Biology:2015:CBSE:[Delhi]:Set-I

A geneticist interested in studying variations and patterns of inheritance in living beings prefers to choose organisms with short life cycles for experiments because it enables the geneticist to study many generations of those organisms in their short lifespans.

Euchromatin is the transcriptionally active region of chromatin in a nucleus.

Industrial melanism was the reason for the increase in the population of dark-coloured moths along with the loss of lichens during industrialisation in England.
After industrialization, the tree trunks became darker with the deposits of soot and smoke. The number of dark moths increased as they were not easily visible to their predators however, the white-winged moths were easily picked up by the predators. Thus, dark ones were naturally selected and light ones fail to survive.

X-rays are potent mutagens and can cause adverse effects in children in the form of genital changes; i.e., they alter the genetic make-up of an organism.

The illegal exploitation of biological material of a country by organisations or multinational companies without proper authorisation from the concerned country is known as biopiracy.

The assisted reproductive technique for such couples is zygote intrafallopian transfer or ZIFT.
In this technique, the ovum is collected from the donor female and the sperm is collected from the donor male. The sperm and the ovum are allowed to fuse in laboratory conditions. They are developed till the 8-blastomere stage. The zygote or early embryo is then transferred to the fallopian tube of the mother for its further development.

Heterogamety means different sex gametes.
Male heterogamety includes human males having XY sex chromosomes and males of some insects, such as grasshopper and bugs, having XO sex chromosomes.

Female heterogamety includes females of some species of birds, fishes and insects. Females of butterfly and moth consist ZO sex chromosomes, while females of fish, reptiles and birds consist ZW sex chromosomes.

Mutation breeding is a technique in which plants having desirable mutations can be selected and chosen as a source for breeding. It has helped mung bean production by providing resistance against yellow mosaic virus and powdery mildew (fungal disease).

a) Lactic acid bacteria (LAB); Lactobacillus is used in the production of curd from milk.

b) Saccharomyces cerevisiae is used in baking industry.

c) Propionibacterium shermanii is used in the production of cheese.

d) Aspergillus niger is used in the production of citric acid.

Many freshwater fish cannot survive in the marine environment as their bodies are not adapted to the marine environment. Freshwater fish lose body water because of the hypertonic environment that has a higher concentration of salt in the surrounding water, making their survival difficult.