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1. Tree Genetics and Improvement
Academic year:2021/2022
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2. 1.1. Fundamentals of Genetics
 It is a branch of biological science which
studies the laws of inheritance
(variation and heredity) in living things.
 Simply put, genetics is the study of similarities and
differences between parents and their offsprings and
between offsprings of the same parents.
CHAPTER1&2. Fundamentals of
Genetics and Molecular
nature of gene
2

3. Cont…
 Terminology
1. Heredity- is the tendency of individuals to resemble
their parents or the transmission of characteristics
from parents to offspring.
• Offspring resemble their parents more than they resemble
unrelated individuals.
2.Traits - expression of a gene or a group of genes
(distinguishing quality or characteristics)
Traits may inherited (influenced) biologically (Eye color, skin
color, hair color) and interaction by biological & environmental
factors (Weight, plant height)
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4. 3. Inheritance:
• The mechanism of transmission of genetic
information from parents and ancestors to
offspring.
4. Variation- is the differences in characteristics observed
among individuals of the same natural population
or species.
• E.g. Height, color, fatness
Or Variation is differences among individuals in a population in
morphology, physiology, and behavior exist among
individuals in a natural population.
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5. 1.1.1. MENDEL’S LAWS OF INHERITANCE AND THE THREE
PRINCIPLES
 Dominance= one allele masks another
 Segregation=genes become separated in gamete formation
 Independent assortment= members of one gene pair
segregate independently from other gene pairs during gamete
1. Monohybrid
cross
2. Dihybrid
cross
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6. 6

7. 1.1.2. Why study genetics? Application of Genetics
How each individual expresses traits in its formation
and throughout its life is the central problem of biology
before the discovery of genetics.
 As a result the discovery of genetics have its own basic
roles :
Role1. Knowledgeof geneticsis basic to progress
in agriculture, biology & medicine.
i. Improvement of agricultural plants
Plant breeding (improvement of crops e.g.
green revolution)
Improvement in disease and insect
resistance
Synthesizing of plants with multiple
qualities
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8. 1.2. Molecular nature of
gene
 It is the field of biology and genetics which studies:
 Expression of genes by studying the DNA sequence of
chromosomes
 The structure and function of genes at a molecular level.
 The natureof the genetic material and the
storage of genetics information, its replication, etc.
 It concerns the chemicalnature of the
gene itself: how genetic information is
encoded, replicated, and expressed.
 It includes the cellular processes of
replication, transcription, and translation and gene
regulation.
 An individual’s characteristics are
determines by factors(genes) 8

9. hereditary units which are
transmitted from one generation
to the net (i.e. inherited) are
called genes.
A gene can be defined functionally
as that part of a chromosome
responsible for the development of
a particular trait in an organism.
Control the function, development,
and ultimate appearance of
individuals.
Genes reside in a long molecule
called deoxyribonucleic acid
(DNA).
The DNA, in conjunction with a
protein matrix, forms nucleoprotein
and becomes organised into
structures with distinctive staining
properties called chromosomes
9

10. 3.1.What is Cell? The cell is the functional basic unit of
life.
 The word cell comes from the Latin word cellula,
meaning, a small room.
 Cell was discovered by Robert Hooke after Anton van
Leuwenhoek invented the microscope and he stated
as it is the functional unit of all known living
organisms.
 The descriptive term for the smallest living biological
structure was coined by Robert Hooke in a book he
published in 1665 when he compared the cork cells
he saw through the microscope to the small rooms
monks lived in.
 It is the smallest unit of life that is classified as a living
10

11.  The Cell Theory, first developed in 1839 by Matthias
Jakob Schleiden andTheodor Schwann, stated that:
 All organisms are composed of one or more cells,
 All cells come from preexisting cells,
 The vital functions of an organism occur within cells i.e.
are units of metabolic processes,
 Each cell contain the hereditary information
necessary for regulating cell function, coding for
structural & functional features & transmitting
information from cell to cell, to the next generation of
cell.
 The three characteristics of cells are:
1.Cells continue to exist until they are old.
2.Cells store food in form of protein. 11

