This document discusses types of variation in plants, including their origin and scale. It covers genetic and environmental variation, as well as qualitative and quantitative traits. Genetic variation arises from processes like recombination, chromosome modifications, and mutations. Qualitative traits are discrete while quantitative traits exhibit continuous variation controlled by multiple genes. The document provides examples and explanations of these concepts.

1. Variation:
types, origin, and scale
2023 – 2024 Dr. Neyaz R. Mustafa
Kurdistan Regional Government
Ministry of Higher Education and Scientific Research
Salahaddin University – Hawler
College of Agricultural Engineering Science

2. • Plant Diversity?
• Plant Diversity means “differences among the plants and variety of characters
observed within them”
• Genetic Diversity?
• Genetic diversity is defined as genetic variability present within species.

3. Total Plant species diversity in World

4. Classifying plants
Plant taxonomy is the science of classifying and naming plants. Organisms are classified into five major groups (kingdoms) –
Plantae, Animalia, Fungi, Protista, and Monera.
Plant breeders are most directly concerned about Kingdom Plantae, the plant kingdom. However, one of the major objectives of
plant breeding is to breed for resistance of the host to diseases and economic destruction caused by organisms in the other four
kingdoms that adversely impact plants. Plant breeding depends on plant variation or diversity for success
The five kingdoms of organisms as described by Whitaker.
1. Monera (have prokaryotic cells)
Bacteria
2. Protista (have eukaryotic cells)
Algae
Slime molds
Flagellate fungi
Protozoa
Sponges
3. Fungi (absorb food in solution)
True fungi
4. Plantae (produce own food by the process of photosynthesis)
Bryophytes
Vascular plants
5. Animalia (ingest their food)
Multicellular animals

5. •Genotype?
• is a word used describes the genetic make - up of the plant.
•Phenotype
• is the assessment of complex plant traits such as growth, development,
tolerance, resistance, architecture, physiology, ecology, yield, and the basic
measurement of individual quantitative parameters that form the basis for
complex trait assessment

6. Types of variation
The plant breeder applies the equation
P = G + E + G x E + error
When practicing selection. Where P is the plant’s phenotype, G is the plant’s
genotype, E is the environment in which the plant is growing, and G x E is the
interaction that occurs between the plant’s genotype and the environment. It is
the reliance on recombination to create novel G’s, the requirement to work with
the E and G x E components of this equation.

7. 1. Environmental variation
When individuals from a clonal population (i.e., identical genotype) are grown in the field, the plants
will exhibit differences in the expression of some traits because of non-uniform environment.
The field is often heterogeneous with respect to biotic and abiotic factors.
For example, disease and pest agents may not uniformly infect plants in the field.
As previously noted, environmental variation is not heritable. However, it can impact heritable
variation.
Plant breeders want to be able to select a plant on the basis of its nature (genetics) not nurture (growth
environment). To this end, evaluations of breeding material are conducted in a uniform environment as
much as possible.

8. 2. Genetic variability
Variability that can be attributed to genes that encode specific traits and can be transmitted from one
generation to the next is described as genetic or heritable variation.
Because genes are expressed in an environment, the degree of expression of a heritable trait is
impacted by its environment, some more so than others.
Genetic variation can be detected at the molecular as well as the gross morphological level. The
availability of biotechnological tools (e.g., DNA markers) allows plant breeders to assess genetic
diversity of their materials at the molecular level. Some genetic variation is manifested as visible
variation in morphological traits (e.g., height, color, size), while compositional or chemical traits (e.g.,
protein content, sugar content of a plant part) require various tests or devices for evaluating them.

9. DNA Based on Their Location
Genomic DNA Mitochondrial DNA Chloroplast DNA
gDNA mtDNA cpDNA

10. Chromosome
DNA Protein
Gene (Allele)
Nucleotide Histone Non-histone
Sugar Phosphate group Nitrogen base
Purine Pyrimidine
Guanine Adenine Cytosine Thymine

11. Origins of genetic variability
There are three ways in which genetic or heritable variability originates in nature – gene recombination,
modifications in chromosome number, and mutations.
1. Genetic recombination
Genetic recombination applies only to sexually reproducing species and represents the primary source of
variability for plant breeders in those species. As previously described, genetic recombination occurs via the
cellular process of meiosis. This phenomenon is responsible for the creation of non-parental types in the progeny
of a cross, through the physical exchange
of parts of homologous chromosomes (by breakagefusion). The cytological evidence of this event is the
characteristic crossing (X-configuration or chiasma) of the adjacent homologous chromosome strands, allowing
genes that were transmitted together (non-independent assortment) in the previous generation to become
independent. Consequently, sexual reproduction brings about gene reshuffling and generation of new genetic
combinations (recombinants). Unlike mutations that cause changes in genes themselves in order to generation
variability, recombination generation variability by assembling new combinations of genes from different parents.
In doing this, some gene associations are broken. The larger the number of pairs of allelic genes by which the
parents differ, the greater the new variability that will be generated.

