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NOTES ON GENERAL BIOLOGY

MODULE ONE
BY KENNETH AWAH. M

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ANIMAL CELL ; STRUCTURE

THE CELL, STRUCTURE AND FUNCTIONS

THE CELL, STRUCTURE AND FUNCTIONS

The cell membrane

1. It is made up of lipids and proteins and is semi-permeable, allowing some substances to pass
through it and excluding others.

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2. its permeability varies because it contains numerous regulated ion channels and other
trans-port proteins that can change the amounts of substances moving across it.
3. The plasma membrane contains phospholipids in its by layer (phosphatidylcholine and
phosphatidylethanolamine)

4. The plasma membrane is both hydrophilic and hydrophobic (water soluble; polar head
and fat soluble non-polar head).
5. The hydrophilic ends are exposed to the water-like cytoplasmic environment around the cell and the
hydrophobic ends are exposed to the water poor ends of the interior membrane

6. FUNCTIONS OF CELLULAR ORGANELLES

The nucleus is centrally located and controls the metabolic activity of the cell as well as
structural characteristics. The chromosomes are responsible for this

The nucleolus is found in the center of the nucleus; its main function is the production of
ribonucleic protein
SMOOTH ENDOPLASMIC RETICULUM

Have no ribosomes; specialized in various lipid synthesis.

ROUGH ENDOPLASMIC RETICULUM

Studded with Ribosomes: synthesizes proteins

GOLGI APPARATUS

The Golgi apparatus contains smaller sacs and responsible for processing, packaging and distribution of
molecules

1. The vacuole and vesicle are made up of membranous sacs in which substances are stored.
2. Lysozome is a sac-like structure containing digestive enzymes responsible for cellular
digestion.

PEROXISOMES: are surrounded by amembrane, and contain enzymes that can either
produceH2O2(oxidases) or break it down (catalases). Proteins are directed to the peroxisome
with the help of peroxins
1. The mitochondrion takes care of cellular respiration.
2. Cilia and flagella facilitate cellular movement.
3. Centriole forms basal bodies of the cell

4. The centrosomes are microtubule-organizing centers (MTOCs).

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5. When a cell divides, the centrosomes duplicate themselves, and the pairs move apart to the poles of the mitotic
spindle, where they monitor the steps in cell division.

MOLECULAR MOVEMENTACROSS THE PLASMA MEMBRANE

1. DIFFUSION: Diffusionis the random movement of molecules from the area of higher concentration
to the area of lower concentration until they are equally distributed.

2. Lipid soluble molecules such as alcohol and gases can diffuse through the plasma membrane

3. Consider the diffusion of oxygen and carbon dioxide across the membrane of the alveoli as an
example.

4. OSMOSIS: This is the diffusion of water across a plasma membrane. It occurs

whenever an unequal concentration of water exists on either side of a selectively permeable
membrane

1. Body fluids are isotonic to cells —that is, there is an equal concentration of solutes
(substances) and solvent (water) on both sides of the plasma membrane.

2. Tonicity is the degree to which a solution's concentration of solute versus water causes water to move into
or out of cells.

3. Solutions (solute plus solvent) that cause cells to swell or even to burst due to an intake of water are said
to be hypo-tonic solutions. If red blood cells are placed in a hypotonic solution, which has a higher
concentration of water (lower concentration of solute) than do the cells, water enters the cells and they
swell to bursting.

4. Cell disruption is called lysis; red blood cell disruption therefore, is haemolysis

5. Solutions that cause cells to shrink or to shrivel due to a loss of water are said to be hypertonic
solutions. If red blood cells are placed in a hypertonic solution, which has a lower concentration of water
(higher concentration of solute than do the cells), water

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leaves the cells and they shrink.The term crenation refers to red blood cells in this condition

6. These changes have occurred due to osmotic pressure. This is the force exerted on a
selectively permeable membrane because water has moved from an area of higher
concentration to an area of lower concentration (higher concentration of solute).