12. Chromosome ( Waldeyer, 1883) basis of inheritance
 It is derived from two words; Chromo=colored in response
to dye, and some = body
 Most of the DNA (hence most of the genes) in plants occurs
in the nucleus in a linear structures is called chromosome.
 Complex structures with distinct structural features that play
important roles in the processes of replication, transcription,
and regulation of gene expression.
 Are darkly stained nucleoprotein bodies that are observed in
cells during cell division.
• The chromosome themselves don’t determine sex, but the
genes they carry do.
 Genes are located on chromosomes, which serve as the
vehicles for gene segregation in meiosis
12

13.  But the great mystery was where and how is this
information stored?
An exciting goal of molecular genetics is to use our
knowledge of DNA structure to understand how DNA
function as the genetic material.
1.2.3. Deoxyribonucleic acid (DNA)
In the early 1800s it was unthinkable for the leading
scientists and philosophers that a chemical molecule
could hold enough information to build a human.
But now it has been found that deoxyribonucleic acid
(DNA) is the genetic material that is passed from one
generation to the next ..a blue print for building living
organisms and it carries the information necessary to
sustain and perpetuate life. 13

14. 1.2.3.1.The discovery of DNA
structure
• Major discoveries that led to discovery of
DNA structure:
Rosalind Frankin Maurice Wilkins
1. X-ray diffraction photo of DNA that describe the
structure of DNA
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15. This is a bit of a simplification as
RNA forms base pairs within a
single strand, but RNA is not double helical over the
 Differences of DNA and RNA structure
• Both –made of nucleotides; contain
phosphate, adenine, cytosine, guanine
• RNA – contains ribose and uracil; single-stranded; only
one gene
• DNA – contains deoxyribose and thymine; double
stranded, many genes
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16. 1.2.4. Central dogma of molecular
biology
 According to the central dogma of molecular biology the
genetic information of the DNA is changed into biological
material principally through proteins.
 The dogma states that genetic information flow is generally
unidirectional from DNA to proteins, except in special cases
 The central dogma of molecular genetics, showing the
information flow involving, DNA, RNA, and proteins within the
cell.
 Simply stated, DNA makes RNA, which in turn makes proteins
RNA
processing
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17.  It is a section or segment/region of DNA
that contains the information to produce a
functional RNA (genetic code) and in turn
produce a polypeptide (protein), or
 It is a stretch of DNA that encodes
information and it is expressed by being
transcribed into RNA, and this transcript
then translated into protein.
 The information carried by DNA is held in
the sequence of pieces of DNA is called
gene.
It is a unit of heredity and have a functional
role in the cell responsible for inheritance of
traits.
Influences a particular characteristic in an
organism, i.e. the molecules that control the
function, development, and ultimate
1.2.5. Gene
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18. 1. Non-coding regions,
called introns, which do not
specify amino acid and their
function are not well known
2. Coding regions, called
exons, which specify a
sequence of amino acids and
used for phenotypic
expression. They are few in
number
3. Regulatory sequences, which play a role in determining
when and where the protein is made (and how much is
made)
 Contain an open reading frame that can be transcribed, as well
as regulatory sequences such as promoters and enhancers,
which control the transcription of the open reading frame.
4. Initiation and termination sequences: these are regions
where gene transcription starts and terminates respectively
5.The interval b/n the start and stop codon that encodes an
The attachment point for RNA polymerases and control the
activity of a gene
The picture can't be displayed.
The structural components of
a gene
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19. 1.2.6. Gene Expression (Protein Synthesis)….
 In genetics, gene expression is the most fundamental
level at which the genotype gives rise to the phenotype, i.e.
observable trait.
 The genetic code stored in DNA is "interpreted" by gene
expression, and the properties of the expression give rise to
the organism's phenotype.
 Such phenotypes are often expressed by the synthesis of
proteins that control the organism's shape, or that act as
enzymes catalyzing specific metabolic pathways
characterizing the organism.
 It is process of decoding genetic information (transcription)
and converting it into molecules (Translation) that perform
the function of the organism
 The structure, function, development, and reproduction of an
organism depend on the properties of the proteins present in
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20. 1.2.6.1. Process of protein synthesis.
 The mRNA is transcribed in the nucleus.
 It travels to the cytoplasm, where it binds to the ribosome.
 The mRNA moves through theA and P sites of the
ribosome.
 The tRNA molecules match up with the exposed codons on
the mRNA.
 The a.a on the other end of each tRNA bind together to form
a polypeptide.
 When the stop codon is reached, the polypeptide is
released.
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21. Eukaryotic Genes are
Segmented
Genes are made of parts represented in the mRNA(exons) and parts that
are transcribed but not present in the mRNA(introns).
Introns are removed from the primary transcript and exons are spliced together to
make mRNA.
In some genes more than 90% of the pre-mRNAis destroyed, never to appear in
the mRNA.
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22. Codons – sequences of three bases on mRNA
Anticodon – sequence of three bases on tRNA 22

