LECTURE 9_ BIO 101 (GENERAL BIOLOGY I) HEREDITY AND EVOLUTION.ppsx

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1. AUGUSTINE UNIVERSITY ILARA,
LAGOS STATE, NIGERIA
FACULTY OF SCIENCE (FACUS)
BIO 101 (GENERAL BIOLOGY I): (2 Units)
LECTURE SLIDES ON HEREDITY AND
EVOLUTION
BY
DR(MRS) E. S OJO

2. Heredity
•This refers to the passing of characteristics
or transfer of traits from one generation to
the next.
 
•This process is carried out by genes which
defines the characters in an organism
• A gene is the functional unit of heredity
and they are short stretches of DNA that
code for a specific protein or RNA

3. Mendelian Laws
•Gregor Johann Mendel (1822 – 1884), was an
Austrian Monk who worked on pea plants
(Pisum sativum) to understand the concept of
heredity.
•His work laid the foundation of modern
genetics so he was known as the ‘Father of
Genetics’.
•He made three basic laws or principles of
inheritance refered to as Laws of Mendel
1) The Law of Dominance
2) The Law of Segregation
3) The Law of Independent Assortment.

4. The Law of Dominance
•States that in heterozygous condition
among two alleles of a character the alleles
which expresses itself is dominant and the
one which can’t express is recessive i.e a
gene has two contrasting alleles and one
always expresses itself in the organism as
the dominant gene while the other is the
recessive gene
• it expresses in any possible combination.

5. The Law of Segregation
•States that although the alleles of a character or
trait remain together for a long time, they do not
mix with each other they separate at the time of
gametogenesis so that each gamete receives only
one alleles of a character either dominant or
recessive i.e traits get segregated completely
during the formation of gametes without any
mixing of alleles.

6. The Law of Independent Assortment
•States that alleles of a character or trait can
undergo any sort of combination to give rise to a
phenotype different from both the parents i.e the
traits can segregate independently of different
characters during gamete formation.

7. Seven pairs of contrasting characters in Garden Pea
CHARACTER DOMINANT TRAIT RECESSIVE TRAIT
Flower colour Purple White
Flower position Axial Terminal
Seed colour Yellow Green
Seed shape Round Wrinkled
Pod shape Inflated Constricted
Pod colour Green Yellow
Height of plant Tall Dwarf

9. Dominant Traits
•The traits that express themselves in an
organism in every possible combination and
can be seen.
•In Mendel’s experiment, the tall trait in the
pea plants expressed itself more than the
short trait.
•Therefore, the tall trait of the pea plant was
said to be dominant over the short trait.

10. Recessive Traits
•A trait which is not expressed in the presence of
a dominant allele
•So, a recessive character/trait is present in an
organism but cannot be seen if a dominant
allele exists.
Monohybrid Cross
•When only one pair of contrasting character is
considered while crossing two organisms.
•The ratio of characters arising out of this cross
at F2 generation is called the monohybrid ratio.

11. •e.g If a tall plant (TT) is crossed with a dwarf
plant (tt), we get 3 tall:1 short plant at the end
of the F2 generation. So, 3:1 is a monohybrid
ratio.
•Here, the height of the plant is considered at a
time.
Parent Tall plant . Dwarf plant
Generation TT . tt
Gametes T . t
F1 Generation Tt (All tall plants)
(first filial generation)

12. •a monohybrid cross between a true-breeding
pea plant with green pods (GG) and yellow
pods (gg).
•Here, the green colour of the pod is the
dominant trait. Hence, in the F1 generation, all
plants contain green pea pods

14. Dihybrid cross
•When two pairs of contrasting characters
are considered while crossing two
organisms
•The ratio of characters arising out of this
cross at F2 generation is called the dihybrid
ratio.
•e.g.,
 If a plant with round and green pea is
crossed with a plant with wrinkled and
yellow pea,
•The first-generation plants would all have
round and green peas.

15. Parent Round . Wrinkled
Generation Yellow Seeds . Green Seeds
Gametes RRYY . rryy
F1 RY . ry

RrYy [round, yellow]

16. •On crossing the same for an F2 generation,
we would observe four combinations of
characters in the ratio of 9:3:3:1.
•Thus, 9:3:3:1 is the dihybrid ratio.