7. FILTRATION is the process of passive diffusion across a plasma membrane from an area of higher
concentration to that of lower concentration. During filtration, larger molecules do not pass through
the semi-permeable membrane but, smaller ones do.

8. When solutes are carried across a plasma membrane by a protein, this is referred to as
transportation by carrier; or facilitated transport.

9. This movement is down the concentration gradient and requires no energy from the cell.

10. During active transportation, the movement is in the opposite direction; from area of lower
concentration to that of higher concentration.

11. Cells involved in active transport have a large number of mitochondria near the plasma
membrane for the break down of Adenosine Triphosphate (ATP) to release energy.

12. The Na+ pump moves sodium ions(Na+) potassium ions(K+) into and out of the cell
respectively.

13. Endocytosis and Exocytosis: absorption of substances from the outside of the cell into the
cytoplasmic medium by formation of vessicles is called endocytosis.

14. a portion of the plasma membrane envaginates to envelope a substance. The membrane breaks
off to form an intracellular vessicle. Digestion may be required before vessicles cross a
membrane.This is also called phagocytosis

15. Exocytosis is the process in which the vesicle fuses with the plasma membrane as secretion
occurs (example: secretion of insulin)

Summary of molecular movements across the plasma membrane

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THE CELL CYCLE

1. The set of stages between cell division and the time the daughter cell divides is called the cell cycle.

2. A cell cycle is controlled by a signal; this is a molecule that triggers or inhibits a metabolic
event In a cell. These signals control cellular events, the order, and the completion of the cellular
cycle. However, not all cells go through the cell cycle; muscle and nerve cells are specialized cells; they
do not go through the cell cycle.

3. STAGES OF CELL CYCLE

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1. The cell cycle consists of interphase, during which cellular components duplicate, and a mitotic
stage, during which the cell divides. Interphase consists of two so-called “growth”
phases (G1and G2) and a DNA synthesis (S) phase. The mitotic stage consists of the phases
noted plus cytokinesis.

The internships are further described in detail

1. . During the interphase stage, the cell carries out regular activities; it does not divide. If the cell
will divide, and completes the cycle, it gets ready to do so and if not, it becomes a specialized
cell. The interphase is sub-divided into the G1 phase, Sphase and G2 phase.

2. During the G1 phase, cell organelles such as the mitochondria and ribosomes and other materials
used in DNA synthesis are doubled

3. The S phase is comprised of DNA replication; this results in chromosome duplication.ie, at the
beginning of the S phase, each DNA consists of a double helix otherwise called chromatid.
At the end of this phase, each chromosome has two identical double helix
molecules – two sister chromatids.

4. In the G2 phase, protein synthesis as that found in microtubules, to assist cell division
occurs;

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5. Chromatin(nuclear genetic material) condenses and chromosomes become visible.

6. Following the interphase, the cell enters the M-stage or mitotic activity in which daughter
chromosomes distribute to two nuclei; cytoplasmic material divides in a process called
cytokinesis.

7. When cytokinesis is complete, two daughter cells are present.

KEY POINTS ABOUT INTRPHASE

1. Replication and protein synthesis occur during interphase.

2. Replication is the production of exact copy of DNA

3. Proteinsynthesis requires transcription and translation.

4. Transcription is the joining of RNA neoclutide strand to DNA neoclutide strand by aid of an emzyme
called RNA polymerase, resulting in an mRNA molecule formation.

5. The formation of mRNA results in a DNA complementary sequence, three of which are called
the condon,.

6. Translation requires many enzymes and two other types of RNA; tRNA and rRNA
(transfer RNA and ribosomal RNA).

7. tRNA brings amino acids to the ribosomes.

8. The mitotic stage consists of mitosis and cytokinesis (cell division and cytoplasmic division).

9. At the end of interphase, double centrioles and chromosomes become visible, duplocates
having two chromatids held together by a centromere.

10. Mitosis is divided into four phases namely; prophase, metaphase, anaphase and
telophase.

11. The prophase is the phase that indicates that the cell is about to divide: two pairs of centrioles move
away from each other outside the nucleus in opposite directions.

