Q.1 How is the sex of a newborn determined in humans?
Ans. The sex of a newborn in humans is determined by the combination of sex chromosomes inherited from the parents. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The presence of Y chromosome determines male sex.
Q.2 Do genetic combination of mothers play a significant role in determining the sex of a new born?
Ans. Yes, the genetic combination of mothers does play a significant role in determining the sex of a newborn. The mother always contributes an X chromosome to the offspring, while the father can contribute either an X or a Y chromosome, determining the sex of the baby.
Q.3 Mention three important features of fossils which help in the study of evolution.
Ans. Three important features of fossils that aid in the study of evolution are:
(a) Fossils provide evidence of past life forms and allow scientists to study the anatomical structures of ancient organisms.
(b) Fossils help in understanding the chronological order of species and the transitions between different forms of life.
(c) Fossils provide insights into environmental conditions and changes over geological time.
Q.4 Why do all the gametes formed in human females have an X chromosome?
Ans. All gametes formed in human females have an X chromosome because females have two X chromosomes (XX). During meiosis, each egg cell receives one X chromosome from the mother.
Q.5 In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.
Ans. In human beings, the statistical probability of getting either a male or female child is 50:50 due to the random assortment of sex chromosomes during fertilization. Each sperm carries either an X or a Y chromosome, and the chance of fertilization by either type of sperm is approximately equal.
Q.6 A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Ans. A very small population of a species faces a greater threat of extinction than a larger population due to genetic factors such as genetic drift and inbreeding. In a small population, there is less genetic diversity, making the population more vulnerable to diseases, environmental changes, and genetic disorders.
Q.7 What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?
Ans. Homologous structures are anatomical features that have a similar structure but may have different functions. An example is the forelimbs of mammals, including humans, bats, and whales. While these structures have a common origin (common ancestor), they may have evolved to serve different purposes in different species.
Q.8 Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Ans. The occurrence of diversity of animals on Earth suggests their diverse ancestry as evolution has led to the emergence of various species with different characteristics adapted to their environments. The diversity of life forms indicates the evolutionary processes that have shaped the development of different species over time.
Q.9 Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive
(i) yellow seed
(ii) round seed
Ans. The pair of contrasting traits in pea plants are:
(i) yellow seed (dominant) and green seed (recessive), and
(ii) round seed (dominant) and wrinkled seed (recessive).
Q.10 Why did Mendel choose pea plant for his experiments?
Ans. Mendel chose pea plants for his experiments because they possess several distinct traits that are easy to observe and manipulate, they have a short reproductive cycle, and they can self-pollinate or be cross-pollinated manually.
Q.11 A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
Ans. A woman having only daughters suggests that the father has been consistently contributing an X chromosome (since females inherit an X chromosome from both parents) during fertilization. This situation does not determine the sex of the offspring solely based on the mother’s genetic contribution.
