Chromosomal Variations, Continuous and Discontinuous Variations, Genotypic & Phenotypic Variations and the recombination

Chromosomal Variations, Continuous and Discontinuous Variations, Genotypic & Phenotypic Variations. Hardy-Weinberg law of random mating, Recombination technology
It also explains the main points for a variation.

1. MUHAMMAD MUBASHIR ALI BBOF19E001 PRESENTATION TOPIC: VARIATIONS SBMITTED TO: DR. HAFIZ MUHAMMAD WARIS PLANT SYSTEMATICS

2. VARIATIONS

3. VARIATIONS The term “variation” refers to observable differences within a species. In biology, any difference between cells, individual organisms or groups of organisms of any species.

4. TYPES OF VARIATIONS PHENOTYPIC VARIATIONS GENOTYPIC VARIATIONS GENOTYPIC VARIATIONS The variations that are caused by differences in number or structure of chromosomes or by the differences in the genes carried by the chromosomes.

5. Genotypic variations comes in many different forms. Different hair color, eye color and skin color and many other examples come in this type of variations.

6. FACTORS OF GENOTYPIC VARIATIONS PANMIXIA RANDOM FERTILIZATION RECOMBINATION MUTATION

7. PANMIXIA Panmixia is also called as random mating which refers to mating in a population that occur in proportion to their genotypic frequencies. Because of this the potential mates have an equal chance of being selected.

8. THE HARDY-WEINBERG LAW OF RANDOM MATING: If a large, random-mating population that is not affected by the evolutionary processes of mutation, migration, or selection, both the allele frequencies and the genotype frequencies are constant from generation to generation. The population is in a state of equilibrium. As an example, consider a diploid pathogen such as an oomycete that has two alleles at an isozyme locus. If the frequency of the fast allele (F) is 0.40 and the frequency of the slow alleles (S) is 0.60, then the expected frequencies of the genotypes FF, FS, and SS would be 0.16, 0.48, and 0.36, respectively.

9. RANDOM FERTILIZATION When a male gamete and a female gamete finally meet, each is the result of an immense number of genetic possibilities created during independent assortment and crossing over. W e can calculate the possible number of random combinations of chromosomes in each gamete (sperm/egg) using the equation: N umber of possible combinations = 2n Human diploid cells have 23 pairs of chromosomes . Here n = 23 which will make 8,388,608 genetically unique gametes.

10. RECOMBINATION “Recombination is a process by which pieces of DNA are broken and recombined to produce new combinations of alleles.” This recombination process creates genetic diversity at the level of genes that reflects differences in the DNA sequences of different organisms. Genetic recombination occurs due to crossing over during the cell division in cell.

11. CROSSING OVER: “Crossing over is the swapping of genetic material that occurs in the germ line.” In humans, there are over 8 million configurations in which the chromosomes can line up during  metaphase  I of  meiosis. It is the specific process of  meiosis , resulting in four unique  haploid cells, that results in these many combinations. Together with random  fertilization , more possibilities for genetic variation exist between any two people than the number of individuals alive today.

12. A  sperm cell , with over 8 million  chromosome combinations, fertilizes an  egg cell , which also has over 8 million  chromosome combinations. That is over 64 trillion unique combinations, not counting the unique combinations produced by  crossing-over.

13. MUTATION A mutation is a change in a DNA sequence. Mutations can result from DNA copying mistakes made during cell division, exposure to ionizing radiation, exposure to chemicals called mutagens, or infection by viruses. Germ line mutations: A gene change in reproductive cell ( eggs & sperm) and can be passed on to offspring. For example cancer and cystic fibrosis. S omatic mutations: A mutation that occurs in the body cells after the embryo has begun to form. Cancer is an example of this mutation type.

14. TYPES OF MUTATIONS Chromosomal Alterations Point Mutations Frameshift Mutations

15. CHROMOSOMAL ALTERATIONS Chromosomal alterations are mutations that change chromosome structure. They occur when a section of a chromosome breaks off and rejoins incorrectly or does not rejoin at all.

16. POINT MUTATIONS A point mutation is a change in a single nucleotide in DNA. This type of mutation is usually less serious than a chromosomal alteration. An example of a point mutation is a mutation that changes the codon UUU(Phenylalanine) to the codon UCU(Serine).

17. FRAMESHIFT MUTATIONS A frameshift mutation is a deletion or insertion of one or more nucleotides that changes the reading frame of the base sequence. Deletions remove nucleotides, and insertions add nucleotides. Consider the following sequence of bases in RNA: Now, assume an insertion occurs in this sequence. Let’s say an  A  nucleotide is inserted after the start codon  AUG : AUG-AAU-ACG-GCU = start-asparagine-threonine-alanine AUG-AAA-UAC-GGC-U = start-lysine-tyrosine-glycine

18. AFFECT OF INSERTION This insertion changes the reading frame and thus all of the codons that follow it. As this example shows, a frameshift mutation can dramatically change how the codons in mRNA are read. This can have a drastic effect on the protein product.

19. PHENOTYPIC VARIATIONS “Phenotypic variation, then, is the variability in phenotypes that exists in a population.” Phenotypes are traits or characteristics of an organism that we can observe, such as size, color, shape, capabilities, behaviors, etc. Not all phenotypes can actually be seen. For example, blood types are phenotypes that we can only observe using laboratory techniques. Phenotypes can be caused by genes, environmental factors, or a combination of both.

20. TYPES OF PHENOTYPE VARIATIONS CONTINUOUS VARIATIONS DISCONTINUOUS VARIATIONS

21. CONTINUOUS VARIATIONS When a characteristic or phenotype normally exists in a range or gradient, it  varies continuously , such as height and skin color. In between the shortest person in the world and the tallest person in the world, any height is possible, not just four feet, five feet, or six feet.

22. GRAPHICAL REPESENTATION OF CONTINUOUS VARIATIONS

23. DISCONTINUOUS VARIATIONS   " A characteristic of any species with only a limited number of possible values shows discontinuous variation.” These phenotypes exist only at discrete intervals, like 'black and white' differences. For example, you can have blood type A, B, AB, or O, but there aren't any intermediate blood types in between. Another example is the ability to roll your tongue. Either you can or you can't, so this phenotype varies discontinuously.

24. GRAPHICAL REPESENTATION OF DISCONTINUOUS VARIATIONS

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