12. Spindle fibers appear between separating centrioles while the nuclear envelope starts fragmenting
while the nucleolus starts to disappear.

KEY POINTS ABOUT MITOSIS

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1. During metaphse, nuclear even lope fragments.

Chromosomes move to equator each with sister chromatid

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KEY POINTS ABOUT MITOSIS

ÿSister chromatids separate with each

chromatid with each called chromosome

ÿEach cell receives copy of each type

of chromosome with same type of
genes
ÿDaughter chromosomes move opposite pole.

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KEY POINTS ABOUT MITOSIS

ÿSister chromatids separate with

each chromatid with each called
chromosome
ÿEach cell receives copy of each type of
chromosome with same type of genes

ÿDaughter chromosomes move opposite

pole.

KEY POINTS ABOUT MITOSIS

ÿChromosomes become
chromatids
ÿNuclei appear and nuclear
envelope reassemble
ÿTwo daughter nuclei appear
ÿCytokinesis occur and
cleavage furrow forms.
ÿActin filaments form
contractile rings to separate cells.

ÿPlasma membrane forms round

each cell.
ÿDue to mitosis, each human cell is
identical and growth and repair is
enhanced.

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EARLY INTERPHASE

SECTION 2: FABRICS

1. A tissue is a group of similar cells that work together to perform a specific structural or physiological role in an
organ.

2. There are four main types of tissue namely, epithelial, connective, nervous and muscular tissues

3. Epithelial tissue is composed of closely spaced cells that cover surfaces, form glands and serve for protection,
secretion and absorption. Examples include: epidermis, inner lining of the digestive tract, liver and other
glands.

4. Connective tissue contains more matrix than cell volume often specialized to support, bind together and
protect other organs. For example, tendon, cartilage and bone and blood.

5. Nervous tissue contain excitable cells specialized for rapid transmission of coded information to other
cells. Examplebrain, spinal cord and nerves.

6. Muscular tissue is made up of elongated excitable cells specialized in traction for example: skeletal,
cardiac and smooth muscles (walls of viscera)

EPITHELIAL TISSUE

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SIMPLE EPITHELIA

1. Three types of simple epithelia are named for the shapes of their cells: simple squamous (thin scaly
cells), simple cuboidal (square or round cells), and simple columnar.

2. thefourthtype,pseudo-stratified columnar,not all cells reach the free surface; the shorter cells
are covered over by the taller ones.

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SIMPLE SQUAMOUS EPITHELIUM

Simple squamous epithelium is
composed of a single layer of
flattened cells, It is found in
areas where secretion,
absorption, and filtration occur.
For example, simple squamous
epithelium lines the lungs where
oxygen and carbon dioxide are
exchanged, and it lines the walls
of capillaries, where nutrients
and wastes are ex-changed.

Stratifiedsquamousepithelium

1. This type has two sub types of squamous tissue; cuboidal and columnal layers; these are
found in the deeper layers while shaping. the outer layer is squamous in shape.

2. Keratin (a protein) strengthens the squamous layer of the skin.

stratified squamous epithelium is found lining the various orifices of the body.

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SIMPLE CUBOIDAL EPITHELIUM

Lines kidney tubules;
ducts of many acorns;
covers surface of
ovary nucleus. Main
function of Simple
Cuboidal Epithelium
are:Secretion and
absorption

SIMPLE COLUMNAR EPITHELIUM

Lines gastrointestinal
tract; the ducts of many glands
mucus goblet cell nucleus

Function:Protection;
secretion; absorption

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Pseudo stratified ciliated columnar

epithelium

Location:lines
respiratory tract; parts of the
reproductive
leaflets
Function:Protection;
secretion; movement of
mucus and sex cells

TransitionalEpithelium

1. This implies changeability, and this tissue changes in response to tension. It forms the lining of the urinary
bladder, the ureters, and part of the urethra—organs that may need to stretch.

