Characteristics of sex-linked inheritance
1. It is criss-cross inheritance,  father passes the X-linked allele trait to the daughters, who pass it on to the grandsons.
2. Mother passes the allele of the trait to both daughters and sons.
3. Only homozygous females express an X-linked trait.
4. Heterozygous females are carriers of X-linked recessive traits and themselves do not express the trait.
5. Any male having an X-linked recessive allele expresses the trait as the Y-chromosome has no counteracting allele.

(i) People are careless, superstitious and unaware.
(ii) We can help in decreasing pollution of rivers by adopting following habits:
(a) By throwing litter or polybags in dustbin instead of rivers.
(b) By using environment friendly household products such as washing powder, household cleaning agents, etc.
(c) By planting more and more trees, which prevent fertilisers, pesticides and contaminated water from running in to nearby rivers.
(iii) Some advantages of saving rivers are:
(a) Constant supply of water and food to us.
(b) Huge supply of all natural fertilisers, which is good for growing crops.
(iv) Government has initiated Ganga Action Plan and Yamuna Action Plan to save these rivers from pollution.

Main steps involved in breeding a new genetic variety of a crop are:
(i) Collection of variability / germplasm collection, collection and preservation of all different wild varieties, species and relatives of cultivated species / entire collection of plants.
(ii) Evaluation and selection of parents, to identify plant with desirable combination of character / purelines are created.
(iii) Cross hybridization among selected parents, cross hybridizing the two parents to produce hybrids which genetically combine desired characters in one plant.
(iv) Selection and testing of superior recombinants, selection among the progeny of the hybrids that have desired character combinations, superior to both the parents / self pollinated for several generations till they reach the state of uniformily and they do not segregate in the progenies.
(v) Testing, release and commercialisation of new dIltivars, newly selected lines are evaluated for yield / other agronomic traits of quality / disease resistance by growing them in research fields followed by testing the material in farmers fields for atleast three growing seasons at different agroclimatic zones.
Release of new variety : The variety evaluated is 'selected certified and released as new variety.

Vegetative reproduction is also considered as a type of asexual reproduction because it does not involve meiotic division and there is no formation and fusion of gamete. In this case characters of parent plants are preserved.

Injections and Implants
1. Progestogens or progestogen-estrogen combination is also used as injections or implants under the skin.
2. Though their mode of action is similar to oral contraceptives, their effective periods are longer.

Typhoid.
1.it is an infectious disease caused by bacteria,Salmonella typhi.
2.The infection is by contaminated food and water.
3.The pathogen enters the small intestine and then the other parts through body fluids.
4.Its symptoms include:(a) sustained high fever (\({ 103 }^{ 0 }-{ 104 }^{ 0 }\) F),(b)stomach pain,(c)loss of appetite, (d) constipation and (e)headache.
5.Intestinal perforation leading to death in severe cases.
6.Typhoid can be confirmed by Widal test.

Golden rice is a genetically modified rice with high levels of β-carotene and other carotenoids. This rice is modified in order to enhance the quantity of vitamin-A in it. It is called golden due to the gold-like colour it gets from β -carotene.

A successful breeding for disease resistance depends mainly on two factors:
(i) A good source of resistance.
(ii) A dependable disease test.

Differences between climate and weather

Fertilisation in flowering plants is referred to as double fertilisation because both the male gametes of the same microspore take part in fusion. One fuses with the egg to form the diploid zygote and the other fuses with the two polar nuclei (or secondary nucleus) to form the triploid primary endosperum nucleus

(i) Haemophilia is sex-linked because:
(a) It is transmitted from an unaffected carrier female to some of the some of the male offsprings.
(b) Female rarely becomes haemophilic as her mother has to be atleast a carrier father should be heamophilic.
(ii)Gene for haemophilia is present on X-chromosome because the heterozygous female for heamophilia may transmit the disease to sons.

Watson and crick had the following information which helped them to develop a model of DNA. 
(i) Chargaff's law suggestion A=T and C=G.
(ii) Wilkins and Roseland Franklins worked on DNA and obtained very fine X-rays photographs of DNA by X-ray diffraction method.
Watson and crick proposed 
(a) The pattern of complementary bases pair
(b) Semi-conservative replication
(c)Mutation through tautomerism.

In birds, female has dissimilar chromosomes(ZW) and males have two similar(ZZ) chromosomes.But in humans,female has a homogametic(XX) and male has hetrogametic (XY) sex chromosome.In human sperm is responsible for sex of offspring.In birds egg is responsible for the sex of the offsprings.

(a) Rupture of Graafian follicleleads to ovulation! release of ovum.
(b) Estrogen level islow.
(c) Disintegtation of endometrium and menstrual cycle begins again.