Aakash AIATS

2021-06-17 15:23:12 Revision Notes on Inheritance and Variation


Exceptions of Conclusions of Mendel

Incomplete Dominance

(1) When neither of the alleles of a character is completely dominant over the other and the F1 hybrid is intermediate between the two parents, the phenomenon is called incomplete dominance.

(2) Incomplete dominance was first discovered by Correns in Mirabilis jalapa. The plant is called as 4’O clock plant or ‘Gul-e-Bans’. Homozygous red (RR) flowered variety of the plant was crossed with white (rr) flowered variety. F1 offspring had pink flowers (Rr). This is called incomplete dominance.

(3) Incomplete dominance is also known to occur in snapdragon. The phenotypic ratio and genotypic ratio in F2 generation in case of incomplete dominance is 1:2:1.

Co-dominance

(1) In co-dominance both the gene expressed for a particular character in F1 hybrid progeny. There is no blending of characters, whereas both the characters are expressed equally.

(2) Co-dominance is seen in animals for coat colour. When a black parent is crossed with white parent, a roan color in F1 progeny is produced.

Sex determination:

(1) Fixing the sex of an individual as it begins life is called sex determination. The various genetically controlled sex-determination mechanisms have been classified into following categories

(2) Chromosomal theory of sex determination: The X-chromosome was first observed by German biologist, Henking in 1891 during the spermatogenesis in male bug and was described as X-body. The chromosome theory of sex determination was worked out by E.B. Wilson and Stevens (1902-1905).

(3) They named the X and Y chromosomes as sex-chromosomes or allosomes and other chromosomes of the cell as autosomes.

(4) Sex chromosomes carry genes for sex. X-chromosomes carries female determining genes and Y-chromosomes has male determining genes.

(5) The number of X and Y chromosomes determines the female or male sex of the individual, Autosomes carry genes for the somatic characters. These do not have any relation with the sex.

Sex Determination by chromosomes:
Those chromosomes which are involved in the determination of sex of an individual are called sex chromosomes while the other chromosomes are called autosomes.

1) XX – XY type: In most insects including fruit fly Drosophila and mammals including human beings the females possess two homomorphic sex chromosomes, named XX. The males contain two heteromorphic sex chromosomes, i.e., XY. Hence the males produce two types of gametes / sperms, either with X-chromosome or with Y-chromosome, so they are called Heterogamety.

2) ZZ – ZW type: In birds and some reptiles, the males are represented as ZZ (homogamety) and females are ZW (heterogamety).

3) XX – XO type: In round worms and some insects, the females have two sex chromosomes, XX, while the males have only one sex chromosomes X. There is no second sex chromosome. Therefore, the males are designated as XO. The females are homogametic because they produce only one type of eggs. The males are heterogametic with half the male gametes carrying X-chromosome while the other half being devoid of it.


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2021-06-15 16:55:33 Notes on Plant Growth and Development

(1) The analysis of growth curve shows that it can be differentiated into three phases:

(i) Lag phase: It represents initial stages of growth. The rate of growth is very slow in lag phase. More time is needed for little growth in this phase.

(ii) Log phase (Exponential phase): The growth rate becomes maximum and more rapid. Physiological activities of cells are at their maximum. The log phase is also referred to as grand period of growth.

(iii) Final steady state (Stationary phase) or Adult phase: When the nutrients become limiting, growth slows down, so physiological activities of cells also slows down. This phase is indicated by the maturity of growth system. The rate of growth can be measured by an increase in size or area of an organ of plant like leaf, flower, fruit etc. The rate of growth is called efficiency index.

(2) Phytohormones:-

(i) Growth hormones also called phytohormones

(ii) Term given by Thimann (1948),

(iii) It can be defined as ‘the organic substances which are synthesized in minute quantities in one part of the plant body and transported to another part where they influence specific physiological processes’.