When the walls of the bladder are relaxed, the transitional epithelium consists of several layers of cuboidal cells. When
the bladder is distended with urine, the epithelium stretches, and the outer cells take on a squamous appearance

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Connective Tissue
Connective tissue binds structures together,
provides support and protection, fills
spaces, produces blood cells, and stores
fat. The body uses this stored fat for
energy, insulation, and organ protection

. connective tissue cells are widely

separated by an extracellular matrix
composed of an organic ground
substance that contains
fibers;collagen,elastin and reticular fibers

TransitionalEpithelium

1. This implies changeability, and this tissue changes in response to tension. It forms the lining of the urinary
bladder, the ureters, and part of the urethra—organs that may need to stretch.

2. When the walls of the bladder are relaxed, the transitional epithelium consists of several layers of
cuboidal cells. When the bladder is distended with urine, the epithelium stretches, and the outer
cells take on a squamous appearance.

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ADIPOSE TISSUE

Rental:
Beneath the skin; around
the kidneys and heart; in
the breast ;nucleus of
adipose cell plasma
membrane fat Adipose
Tissue
Function:
Insulation; fat storage

Classification of connective tissue

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MUSCLE TISSUE

1. Muscle tissue is classified either as skeletal, cardiac or smooth.

2. Contractile tissue contains actin and myosin (protein filaments) whose interaction counts for movement.

3. Skeletal muscles, also called voluntary muscles; its contraction result in movement of body parts (arms,
legs)

4. Voluntary muscle contraction is short but forceful

5. These are striated due to the placement of myosin and actin bands.

6. Smooth muscle tissue (visceral) is involuntary.

7. Its placement of actin and myosin does not result in cross-striation.

8. These are spindle-shaped cells with an irregular nucleic pattern.

9. They are found in the walls of hollow viscera (intestine, stomach, uterus, urinary bladder and blood vessels)

10. Contractility is slow but last longer, rhythmic and wavelike (as in the stomach) and controlled by the
nervous system.

11. Contractility of smooth muscle of blood vessels result in vaso-constriction and regulation of blood
pressure.

Cardiac Muscle

1. Cardiac muscle is found only in the heart.

2. Its contraction accounts for the pumping action of the heart and heart beat. It has mixed properties (like skeletal
and smooth muscle): strong contractions, involuntary and controlled by nervous system and rhythmic

3. Has striations and centrally placed single nucleus. Are bound by intercarlated disk for easy transmission of
contractile stimuli.

NERVOUS TISSUE

1. This is found in the brain and spinal chord. Its specialized cells are called neurons.

2. A neuron has three parts: dendrites, cell body and axon.

3. A dendrite collects signals that may result in a nerve impulse

4. the cell body contains the nucleus and most of the cytoplasm of the neuron;

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5. and the axon conducts nerve impulses from sense organs to the spinal cord and brain, where the
phenomenon called sensation occurs. They also conduct nerve impulses away from the spinal cord
and brain to the muscles, causing the muscles to contract. In addition to neurons, nervous
tissue contains neuroglia.

A neuron

NEUROGLIA

1. These cells occupy more than half of the brain`s volume.

2. The primary function is to support and nourish neurons. There are three types of neuroglia
found in the brain; microglia, astrocytes, and oligodendrocytes.

3. Microglia, in addition to supporting neurons, engulf bacterial and cellular debris.

4. Astrocytes provide nutrients to neurons and produce a hormone known as glia-derived growth factor.

5. Oligodendrocytes form myelin, a protective layer of fatty insulation.

SCHWAN CELLS

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1. Schwann cells are the type of neuroglia that encircles all long nerve fibers located outside the brain or
spinal cord.

2. Each Schwann cell circles only a small section of a nerve fiber. The gaps between Schwann cells are
called nodes of Ranvier.

3. Collectively, the Schwann cells provide nerve fibers with a myelin sheath interrupted by the nodes.

4. The myelin sheath speeds conduction because the nerve impulse jumps from node to node. Because the
myelin sheath is white, all nerve fibers appear white.

