Biology Test - 20

The correct option is 'A - II, B - IV, C - I, D - III'.

Key Points

• Human skin colour is determined by Polygenic inheritance (II).
  • Polygenic inheritance refers to the inheritance of a phenotypic trait that is attributable to two or more genes and can be measured along a continuum.
  • Human skin color is an excellent example of polygenic inheritance, which is influenced by more than one gene and shows a wide range of phenotypes.
• A pair of alleles expressing contrasting traits refers to being Heterozygous (IV).
  • Heterozygous individuals have two different alleles for a given gene.
  • This condition often results in a phenotype that may express a dominant trait over a recessive one, illustrating the concept of dominance and recessivity in genetics.
• The ABO blood group system demonstrates Multiple allelism (I).
  • Multiple allelism occurs when three or more alleles for a gene exist within a population.
  • In the ABO blood group system, the A, B, and O alleles interact to produce the four blood types: A, B, AB, and O, showcasing multiple allelism.
• Antirrhinum flower colour is an example of Incomplete dominance (III).
  • Incomplete dominance occurs when the phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes.
  • For Antirrhinum (snapdragon) flowers, a cross between a red-flowered plant and a white-flowered plant results in offspring with pink flowers, demonstrating incomplete dominance.

Therefore, the correct pairing is:

A - II: Human skin colour - Polygenic inheritance

B - IV: Pair of alleles expressing contrasting traits - Heterozygous

C - I: ABO blood group - Multiple allelism

D - III: Antirrhinum flower colour - Incomplete dominance

Key Points

• During transcription, the sequence of the template strand of DNA is used to create a complementary mRNA transcript.
• Adenine (A) pairs with Uracil (U) in RNA, and Cytosine (C) pairs with Guanine (G).
• The template DNA strand sequence given is 3'-ATTGAACTG-5'. To find the mRNA sequence, we must use complementary base pairing and remember that RNA uses Uracil (U) instead of Thymine (T).
• The correct mRNA sequence is 5'-UAACUUGAC-3' because it is complementary and antiparallel to the DNA template strand.

Key Points

• The correct answer is option 3: (A), (C) and (D) only.
• This means the regions of the transcription unit include the Promoter, Terminator, and the Structural Gene.
• The Promoter is a region of DNA that initiates transcription of a particular gene. It is where the RNA polymerase binds to start transcription.
• The Terminator is a sequence of nucleotides in DNA that marks the end of a gene or operon in genomic DNA during transcription.
• The Structural Gene consists of the DNA sequence that is actually transcribed into RNA, which may then be translated into a protein.

Key Points

• Microbes play an important role for the production of industrial products.
• They are used for fermented beverages, antibiotics, bioactive molecules as well as food products like cheese.
• Microbes may include bacteria as well as fungi.
• Monascus purpureus is a type of yeast that is used to produce statins.
• Statins are blood cholesterol-lowering agents.
• It can induce competitive inhibition of the enzyme responsible for synthesis of cholesterol.

The correct answer is The energy and biomass relationship between the organisms at different trophic levels

• Ecological pyramids can determine the energy and biomass relationship between organisms at different trophic levels.
• These pyramids depict the flow of energy or biomass through the various levels of a food chain or food web.
• As you move up the pyramid, typically from producers (plants) to primary consumers (herbivores) to secondary consumers (carnivores), the energy or biomass available decreases, representing the loss of energy as it is transferred between trophic levels.

(A) Correct. Sex education in schools increases awareness about reproductive health, contraception, STIs, and safe practices, reducing misconceptions and promoting informed decisions.

(B) Correct. Family planning programs, such as those promoting contraceptives, sterilization, and education, aim to control population growth by enabling couples to plan family size and spacing.

(C) Incorrect. Female contraceptive options (e.g., pills, IUDs, implants, tubectomy, injectables) are more diverse than male options, which are primarily limited to condoms and vasectomy. Male hormonal contraceptives are still experimental.

(D) Incorrect. Surgical contraception methods (vasectomy and tubectomy) are highly effective but designed to be permanent. Reversal is possible in some cases (e.g., vasovasostomy or tubal ligation reversal), but success is not guaranteed, making “reversible” inaccurate.

(E) Correct. Medical Termination of Pregnancy (MTP) is legal in India under the MTP Act, 1971 (amended in 2021), but only under strict conditions, such as within 24 weeks (with exceptions), medical necessity, or consent, to prevent misuse.

(A) Correct: Mendel conducted experiments on garden peas to study inheritance patterns.

(B) Incorrect: Mendel's experiments showed that traits do not blend in F1; only one trait from the parent is expressed.

(C) Correct: According to the Law of Dominance, in a heterozygous pair, one allele (dominant) masks the expression of the other (recessive).

(D) Correct: In a monohybrid cross, F1 progeny only show the dominant trait of the parents.

(E) Correct: The Law of Segregation states that alleles separate randomly during gamete formation.

(A) Correct: A Punnett square is used to calculate the probability of different genotypes in offspring.

(B) Incorrect: Genotype cannot always be determined from phenotype, especially in heterozygous organisms.

(C) Incorrect: The Law of Segregation (alleles separate into gametes) is distinct from the Law of Independent Assortment (genes assort independently).

(D) Correct: In co-dominance, both alleles are expressed equally, such as in the case of human blood types.

(E) Incorrect: The Law of Dominance applies when one allele is dominant over the other, regardless of whether the alleles are identical or not.

(A) Correct: Females have two X chromosomes (XX), which determine the female genotype.

(B) Correct: In the XY system, the presence of the Y chromosome determines male traits.

(C) Correct: Down's syndrome is caused by trisomy of chromosome 21, leading to an extra chromosome.

(D) Incorrect: Haemophilia is a sex-linked recessive disorder, but it is carried on the X chromosome, not the Y chromosome.

(E) Incorrect: Klinefelter’s syndrome is characterized by an extra X chromosome (XXY), not the absence of an X chromosome.

(A) Correct: The human genome contains approximately 3 billion base pairs.

(B) Incorrect: The lac operon is regulated by the presence of lactose, not glucose.

(C) InCorrect: In the double helix, the sugar-phosphate backbone is on the outside, and the nitrogenous bases face inward.

(D) Correct: mRNA is synthesized in the 5' to 3' direction during transcription.

(E) Correct: Translation occurs in the cytoplasm, not in the nucleus of eukaryotic cells.