18. BACK CROSS
•It may be defined as the cross between F1
hybrid and of its parents.
•It is used by animal and plant breeders to
rapidly improve a breed or variety by
making a useful trait (gene) homozygous,
or ‘pure’.
•It is of two kinds namely test cross and out
cross.

19. TEST CROSS
•It may be defined as the cross between F1
hybrid and it receiving parents.
•It is used by plant breeders to the validity of
cross.
CHROMOSOMES
•From the Greek word (chrome means color
and soma means body).
•Chromosomes are the thread-like structure
present in the nucleons of cell which
contain hereditary information of the cell.

20. GENES
•The term ‘gene’ was introduced by
Johannson. Genes are the units of
inheritance forming part of a chromosome.
•These are passed from parents to the
offspring’s via chromosomes in the nuclear
of the parent’s gametes.
DNA (DEOXYRIBOSE NUCLEIC ACID)
•This is the genetic material in all organisms.

21. •It occurs in the cytoplasm in nucleotides
and plasmids.
•In eukaryotic cells, DNA s largely confixed
to the nucleons and is the main component
of chromosomes.
SEX CHROMOSOMES
•The chromosomes which determine the sex
of a person are called sex chromosomes.
•There are two types of sex chromosomes,
one is called X chromosome and the other
is called Y chromosome.

22. Evolution
•This is the process by which nature selects,
from the genetic diversity of a population,
those traits that would make an individual
more likely to survive and reproduce in a
continuously changing environment.
•Evolution is therefore the gradual process
of sequential changes by which a simple
life form leads to the development of
complex organisms over a period of time,
spanning several generations.

23. •Members of species changes generation
after generation accordance with
environmental requirements to turn into
better organized and more complex new
species.
•Since evolution refers to living organisms,
it is called ‘organic evolution’.

24. Lamarckism
•The first general theory of evolution based
on the principle that physical changes in
organisms during their lifetime such as
greater development of an
 organ or a part
through increased use could be transmitted
to their offspring
•It is about succession of life forms their
history and transformation
•Outlined in 1802 and fully reported in
1809 by a Frenchman naturalist, Jean
Baptiste de Lamarck (1744-1829)

25. •He proposed the theory of ‘inheritance of
acquired characters’ i.e acquired
characteristics were inheritable
•The theory of inheritance of acquired
character is simply known as Lamarckism.
•The environment affects the shape and
organization of organisms; frequent or
continuous use develops and enlarges any
organ, while by permanent disuse it weakens
until it finally disappears; all acquisitions or
losses wrought through influence of the
environment, and hence through use and
disuse are preserved by reproduction

26. e.g as a giraffe stretches its neck to browse
higher in trees, the continuation of the habit
over an extended period results in a gradual
lengthening of the limbs and neck

27. •And this theory consists of the following
postulates or ideas;
1) Effect of environment and new needs
2) Effect of use and disuse of organs
3) Inheritance of acquired characters
4) Internal vital force

28. Effect of environment and new needs
•The environment changes regularly due to
different geological or bio-physical
processes.
•The change in environment greatly affects
the habit, habitat and composition of living
organisms.
•This change in environment increases the
possibility of new organisms with respect to
various habitats.

29. Effect of use and disuse of organs
•This affects the development of organ and
body too.
•According to change in environment, the body
tends to increase the size of the organ which
are used most frequently and continuously.
•It means the frequently used organs become
more developed and become more strong and
large.
•When the organ is not in continuous use, it
gradually reduces in size and disappears or
remains as less developed form (Vestigial
form).

30. Inheritance of acquired characters
•All the changes occurring in an organism are
preserved within the body.
•These acquired characters are then transmitted to
their offspring through the gametes.
•This inheritance of acquired characters is also
due to use and disuse of organs therefore, after
many generations, new species are formed which
are distinctly different form their ancestors.
Internal vital forces
•The internal forces of life tend to increase
continuously the size of an organism and its
components.

