Microevolution (evolution on a small scale) refers to the changes in allele frequencies within a population. Allele frequencies in a population may change due to four fundamental forces of evolution such as natural selection, genetic drift, mutation and gene flow.

In DNA, the two strands being complementary, if separated (denatured) by heating can come together (renaturation) when appropriate condition is provided. Further, 2' OH group present at every nucleotide in RNA is a reactive group that makes RNA liable and easily degradable. RNA is also known to be catalytic and reactive. Hence, DNA is chemically more stable and chemically less reactive when compared to RNA. Presence of thymine instead of uracil in DNA confers additional stability to DNA.

Ozone layer depletion can be controlled by
(1) Phase down or ban the use of CFCs (CFC free refrigerants).
(2) Minimizing the use of chemicals such as halons and halocarbons.
(3) Creating awareness about ozone depleting agents.

Propionibacterium shermanii.
The holes are due to the formation of large amount of carbon-di-oxide during fermentation

Direct and indirect human activities have a detrimental effect on biodiversity. Direct human activities like change in local land use, species introduction or removal, harvesting, pollution and climate change contribute a greater pressure on loss of biodiversity. Indirect human drivers include demographic, economic, technological, cultural and religious factors.

The PCR technique can also be used for amplifications of RNA in which case it is referred to as reverse transcription PCR (RT-PCR). In this process the RNA molecules (mRNA) must be converted to complementary DNA by the enzyme reverse transcriptase. The cDNA then serves as the template for PCR.

A genetic disorder is a disease or syndrome that is caused by an abnormality in an individual DNA. Abnormalities can range from a small mutation in a single gene to the addition or subtraction of an entire chromosome or even a set of chromosomes. Genetic disorders are of two types namely, Mendelian disorders and chromosomal disorders.

As the pregnancy progresses, increase in the oestrogen concentration promotes uterine contractions. These uterine contractions facilitate moulding of the foetus and downward movement of the foetus. The descent of the foetus causes dilation of cervix of the uterus and vaginal canal resulting in a neurohumoral reflex called Foetal ejection reflex or Ferguson reflex. This initiates the secretion of oxytocin from the neurohypophysis which in turn brings about the powerful contraction of the uterine muscles and leads to the expulsion of the baby through the birth canal.

(i) Sertoli cells are elongated and pyramidal cells.
(ii) They provide nourishment to sperm till maturation.
(iii) They secrete a hormone called inhibin which is involved in negative feedback control of sperm production.

(a) Fungal STI - Candidiasis
(b) Bacterial STI - Gonorrhoea
(c) Protozoan STI - Trichomoniasis

Incomplete parthenogenesis is a type of reproduction in which both sexual reproduction and parthenogenesis occur. Example: In honey bees, the fertilized eggs develop into a queen bee and worker bees, whereas the unfertilized eggs develop into drones (male).

The phenomenon in which two alleles are both expressed in the heterozygous individual is known as codominance. The codominance was demonstrated in plants with the help of electrophoresis or chromatography for protein or flavonoid substance. Example: Gossypium hirsutum and Gossypium sturtianum, their F ₁ hybrid (amphiploid) was tested for seed proteins by electrophoresis. Both the parents have different banding patterns for their seed proteins. In hybrids, additive banding pattern was noticed. Their hybrid shows the presence of both the types of proteins similar to their parents.

Artificial selection is a byproduct of human exploitation of forests, oceans, and fisheries or the use of pesticides, herbicides or drugs. For hundreds of years, humans have selected various types of dogs, all of which are variants of the single species of dog.

Cryopreservation (or freezing) of embryos is often used when there are more embryos than needed for a single IVF transfer. Embryo cryopreservation can provide an additional opportunity for pregnancy, through a Frozen embryo transfer (FET), without undergoing another ovarian stimulation and retrieval.

Single cell protein refers to edible unicellular microorganisms like Spirulina. Protein extracts from pure or mixed cultures of algae, yeasts, fungi or bacteria may be used as ingredient or as a substitute for protein rich foods and is suitable for human consumption or as animal feed.

The growth or orientation of an organism in response to light, either towards the source of light (positive phototropism) as seen in sunflower, or away from light (negative phototropism) as in case of the root of plants

(i) Throughout pregnancy the uterus undergoes periodic episodes of weak and strong contractions.
(ii) These contractions called Braxter-Hick's contractions lead to false labour.

(i) Sertoli cells are elongated and pyramidal and provide nourishment to the sperms till maturation.
(ii) They also secrete inhibin, a hormone which is involved in the negative feedback control of sperm production.

The clusters of gene with related functions are called operon. They usually transcribe single mRNA molecules. Eg Lac operon in E.coli

(i) Buds are formed on the outer surface of the parent body, it is known as exogenous budding e.g. Hydra.
(ii) In Hydra when food is plenty, the ectoderm cells increase and form a small elevation on the body surface.
(iii) Ectoderm and endoderm are pushed out to form the bud. The bud contains an interior lumen in continuation with parent's gastrovascular cavity.
(iv) The bud enlarges, develops a mouth and a circle of tentacles at its free end.
(v) When fully grown, the bud constricts at the base and finally separates from the parent body and leads an independent life.

(i) The science of improvement of existing human race by improving the environmental conditions is called euthenics.
(ii) It can be achieved by subjecting them to better nutrition, better unpolluted ecological conditions, better education and sufficient medical facilities.

(i) It is a disease caused by a recessive X -linked gene.
(ii) If a normal female marries a colour blind male or vice versa, the gene is carried in the X - chromosome of the female (female has 2 X Chromosomes).
(iii) If both the chromosomes carry the receive gene she becomes colour blind.
(iv) If one X chromosome caries the recessive gene she may not suffer from the disease but will be a carrier carrying the gene to the next generation.
(v) Haemophilia follows the characteristics criss - cross pattern of inheritance.
(vi) The females are carriers of the disease and world transmit the disease to 50% of their son's even if a male parent is normal.