12. Steps And Difference Between Mitosis And Meiosis

13. Difference between Mitosis and Meiosis
Mitosis Meiosis
Interphase
Each chromosome replicates during the S phase of the interphase. The result is
two genetically identical sister chromatids (However, do note that interphase is
technically not a part of mitosis because it takes place between one mitotic phase
and the next).
Chromosomes not yet visible but DNA has been duplicated or replicated.
Prophase
Prophase –Each of the duplicated chromosomes appears as two identical or equal
sister chromatids. The mitotic spindle begins to form. Chromosomes condense and
thicken.
Prophase I – crossing-over and recombination – Homologous chromosomes (each
consists of two sister chromatids) appear together as pairs. Tetrad or bivalent is
the structure that is formed. Segments of chromosomes are exchanged between
non-sister chromatids at crossover points known as chiasmata (crossing-over).
Metaphase
Metaphase -The chromosomes assemble at the equator at the metaphase plate.
Metaphase I – Chromosomes adjust on the metaphase plate. Chromosomes are
still intact and arranged as pairs of homologues (bivalent).
Anaphase
Anaphase – The spindle fibres begin to contract. This starts to pull the sister
chromatids apart. At the end of anaphase, a complete set of daughter
chromosomes is found on each pole.
Anaphase I – Sister chromatids stay intact. However, homologous chromosomes
drift to the opposite or reverse poles.
Mode of Reproduction
Asexual Reproduction Sexual Reproduction
Occurrence
All the cells Reproductive cells
Function
General growth and repair, Cell reproduction Genetic diversity through sexual reproduction
Cytokinesis
Occurs in Telophase Occurs in Telophase I and in Telophase II
Discovered by
Walther Flemming Oscar Hertwig

14. Types of Nucleic Acid
DNA RNA
Deoxy Ribonucleic Acid Ribonucleic Acid
mRNA
tRNA
rRNA

16. Protein Synthesis

17. 2 Ploidy modifications
New variability may arise naturally through modifications in chromosome number as a result of hybridization (between
unidentical genotypes), or abnormalities .
Sometimes, instead of variations involving complete sets of chromosomes, plants may be produced with multiples of only
certain chromosomes or deficiencies of others (called aneuploidy). Sometimes, plants are produced with half the number of
chromosomes in the somatic cells (called haploids). Like genetic recombination, plant breeders are able to induce various kinds
of chromosome modification to generate variability for breeding.

18. 3. Mutation
Mutation is the ultimate source of biological variation. Mutations are important in biological
evolution as sources of heritable variation. They arise spontaneously in nature as a result of
errors in cellular processes such as DNA replication (or duplication) and by chromosomal
aberrations (deletion, duplication, inversion, translocation). From the point of view of the
breeder, mutations may be useful, deleterious, or neutral. Neutral mutations are neither
advantageous nor disadvantageous to individuals in which they occur. They persist in the
population in the heterozygous state as recessive alleles and become expressed only when in
the homozygous state, following an event such as selfing

19. Transposable elements
The phenomenon of transposable elements (genes with the capacity to relocate within the genome), creates new
variability. Transposable genetic elements (transposable elements, transposons, or “jumping genes”) are known to
be nearly universal in occurrence. These mobile genetic units relocate within the genome by the process called
transposition.
The presence of transposable elements indicates that genetic information is not fixed within the genome of an
organism.
The members of each family may be divided into two classes:
autonomous elements or non-autonomous elements. Autonomous elements have the ability to transpose whereas
the non-autonomous elements are stable

20. Scale of variability
Some variability can be readily categorized by counting and placing into distinct non-
overlapping groups; this is said to be discrete or qualitative variation. Traits that exhibit this
kind of variation are called qualitative traits.
Other kinds of variability occur on a continuum and cannot be placed into discrete groups by
counting. There are intermediates between the extreme expressions of such traits. They are
best categorized by measuring or weighing and are described as exhibiting continuous or
quantitative variation. Traits that exhibit this kind of variation are called quantitative traits.

21. 1 Qualitative variation
Qualitative variation is easy to classify, study, and utilize in breeding. It is simply
inherited (controlled by one or a few genes) and amenable to Mendelian
analysis. Examples of qualitative traits include diseases, seed characteristics, and
compositional traits.
Breeding qualitative traits
Breeding qualitative traits is relatively straightforward. They are readily identified
and selected. Breeding recessive traits is a little different from breeding
dominant traits. It is important to have a large segregating population, especially
if several loci are segregating, to increase the chance of finding the desired
homozygous recessive genotypes.

22. 2 Quantitative variation
Most traits encountered in plant breeding are quantitatively inherited. A principal distinguishing feature of this variation
is that the trait, whether controlled by few or many genes is influenced significantly by environmental variability.
Traits that exhibit continuous variations are also called metric traits. Any attempt to classify such traits into distinct
groups is only arbitrary.
Quantitative traits are conditioned by many to numerous genes (polygenic inheritance) with effects that are too small to
be individually distinguished. They are sometimes called minor genes.
Continuous variation is caused by environmental variation and genetic variation due to the simultaneous segregation of
many genes affecting the trait.
Breeding quantitative traits
Breeding quantitative traits is more challenging than breeding qualitative traits. A discussion of quantitative genetics will
give the reader an appreciation for the nature of quantitative traits and a better understanding of their breeding.