23. Summary of transcription and
translation
23

24.  There are three major classes of RNA known to be involved in
gene expression:
 Messenger RNA, carries the message from DNA to be used to
create proteins
 Transfer RNA – reads the mRNA and matches up
complementary amino acid
 Ribosomal RNA – makes up ribosomes, the site of protein
synthesis
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25. In both prokaryotes and eukaryotes transcription is catalyzed by an
enzyme called RNA polymerase.
In transcription, the codons of agene are copied into mRNA by RNA
polymerase.
RNA processing (removal of non-coding part) by the process of
splicing takes place 25

26. 1.2.6.2. The genetic code
 The relationship between the nucleotide sequences of
genes and the amino-acid sequences of proteins is
determined by the rules of translation, known
collectively as the genetic code.
 The genetic code consists of three-letter 'words' called codons
formed from a sequence of three nucleotides (e.g. ACT,
CAG,TTT).
 In transcription, the codons of a gene are copied into
messenger RNA by RNA polymerase.
 This RNA copy is then decoded by a ribosome that reads the
RNA sequence by base-pairing the messenger RNA to
transfer RNA, which carries amino acids.
 Since there are 4 bases in 3-letter combinations, there are 64
possible codons (43 combinations). 26

27. 27

28. Nature and characteristics of the genetic code
1.The code is a triplet code. Each mRNA codon that specifies
an amino acid in a polypeptide chain consists of three
nucleotides.
2.The code is comma free; that is a continuous.
3.The code is non-overlapping
4.The code is almost universal (All life on Earth uses the
same code (with a few minor exceptions)
5.The code is degenerate except AUG which codes for Met
and UGG which codes for tryptophan, more than one codon
occurs for an amino acid, each amino acid can be coded for
by more than one codon. For example, AGC and ACC both
code for the amino acid serine.
6.The code has start and stop signals.
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29. The genetic code: three nucleotides= one
amino acid
 A codon table sets out how the triplet codons code for specific
amino acids.
 Sixty one of the sixty four codons specify a.a and are called
sense codons.
 The other three (UAG, UAA and UGA) do not specify an amino
acid and no tRNAs carry the appropriate anticodons and are
29

30.  It refers to any variation in the nucleotides, genes,
chromosomes, or whole genomes of organisms.
 Genetic diversity at its most elementary level is represented
by differences in the sequences of nucleotides (adenine,
cytosine, guanine, and thymine) that form the DNA
(deoxyribonucleic acid) within the cells of the organism.
 Nucleotide variation is measured for discrete sections of the
chromosomes, called genes.
 Thus, each gene compromises a hereditary section of DNA
that occupies a specific place of the chromosome, and
controls a particular characteristic of an organism (Aremu,
2012).
1.2.7. Genetic
diversity
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31. 31
Putting ItAll Together
• The fundamental question of genetics -
• What is the relationship between genes and traits? The answer –
Genes Protein Traits

32. 1.3. Mechanism of heredity/
inheritance
1. DNA Replication
2. Cell division (Meiosis and Mitosis) 32