Growth Hormones and Growth Regulators
(1) Auxins:
(i) Auxins (Gk. auxein = to grow) are weakly acidic growth hormones having an unsaturated ring structure and capable of promoting cell elongation, especially of shoots (more pronounced in decapitated shoots and shoot segments) at a concentration of less than 100 ppm which is inhibitory to the roots. Among the growth regulators, auxins were the first to be discovered.

(ii) Types of auxins: There are two major categories of auxins natural auxins and synthetic auxins:

(a) Natural auxins: These are naturally occurring auxins in plants and therefore, regarded as phytohormones. Indole 3-acetic acid (IAA) is the best known and universal auxin. It is found in all plants and fungi.

(b) Synthetic auxins: These are synthetic compounds which cause various physiological responses common to IAA. Some of the important synthetic auxins are 2, 4-D (2, 4-dichlorophenoxy acetic acid) is the weedicide. IBA is both natural and synthetic auxin.

(iii) Functions of auxins: Auxins control several kinds of plant growth processes. These are as follows:

(a) Cell elongation: Auxins promote elongations and growth of stems and roots and enlargement of many fruits by stimulating elongation of cells in all directions.

(b) Apical dominance: In many plants, the apical bud grows and the lower axillary buds are suppressed. Removal of apical bud results in the growth of lower buds. The auxin (IAA) of the terminal bud inhibits the growth of lateral buds. This phenomenon is known as apical dominance.

(c) Weed control: Weeds are undesirable in a field with a crop. By the spray of 2, 4-D, broad-leaved weeds can be destroyed but 2, 4-D does not affect mature monocotyledonous plants.

(d) Root differentiation

(e) Control of lodging

(f) Parthenocarpy: Parthenocarpy can be induced by application of IAA in a paste form to the stigma of a flower or by spraying the flowers with a dilute solution of IAA.

(2) Gibberellins:
(i) Gibberellins are weakly acidic hormones having gibbane ring structure which cause cell elongation of intact plants in general and increased internodal length of genetically dwarfed plants (i.e., corn, pea) in particular.

(ii) Functions of gibberellin

(a) Stem elongation: The gibberellins induce elongation of the internodes.

(b) Leaf expansion: In many plants leaves become broader and elongated when treated with gibberellic acid.

(c) Reversal of dwarfism: One of the most striking effects of gibberellins is the elongation of genetic dwarf (mutant) varieties of plants like corn and pea. Open / Comment

2021-06-13 15:18:19 List of 🇳 🇨 🇪 🇷 🇹  Quizzes

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Hydrogen Peroxide

Hydrogen

Acid and bases

Hydride of Oxygen

Work power and energy

Kinetic theory

Solid state

Chemical bonding

Laws of motion

Gravitational force

Surface chemistry

Motion in straight line

Mechanical properties of solids

Motion in a plane

System Of particles & rotational motion

Chemical kinetics

Kinematics

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2021-06-10 17:09:20 Revision Notes on Inheritance and Variation


Numerical aberrations of chromosomes:
Each species has a characteristic number of chromosome. Variations or numerical changes in chromosomes (Heteroploidy) can be mainly of two types:

(1) Euploidy: The somatic chromosome number in euploids is the exact multiple of basic haploid number. In euploidy an organism acquires an additional set of chromosomes over and above the diploid complement.

(a) Monoploidy or haploidy: Monoploids possess only one set or single basic set of chromosomes. Haploids on the other hand have half the somatic chromosome number. In diploid organisms monoploids and haploids are identical while in a tetra-or hexaploid with 4n or 6n chromosomes the haploids will possess 2n or 3n chromosome whereas its monoploid will possess only one set (n) of chromosome.
(b) Diploidy: The common chromosome number in the somatic cells of plants and animals.
(c) Polyploidy: Organism with more than two sets of chromosomes are known as polyploids. It may be triploid with three sets of chromosomes (3n) or tetraploid with four sets of chromosome (4n) and so on.

