Biology Review
Biology
Biology is the science that studies living organisms.
Includes structure, function, growth, origin, evolution and distribution
Cell Theory
1. All living organisms are composed of one or more cells. (unicellular or multi-cellular)
2. The cell is the basic unit of life.
3. Cells arise from pre-existing cells.
The Cell theory was first started by Schelden, Schwan and Virchow in 1838-1839.
What does it mean to be alive?
-
Living things have highly organized, complex structure
Living things maintain a chemical composition that is difference from surroundings
Living things take in, transform and use energy from the environment
Living things can respond to stimuli
Living things have the capacity to reproduce themselves
Living things grow and develop
Living things are well suited to their environment
Modern Version
-
Having life in opposition to dead
Being in a state in which the organs perform their functions (in a state of action/operation/ motion/
activity)
Living organisms possess ‘life’ unlike non-living organisms because of fundamental characteristics
such as cellular organization, nutrition, metabolism, growth and reproduction.
Living beings are organized
Being made up of one or more cells
There is an energy transfer in living organisms (all living organisms require energy to carry on vital
metabolic activities)
Living organisms are able to adapt
All living organisms have a life cycle (growth, birth, death)
Every organism dies after attaining a certain age or due to predation, disease, accident or other
factors
The Cell Cycle
-
Cells reproduce through a continuous sequence of growth and division, known as the cell cycle
The cell cycle consists of two main stages:
1) The growth stage (interphase)
2) Cell division (mitosis)
Interphase:
-
Cell grows in size and volume and replicates its DNA
Most of the life of the cell is spent in interphase
When cells obtain energy, synthesize products (i.e. proteins) repair damage and fights disease
Divides into three distinct stages:
1) G1 phase (first gap phase):
The cell grows and prepares for DNA replication
2) S phase (Synthesis phase):
DNA replication (chromosome duplication)
3) G2 phase (second gap phase): Preparation for mitosis
Cell division:
-
-
Mitosis:
Division of the nucleus
Cytokinesis:
Division of the cytoplasm and organelles
Cell division is necessary for:
Growth/ development of multicellular organisms
Tissue repair and replacement of dead damaged cells
Cell division occurs at varying rates depending on the cell: Embryos and cells that wear out
quickly (i.e. skin, gut lining)
Muscles and Nerves are unable to
divide after a young age… may account
for the ageing process
Everytime a cell (parent cell) divides by mitosis, two identical daughter cells are produced
An exact copy of the DNA is passed onto each daughter cell
With each mitotic division the number of cells is doubled but the hereditary information stays the
same
The transmission of the hereditary material through cell division is called genetic continuity
Chromosomes are the hereditary material made up of long strands of condensed with associated
proteins  DNA
Cancer:
-
Cancer cells undergo abnormal cell division… these cells divide uncontrollably
As they rapidly reproduce errors in replication occur
These lead to the abnormal appearance of cells
Cell division occurs so fast that cells pile up on top of one another, forming a tumor  abnormal
growth
Mitosis
Facts about Mitosis
-
Mitosis occurs when a parent cell divides to produce two daughter cells
The daughter cells are genetically identical to each other because the DNA replicated from the
nucleus was an exact copy of the parent cell
With every round of mitotic division, the total number of cells is double but hereditary information
stays the exact same
Mitosis
Interphase
-
Most of the cell life is spent in interphase
Cell undergoes growth
DNA strands duplicate, Centrioles Double
Chromosomes are not readily visible
Chromatin are spread throughout the nucleus
Prophase
-
The centrioles move toward opposite poles
Astral rays form around each centriole
Chromatins become visible as they condense into shorter, thicker
strands
The nuclear envelope breads down and nucleolus disappears