33. Cont…
Principles of Heredity
 For each biological triats, an organism
inherits two alleles, one from each parent.
 These alleles may be the same or different.
 Traits are controlled by alleles on chromosomes. e.g. tallness
and dwarfness.
 An alleles effect is dominant or recessive
 When a pair of chromosomes separate during meiosis the
different alleles for a trait move to separate sex cells.
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34. 1.3.1. DNA/Gene Replication (synthesis)
 It is the process of copying a double-stranded DNA
molecule.
 It involves the polymerization of nucleotides into
polynucleotides
 As each DNA strand holds the same genetic
information, both strands can serve as templates for
the reproduction of the opposite strand
 Process of DNA replication is simple, but
it takes a large team of enzymes
and proteins to carry out the process:
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35. Process of DNA/Gene Replication Process
 Aportion of the double helix is unwind by a
helicase.
 The hydrogen bonds between the bases are
broken.
 Enzymes match up bases according to the
base-pairing rules.
 This ensures that the two DNA strands are
identical.
 The leading and lagging strands
are assembledin opposite directions.
 Once the strands are fully
replicated, the new DNA molecules are
proof-read.
 Each new molecule is comprised
of one new strand and one original
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36. 1.3.2. Cell division (Meiosis and Mitosis)
 To understand the mechanism of laws of inheritance
knowledge of the formation of cells or process of cell
division is necessary.
 All livingthings are composedof a
sexual reproductivecell; (sex cells).
 Female gamete is an ovum or egg cell and a male
gamete is sperm cell.
Cell division is a fundamental process for
reproduction in unicellular or multicellular organisms
 Involve the distribution of genetic material, DNA, to the
daughters’
Necessary to replace worn out
cells/tissuerenewal in multicellular organisms
 Required for growth and development in multicellular
36

37. Cell Mechanics: Within all organisms, cells divide to
produce new cells, each of which requires the
genetic information found in DNA.
Cell cycle- The sequence of events from the start of
one cell division to the next
 All multicellular organisms, plants or
animals, no matter their size started
their existence as a single cell.
 Thisinitialcell grows to their (plants or
animals) normal size and form.
 Thisgrowthis initiated by the formation of
new cells and their enlargement.
 Hence increase in size of any multicellular organism is
due to division of the existing cells of the organism, 37

38. 1. The direct division of cell, otherwise known as
AMEITOSIS.This is the way unicellular organisms
reproduce.
2.The indirect method of cell division.
 There are two types:
(i) Mitosis
(ii) Meiosis
 An understanding of reduction division (meiosis) r
halving of chromosome no in the formation of the
gametes and the knowledge that the genes carried on
the chromosomes are the factors responsible for the
transmission of inherited xtics
Methods of cell
division.
38

39. On the basis of the number of chromosomes, there are two kinds of cells in a
sexually reproducing plant.
1. Body (somatic cells).
 The somatic chromosome number is called the diploid number (2n).
Further, the somatic chromosomes can be arranged in pairs called
homologous chromosomes, based on morphological features (size,
length, centromere position).
2. Cells in the gametes (gametic cells)
 Gametes- Male and Female Sex Cells of the plant (pollen grains, eggs)
 Contain half the set of chromosomes (haploid number (n).
In sexually reproducing plants, one member of each pair is derived from the
maternal parent (through the egg) and the other from the paternal parent
(through the pollen).
This occurrence is called biparental inheritance and as a result each
diploid cell contains two forms of each gene (called alleles).
39

40. 40

41. • Crossover is preceded by the formation of bivalents, the pairing
of homologous chromosomes. Adjacent chromatids physically
exchange parts during the formation of a characteristic x-
41

42.  At various stages in the plant life cycle,
a cell nucleusmay divide according to one of
two processes – mitosis and meiosis.
How genes
transmitted/pass
ed offspring?
and traits
are from
parents
to
• Whena diploidindividual makes
haploid
cells for sexualreproduction the
cells
contain half the number of
chromosomes.
• When two haploid cells (e.g sperm
and egg combine with each other a
zygote is formed that begins the life
of a new individual,
• This zygote had inherited half of its
chromosome and therefore half of its
genes from each parent (father and
42

