Principles of Inheritance and VariationNEET Botany · Class 12 · NCERT Chapter 2

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Fruit colour in squash is an example of dominant epistasis, where one gene masks the expression of another gene. NCERT XII chapter Principles of Inheritance and Variation explains that in squash, the white fruit colour gene is epistatic over the yellow or green fruit colour genes, so option (b) is correct.

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The man has a genotype of $X^{B}Y$ (since his father was colour blind, $X^{b}Y$) and the woman has a genotype of $X^B{X}^b$ (since her mother was colour blind, $X^b{X}^b$). The cross $X^{B}Y\times X^B{X}^b$ results in 50% of male children being $X^{b}Y$ (colour blind), so option (c) is correct.

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The frequency of allele $A$ is calculated as $\frac{2\times \text{AA}+\text{Aa}}{2\times \text{Total individuals}}$. Substituting the values, $\frac{2\times 360+480}{2\times 1000}=\frac{1200}{2000}=0.6$, so option (c) is correct.

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A human female with Turner's syndrome has 45 chromosomes with an XO genotype. NCERT XII chapter Principles of Inheritance and Variation states that Turner's syndrome results from the absence of one X chromosome, leading to the 45,X karyotype, so option (a) is correct.

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Sulphur and phosphorus are found on earth crust in the form of rocks

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Colour blindness is an X-linked recessive trait. The man is $X^{c}Y$ and the woman is $X^B{X}^B$. Their daughter will be $X^B{X}^c$. If the daughter marries a normal man ($X^{B}Y$), their son has a 50% chance of being colour blind ($X^{c}Y$). Thus, the probability of their grandson being colour blind is 0.5, so option (a) is correct.

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The term "linkage" was coined by T.H. Morgan.

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The sequence of event during meiosis are

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The gene which controls multiple traits in an individual.

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Mendel did not selected Pod length as a character for study

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The given pedigree represents inheritance of Autosomal recessive trait. `

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The members of kingdom-Monera are prokaryotes they lack nuclear membrane.

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Genes related with hemophilia are always present on X chromosome and it is a recessive gene disorder as it expresses itself in females when it comes a homozygous condition. It causes a defect in the clotting factor formation, thus a simple cut can bleed continuously leading to even death. Thus, it is also known as ‘Bleeders’ disease or ‘Royal Disease’ as Queen Victoria is a carrier for this disease.

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Phenotypic ratio : tall : dwarf Genotypic ratio : TT : Tt : tt 1 : 2 : 1

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www.vedantu.com 58 Dominance – In a heterozygous organism only one allele expresses itself. Codominance – In a heterozygous organism both alleles express themselves equally. Pleiotropy – A single gene influences many characters. Polygenic Inheritance – Many genes govern a single character.

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If a plant genotype Aa Bb is crossed with aabb then Independent Assortment would result in production of 4 type of offsprings in equal proportion. Aa Bb – gametes AB Ab aB ab Aa bb – Gametes ab ab ab ab Offspring according to independent assortment AaBb Aabb aaBb aabb 1 : 1 : 1 : 1 (Parental) (Recombinants) (Parental) Since parental percentage is more than recombinants it is due to linkage between genes A and B.

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Down’s syndrome is caused by non-disjunction of 21 st chromosome.

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AB AII Ii Husband Wife× I A I B I A I A I A I A I B iI i A Ii B + Number of genotypes = 4 Number of phenotypes = 3 I AIA and IAi = A IAIB = AB IBi = B

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During his experiments Mendel studied seven characters. Nature of trichomes i.e., glandular or non-glandular was not considered by Mendel. www.vedantu.com 27

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Mendel conducted hybridization experiments on Pea plant for 7 years between 1856 to 1863 and his data was published in 1865 (according to NCERT).

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An X-linked condition on one of the woman's X chromosomes can be inherited by both her sons and daughters. Sons receive their X chromosome from their mother, while daughters receive one X chromosome from each parent, so option (d) is correct.

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The inheritance of blood groups in humans is characterized by dominance, co-dominance, and multiple alleles. These concepts are explained in NCERT XII chapter Principles of Inheritance and Variation, making option (b) correct.