Spindle fibres made of microtubules form between the centrioles
and attach themselves to the centromere of chromatids
The lining up of the chromosomes across the metaphase plate/
equator
Chromosomes are held midway between poles by the spindle
fibres (attached at centromere)
Chromomes are very short and thick
Metaphase
-
Anaphase
-
Begins with the separation of the chromatids at the centromere to
produce two identical single-stranded chromosomes
Each separated chrosome is slowly pulled toward opposite poles
Anaphase ends once a complete set of chromosomes arrives at
each of the poles
Telophase
-
The nuclear envelope reforms and the nucleoli reappear
Chromosomes elongate by uncoiling to become chromatin
The spindle and aster disappear
Two nuclei are visible within the single cell
Cytokinesis
-
The division of cytoplasm to form two new separate daughter cells
Begins during telophase
The cell membrane pinches inward t the equator of the cell
producing a furrow
The furrow deepends until two daughter cells are formed, each
with its own nucleus
-
Meiosis
Facts about Meiosis
-
-
Meiosis insures that the number of chromosomes does not double from sexual repdouction
 Ensures that sex cells have the right type (one of each homologous pair) and number (haploid) of
chromosomes
Meiosis allows one diploid cell to produce four haploid cells
Human somatic cells contain 46 chromosomes arranged in 23 homologous chromosomes
 23 maternal, 23 paternal
Meiosis
Interphase 1
-
DNA has already duplicated
Prophase 1
-
The chromosomes begin to condense and shorten
Homologous chromosomes come together in a process called
synapsis (lie side by side along their entire length)
As the chromosomes because thick, replicated chromosomes are
composed of two identical chromatids joined by a centromere
It now consists of four chromatids and is called a tetrad
As the chromosomes previously came together, they had broken
and rejoined a several places. That spot is called the chiasmata
The breakage/reunion allows for the exchange genetic material
The centrioles move toward the poles
The nuclear membrane and nuclei have broken down/disappeared
Tetrads have attached themselves to asters and spindle fibres and
are being moved toward the equator of the cell
The tetrads move onto the spindle and line up with their
centromeres at the equator
Metaphase 1
-
Anaphase 1
-
Chromatids do not separate
Instead homologous pairs separate with one chromosome going to
each pole
Telophase 1
-
Chromosomes condense slightly and nuclear membrane may form
At the end, two daughter cells each with exactly half the number of
chromosomes of the parent cell (2 diploid cells)
Interphase 2
-
Very Brief
There is no duplication of chromosomes in the interphase between
meiotic divisions
Prophase 2
-
The spindle fibres form at the end of this stage
Metaphase 2
-
Each chromosome (that contains two chromatids) lines up at the
middle of the cell (equator)
Anaphase 2
-
The centromeres split and one chromatid of each chromosome is
pulled to each of the opposite poles of the cell
Telophase 2
-
The nuclear membrane begins to reform as the meiotic process
nears completion
Each of the cells produced will contain the haploid number of
chromosomes
-
Meiosis
Crossing Over:
The interchange of sections between (non sister chromatids) pairing homologous
chromosomes during the prophase of meiosis
Independent Assortement:
Random alignment of maternal/paternal chromosomes at the metaphase
plate (gives all possible combinations an equal frequency). It explains the
random distribution in the gametes of genes or homologous
chromosomes.
The Origin of Genetics
-
Hereditary information is passed from generation to generation in the form of genes
Gregor Mendel (“Father of Genetics”) first demonstrated the basis of heredity in the mid 1800s
Mendel focused mainly on the pea plant because:
1) It was easy to control parentage (self-pollinating)
2) IT was easily grown and it matured quickly
3) It produced many seeds
4) It had several easily identifiable contrasting traits
Stem Length, (tall vs. dwarf), Seed Shape (smooth vs. wrinkled)
Mendel’s Experiment
-
Mandel self-pollinated pea plants for several years to establish pure lines (pure bred) homozygous
