GENETICS & EVOLUTIONARY BIOLOGY
►Unit 1:Mendelian Genetics and its Extension
Principles of Inheritance, Chromosome theory of inheritance, Incomplete dominance and co dominance, Multiple alleles, lethal alleles, sex linked inheritance in Drosophila (White eye locus) & Human (Thalassemia).
Q. How do Mendel's laws relate to meiosis?
Meiosis is the process of creating gametocytes (sperm and eggs) which have half (haploid) of the DNA of each parent. Mendel’s law of segregation states that the genes of the parents must segregate equally into haploid gametes in such a way that their offspring have an equal likelihood of inheriting either one, which is what, happens during meiosis. Mendel also discovered the law of simple dominance which means that for a pair of genes of a given trait, the dominant gene is always expressed in the offspring. The only way for the recessive gene to be expressed is for the offspring to receive it from both parents. During meiosis, the dominant and recessive traits of the parents segregate equally into haploid gametes and the offspring have equal likelihood of inheriting either one.
►Unit 2: Linkage, Crossing Over
Linkage and crossing over, Complete & Incomplete Linkage, Recombination frequency as a measure of linkage intensity. Holiday Model
►Unit 3: Mutation
Chromosomal mutation, Deletion, duplication, inversion, translocation, aneuploidy, gene mutation, induced mutation, types & example
Q.Why heterozygous individuals show more impact of deletion?
i)Some human disorders are caused by deletions of chromosome segments.
ii)In many cases, the abnormalities are found in heterozygous individuals, homozygotes for deletions usually die if the deletion is large.
iii)This distinction tells us that, in humans at least, the number of copies of genes is important for normal development and function.
iv)Typically, several to many genes are lost in a deletion, so the syndrome that results is caused by the loss of the combined functions of those genes, rather than the loss of just one gene.
►Unit 4: Sex determination
Genic Balance theory and dosage compensation in Drosophila.
Q.What are the major types of sex determination mechanism?
(a)Sex determination by environment, (b)Haploid-diploid sex determination, (c)Sex determination by chromosomes— male and female individuals are distinguished according to their chromosomal constitution. There are two types of chromosomes present in soma- Autosome (AA) and sex chromosome (XX in female and XY in male).
Q.State the effect of X: A on sex determination of Drosophila.
►Unit 5: Origin of Life
Chemical Origin of life
Q.What are proteinoids?
[A polypeptide or mixture of polypeptides obtained by heating a mixture of amino acids]
In the 1950s, Fox and coworkers developed a technique in which heat could also be used to produce peptides from dry mixtures of amino acids. Depending on the kinds of amino acids in the mixture, they found that temperatures of 150°C to 180°C could produce as much as 40 percent yield of peptide like products with molecular weights between 4k and 10k daltons. Fox called these polymers proteinoids (also thermal proteins), and he and his group proposed that these compounds bear protein like features.
i)According to their analyses, the proteinoids possess nonrandom proportions of amino acids; that is, their compositions are not simply based on the frequency of the different amino acids in the initial mixture ii)They also suggest that the positions of the amino acids in the polymer are not based on their overall frequencies in the chain, since some amino acids preferentially occupy the N- and C-terminals of the proteinoids.
iii)The nonrandomness of proteinoid structure also seems supported by the finding that these polymers all show similar properties as tested by sedimentation rates, electrophoretic techniques, column fractionation, and other measurements. 'Thus, some preferential interaction between amino acids in proteinoid formation seems to dictate their position and frequency and lead to some degree of uniformity in the kinds of molecules produced.
iv)Although not all the amino acid bonds formed in such proteinoids are of the usual peptide variety, nor do the Shapes of these molecules follow the familiar α-helix of protein structure, there still seem to be enough peptide linkages to characterize them as proteins in many tests.
v)Thus, proteinoids give positive colour tests with the same reagents that proteins do; their solubilities resemble proteins; they are perceptible with similar reagents; and Fox and Dose propose they have other protein like traits listed in Table 1. They therefore suggest that some proteinoid reactions, combined into a particular sequence, may have served as the beginnings of later metabolic systems. Thus, decarboxylation of oxaloacetic acid can be followed by decarboxylation of its product, pyruvic acid, leading to acetic acid and carbon dioxide; or amination of pyruvic acid can lead to alanine.
Furthermore, some proteinoids even show relatively sophisticated hormonal activity and can stimulate the production of melanin-producing cells.
Although researchers have debated whether the thermal synthesis of proteins could occur extensively in present natural surroundings, the exact conditions encountered on the primitive Earth are certainly not known. Surfaces near some volcanic regions, or upwelling’s from shallow marine hydrothermal plumes, may have maintained appropriate temperatures for the condensation of amino acids.
►Unit 6: Evolutionary Theories
Lamarckism, Darwinism, Neo-Darwinism.
Q.What do you mean by “Directed Mutation” theory?
This theory suggests that the offspring, for some unspecified reason to do with the hereditary mechanism, consistently tend to differ from their parents in a certain direction. In the case of wings, the explanation by the directed variation with proto wings, even though there was no advantage to it.
►Unit 7: Process of Evolutionary changes
Isolating mechanism, Natural Selection.
Q. What was the genetic basis of the melanin-related character of Biston betularia?
i)The difference in colour was controlled by one main locus, ii)The originals, peppered form was one homozygote (cc) and the melanic form was another homozygote (CC), and the C allele is dominant, iii)However, in other cases the melanin allele was less dominant and the heterozygotes were intermediate, there seem to be a number of different melanic alleles, iv)Selection may initially favoured a melanic allele with no or weak dominance and sub-sequently some other melanic alleles with stronger dominance
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►Unit 8: Speciation
Sympatric, Allopatric, Parapatric
Q.Climatic changes have driven the evolution of beak size in one of Darwin’s finches”-Justify the statement.
Peter and Rosemary (1973) evidenced influence of beak size on feeding efficiency in large beaked Geospiza magnirostris and smaller G. fortis (feeding on the same kind of hard fruit).
(a)Beak size influences feeding efficiency on different food types:
Natural selection would favour larger finches when large fruits and seeds are abundant.
(b)Inherited property on beak size :
Parents with larger than average beaks produce offspring with larger than average beaks in G. fortis on Daphne major, showing that beak size is inherited. Results are shown here for 2 years in the 1970s. Grant & Grant (2000) show that the result persisted in future years.
Quantitative genetic is concerned with characters influenced by many genes. Called polygenic characters. The value of a character, like beak size, will usually also be influenced by the environment in which the individual grows up. Beak size is probably related to general body size and all characters to do with bodily stature will be influenced by the amount of food an organism happens to find during its life.
(c) Influence of food supply:
At the beginning of drought, the various types of seeds were present in their normal proportions. G. fortis of all sizes take small seeds and as the drought persisted, these smaller seeds are relatively reduced in numbers. The average available seed size became larger with time. Now the larger finches were favoured, because they eat the larger, harder seeds more efficiently. The average finch size increased as the smaller birds die off.
(d)Selection fluctuates over time:
The fluctuations in the direction of selection on beak shape-with beaks evolving up in some years, down in other years and Staying constant in yet other years-probably results in a kind of 'stabilizing selection over long period of time such that the average size of beak in the population is the size favoured by long-term average weather.