Class 10 – Science Extra Questions – Ch. 8 – Heredity

Ans: B

Explanation: The scientific consensus, supported by extensive genetic and fossil evidence, is that the human species originated in Africa. Genetic studies have traced the deepest roots of human ancestry to the African continent, and numerous hominin fossils, including early Homo sapiens, have been discovered there. The “Out of Africa” theory is the most widely accepted model for human evolution and migration.
Correct Option: B

Ans: A

Explanation: Charles Darwin is most famously known for his theory of evolution by natural selection. While mutations are a source of genetic variation that fuels evolution, and inorganic evolution describes the chemical and physical evolution of the universe, Darwin’s primary contribution and the concept most directly and strongly associated with his name is natural selection.
Correct Option: A

Ans: A

Explanation: A monohybrid cross involves the inheritance of a single trait. When two heterozygous parents are crossed (e.g., Tt x Tt), each parent can produce gametes with either the dominant allele (T) or the recessive allele (t). Using a Punnett square, we can determine the possible genotypes of the offspring. The possible combinations are TT (from T from parent 1 and T from parent 2), Tt (from T from parent 1 and t from parent 2, or t from parent 1 and T from parent 2), and tt (from t from parent 1 and t from parent 2). The probabilities of these combinations are 1/4 for TT, 2/4 (or 1/2) for Tt, and 1/4 for tt. Therefore, the expected genotypic ratio is 1 TT : 2 Tt : 1 tt.
Correct Option: A

Ans: C

Explanation: In humans, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). During fertilization, the father contributes either an X or a Y chromosome, while the mother always contributes an X chromosome. If the father contributes an X chromosome, the offspring will be XX (female). If the father contributes a Y chromosome, the offspring will be XY (male). Therefore, the presence of a Y chromosome from the father determines that the child will be male.
Correct Option: C

Ans: A

Explanation: Gregor Johann Mendel, an Austrian monk, is widely recognized for his meticulous experiments with pea plants, which laid the foundation for the field of genetics. His work demonstrated the principles of inheritance, showing how traits are passed from parents to offspring in predictable patterns. The other options are either abbreviated or incorrect versions of his name.
Correct Option: A

Ans: A

Explanation: Homologous organs are structures in different species that are similar because of common ancestry, even though they may have different functions. Analogous organs, on the other hand, have similar functions but different underlying structures and evolutionary origins. Homolytic and analytic are not standard biological terms for classifying organs in this context.
Correct Option: A

Ans: C

Explanation: Human blood types (A, B, AB, O) are determined by alleles for the ABO gene. Alleles A and B are codominant, meaning that if an individual inherits both the A and B alleles, both traits are expressed, resulting in blood type AB. Allele O is recessive to both A and B. Therefore, the relationship between A and B is codominance.
Correct Option: C

Ans: C

Explanation: Neanderthals (C) had cranial capacities that were, on average, larger than those of modern humans. While Australopithecus (A) had much smaller brains, and Java man (B) and Peking man (D) (both *Homo erectus* or related species) had brains that were larger than Australopithecus but still smaller than modern humans and Neanderthals. Therefore, Neanderthal man exhibited a brain size comparable to, and often exceeding, that of contemporary humans.
Correct Option: C

Ans: B

Explanation: Option B is the false statement. The reduction in the weight of an organism due to starvation is an environmental factor and not a genetic trait. While genetics plays a role in an organism’s potential for weight gain or loss, starvation itself is an external condition that affects the phenotype, not a change in the inherited genes. Options A, C, and D are true statements. Option A describes the fundamental process of evolution: changes in allele frequencies over time. Option C is true because offspring inherit a combination of genes from both parents, and the genetic potential for weight can lead to heavier progeny even if parents are not heavy. Option D is also true, as evolution is driven by heritable changes; acquired traits due to environmental influences are not passed down.
Correct Option: B

Ans: C

Explanation: The most compelling evidence that humans and chimpanzees share a common ancestor comes from the genetic and chromosomal similarities between the two species. Humans and chimpanzees have a very high degree of DNA similarity, and crucially, they share a similar chromosome structure. Humans have 23 pairs of chromosomes, while chimpanzees have 24 pairs. However, research has shown that human chromosome 2 is the result of a fusion of two separate ancestral chromosomes that are still found independently in chimpanzees and other great apes. This fusion event is a strong indicator of shared ancestry. While cranial capacity and binocular vision are traits that have evolved in primates, including humans and chimpanzees, and dental formulas can provide some insights into evolutionary relationships, these are not as direct or powerful as the chromosomal evidence in demonstrating a recent common ancestor.
Correct Option: C