31. Evidence and examples to prove or support
Lamarckism
•There are some examples by which theory
of evolution can be best explained in favour
of Lamarck, such as;
a)Long neck of giraffe
b)Disappearance of limbs in snakes
c)Webbed limb/feet of frogs and ducks
d)Blindness of moles
e) Flat Fishes
f) Flightless Birds

32. g) Retractile Claws of Carnivorous Mammals
h) Speed of Deer
i) Cave Dwellers
j) Emergent Hydrophytes
k) Dimorphism of submerged and aerial
leaves in aquatic plants
l) Aquatic Birds
m) Whales
n) Wadding birds

33. Long neck of giraffe
•The evolution of long necked giraffe took
place from short-necked giraffe due to
continuous stretching of the neck muscles
in order to find food from tall trees.
•In the beginning, the short-necked giraffe
used to eat the grasses.
•Later on, sources of grass on land reduced
and it forced to eat the leaves of tall trees
stretching of neck is continuous and is
gradually transmitted to offsprings.

35. Disappearance of limbs in snakes
•The continuous creeping through holes and
crevices made snakes body elongated and due to
continuous disuse of the limbs because they
hinder while creeping in burrows results in loss
of their limbs.
•In the same way, vestigial organs in human and
other animals show disuse of those organs.
Web of hind limb/feet of frog and Duck
•Development of webs on hind limbs of frog and
ducks for swimming in water because they are
used more continuously in search of food.

36. Aquatic Birds
•The evolution of  Ducks occurred from
terrestrial ancestors.
•Due to the lack of food on land, these aquatic
animals need to go to water.
•Hence, some web-like structures are
developed between the toes in them making
their lives easy in the water.
Flat Fishes
•Deep-sea fishes are found at the sea bottom
where no sunlight is present.

37. •So, they had to lead an inactive life.
•The eye of one side which lies on the bottom
then migrates towards the upper side.
•Thus, both eyes are on the single side of the
body.
Whales
 
•As an outcome of the inherited effect of disuse,
lost their hind limbs.
Wading Birds
•Birds like Jacana keep their body above the
water level by developing long legs through the
sustained stretching generation.

38. Drawbacks/Criticism in Lamarckism
•It is not proved experimentally
• It does not have any ground since there is no
vital force in an organism which increases its
body parts
•The environment can affect the animal but it is
doubtful that a new need brings about new
structures
•New organs are not formed in organisms as per
their wish.
•It is not necessary that the acquired characters
transmit into the new generation
•Though the use and disuse of organs is correct to
an extent

39. Evidences in Favour of Lamarckism
1)Formation of germ cells from somatic cells
• vegetative propagation in plants and
regeneration in animals
2) Effect of environment directly on germ cells

•Tower’s observations indicate direct effect
of environment on germ cells, by exposing
the young developing Potato Beetles to
extremes of temperature and humidity at the
time of the development of their
reproductive organs

40. 3) Effect of radiation
•a number of mutations and chromosome
aberrations was obtained in Drosophila with
the help of mustard gas
4) Agar
• Agar reared water fleas in a culture of green
flagellates and found that some
abnormalities were developed in their
structures
5) Effect of Chemicals
• Change in the secretion of hormones results
in the change of different parts of the body

41. 6) Guyar and Smith
•Guyar and Smith took the solution of the
eye lens of rabbit and inoculated the same
into fowl
7) Effect of Change of Environment
•Radish is a two-year crop in cold countries
but completes its growth in one year in
tropical areas

42. Theory of Evolution by natural selection
•This is a theory
 of biological evolution 
developed by the English naturalist
 Charles
Darwin
 (1809–1882) after a lifetime of
travel, observation, experimentation and
discussion
•This theory states that all
 species of organisms
arise and develop through the
 natural
selection
 of small, inherited variations that
increase the individual's ability to compete,
survive, and
 reproduce.
•This theory is also called
 Darwinian theory or
Darwinism

43. Darwin’s theory of evolution by natural
selection or Darwinism can be summarized
and explained thus as its core idea; That
a)all living things consist of a unique
combination of chemicals organized in
unique ways i.e variation occur in every
species, no two individuals of a species are
alike
b)species’ populations are able to adapt to
gradually changing environments i.e the
same species in different parts of the world

44. have different tolerances and slightly different
characteristics to survive the local conditions
in which it lives
c) Most of these variations have genetic basis
so they can be passed on to their offspring.
•At this time, Darwin was not aware of
Mendel’s work, neither did he know how
traits were passed on, he just observed
•It took another 50-60 yrs before hereditary
information was added to Darwin’s original
theory which made the theory even more
powerful

45. d) each species produces more offspring than
will survive into maturity e.g a single bacterial
cell within 36 hours would cover earth 3-4 ft
deep, fruit fly in 7 months would produce
enough offspring equal the mass of the earth
e) those individuals whose variations best fit
their environment will be more likely to
survive and reproduce i.e fittness equals ability
to reproduce. Organisms with less favorable
variations will be less likely to survive ,“there
is a “struggle for existence” " with “survival of
the fittest”

46. f) by a process of natural selection, evolution
sorts through these numerous variations within
a population and “chooses” the most fit
combination. As the environment slowly
changes and certain variations are selected,
over 100’s or 1000’s of generations new forms
will arise

47. Additional evidence supporting
evolutionary theory
1.Today layers of rock can be accurately
dated by strata and by radioactive decay
methods
•By this we can see that species have been
altered over geologic time the fossil record
shows clearly that all organisms did not
appear at the same time
•many that once existed have become extinct
~99% of all life that ever existed on earth is
now extinct

48. •fossil record also shows there has been an
orderly sequence species change and
replacement over billions of years from the
simplest forms of live to the most complex
2. Fossils of many “intermediate forms”
between major groups in the fossil record:
•e.g. between fish and amphibians, between
dinosaurs and birds, evolutionary stages of
the horse, elephant, etc, human ancestors in
a few cases we have essentially every major
step in the evolutionary process from one
species to another

49. 3. we have learned the science of genetics and
can explain how mutations occur and how they
are passed on (this process was completely
unknown to Darwin)
4. In modern times we have added a massive
amount of molecular evidence that supports
evolutionary theory, similarities and
differences in biochemistry correlates with
assumed evolutionary relationships. The more
closely related an animal is the more similar its
biochemistry in terms of DNA, antibodies,
protein structure

50. e.g. nematode worm shares 40% of its DNA
with humans, chimpanzees and humans share
98% of their DNA.
5. We can even quantify the degree of
difference and the evolutionary timelines for
virtually all forms of life virtually everything
we know about the nature
6. We can contribute to current understanding
of the process of evolution

51. Struggle for existence: Due to over
population, there is struggle between the
members of same species as well as from other
species for food, water, air and space. Only a
few are able to get it and survive and the rest
perish and get eliminated.
Variations exist within population. The
offspring’s of the same parents also differ
from one another and show variations. Also
apart from visible variations, certain hidden
variations also exit.

52. The variations are very important for evolution
for some of these help the individual to survive
in a certain type of environment while others
may not.
Survival of the fittest or Natural selection.
The individuals with favorable variations
survive in the struggle. The organism with
unfavorable variations die out and so only the
fittest individuals survive, reproduce and
transmit their favorable characters to the next
generation.

53. Origin of new species. As the favourable
variations of the fittest animals are inherited to
the offspring’s these variations when
accumulated over for a long time, lead to the
origin of new species.
ACQUIRED TRAITS : Changes in the
environment (food, temperature, light etc.)
influence the functioning and behavior of
living organisms and introduce changes in
their structure.

54. New characters are acquired or accumulated in
an organism during its life time by use and
disuse of organs or by the influence of the
environment. Acquired characters are
restricted to somatic cells alone and do not
influence germ cells. So, these traits cannot be
inherited.
Examples:-
The weight of the beetle is reduced because
of starvation that will not change the DNA of
the germ cells.

55. So, this change in weight is not an example of
evolution. It is also not passed (inherited) over
generations.
If any of the parent becomes blind or deaf or
lame before producing the offspring, they do
not produce blind, deaf or lame offspring.
The strong muscles of a wrestler are not
inherited by his children.