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Ref. XII NCERT Chapter- 02, Page No. 34

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Factual NCERT

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Given (𝑝)=0.4 (𝑝+𝑞=1) Hence (𝑞)=0.6 To find Homozygous dominant = 𝑝2 =(0.4)2=0.16 Heterozygous = 2pq = 2 × 0.4 × 0.6 = 0.48 Homozygous recessive = 𝑞2 = (0.6)2 = 0.36

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Ref. XI NCERT Chapter- 02, Page No. 22

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Ligases join two DNA molecules by forming a phosphodiester bond between the 3' hydroxyl and 5' phosphate ends. NCERT XII chapter Principles of Inheritance and Variation describes ligases as essential for DNA replication and repair, so option (a) is correct.

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Thomas Hunt Morgan provided experimental verification of the chromosomal theory of inheritance through his work with Drosophila melanogaster. NCERT XII chapter Principles of Inheritance and Variation credits Morgan for this contribution, so option (d) is correct.

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The gene ‘I’ has three alleles: $I^A$, $I^B$, and $i$. A person will have only two of these alleles. When $I^A$ and $I^B$ are present together, they express different types of sugars, not the same type. The allele $i$ does not produce any sugar. Therefore, option (c) is incorrect.

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- Haemophilia is X-linked recessive.
- Phenylketonuria is autosomal recessive.
- Sickle cell anaemia is an autosomal recessive trait linked to chromosome 11.
- Thalassemia is autosomal recessive, not X-linked.

Therefore, option (c) is correct.

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Mendel selected 14 true breeding pea plant varieties as pairs, each differing in one character with contrasting traits. This is detailed in NCERT XII chapter Principles of Inheritance and Variation, so option (c) is correct.

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The production of gametes, formation of zygotes, and the F1 and F2 generations are illustrated using a Punnett square. This diagram helps predict the genotypic and phenotypic ratios of offspring, so option (c) is correct.

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Mature sieve tube elements lack a nucleus and most cytoplasmic organelles, making option (a) incorrect. NCERT XI chapter Cell: The Unit of Life describes sieve tube elements as enucleated and having a minimal cytoplasm.

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Mutations in plant cells can be induced by gamma rays, which are ionizing radiation known to cause genetic changes. NCERT XII chapter Principles of Inheritance and Variation discusses the role of physical mutagens like gamma rays in inducing mutations, so option (c) is correct.

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The pyramid of biomass in the sea is generally inverted because the biomass of consumers exceeds that of producers. NCERT XII chapter Ecosystem explains that in aquatic ecosystems, the biomass of phytoplankton is less than that of zooplankton, making option (b) incorrect.

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In the Electron Transport Chain (ETC), one molecule of NADH + H${}^{+}$ gives rise to 3 ATP molecules, and one FADH${}_2$ gives rise to 2 ATP molecules. This is a key concept in cellular respiration as described in NCERT XI chapter on Respiration in Plants, making option (b) incorrect.

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RNA polymerase binds with the Rho factor to terminate transcription in bacteria. This is a key mechanism of transcription termination in prokaryotes, as described in NCERT XII chapter Principles of Inheritance and Variation, making option (b) correct.

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- Large colorless empty cells in the epidermis of grass leaves are subsidiary cells, which assist in the opening and closing of stomata.
- Option (a) is correct as it accurately describes the function and location of subsidiary cells.

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Fusion of protoplasms between two motile or non-motile gametes is called plasmogamy, as stated in NCERT XII chapter Principles of Inheritance and Variation. Option (b) is correct.

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Cyclic photophosphorylation involves only PS I, not PS II. NCERT XI chapter Photosynthesis in Higher Plants states that cyclic photophosphorylation generates ATP but not NADPH, and it occurs without the involvement of PS II, so option (d) is incorrect.

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In a cross between two heterozygous individuals (Aa x Aa), the expected phenotypic ratio is 3:1, with 25% of the progeny being homozygous recessive (aa) and thus diseased. NCERT XII chapter Principles of Inheritance and Variation explains this using a Punnett square, so option (c) is correct.

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Ricin is a toxin, not a drug. Alkaloids include codeine, toxins include abrin, and lectins include concanavalin A, as per NCERT XII Principles of Inheritance and Variation. Therefore, option (d) is incorrect.