43. 3.3.1. Mitosis:Reproduction of somatic
cell=Equational division
 It was first worked out by Flemming; a German
histologist, in 1882, takes place in the processes
connected with growth
Occurs only in somatic cells and is characterized by a
division of the nucleus (karyokinesis) into two so that
two identical daughter cells are produced and nucleus
contains the same number of chromosomes as the
mother cell.
 The cytoplasm divides (cytokinesis) so that the mitotic
products are genetically identical (equational division).
 This conservative process produces new cells for
growth and maintenance of the plant. 43

44. Mitosis occurs in the following circumstances:
 Development and growth
• The number of cells within an organism increases by
mitosis.
• This is the basis of the development of a multicellular
body from a single cell, i.e., zygote and also the basis of
the growth of a multicellular body.
 Cell replacement
• In some parts of body, e.g. skin and digestive tract,
cells are constantly sloughed off and replaced by new
ones.
• New cells formed and so are exact copies of the cells
being replaced.
 Regeneration
• Some organisms can regenerate body parts, via
production of new cells. For example, starfish
regenerate lost arms through mitosis. 44

45. Occurrence of mitosis:
Mitosis is mostly restricted to the meristematic regions
of plants where active cell elongation is going on such
as:
 The root-tip,
leaf apices(Young leaves,
stem-tips (Shoot tips),
 Flower buds and cambium
 In Animals: Blood cells, and gut
epithelium
A mitotic division has four major
phases:
1) Prophase
2) Metaphase 45

46. Diagrammatic presentation of mitosis in a cell with a diploid
and female chromosomes are presented in black and
Structures that
pull the
chromosomes to
opposite
poles of the
cell).
Spindle
fibers
When a cell is not undergoing division, the nucleus contains
numerous crooked, often coiled, delicate thread-like structures
called chromonemata. These chromonemata cannot be seen by
light microscope.
Typically the
entire process
takes about an
hour and is
followed by
interphase.
46

47. Meiosis (first worked out by strasburger, a German
botanist in 1888) is a complicated process of nuclear
division whereby the chromosome no is reduced to half
(n) in the four nuclei so formed by this method.
Meisis occurs in reproductive cells resulting in the
formation of spores or gametes.
It is the mechanism for the transmission of hereditary
xters, which are carried by the chromosomes.
Meiosis actually involves two divisions.
The first meiotic division (meiosis I) is a reductional
division producing two haploid (n) cell from a single
diploid (2n) cell.
The second meiotic division (meiosis II) is an equational
3.3.2. Meiosis or Reduction
Division
47

48. Phases of
Meiosis I
48

49. •
Diagrammatic presentation of meiosis in a cell with a diploid
number of 4. The process has two distinct cell divisions. Prophase
I consists of five distinguishable stages; the most genetically
significant event of crossing over occurs in the fourth stage,
Phases of
Meiosis II
49

50. • In sexually reproducing organisms the gametes are
haploid (n) (Geek word haploos, meaning single); and
two gametes fuse to form a diploid (2n) zygote
(1)Meiosis for reduction division is important because
it causes the reduction in chromosome number which is
very essential during the time of gamete formation in
order to maintain a particular diploid number through
successive generations of sexually reproducing
organisms.
(2)Chiasmata help in exchanging parts of chromatids
between homologous (similar) chromosomes (during
meiotic division), thus further ensuring new combinates
of xters.
• Meiosis, therefore, helps in bringing about variation in a
THE IMPORTANCE OF
MEIOSIS
50

51. Differences between mitosis and Meiosis
Mitosis
1. Somatic cells
2. Prophase normal
duration
3. No crossing over
4. Chromosome not
come plate in pairs
5. Equational
division
equational division
Meiosis
1. Reproductive cell
2. Prophase long duration
3. Crossing over
4. Chromosomes come in pairs in
metaphase
5. Meiosis I reduction division,Meiosis II
6. 1 cell divides into two cells 6. 1 cell gives 4 cells
7. Keeps chromosome no. constant from one cell to another, while
meiosis reduces the no. of chromosome to half
8. In mitosis chromosomes have centromere at metaphase plate with arms
in any direction.
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