Q.1. How is it possible for a child to have a blood group O if the parents have blood groups A and B?
Answer- Case I- If the father is IA and mother is IB, the child will have blood groups AB, A, B, O.
Case II- If a father is IA and mother is IB, the child will have the same blood groups as in the case I, i.e., AB, A, B, and O. Thus if the parents have heterozygous alleles, the child will have blood group O.
Q.2. Why is it that women exceeding 40 years of age have more chances of having a child with Down’s syndrome?
Answer-The women exceeding 40 years of age have more chances of having a child with Down’s syndrome because increased age affects the meiosis of chromosomes adversely. The meiosis remains incomplete until fertilization. It remains arrested at prophase-I and the chromosome is unpaired. If the fertilization occurs after a very long gap, the chromosomes will have to remain unpaired for a longer time. The longer the time of unpairing, the greater are the chances of its non-disjunction, and hence conditions like trisomy arise.
Q.3. How was it known that the genes are located on chromosomes?
Answer-The chromosomal theory of inheritance proposed by Bovine and Sutton stated that the genes are present on specific locations on a chromosome. Later, Thomas Morgan observed mutation in the eye colour of the fruit flies and based on the inheritance patter concluded that the gene responsible for the eye colour is located on the X-chromosome.
Q.4. A plant with yellow flowers was crossed with a plant with red flowers. The F1 progeny obtained had orange flowers. What is the inheritance pattern?
Answer-The inheritance is incomplete dominance. In this, a new intermediate phenotype between the two original phenotypes is obtained. One allele for a specific trait is not completely expressed over the other allele for the same trait.
Q.5. Mention the characteristics of a true-breeding line.
Answer- Characteristics if true breeding is as follows:
- It undergoes self-pollination.
- It depicts stability in the inheritance for several generations.
- Provide gametes with similar traits, hence used as parents for artificial hybridization.
- Homozygous recessive plants are used to identify the genotype through a test cross.
Q.6. Who had proposed the chromosomal theory of inheritance?
Answer-Theodor Boveri and Walter Sutton are the two scientists who were credited with developing the Chromosomal Theory of Inheritance during the early 1900s.
Q.7. Why does sickle-cell anaemia persist in the human population when it is believed that the harmful alleles get eliminated from the population after a certain time?
Answer-Sickle cell anaemia is an autosomal recessive disease in which the red blood cells become sickle-shaped, inhibiting the oxygen-carrying capacity of the blood. Despite this, it protects the carrier from malaria. Individuals with heterozygotes HbAS survive more than the homozygotes HbSS because they are not exposed to the same severity of risks.
Q.8. Define artificial selection. Has it affected the process of natural selection?
Answer-Artificial selection is the intentional breeding of plants and animals where the breeders select the desired traits and make them breed to produce offsprings with the required characteristics. It is an ancient method of genetic engineering. It surely affects the process of natural selection. The individuals cannot evolve on their own. The process is a threat to biodiversity. The traits are not selected considering the fitness of the organism.
Q.9.What are Sex chromosomes?
Answer- Sex chromosomes are defined as a pair of chromosomes, which determine whether an individual is male or female. In all mammals, including humans, have sex chromosomes X and Y in their cells. Females have two X chromosomes(XX), and males have an X and a Y chromosome (XY).
Q.10.What are chromosomes and who discovered chromosomes?
Answer- Chromosomes are thread-like structures present within the nucleus of a cell. Each species has a unique number of chromosomes and it varies from one organism to another. Humans have 23 pairs of chromosomes and Humans have 23 pairs of chromosomes.
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