appear
normal, but tend to score slightly below average in
intelligence.
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.
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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.
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Autosomal Disorders
• Disorders involving the other 22 pairs of
chromosomes.
• Can result from an extra chromosome or
defective genes
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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.
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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.
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Genetic Autosomal Disorders
4- Phenylketonuria (PKU)
A recessive disorder that occurs in about 1 of
10,000 people. A defective gene on
chromosome 12 is responsible
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.
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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.
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Chromosomal Autosomal
Disorders
Down Syndrome
Occurs in about 1 in 1,000 live births. An
extra chromosome is attached to the 21st
pair. Risk increases with maternal age.
Pregnancies of women over age 35 accounts
for 20% of Down syndrome birth
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Genetics and Environment
Sandra Scarr
• Active genotype-environment effects
• Passive genotype-environment effects
• Evocative genotype-environment effects
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Stop and Discuss
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Gametes
Zygote
Monozygotic twins
Dizygotic twins
Diploid cells
Haploid gametes
Dominant/recessive genes
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Chromosomes
Genes
DNA
Meiosis
Mitosis
Allele
Phenotype/genotype
Homozygous/hetrozygous
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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.
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Family History
Parental Conditions
Neonatal deaths
Malformations
Mental retardation
Congenital anomalies
(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
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Detecting Birth Defects
Amniocentesis
Chronic Villus Sampling
Ultrasound Sonography
Maternal Blood Test
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Genetic Engineering
• Alteration of Human Genes
• 1- Gene Therapy
• 2- Germ-line Genetic Alterations
Germ-line Genetic Intervention
• 3- Genetic Enhancement
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1- Gene Therapy
• Genetic alteration of somatic cells to treat
disease.
• Researchers inject genes that are targeted to
treat a particular disease in to a patient’s
blood stream.
• When the genes arrive at the site of the
defective genes, they produce chemicals
that can treat the problem.
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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.
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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)
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What Do You Think?
Genetic Engineering
Gene Therapy
Germ-Line Genetic
Alterations
Genetic enhancement
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Cloning
• Producing genetic replicas of
the organism
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Stop and Discuss
• In the light of scriptural truth, how ethical
are these issues?
• 1-Amniocentesis
• 2-Chronic villus sampling
• 3-Gene therapy
• 4-Germ-line genetic alteration
• 5-Genetic enhancement
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Stages of Prenatal Period
1- Germinal Stage
(fertilization to 2 weeks)
Blastocyst
Cell Division
Specialized Cells
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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
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3- Fetal Stage
(8 weeks to birth)
Fetus
Increases in size
Proportions similar to adults
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Environmental Influences
1- Habituation
2- Classical Conditioning
3- Operant Conditioning
4- Social Learning
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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)
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Prenatal Care
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Diet
The father’s involvement
Age of mother
Illness of mother
Drug use
Alcohol
Teratogens
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