He began studying crosses between pure-breeding plants that were different for only one contrasting
pair of traits
These parent plants were called P generation and produced offspring called hybridsheterozygous
Mendel’s Law of Segregation
Members of a pair of allele for a given trait are segregated (separated) when gametes are formed
-
-
When segregation occurs in the P generation, for pure tall (TT) and pure dwarf (tt) plants, the
gametes of the TT plants contain one dominant allele (T) while those of the tt plants contain one
recessive allele (t)
When segregation occurs in the P generation for a heterozygous tall (Tt) plant there are two types of
gametes produced, T and t
Example 1: Cross a homozygous tall plant (TT) and a homozygous dwarf plant (tt)
T
T
t
Tt
Tt
t
Tt
Tt
F1 Generation Genotype:
100% heterozygous tall
F1 Generation Phenotype:
100% are tall
Note: Capital letter always goes first; Make sure junior has the same number of letters as any one parent
Example 2: Cross the F1 Generation
T
t
T
TT
Tt
t
Tt
tt
F1 Generation Genotype:
25% homozygous tall
25% homozygous dwarf
50% heterozygous tall
F1 Generation Phenotype:
75% tall
25% dwarf
Heterozygous: Mix, Homozygous: The same, Phenotype: What we see, Genotype: What makes it
Mendel’s Law of Independent Assortment
When two or more pairs of characteristics are considered at one time, each pair shows dominance
and segregation independently of the other
Example 1: A P generation cross involving a dwarf plant with pure round seeds and a pure tall plant with
wrinkled seeds ttRR x TTrr
tR
tR
tR
tR
Tr
TtRr
TtRr
TtRr
TtRr
Tr
TtRr
TtRr
TtRr
TtRr
Tr
TtRr
TtRr
TtRr
TtRr
Tr
TtRr
TtRr
TtRr
TtRr
F1 Generation Genotype:
100% heterozygous tall
100% heterozygous round
F1 Generation Phenotype:
100% tall
100% round
Example 2: Cross the F1 Generation
TR
Tr
tR
tr
TR
TTRR
TTRr
TtRR
TtRr
Tr
TTRr
TTrr
TtRr
Ttrr
tR
TtRR
TtRr
ttRR
ttRr
tr
TtRr
Ttrr
ttRr
ttrr
F1 Generation Genotype:
50% heterozygous tall
25% homozygous tall
25% homozygous dwarf
50% heterozygous round
25% homozygous round
25% homozygous wrinkled
F1 Generation Phenotype:
75% tall
75% round
Genetics Assignment
B: black coat
b: white coat
L: long hair
l: short hair
C: curly hair
c: straight hair
Cc: wavy hair
Male:
Bbllcc = 2 combinations
Female:
bbLlCc= 4 combinations
Blc
Blc
Blc
Blc
blc
blc
blc
blc
bLC
BbLlCc
BbLlCc
BbLlCc
BbLlCc
bbLlCc
bbLlCc
bbLlCc
bbLlCc
bLc
BbLlcc
BbLlcc
BbLlcc
BbLlcc
bbLlcc
bbLlcc
bbLlcc
bbLlcc
blC
BbllCc
BbllCc
BbllCc
BbllCc
bbllCc
bbllCc
bbllCc
bbllCc
blc
Bbllcc
Bbllcc
Bbllcc
Bbllcc
bbllcc
bbllcc
bbllcc
bbllcc
bLC
BbLlCc
BbLlCc
BbLlCc
BbLlCc
bbLlCc
bbLlCc
bbLlCc
bbLlCc
bLc
BbLlcc
BbLlcc
BbLlcc
BbLlcc
bbLlcc
bbLlcc
bbLlcc
bbLlcc
blC
BbllCc
BbllCc
BbllCc
BbllCc
bbllCc
bbllCc
bbllCc
bbllCc
blc
Bbllcc
Bbllcc
Bbllcc
Bbllcc
bbllcc
bbllcc
bbllcc
bbllcc
F1 Generation Phenotype:
6.25% Heterozygous Black Coat with Heterozygous Long and Wavy Hair
6.25% Heterozygous Black Coat and Long Hair with Homozygous Straight Hair
6.25% Heterozygous Black Coat and Wavy Hair with Homozygous Short Hair
6.25% Heterozygous Black Coat with Homozygous Short and Straight Hair
6.25% Heterozygous White Coat with Heterozygous Long and Wavy Hair
6.25% Heterozygous White Coat and Long Hair with Homozygous Straight Hair
6.25% Heterozygous White Coat and Wavy Hair with Homozygous Short Hair
6.25% Heterozygous White Coat with Homozygous Short and Straight Hair
F1 Generation Phenotype:
12.5% Black Coat with Long and Wavy Hair
12.5% Black Coat with Long and Straight Hair
12.5% Black Coat with Short and Wavy Hair
12.5% Black Coat with Short and Straight Hair
12.5% White Coat with Long and Wavy Hair
12.5% White Coat with Long and Straight Hair
12.5% White Coat with Short and Wavy Hair
12.5% White Coat with Short and Straight Hair
Note:
2²(allele)= 4 squares= Mono
4²(allele)= 16 squares= Di
8²(allele)= 64 squares= Tri
Genetics after Mendel
Incomplete Dominance:
Not all traits are purely dominant or purely recessive. In some instances neither of the alleles controlling
the trait is dominant. When this happens a blending of the two traits can occur called incomplete
dominance. Heterozygous individuals produce an intermediate trait.
Example:
White (WW) or Red (RR) snapdragon flowers are homozygous, while pink (RW) flowers
are heterozygous. Individuals with only one R do not produce enough red pigment to
produce red flowers, so they appear pink.
Not all Traits follow Mendel’s Law
In snapdragon’s, red flowers crossed with white flowers produce pink flowers.
 Traits for colour show incomplete dominance
Example:
Genes: R=Red
W=White
Note: Capital letters can be used for each allele since both alleles influence the phenotype.
Parents:
Gametes:
RR
R,R
*
WW
W,W
F1: All flowers are (4/4) RW or pink in colour
W
W
R
RW
RW
R
RW
RW
Now, if two F1 pink flowers get together
Genes:
Gametes:
RW
R,W
*
RW
RW
RW
RR
RW
RW
RW
WW
RW
R,W
Genotype:
25% WW
25% RR
50% RW
Phenotype:
25% White
25% Red
50% Pink
Co-Dominance
- In some cases, the heterozygote’s will show some of the characteristics of each of the homozygote’s
- Both alleles for a trait may be dominant
- Co-dominance is when both alleles are exposed at the same time in the heterozygous individuals and
no blending occurs
Example:
In cattle, “roan” coat colour is due to the presence f a (R) red allele and a white (W) allele. Both Alleles
are active and lead to a coat of red hairs and white hairs which when ruffled together gives an overall
roan appearance to the cattle’s coat colour. Since each hair is entirely red or entirely white (not a blend)
the condition shows co-dominance.
What are the genotypes and phenotypes of the F1 generation if a red bull mates with a white cow?
Parents:
Gametes:
C= Cow
RR
R,R,
*
Cr
Cr
Cw
CrCw
CrCw
Cw
CrCw
CrCw
WW
W,W
CrCr + CwCw
Cr,Cr Cw,Cw
100% CrCw (roan)
If the two F1 individuals are mated, what are the genotypes and phenotypes of their offspring?
Cr
Cw
Cr
CrCr
CrCw
Cw
Crw
CwCw
Genotype:
25% CrCr
50% CrCw
25% CwCw
Phenotype:
25% red
50% roan (not a new colour)
25% white
Multiple Allelism
- Genes that have more than two alleles have more genotypic combination possibilities and a greater
variety of phenotypes
- This is displayed in human blood types and skin colour
Human Blood Types
- The presence or absence of specific antigens (glycoproteins) determines four different phenotypes of
blood cells A, B, AB, O
- There are three alleles involved represented by the letter I
- Blood type A and B are co-dominant so blood type AB is the blended intermediate and blood type O is
recessive
- There are six possible genotypes with the four possible phenotypes:
Blood Type
Phenotype
Genotype
Antigens
Antibodies
Blood they can
receive
A
I I or I i
A
Anti-B
A,O
B
I I or I i
B
Anti-A
B,O
AB
II
A and B
None
A,B,AB,O
Universal Recipient
O
ii
None
Anti A and Anti B
O
Universal Donor
Example 1
A man with blood Type A and his wife who has blood type B have a child with Blood type O. Is this
possible? Explain using a Punnett square.
I I or I i
I I or I i
I
i
I
II
Ii
i
Ii
ii
Therefore there is a 25% chance of their child having type O blood if both parents
were heterozygous for their blood types.
Example 2
A man with blood type B marries a woman with blood type AB. What blood type would the children get?
How would you know if the father was homozygous or heterozygous for type B?
Woman: I I
Man: I I or I i
AB or B
I
I
I
II
II
I
II
II
Ib
i
Ia
IaIb
Iai
Ib
IbIb
Ibi
AB, B or A
Therefore if child has type A, the father is heterozygous for blood type B
Multifactorial Traits
- This term is used for traits whose phenotypic expressions is controlled by genes found at many loci
(polygenic)
- Expression of a multifactorial trait is influenced by both individuals internal and external environments
- Height and hair colour show a large number of different phenotypes that are not explained by a multiple
allelism. They show a continuous distribution of phenotypes with an “average phenotype” which indicate
that they are MULTIFACTORIALTRAITS
- Traits with only ONE pair of alleles shows a discontinuous distribution (e.g. tall, dwarf, blood types) and
are NOT multifactorial
Genes Chromosomes and DNA
- Each cell in the human body (except for gametes) contain 23 pairs of chromosomes
- 22 of these pairs are called outsomes
- 1 pair is called the sex chromosomes
 The egg always contains an X chromosome
 Sperm can have an X or a Y chromosome
Female = XX
Male= XY
Sex linkage
-
the human x chromosome is larger than the Y chromosome and contains many more genes
Genes on the Y chromosome are involved in determining male-characteristics
Any traits controlled by genes on the X chromosomes are called X-linked traits
X and Y chromosomes are not homologous- they contain different genes
The Tragic Consequences
- With the x-linked traits, it is easier for Male to get the recessive trait because only 1 of 2 sex
chromosome express that trait
- So Male are more prone to certain conditions: red green colour blindness, hemophilia, muscular
dystrophy and male pattern baldness
- Example
Using a punnett square, show the possible offspring of a normal female and a bald male
x
y
x
Xy
xy
x
Xx
xy
No males are bald, all females are carriers
Cross an F1 Female with a normal Male
x
y
x
xx
xy
x
xx
xy
25% chance of having a bald male
Note:
x-linked traits tend to skip generation
Genetic Mutations
A mutation is any change in a gene that causes it to lose or change its functioning of the genetic
information, thus causing a genetic disorder.
Many mutations are harmful, but DNA is not easily altered because it is quite stable.
A mutagen is any factor that causes a mutation such factors includes:
- Radiation (x-rays, microwaves, sun/solar radiation)
- Abnormal temperatures
- Chemicals- carcinogen
- Environmental agents (tetratogens)
- in adults (e.g. nuclear waste/radiation) * in babies (womb environment)
Most times when mutations do occur, it is in the somatic cells and becomes a recessive allele that is
rarely expressed.
It is much more dangerous when mutations occur in the sex chromosomes of the gametes because this
mutation can be passed on; affecting every cell in the offspring and it may continue to be passed on to
future generations.
Congenital Defects are conditions that are noticeable at birth that are a result of mutation. They are
generally caused either by inheriting affected genes or by tetratogens or both. (Environmental factors)
Example:
Spinal bifida (open spine), club foot, congenital heart defects, congenital myopia, FAS (foetal alcohol
syndrome) etc.
Definitions
Part 1
Anaphase:
Centromere:
Centriole:
Chiasmata:
Chromatid:
Zygote:
Third phase of mitosis; paired chromatids are separate
Union point of two chromatids that join to form a chromosome pair
Organize mitotic spindle
Site/sites on a tetrad where chromatids separate and reunite
Each of the two identical chromosome strands in a replicated
chromosome attached by their shared centromere
Thread-like structure made up of DNA and proteins in the nucleus
Carries genes, formed when chromatin condenses, in the nucleus
Genetically identical copy of an organism
Exchange of chromosome segments between homologous
chromosomes during meiosis
Division of a cells’ cytoplasm into two distinct cells
One of two genetically identical cells produced when a cell divides by
mitosis
Number of chromosomes in a body cell of an organism
Neucleic acid, encoded with instructions
Attachment of a chromosome fragment to a homolog that is already
complete during crossing over
Specialized reproductive cell that unites with another of a different sex to
produce a zygote through sexual reproduction; eggs and sperm
Segment of DNA that carries the code for a specific protein
Transmission of hereditary information from a parent cell to the daughter
cells in mitosis or from generation to generation in sexual reproduction
Differences among individuals caused by the recombination of genetic
material during meiosis
Number of chromosomes in a cell that contains a single set of
chromosomes; present in gametes
One of a pair of chromosomes that each carry genes for the same trait at
the same location on the chromosome; one from the mother, one from
the father
Period of the cell cycle between cell divisions
(Loci) specific location of a gene on a chromosome
Cell division process that involves two divisions with only one duplication