MEMBRANES

1. Membranes line the internal spaces of organs and tubes open to the outside.
Theseinclude mucus membranes, serous membranes, synovial, meninges and cutaneous membranes

MEMBRANES, LOCATION AND

FUNCTIONS
MEMBRANE RENTAL FUNCTIONMU
MUCUS MEMBRANES INTERNAL WALLS OF SECRET MUCUS THAT
ORGANS OF PROTECT WALLS OF
DIGESTIVE, RESPIRATORY, UR INTERNALORGANS
INARY AND REPRODUCTIVE AGAINST BACTERIAL AND
SYSTEMS VIRAL IVATION
SEROUS MEMBRANES LINE CAVITIES OF THE LUBRICATE
ABDOMINO-PELVIC CAVITIES,PREVENT
CAVITIES CAVITIES FROM INFECTION
SYNOVIAL MEMBRANES FREELY MOVABLE SEALS LUBRICATE ENDS OF BONES
MENINGES FOUND IN THE PROTECTIVE COVERING OF
POSTERIORC AVITIES BRAIN AND SPINAL CORD
CutaneousMembrane SKIN FORMS OUTER COVERING
OF THE BODY.

SECTION 3: GENETICS

1. The study of the transmission of biological material from one generation to the other and its consequences is
referred to as genetics.

2. Hereditary is the transmission of genetic characteristics from parent to offspring.

3. Several traits and diseases are transmitted in like manner; for example, baldness, blood types, color
blindness, heamophilia, sickle cell anemia(anaemia) height etc.

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BASIC PRINCIPLES OF NORMAL HEREDITARY

1. KARYOTYPE: is a chart of the chromosomes isolated from a cell at metaphase, arranged in order by size
and structure. It reveals that most human cells, with the exception of germ cells chromosomes). Two
chromosomes, contain 23 pairs of similar-looking chromosomes (except for X and Y
in each pair are called homologous chromosomes (looking alike)

In the homologous pair, one chromosome is inherited from the mother and the other from the father.

Two chromosomes, designated x and y are called sex chromosomes and the other 22 pairs are called
autosomes.

A female has a homologous pair of X chromosomes where as the male has one X chromosome and a
much smaller y chromosome.

The sperm and egg cells prior to fertilization are called germ cells; each has 23 pairs of homologous
chromosomes.

The shape of the outer ear presents an example of dominant and recessive genetic effects. When the
ears are developing in a fetus, a “death signal” is often activated in cells that attach the earlobe to the side
of the head. These cells die, causing the earlobe to separate from the head. A person will then have “detached
earlobes

This occurs in people who have either one or two copies of a dominant allele which we will denote D.

If both homologous chromosomes have the recessive version of this gene, the cell suicide program is not
activated, and the earlobes remain attached

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BASIC PRINCIPLES OF NORMAL

HEREDITARY
Genetics of Attached and Detached
Earlobes.(a)
Detached earlobes occur if even one allele
of the pair is dominant

(D).Attached earlobes occur only when both

alleles are recessive (d). (b)A Punnett
square shows why
such a trait can “skip a generation.”

Both parents in this case have heterozygous

genotypes (Dd) and detached earlobes,

but there is one in four

chance that their offspring could have
attached earlobes.
Each parent is a carrier for attached
earlobes.

BASIC PRINCIPLES OF NORMAL HEREDITARY

Multiple Alleles, Codominance, and Incomplete Dominance

1. Some genes exist in more than two allelic forms- multiple alleles.

2. There are 3 alleles for ABO blood types. Two of the ABO blood type alleles are dominant and
symbolized with a capital I (for Immunoglobulin) and a super-script IA and IB

3. There is one recessive allele, symbolized with a lowercase i. Which two alleles one inherits
determines the blood type, as follows:

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Some alleles are equally dominant, or co-dominant. When both of them are present,
both are pheno typically expressed. For example, a person who inherits allele IA from
one parent and IB from the other has blood type AB

These alleles code for enzymes that produce the surface glycoproteins of red blood cells.
Type AB means that both A and B glycoproteins are present, and type O means that
neither of them is present.