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Grasshopper is an example of XO type of sex determination in which the males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.

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Gregor J. Mendel, conducted hybridisation experiments on garden peas and selected 14 true breeding pea plant varieties (seven contrasting traits). Contrasting traits studied were smooth or wrinkled seeds, yellow or green seeds, inflated on constricted pods, green or yellow pods, tall or dwarf plants, violet or white flowers and axial or terminal flower positions. SECTION-B

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Haemophilia is a X-linked recessive disorder. Thalassemia is an autosomal recessive disorder. Sickle cell anaemia is an autosomal recessive disorder. Myotonic dystrophy is an autosomal dominant disorder i.e. it occurs due to the presence of autosomal linked dominant trait.

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Closely located genes do not show independent assortment. Mendel’s law of independent assortment holds good for those genes which are located on different chromosomes.

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If mother of man is colourblind, then man will also be colourblind as colour blindness is a X -linked recessive trait and shows criss-cross inheritance. - 63 - NEET (UG)-2022 (Code- Q1)

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1% recombination frequency = 1 centi Morgan To place the genes on a linear chromosome, decreasing order of recombination frequency will be considered.

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Pleiotropism is the phenomenon where a single gene affects multiple phenotypic traits. NCERT XII chapter Principles of Inheritance and Variation defines pleiotropism as the ability of a single gene to have multiple effects, so option (d) is correct.

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Alfred Sturtevant used the frequency of recombination between gene pairs to map their positions on chromosomes, pioneering the concept of genetic mapping. NCERT XII chapter Principles of Inheritance and Variation credits Sturtevant with this method, so option (d) is correct.

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A. Two or more alternative forms of gene are called alleles. B. Cross of F1 progeny with homozygous recessive parent is a test cross. C. Cross of F1 progeny with any of the parents is a back cross. D. Number of chromosome sets in plant is called ploidy.

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To determine the genotype of a black seed colour at F2, the black seed from F2 is crossed with the white seed colour. This is called a test cross. ∴ To determine the genotype of (BB/Bb) black seed we need to cross them with white seed i.e. bb.

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According to Law of Dominance (1) Characters are controlled by discrete units called factors (2) Factors occur in pairs (3) In a dissimilar pair of factors one member of the pair dominates (dominant) the other recessive The law of dominance is used to explain the expression of only one of the parental characters in a monohybrid cross. Law of segregation is based on the fact that the allel es do not show any expression and both the characters are recovered as such in F2 generation

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Pink colour flower in snapdragon have genotype Rr Red flowered snapdragon have genotype RR when they both are crossed ♂ ♀ R R Phenotype R RR RR Red : Pink : White r Rr Rr 2 2 0 So the progeny that we get are red and pink flowered plants only

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The correct answer is option (4) as a constant gene pool will not disturb the Hardy-Weinberg equilibrium. Option (1), (2) & (3) will affect the equilibrium leading to evolution.

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Genotype of father with blood group B+ = IBi/iIB Genotype of mother with blood group A+ = IAi/iIA Genotype of child with blood group O+ = ii Hence only ‘A’ is correct.

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Polygenic inheritance refers to the inheritance of a trait controlled by two or more genes. When human disorders are determined by mutation in the single gene then they are transmitted to the offspring as per Mendelian principle. Polygenic trait shows non-Mendelian inheritance pattern.

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The unequivocal proof that DNA is the genetic material came from the experiment of Alfred Hershey and Martha Chase.

Euchromatin are lightly stained region with loosely packed chromatin fibre.

Frederick Griffith performed series of experiments by selecting the different strains of Streptococcus pneumoniae.

Heterochromatin are darkly stained region with tightly packed chromatin fibre.

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Sol. A classical dihybrid cross performed by Mendel involves.

A cross which was made between a pure round yellow seeded pea plant (RRYY) with wrinkled green seeded plant (rryy). Yellow colour is dominant over green and round seed shape over wrinkled seed shape.

Phenotypic ratio in F2 generation

9 : 3 : 3 : 1

Round yellow Round green Wrinkled yellow Wrinkled green