Class 10 Science Chapter 9 MCQ

Here, all the statements are correct. Hence, your answer will be option [D].

When pure bred tall plant with phenotype (TT) crossed with short plant with phenotype (tt), the possible progeny in F2 generation: TT (1), tt (1) and Tt (2). Thus the ratio of pure tall (TT) to pure short (tt) is 1:1.

Father is responsible for the sex of the baby boy or girl which is born. If the husband contributes a “Y sex chromosome” at fertilization through his sperm, then the baby born will be a boy. This means that it is the sex chromosome contributed by husband which decides the sex of the baby which the wife will give birth to. Thus, husband is responsible for the sex of the baby (boy or girl) which is born.

Two individuals of a species share maximum number of common characters. A species is a population of organisms consisting of similar individuals which can breed together and produce fertile offspring.

All variations in a species do not have equal changes of survival. Some of the variations may be so drastic that the new DNA copy cannot work with the cellular apparatus it inherits. Such a newborn cell dies soon. Depending on the nature of variations, different individual will have different kinds of advantage. Variations results from changes in genetic composition. Advantages of variations are selected by environmental factors. This leads to evolution and speciation. In asexual reproduction, there is minimum variation that is due to small errors in DNA copy.

The weight reduction due to starvation will not change the DNA of the germ cells, because low weight is not a trait that is genetically controlled or inherited. Thus, low weight parents may have heavy weight progeny. Traits which are not inherited, i.e. the acquired traits are simply changes in non-reproductive tissues, so, cannot be passed on to DNA of germ cell. Evolution results from change in frequency of genes in a population over several generations.

In human males, one pair called the “Sex chromosomes” are unpaired. Here, one is a normal sized X-chromosome while other is a short Y-chromosome. Women have a perfect pair of sex chromosomes, both called X.

In F1 generation, the cross between “TT” and “tt” will result into all tall plants. Thus, tallness is the dominant trait or character. Whenever the two traits of a character are crossed, the F1 plants show only one of the traits. This trait is called the dominant trait. The other trait (dwarfness in this case) that does not express itself in F1 generation is called the recessive trait.

F2 generation can be obtained by allowing flowers on the plants of F1 generation to be self-pollinated.

The accumulation of “heat resistant variation” or trait in some bacteria will ensure its survival, even when the temperature in its environment rises to much due to a heat wave or some other reasons. On the other hand, the bacteria which did not have these variations to withstand heat would not survive under these circumstances and die.