of chromosome  Haploid gametes containing one chromosome from
each homologous pair
In a cell division, division of a nucleus into genetically identical nuclei
Second phase of mitosis; chromosomes line up in the middle
First phase of a mitosis; chromatin condenses and duplicated
chromosomes become visible; mitotic spindle begins to form
Duplication of DNA before mitosis/meiosis
Fourth phase of mitosis; the nuclear envelope reforms, the
chromosomes uncoil and the nucleoli reappear
Paired set of homologous chromosomes, each chromosome with two
chromatids, four chromatids total
Union of gametes that produces the first cell of a new organism
Part Two
Allele:
Co-dominance:
Dihybrid:
Dihibrid (cross):
Dominant Trait:
One for of a gene for a specific trait
Complete expression of two different alleles of a gene in a heterozygote
An individual who is heterozygous for two traits; ie AaBb
Mating of two individuals both heterozygous for two particular traits
Allele that is expressed in a heterozygous individual
Chromatin:
Chromosome:
Clone:
Crossing over:
Cytokinesis:
Daughter Cells:
Diploid 2n:
DNA:
Duplication:
Gametes:
Gene:
Genetic Continuinity:
Genetic Variation:
Haploid, n:
Homolog:
Interphase:
Locus:
Meiosis:
Mitosis:
Metaphase:
Prophase:
Replication:
Telophase:
Tetrad:
F1 Generation:
F2 Generation:
Genetics:
Genotype
Heredity:
Offspring of two P generation individuals in a study of inheritance
Offspring of two F1 generation individuals in a study of inheritance
Science of heredity
Genetic makeup of an organism
The transfer of genetically controlled characteristics such as hair color or
flower color from one generation to the next
Heterozygous:
Describes an organism with two different alleles for a certain gene
Homozygous:
Describes an organism with two identical alleles of a certain gene
Incomplete Dominance:
Incomplete expression of two different alleles of a gene in a heterozygote
Law: Segregation:
Separation of the members of an allele pair when a gamete forms
Law: Independent Assortment: Describes the independent segregation of genes for different traits when
a gamete forms
Linkage Group:
Genes on the same chromosome that fail to sort independently of one
another and are inherited together
Monohybrid (Cross):
Mating of two individuals both heterozygous for a particular trait
Multiple Allelism :
When there are more than two possible alleles for a given gene (at a
specific locus)
Multifactorial Traits:
Describes a trait whose expression is controlled by genes found at many
loci expression of this trait may be influenced by other contributing
factors
Phenotype:
Physical characteristics of an organism
P Generation:
Parent individuals that produce offspring in a study of inheritance
Purebred:
Describes an organism bred to express a particular form of a trait
Pure breeding:
Describes plants that produce offspring identical to the parent plant for a
particular trait
Recessive Trait:
Describes the form of a trait that is only expressed I the homozygous
condition
Part Three
Autosomes:
Congenital defect:
Hemophilia:
Homogeneity:
Karyotype:
Mutagen:
Mutation:
Chromosome not involved in determining the sex of an organism
Mutation present at birth
Human genetic disease caused by the failure of blood to form clots
Possession of a homozygous genotype
Number and form of chromosomes in cell
Substance or agent that causes a mutation
Change In the DNA of a gene
Biology Review
Asexual/ Sexual
-
A sexual organism would benefit more in a constantly changing environment because some of
the unique offspring will adapt to the changes and pass their genes onto future generations
A sexual organisms produce identical offspring so they will all be wiped out if they are affected
negatively by a change
Should Employers screen job applicants for genetic abnormalities: No because…
-
They required a source of income
Knowing you have a lethal disease may have a negative impact on your life
Employers may reject abnormal job applicants
Discrimination against people with genetic abnormalities
Ethical considerations that must be taken before cloning animals and humans
-
Changing the natural order of the earth
Some religions do not support cloning
Are we supporting the idea of having a ‘perfect’ society
Should people lose the spark that makes them unique
Is cloning ever ok?
-
Yes when we study an animal’s particular gene
Can help to aid the understanding of the ageing process
Can prevent people from suffering (diabetics, Parkinson’s)
Tissues and organs could be cloned for transplant purposes
How was Dolly the Sheep Cloned?
-
A cell from the udder of a sheep was extracted
An egg from a different sheep was extracted and the nucleus was removed
The enucleated egg was placed next to the udder cell in a Petri dish
The two cells were fused together with an electric current
The egg began behaving as if it were fertilized and an embryo began to form
The embryo was placed into a surrogate sheep and Dolly was born 21 weeks later