Principles of Inheritance and Variation Test - 40

In biology, a mutation is a permanent change of the nucleotide sequence of the genome of an organism, virus, extrachromosomal DNA or other genetic elements. Mutations are the raw materials of evolution. Evolution absolutely depends on mutations because this is the only way that new alleles and new regulatory regions are created.

Backcross, the mating of a hybrid organism with one of its parents or with an organism genetically similar to the parent. The backcross is useful in genetic studies for isolating certain characteristics in a related group of animals or plants. In animal breeding, a backcross is often called as top cross.

The gene balanced theory was proposed by the Bridge. In Drosophila, Y chromosome does not use in sex determination. A single X chromosome in a diploid individual will make it male. The pair of  X chromosomes in a diploid individual make it female. Although both mammals and fruit flies produce XX females and XY males, their chromosomes achieve these ends using very different means. The sex-determining mechanisms in mammals and in insects such as Drosophila are very different. In mammals, the Y chromosome plays a pivotal role in determining the male sex.

A test cross is a way to explore the genotpye of an organism. Early use of the test cross was as an experimental mating test used to determine what alleles are present in the genotype. In genetics, a test cross, first introduced by Gregor Mendel, involves the breeding of a phenotypically dominant individual with a phenotypically recessive individual, in order to determine the zygosity of the former by analyzing proportions of offspring phenotypes. Zygosity can either be heterozygous or homozygous. Those that are heterozygous have one dominant and one recessive allele. Individuals that are homozygous dominant have two dominant alleles, and those that are homozygous recessive have two recessive alleles.

Correct Option: B

Explanation:

Mendelian inheritance is that the inheritance of biological options that follows the laws projected by G.J. Mendel, scientist in 1865 and 1866 and re-discovered in 1900. Once Mendel's theories were integrated with the body theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetic science. Following traits were studied by botanist during a garden pea :

• Flower colour is purple or white.
• Flower position is angle or terminal.
• Stem length is long or short.
• Pod form is inflated or constricted.
• Pod colour is yellow or inexperienced.
• Seed form is spherical or wrinkled.
• Seed colour is yellow or inexperienced.

Hence the proper answer is possibly green cotyledon colour.        

Polygenic inheritance occurs when one characteristic is controlled by two or more genes. Often the genes are large in quantity but small in effect. Examples of human polygenic inheritance are height, skin color, eye color and weight.

Nettie Maria Stevens was an early American geneticist. She and Edmund Beecher Wilson were the first researchers to describe the chromosomal basis of sex. She identified the Y chromosome in the mealworm, Tenebrio. She deduced the chromosomal basis of sex depended on the presence or absence of the Y chromosome.

Mutagenesis is a process by which the genetic information of an organism is changed in a stable manner, resulting in a mutation. It may occur spontaneously in nature, or as a result of exposure to mutagens. It can also be achieved experimentally using laboratory procedures. Mutagenesis in the laboratory is an important technique whereby DNA mutations are deliberately engineered to produce mutant genes, proteins, or strains of organism. Various constituents of a gene, such as its control elements and its gene product, may be mutated so that the functioning of a gene or protein can be examined in detail. The mutation may also produce mutant proteins with interesting properties, or enhanced or novel functions that may be of commercial use. Mutant strains may also be produced that have practical application or allow the molecular basis of particular cell function to be investigated.

Natural selection is the gradual process by which heritable biological traits become either more or less common in a population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment. It is a key mechanism of evolution. It is not a sudden genetic change. Thus, option D is wrong.
Hereditary is passing, or capable of passing, naturally from parent to offspring through the genes. It is not the sudden genetic changes which breed truely in an organism. Thus, option B is wrong.
Variation in biology is any difference between cells, individual organisms, or groups of organisms of any species caused either by genetic differences (genotypic variation) or by the effect of environmental factors on the expression of the genetic potentials (phenotypic variation). Variation may be shown in physical appearance, metabolism, fertility, mode of reproduction, behaviour, learning and mental ability, and other obvious or measurable characters. It is not the sudden genetic changes which breed truly in an organism. Thus, option A is wrong.
Mutation is the changing of the structure of a gene, resulting in a variant form which may be transmitted to subsequent generations, caused by the alteration of single base units in DNA, or the deletion, insertion, or rearrangement of larger sections of genes or chromosomes. Mutation is the concept of sudden genetic changes which breed truly in an organism. Thus, option C is correct.

Muton is the smallest hereditary element that can be altered by mutation. It is the functional unit of mutation.
Whereas cistron is a segment of DNA that is involved in producing a polypeptide chain. Recon is a unit of recombination. Gene is a unit of heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring.