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It is a mechanism which determines the individual to be a male or a female based on the sex chromosomes present in it. In human beings, sex is determined by genetic inheritance. Genes inherited from the parents determine whether an offspring will be a boy or a girl. Gene for all the characters are linearly arrange on the chromosomes. The chromosomes that carry genes for sexual characters are called autosomes or sex chromosomes while those that carry genes for the vegetative characters are called autosomes or non sex chromosomes.

Women have XX chromosomes while men have XY.

All the children will inherit an X chromosome from their mother regardless of whether they are boys or girls. Thus the sex of the children will be determined by what they inherit from their father.

1. Fossils helps to trace the racial history of organisms. 

2. They help to analyse the past climatic conditions. 

3. They help to measure the geological time.

Appendix, tail-bone or coccyx, wisdom teeth and body hair.

(i) Fossils showing imprints of feathers along with the bones in dinosaurs/reptiles found.

(ii) They could not fly and presumably use the feathers for insulation.

(iii) Later they developed/evolved and adapted feathers for flight.

(iv) Thus, they give evidence that birds have evolved from reptiles.

Drwafness and wrinkled seeds are the recessive characters.

Charles Darwin.

(d) All of these 

Species 'X' is more closely related with species 'Y'. The more closely related species will have more characteristics in common. Hence species X and Y are closely related.

Eukaryotic organisms are further classified on the basis of whether they are unicellular or multicellular.

This basis marks a very fundamental difference in body design, because of the specialization of cell types and tissues.

Homologous organs help to identify an evolutionary relationship between apparently different species.

(a) They both have feathers

No, the structure of the eye in each of, these , organisms is different/they have . separate evolutionary origins.

Genes which code for a pair of contrasting traits are known as alleles, i.e., they are different forms of the same gene.

Gene is a segment of a DNA molecule which carries the code for the synthesis of a specific protein.

(c) Same structure, different function

Correct option (A) Temporal isolation   

Explanation:

Reproductive isolation, i.e., prevention of interbreeding between two. species may happen in a number of ways. Temporal isolation is one of them. lt prevents interbreeding of two groups due to differences in their mating seasons.

It is the detail of appearance or behaviour; in other words, a particular form or a particular function.
Example: Four limbs of human beings is a characteristic and that plant can perform photosynthesis is also a characteristic.

Chromosome is a thread-like structure that bears genes and are enclosed within a nucleus. It is composed of DNA and protein

GregorJohann Mendel is known as the father of genetics.

Evolution is the sequence of gradual changes which take place in living organisms over millions of years to give rise to new species.

It is because they resemble with each other but do not resemble with other group elements.

G.J. Mendel is called the ‘‘father of Genetics’’. 

Flowers with blue petals, nectar and strong scent are most likely pollinated by Insects.

Gene is the unit of inheritance. It is a part of the chromosome which controls the appearance of a set of hereditary characteristics. 

Scandium and Germanium.

Noble gases are very inert and they are different when compared to other elements. Hence, these are placed in separate group.

Penicillin was an accidental discovery. Sir Alexander Fleming observed that in unwanted culture plates of Staphylococcus a mould of Penicillium was growing This mould inhibited the growth of Staphylococcus around it. Later the antibiotic penicillin was isolated from this fungus.

Its full potential as an effective antibiotic was established much later by Ernest Chain and Howard Florey. This antibiotic was extensively used to treat American soldiers wounded in World War II. Fleming, Chain and Florey were awarded the Nobel Prize in 1945, for this discovery.

The mycorrhizal fungi absorb phosphorus from the soil and transfer them to the host cells. They also’impart resistance to host plants against root pathogens. They also help plant tolerate salinity and draught.

Penicillin was an accidental discovery. Sir Alexander Fleming observed that in unwashed culture plates of Staphylococcus, a mould Penicillium was growing. This mould inhibited the-growth of Staphylococcus. Later the antibiotic Penicillin was isolated from this fungus.

Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc. In paddy fields, cyanobacteria serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility.

(b) it has a dangerous substance named nicotine

(a)  Cannabinoids

(b)   Generally taken by inhalation and oral ingestion

(c)  Affect the cardiovascular system of the body

Measures for personal hygiene include keeping the body clean; consumption of clean drinking water, food, vegetables, fruits, etc. Public hygiene includes proper disposal of waste and excreta; periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks, and observing standard practices of hygiene in public catering. These measures are particularly essential where the infectious agents are transmitted through food and water such as typhoid, amoebiasis and ascariasis.

(i)  Maintenance of personal and public hygiene is very important for prevention and control of many infectious diseases. Measures for personal hygiene include keeping the body clean; consumption of clean drinking water, food, vegetables, fruits, etc. Public hygiene includes proper disposal of waste and excreta; periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks and observing standard practices of hygiene in public catering.

(ii)  In cases of air-borne diseases such as pneumonia and common cold, in addition to the above measures, close contact with the infected persons or their belongings should be avoided.

(iii)  For diseases such as malaria and filariasis that are transmitted through insect vectors, the most important measure is to control or eliminate the vectors and their breeding places. This can be achieved by avoiding stagnation of water in and around residential areas, regular cleaning of household coolers, use of mosquito nets, introducing fishes like Gambusia in ponds that feed on mosquito larvae, spraying of insecticides in ditches, drainage areas and swamps, etc. In addition, doors and windows should be provided with wire mesh to prevent the entry of mosquitoes.

Heroin is an opioid drug obtained from the poppy plant Papaver somniferum. It is a depressant and slows down the body functions.

Layering is the natural method by which strawberry plants are propagated.

(B) two phenotypes and three genotypes.

F₂ progeny of monohybrid cross shows two phenotypes and three genotypes.

Principle of vaccination is based on the property of ‘memory’ of immune system. In vaccination, a preparation of antigenic proteins of pathogens or inactivated/live but weakened pathogens is introduced into the body. The antigens generate primary immune response by producing antibodies along with forming memory B-cells and Tcells. When the vaccinated person is attacked by the same pathogens, second time/subsequent time the existing memory B-cells and T-cells recognise the antigen and overwhelm the invaders with massive production of lymphocytes and antibodies. Hepatitis B vaccine is produced from yeast.

(i) Balanced diet 

(ii) Proper personal hygiene 

(iii) Regular exercise 

(iv) Yoga 

(v) Proper rest/sleep.

(a) Retroviral infection :

Presence of retroviral vectors, such as some viruses, which use their recombinant DNA to insert their genetic material into the chromosomes of the host's cells. The virus is then propogated by the host cell. 

(b) Reverse transcriptase :

Enzyme used by retroviruses to form a complementary DNA sequence (cDNA) from their RNA. The resulting DNA is then inserted into the chromosome of the host cell. 

(c) Reverse transcription-PCR (RT-PCR) 

PCR technique in which the starting material is RNA. The first step in the procedure is conversion of the RNA to cDNA with reverse transcriptase. 

(d) Satellite 

Chromosomal segment that branches off from the rest of the chromosome but is still connected by a thin filament or stalk.

Virus infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.

Fisher and Race hypothesis: Rh factor involves three different pairs of alleles located on three different closely linked loci on the chromosome pair. This system is more commonly in use today, and uses the ‘Cde’ nomenclature. In the given figure, three pairs of Rh alleles (Cc, Dd and Ee) occur at 3 different loci on homologous chromosome pair-1.

The possible genotypes will be one C or c, one D or d, one E or e from each chromosome. For e.g. CDE/cde; CdE/cDe; cde/cde; CDe/CdE etc. All genotypes carrying a dominant ‘D’ allele will produce Rh+positive phenotype and double recessive genotype ‘dd’ will give rise to Rh negative phenotype.

Wiener Hypothesis: Wiener proposed the existence of eight alleles (R¹ , R² , R⁰ , R^Z , r, r¹ , r¹¹ , r^Y ) at a single Rh locus.

All genotypes carrying a dominant ‘R allele’ (R1 , R² ,R⁰ ,R^Z ) will produce ‘Rh-positive’ ^phenotype and double recessive genotypes (rr, rr¹ , rr¹¹ , rr^Y ) will give rise to Rh-negative phenotype.

In many birds (ZZ / ZW) 

Male / female/heterogamety

Detailed answer:

Birds show female heterogamety as the female birds produce two different types of ova i.e. (A+Z) and (A + W) whereas males produce only one type of sperms.

Male heterogamety (XY males) is a type of sex determination in which males produce two different types of gametes. 

For example, human males produce two kinds of sperms that is sperm with X-chromosome and sperms with Ychromosome.

Gene causing phenylketonuria causes multiple phenotypic expressions. Such genes are called pleiotropic genes. This effect of multiple phenotypic expressions is caused due to single gene mutation.

Female heterogamety (ZO females) refers to the condition, where female produces two types of egg cells. Some with Z chromosome and some without Z chromosome.

(B) 3 : 1

In a cross between tall heterozygous pea plants, what would be the phenotypic ratio in the F₁ generation is 3 : 1.