(2) Aneuploidy: Aneuploidy is the term applied for the chromosomal mutations involving only a part of a set, i.e., loss (hypoploidy) or addition (hyperploidy) of one or more chromosomes. Aneuploidy may result from non disjunction of chromosome during cell division.
(a) Monosomy: Diploid organism that are missing one chromosome of a single pair with genomic formula 2n – 1. Monosomics can form two kinds of gametes, (n) and (n –1).
(b) Nullisomy: An organism that has lost a chromsome pair is nullisomic. The result is usually lethal to diploids (2n – 2).
(c) Trisomy: Diploids which have extra chromosome represented by the chromosomal formula 2n + 1. One of the pairs of chromosomes has an extra member, so that a trivalent may be formed during meiotic prophase.
(d) Tetrasomy: In tetrasomic individual particular chromosome of the haploid set is represented four times in a diploid chromosomal complement. The general chromosomal formula for tetrasomics is 2n + 2 rather than 2n + 1+ 1. The formula 2n + 1 + 1 represents a double trisomic.

Types of aneuploidy: Aneuploidy may be of following types on the basis of chromosomes involved in non disjunction.

(a) Aneuploidy involving non-disjunction in sex chromosomes: This kind of aneuploidy is brought about due to non-disjunction in sex chromosomes. It may lead to following types of syndromes:

(1) Turner’s syndrome: Such persons are monosomic for sex chromosomes i.e. possess only one X and no Y chromosome (XO). In other words they have chromosome number 2n – 1 = 45. They are phenotypic females but are sterile because they have under developed reproductive organs. They are dwarf about 4 feet 10 inches and are flat chested with wide spread nipples of mammary glands which never enlarge like those in normal woman. They develop as normal female in childhood but at adolescence their ovaries remain under developed. They lack female hormone estrogen. About one out of every 5,000 female births results in Turner’s syndrome. Open / Comment

2021-06-09 17:54:21 12TH PHYSICS NOTES

1) Rotational dynamics


https://drive.google.com/file/d/1H1pOOAsKwXgv4ruvDEFEIypkezRGSZf4/view

2) Mechanical properties of fluid

https://drive.google.com/file/d/1LW9AHpdHg5JgT_7LYO2QjcZPgp7A6EQy/view

3) KTG

https://drive.google.com/file/d/1P_mHPezVH0LWiFhcbz1pJUXGfhMBy2YG/view

4) Thermodynamics


https://drive.google.com/file/d/1V2TStC1CfGTke3cmNImbzXDq6tHihR_0/view

5) Oscillation

https://drive.google.com/file/d/1VYlDddBw9TJEvi4hLvKjWS1_tKh6eRYw/view


6) Superposition of Waves

https://drive.google.com/file/d/1YujY6MH89NTUpGa1HFOcAdRDlpnfjCyb/view

7) Wave Optics

https://drive.google.com/file/d/1zSjU-GHkLTcY1dRYuJSD1EFr19igs-xV/view


8) Electrostatics

https://drive.google.com/file/d/13MFw_iNb2kxxAiLNnsIoGwB5uNcyAwSy/view


9) Current electricity

https://drive.google.com/file/d/18djcCw6snTCzQRVWmgcc0VComCcOxygS/view

10) Magnetic field Due to Electric current

https://drive.google.com/file/d/1Aut65pVF1912TogkOPljmQv2cj01x2uu/view



11) Magnetic Materials

https://drive.google.com/file/d/1DK2ccD5RZ6pGAHwGmo9QkcxrFUcC-8_z/view

12) Electromagnetic Induction

https://drive.google.com/file/d/1EqQ0rVeF3Prc-kZRJ3phMQpxIpRRz39H/view


13) AC Circuits

https://drive.google.com/file/d/1FTWDq7X35Zj31UZxmIxImmu_yzOhkKzk/view



14) Dual Nature of Radiation

https://drive.google.com/file/d/1GIAXs1XERyclzPrX7V4DRcygbw4tKOKL/view


15) Structure of atom and nuclei

https://drive.google.com/file/d/1HWOgO11ZsaRZzMJxbMMjkF6AnWyg1KEc/view


16) Semiconductor Device

https://drive.google.com/file/d/1IOUBKiHTXCtL1-p3K_oiHG0RVgDaircF/view Open / Comment