Polygenic Inheritance and Pleiotropy

1. This is a phenomenon in which genes at two or more loci or even different

chromosomes contribute to a single phentypoc trait. Human eye and skin color are
normal polygenic traits which result from a combined expression for all the traits.

2. Several diseases stem from some form of polygenic inheritance; these may include;
alcoholism, mental illness, cancer, and heart disease.

3. Pleiotropy is a phenomenon in which one gene produces multiple pheno-typic effects.

Sickle-cell disease, for example, is caused by a recessive allele that changes one amino
acid in haemoglobin.

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Polygenic Inheritance and Pleiotropy. (a)Inpolygenic inheritance, two or more genes combine their
effects to produce a single phenotypic trait, such as skin color. (b) In pleiotropy, a single gene
causes multiple phenotypic traits, as in sickle-cell disease

1. Sickle cell causes red blood cells (RBCs) to assume an abnormally elongated, pointed shape when oxygen
levels are low, and it makes them sticky and fragile. As RBCs rupture, a person becomes anemic and
the spleen becomes enlarged. Because of the deficiency of RBCs, the blood carries insufficient oxygen to
the tissues, resulting in multiple, far-reaching effects on different parts of the body.

SEX LINKAGE

1. Sex-linked traits are carried on the X or Y chromosome and therefore tend to be inherited by one sex

more than the other. Men are more likely than women to have red-green color blindness or hemophilia, for
example, because the allele for each is recessive and located on the X chromosome (X-linked)
Women have two X chromosomes.

2. If a woman inherits the recessive hemophilia allele(h)on one of her X chromosomes, there is still a good
chance that her other X chromosome will carry a dominant allele (H).
H codes for normal blood-clotting proteins, so her blood clots normally.

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3. Men, on the other hand, have only one X chromosome and normally express any recessive allele
found there (fig. 4.18). Ironically, even though this hemophilia is far more common among men than women, a
man can inherit it only from his mother.

4. ASSIGNMENT: WHY IS IT THAT MEN CANNOT INHERIT HAEMOPHILIA FROM THEIR

FATHERS?

Sex-related Inheritance of Hemophilia.

Left:A female who inherits a recessive allele (h) for hemophilia from one parent may not exhibit the
trait, because she is likely to inherit the dominant allele (H) for a normal blood-clotting protein
from her other parent. Right:

A male who inherits h from his mother will exhibit hemophilia, because the Y chromosome
inherited from his father does not have a gene locus for the clotting protein, and therefore has no
ability to mask the effect of h

Penetrance and Environmental Effects

1. Penetrance is the percentage of a population with a given genotype that actually exhibits the predicted
phenotype.

2. However, people don't exhibit the phenotype that is predicted by their genotype. For example, the occurrence
of polydactyly (extra fingers or toes) is caused by a dominant allele. This might be predicted from the
dominance of this allele. However, not all who have this allele present with the condition.

3. Environmental factors play an important role in the expression of all genes. All gene expression depends
on nutrition.

4. No gene can produce a phenotypic effect without nutritional and other environmental input, and no nutrients
can produce a body or specific phenotype without genetic instructions that tell cells what to do with
them.

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5. Children born with the hereditary disease phenylketonuria (PKU), for example, become retarded
if they eat a normal diet. How-ever, if PKU is detected early, a child can be placed on a diet
low in phenylalanine (an amino acid) and achieve normal mental development.

Dominant and Recessive Alleles at the Population Level

It is a misconception that dominant alleles are common and recessive alleles are rare; the
dominance or recessiveness of alleles have nothing to do with this. For example blood type O
is the most common type but it is caused by the allele I which is rare and blood type AB is caused
by two dominant ABO alleles AB but it is very rare

CONCLUSION

1. An understanding of cell biology and the functioning of each organelle is required to understand
of genetics.

2. the different processes required in cell division and the roles played by DNA and the various
RNA will make genetics very interesting.

3. GO BACK AND REVIEW THE TOPIC ON CELLS BEFORE REVIEWING GENETICS

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