Biology Test - 66

A chromatid is one-half of two identical copies of a replicated chromosome. During cell division, the identical copies are joined together at the centromere. Joined chromatids are known as sister chromatids. Once the joined sister chromatids separate from one another in the anaphase of mitosis, each is known as a daughter chromosome.

The sum of genes in a population is called a gene pool.

Genotype is an individual's collection of genes.

Karyotype is the set of chromosomes as viewed under the microscope.

A gene can be defined as a polynucleotide chain that consists of segments each controlling a particular trait. Now, genes are considered as a unit of function (cistron), a unit of mutation (mutant) and a unit of recombination (recon).

In human fertilization, a released ovum (a haploid secondary oocyte with replicate chromosome copies) and a haploid sperm cell (male gamete)—combine to form a single 2n diploid cell called the zygote.

DNA has the double helical structure where the two strands are tightly coiled over each other. B- DNA has right-handed helix with the major and minor groove. The diameter of the DNA is 20 A. The number of base pairs in one turn is 10 and the distance between base pairs is 3.4 A.The total length of one turn of DNA is 34 A.

Mendel proposed the Law of Segregation after observing that pea plants with two different traits produced offspring that all expressed the dominant trait, but the following generation expressed the dominant and recessive traits in a 3:1 ratio.

A single attribute of an animal or plant transmitted at one locus from generation to generation in accordance with genetic principles is called inheritable character. Since, it is inherited from one generation to other its frequency keeps on increasing.

The gene increasing the frequency of mutations in other genes is Mutagene.

A gene that masks the phenotypic effect of another gene is called as an epistatic gene; the gene it subordinates is the hypostatic gene.

The lac operon (lactose operon) is an operon required for the transport and metabolism of lactose in Escherichia coli and some other enteric bacteria. The trp operon is an operon; a group of genes that are used or transcribed, together that codes for the components for production of tryptophan. The trp operon is present in many bacteria, but was first characterized in Escherichia coli.

The character of the chromosomal complement with reference to the comparative size , shape and morphology of different chromosomes .

Humans have 22 pairs of autosomesand one allosome pair (46 chromosomes total).

An autosome is a chromosome that is not a sex chromosome.The autosome pairs are labeled with numbers (1-22 in humans) roughly in order of their sizes in base pairs, while allosomes are labeled with their letters. By contrast, the allosome pair consists of two X chromosomes in females or one X and one Y chromosome in males.