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Exam Focus:
Heredity, variation, genes, alleles, Mendel's experiments,
dominant and recessive traits, monohybrid cross, dihybrid
inheritance, sex determination, inherited and acquired traits,
natural selection, speciation, fossils and evolutionary evidence.
A. Very Short Answer Questions
Question 1
What is heredity?
Heredity is the transmission of inherited characteristics
from parents to offspring through genetic material.
Question 2
What is variation?
Variation refers to differences in characteristics among
individuals of the same species or population.
Question 3
What is a gene?
A gene is a unit of heredity that carries genetic information
related to inherited characteristics.
Question 4
What is an allele?
An allele is an alternative form of a gene.
Question 5
What is a dominant trait?
Under complete dominance, a dominant trait is expressed
when at least one dominant allele is present.
Question 6
What is a recessive trait?
A recessive trait is expressed under complete dominance
when the individual has two recessive alleles.
Question 7
What is a phenotype?
Phenotype is the observable expression of a trait.
Question 8
What is a genotype?
Genotype is the genetic constitution or allele combination
associated with a trait.
B. Mendel's Experiments
Question 9
Why did Mendel choose pea plants for his experiments?
Pea plants have many easily distinguishable contrasting
traits, can self-pollinate and can also be cross-pollinated
under controlled conditions. They also have a relatively
short generation time.
Question 10
What is a monohybrid cross?
A monohybrid cross studies the inheritance of one pair of
contrasting traits.
Question 11
What is a dihybrid cross?
A dihybrid cross studies the inheritance of two pairs of
contrasting traits simultaneously.
Question 12
What is the typical F₂ phenotypic ratio in a classical
monohybrid cross with complete dominance?
The typical phenotypic ratio is 3 : 1.
Question 13
What is the typical F₂ genotypic ratio in a classical
monohybrid cross?
The typical genotypic ratio is 1 : 2 : 1.
Question 14
What is the classical F₂ phenotypic ratio of a standard
dihybrid cross under Mendel's assumptions?
The classical phenotypic ratio is 9 : 3 : 3 : 1.
C. Monohybrid Cross Practice
Question 15
Cross a homozygous dominant individual RR with a homozygous
recessive individual rr.
All F₁ offspring are heterozygous under the stated model.
Question 16
What happens when two heterozygous individuals Rr × Rr
are crossed?
Rr × Rr → RR : Rr : rr = 1 : 2 : 1
Dominant phenotype : Recessive phenotype = 3 : 1
Question 17
What is the difference between homozygous and heterozygous?
Homozygous:
Both alleles for a trait are the same, such as RR or rr.
Heterozygous:
The two alleles are different, such as Rr.
D. Inheritance of Traits
Question 18
How are genes related to chromosomes?
Genes are segments of DNA located on chromosomes and carry
hereditary information.
Question 19
Why do offspring resemble their parents but are not always
identical to them?
Offspring inherit genetic information from their parents,
producing similarities. At the same time, DNA copying,
recombination and other biological processes can introduce
variations.
Question 20
How does sexual reproduction contribute to variation?
Sexual reproduction combines genetic material from two
parents, producing new combinations of alleles in offspring.
E. Sex Determination
Question 21
What are the sex chromosomes in typical human females and males?
Typical females have XX sex chromosomes and typical males
have XY sex chromosomes.
Question 22
Which sex chromosome can an ovum normally carry?
An ovum normally carries an X chromosome.
Question 23
Which sex chromosomes can sperm carry?
Sperm can carry either an X chromosome or a Y chromosome.
Question 24
Explain the two possible combinations of sex chromosomes.
X Ovum + X Sperm → XX
X Ovum + Y Sperm → XY
F. Inherited and Acquired Traits
Question 25
Differentiate between inherited and acquired traits.
Inherited traits are influenced by genetic information
passed from parents to offspring.
Acquired traits develop during an individual's lifetime and
are generally not passed to offspring through the ordinary
inheritance of DNA sequences.
Question 26
Is an increase in muscle mass due to exercise generally an
inherited trait?
No. It is an acquired change produced during an individual's
lifetime and is not normally inherited as a genetic trait.
G. Variation & Evolution
Question 27
Why are variations important for evolution?
Heritable variations provide differences on which natural
selection and other evolutionary processes can act. Over
generations, such changes can alter populations.
Question 28
Are all variations beneficial?
No. A variation may be beneficial, harmful or have little
effect depending on the environment and circumstances.
Question 29
What is natural selection?
Natural selection is a process in which heritable
characteristics associated with greater survival or
reproductive success tend to become more common in a
population over generations.
Question 30
Does an organism develop a useful trait simply because it
needs it?
No. Evolution does not work by an organism intentionally
producing a required trait. Heritable variations already
present in populations can be favoured by environmental
conditions.
H. Natural Selection
Question 31
Explain natural selection using a simple population example.
Suppose a population contains a heritable variation in
colour. If one colour makes individuals less visible to
predators, those individuals may survive and reproduce
more successfully.
Over generations, the associated trait may become more
common in the population.
Question 32
What is meant by differential reproduction?
Differential reproduction means that individuals with
certain characteristics leave more viable offspring than
others under particular environmental conditions.
I. Speciation
Question 33
What is speciation?
Speciation is the formation of new species from existing
populations.
Question 34
What is geographical isolation?
Geographical isolation occurs when physical barriers
separate populations and reduce or prevent gene flow between
them.
Question 35
How can geographical isolation contribute to speciation?
Separated populations can accumulate different genetic
variations and experience different environmental pressures.
Over many generations, this divergence can contribute to
reproductive isolation and formation of new species.
Question 36
What is genetic drift?
Genetic drift is a change in allele frequencies caused by
chance events, especially in relatively small populations.
J. Fossils & Evolutionary Evidence
Question 37
What is a fossil?
A fossil is a preserved remain, impression or trace of an
ancient organism.
Question 38
How do fossils provide evidence for evolution?
Fossils provide evidence of organisms that lived in the past
and help scientists study changes in life forms over
geological time.
Question 39
What does the position of fossils in sedimentary rock layers
tell us?
In undisturbed sedimentary layers, fossils in deeper layers
are generally older than fossils found in overlying layers.
K. Homologous & Analogous Structures
Question 40
What are homologous structures?
Homologous structures have a similar basic structural plan
and evolutionary origin but may perform different functions.
Question 41
Give an example of homologous structures.
The forelimbs of humans, bats and whales show a similar
basic structural plan but are adapted for different functions.
Question 42
What are analogous structures?
Analogous structures perform similar functions but have
different structural or evolutionary origins.
Question 43
Give an example of analogous structures.
Wings of birds and wings of insects perform the function
of flight but do not have the same basic structural origin.
L. Molecular Evidence
Question 44
How can DNA comparisons help in studying evolution?
DNA sequence similarities can provide evidence about
evolutionary relationships and shared ancestry between
organisms.
Question 45
What can greater similarity in important DNA sequences
indicate?
When considered with other evidence, greater similarity can
indicate a closer evolutionary relationship or more recent
common ancestry.
M. Reasoning-Based Questions
Question 46
Why do genetic variations matter more for evolution than
changes that are acquired during an individual's lifetime?
Heritable genetic variations can be passed to offspring,
whereas most acquired changes are not transmitted as
inherited genetic information.
Question 47
Why is natural selection described as population-level
change rather than an individual deliberately changing?
Selection changes the relative frequency of heritable
characteristics across generations in a population.
Individual organisms do not intentionally evolve during
their lifetime.
Question 48
Why can the same variation be useful in one environment
but harmful in another?
The effect of a trait depends on environmental conditions.
A characteristic that improves survival in one environment
may provide little or no advantage in another.
Question 49
Why is evolution not considered a ladder of progress?
Evolution has no predetermined direction. Populations change
in response to inherited variation, environmental conditions
and other evolutionary processes rather than moving towards
a fixed idea of perfection.
N. Competency-Based Practice
Question 50
In a population, a heritable trait helps some individuals
escape predators more successfully. What could happen to
the frequency of that trait over several generations?
If the trait improves survival and reproductive success,
its frequency may increase in the population over generations.
Question 51
A small isolated population experiences a random event that
removes many individuals. Why could the genetic composition
of the surviving population change greatly?
In a small population, chance events can cause large changes
in allele frequencies. This is an example of genetic drift.
Question 52
Two populations of the same species become separated by a
mountain range for a very long period. How could this
eventually contribute to speciation?
Geographic separation reduces gene flow. Over time the
populations may accumulate different variations and become
sufficiently different to develop reproductive isolation.
Question 53
An organism has a genetic change that does not affect its
survival or reproduction in its environment. What can be
said about this variation?
The variation may be neutral in that particular environment.
Not every genetic variation produces a noticeable advantage
or disadvantage.
O. Long Answer Questions
Question 54
Explain Mendel's monohybrid inheritance using a suitable cross.
Consider a cross between a homozygous dominant parent RR
and a homozygous recessive parent rr.
The F₁ generation consists of Rr individuals.
On crossing two F₁ individuals:
Rr × Rr → RR : Rr : rr = 1 : 2 : 1
Under complete dominance, the corresponding phenotype ratio
is 3 dominant : 1 recessive.
Question 55
Explain how variations can contribute to evolution by natural
selection.
Individuals in a population show variations. If some
heritable variations improve survival or reproductive
success in a particular environment, individuals carrying
those characteristics may leave more offspring.
Over many generations, the associated inherited
characteristics can become more common in the population.
Question 56
Explain the main factors that can contribute to speciation.
Speciation can be promoted by accumulation of genetic
variation, natural selection, genetic drift and reduction
of gene flow between populations.
Geographic isolation can separate populations and allow
them to diverge over generations. If reproductive isolation
develops, the populations may become separate species.
Question 57
Explain how fossils, homologous structures and DNA evidence
can be used together to study evolution.
Fossils provide evidence about organisms that lived in the
past and changes through geological time.
Homologous structures reveal similarities in basic structural
plans that can reflect common ancestry.
DNA sequence comparisons provide molecular evidence about
relationships among organisms.
Together these forms of evidence can strengthen conclusions
about evolutionary history.
P. Quick Revision Questions
-
Define heredity and variation.
-
Differentiate between gene and allele.
-
Differentiate between genotype and phenotype.
-
Explain dominant and recessive traits.
-
Solve a monohybrid cross.
-
State the classical monohybrid and dihybrid ratios.
-
Explain human sex determination.
-
Differentiate between inherited and acquired traits.
-
Explain natural selection.
-
Explain speciation and geographical isolation.
-
Explain the role of fossils in studying evolution.
-
Differentiate between homologous and analogous structures.
-
Explain how DNA evidence supports evolutionary studies.