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2021-05-07 11:07:29 OPTICS MNEMONICS

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2021-05-07 10:42:57 MATHS TRICK

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2021-05-07 10:10:15 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.

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2021-05-06 22:33:04 𝗣𝗥𝗜𝗡𝗖𝗜𝗣𝗟𝗘 𝗢𝗙 𝗜𝗡𝗛𝗘𝗥𝗜𝗧𝗔𝗡𝗖𝗘

Heredity is a process of transmission of heritable traits from parents to their offsprings.

Genetics is the branch of biology dealing with the principles and mechanism of inheritance and variation.

Inheritance is the basis of heredity and by this process, traits are passed on from the parents to the offsprings. Continuity of the gene pool is maintained by the process of inheritance.

Genes are the basic unit of inheritance and located on chromosomes.

Variation exists among individuals of one species. Variation is due to crossing over, recombination, mutation and environmental effects on the expression of genes present on chromosomes.

𒊹Mendel’s Laws of Inheritance

Gregor Johann Mendel is called “Father of genetics”.

Mendel performed experiments on Garden pea. He took 14 true-breeding plants of pea having seven distinguishable characters, which have two opposite traits.

He called genes as “factors”, which are passed from parents to offsprings.

Genes, that code for a pair of opposite traits are called “alleles”.



He gave three laws of inheritance based on his observation:

𒊹Law of Dominance

: One of the alleles is dominant and gets expressed in the phenotype in case of the heterozygote, e.g. When we cross homozygous tall (TT) and dwarf (tt) plants, in the offsprings we get all the tall plants having the genotype Tt, so tallness is a dominant trait over dwarfness.

➪Law of Segregation of genes:

Each allele separates during meiosis at the time of gamete formation. There is no blending and characters are passed to different gametes. Homozygotes produce only one kind of gametes and heterozygotes produce different kinds of gametes.



♲Law of Independent assortment:
It states that alleles for different traits are inherited independently. He showed that using a dihybrid cross.



Test Cross: It is to find out the genotype of the plant showing dominant trait, the given plant is crossed with the recessive homozygote. The two observations are:

If the phenotype of offsprings shows only the dominant trait, then the parent plant was homozygote to the dominant trait

If the offsprings produced are of both phenotypes, then the parent plant was heterozygote to the dominant trait

𒊹Incomplete Dominance

When neither of the two alleles is dominant and the phenotype of the heterozygote does not resemble any of the parents. The heterozygote expresses intermediate or a mixture of two parents’ traits

Example: The flower colour inheritance of snapdragon (dog flower). On crossing true breeding red (RR) and whiteflower (rr), we get all pink colour flowers in the F1 generation, which on self-pollination give red: pink: white flowers in the ratio 1:2:1 in the F2 generation



☞Co-dominance

When both the alleles express themselves together in an individual, they are said to be co-dominant

Example: The inheritance of the ABO blood group in humans is controlled by the gene I. The gene I has three allelic forms, IA, IB and i. In a human being, any two out of three alleles are presentIA and IB code for different kinds of sugar polymers present on the surface of RBC and ‘i’ does not produce any sugarIA and IB are dominant over ‘i’, but IA and IB are co-dominant and express themselves together.



➪Chromosomal Theory of Inheritance

Sutton and Boveri supported Mendel’s observations and stated that chromosomes are the carrier of genes

Chromosomes occur as a homologous pair and the two alleles of a gene are located on the homologous pair of chromosomes at the same site

Homologous chromosomes separate during meiosis in the process of gamete formation

Chromosomes segregate and assort independently

During fertilization, gametes combine and produce the offsprings with the diploid no. of chromosomes, that is similar to the parent

Morgan extensively worked on fruit flies, Drosophila melanogaster and provided experimental evidence to support the chromosomal theory of inheritance

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2021-05-06 17:24:26 QUESTION OF THE DAY IN ALL NEW WAY

QUESTION>TIMER>ANSWER >SOLUTION

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2021-05-06 12:42:15 PANDEMIC EXIST - Prep. TENSION

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Ap pandemic me paise save rkho, free me badhiya preparation ka intezaam hum karte hai

ANNOUNCING BOON SERIES

TOPPERS LIVE INTERACTIVE SESSION ME GUIDE BHI KARNGE, STUDY PLAN V DNGE
TOP NOTES V MILEGA
MOST IMPORTANT QUES..!

[watch above video for complete info.]

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2021-05-06 08:23:20 IMP OF PLANT KINGDOM

Isogamous sexual reproduction in algae- Ulothrix (flagellated)
Spirogyra (non-flagellated)

Anisogamous sexual reproduction in algae- Udorina

Oogamous sexual reproduction in algae- Volvox, Fucus

Algin- Brown Algae

Carragreen - Red Algae

Agar- Gelidium, Gracilaria
(Red algae)

Motile asexual spores in algae- Zoospores

Laminarin, Mannitol- Complex carbohydrates of Brown algae

Fucoxanthin- Brown Algae

Phycoerythrin- Red Algae

Floridean Starch Found in Red algae, similar to amylopectin and glycogen

The main plant body is a gametophyte- Bryophytes

Peat- Sphagnum

Microphylls- Selaginella

Macrophylls- Fern

Heterosporous pteridophytes- Selaginella
Salvinia

Vascular plants without seeds- Pteridophytes

Mycorrhiza- Pinus
(symbiotic association with fungi in the roots)

Coralloid roots- Cycas
(nitrogen-fixing cyanobacteria in the roots)

The tallest gymnosperm- Sequoia (redwood tree)
Microscopic angiosperm Wolffia

Parallel venation- Monocotyledons

Reticulate venation- Dicotyledons

The cells of embryo sac are- Haploid

Algae showing haplo-diplontic life cycle- Ectocarpus, Polysiphonia, Kelps

Algae showing the diplontic life cycle- Fucus

Zygotic meiosis- Haplontic life cycle

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2021-05-05 19:37:49 AIIMS PREVIOUS YEAR PAPERS (1994-2019)

BIOLOGY - CLICK HERE

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2021-05-05 17:39:39 QUESTION OF THE DAY IN ALL NEW WAY

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