HEREDITY AND EVOLUTION Heredity and Evolution - Mr. Ajay KumarHEREDITY : - The transmission of characters from the parents to their offsprings is called heredity.VARIATION : - The differences in the characters among the individuals of a species in called variation. The great advantage of variations to a species is that it increases the chance of its survival in a changing environment.CHROMOSOME : - Chromosome is a thread-lie structure in the nucleus of a cell formed of !"A #hich carries the gene.GENE : - A gene is a unit of !"A on a chromosome #hich governs the synthesis of one protein that controls a specific characteristic of an organism. $enes are actually units of heredity #hich transfer characteristics from parents of their offsprings during reproduction.DOMINANT GENE : - The gene #hich decides the appearance of an organism even in the presence of an alternative gene is no#n as a dominant gene. %t dominated the recessive gene for the same characteristic on the other chromosome of the pair.RECESSIVE GENE : - The gene #hich can decide the appearance of an organism only in the presence of another identical gene is called a recessive gene.GENOTYPE : - $enotype is the description of genes present in an organism and a pair of letters TT& Tt or tt.PHENOTYPE : - The characteristic #hich is visi'le in an organism is called its phenotype and (tall or (d#arf(.FIRST FILIAL GENERATION OR F1 GENERATION : - )hen t#o parents to produce progeny& then their progeny is called first filial generation or *+ generation.SECOND FILIAL GENERATION OR F, GENERATION : - )hen the first generation progeny cross among themselves to produce second progeny& then this progeny is called second filial generation or *, generation. HYBRID : - A ne# form of plant resulting from a cross of different varieties of a plant is no#n as a hy'rid. RULES FOR THE INHERITANCE OF TRAITS: MENDEL'S CONTRIBUTION : - %nheritance is the transmission of genetically controlled characteristics from one generation to the ne-t.1. MONOHYBRID INHERITANCE AND THE LAW OF SEGREGATION : - According to Mendels first la# of inheritance& .The characteristics of an organism are determined 'y internal factors #hich occurs in pairs. /nly one of a pair of such factors can 'e present in a single gamete. The ratio 01+ is no#n as the monohy'rid ratio.2. DIHYBRID INHERITANCE AND THE LAW OF INDEPENDENT ASSORTMENT : - According to Mendels second la# of inheritance1 %n the inheritance of more than one pair of traits in a crosssimultaneously& the factors responsi'le for each pair of traits are distri'uted independently to the gamete. The ratio of each phenotype of the seeds in the *, generation is 21 01 01 +. This is no#n as the dihy'rid ratio. $ametes from one hy'ridFUSION OF GAMETESRY Ry rY ryRY33443ound yello#334y3ound yello#3r443ound 3r4y3ound yello#Ry334y3ound yello#33yy3ound green3r4y3ound yello#3ryy3ound greenrY3r443ound yello#3r4y3ound yello#rr44)rinled yello#rr4y)rinled yello#ry3r4y3ound yello#3ryy3ound greenrr4y)rinled yello#rryy)rinled greenHOW ARE CHARACTERISTICS TRANSMITTED TO PROGENY : - The characteristics of traits of parents are transmitted to their progeny through genes present on their chromosomes during the process of se-ual reproduction.HOW BLOOD GROUPS ARE INHERITED : - A person has one of the four 'lood groups1 A& 5& A5 or /. This 'lood group system is controlled 'y a gene #hich has three different forms denoted 'y the sym'ols %A& %5 and %/. The genes %A and %5 sho# no dominance over each other& that is& they are co dominant. Ho#ever& genes %A and %5 'oth are dominant over the gene %/.SEX DETERMINATION : - A person can have a male se- or a female se-. The process 'y #hich the se- of a person is determined is called se- determination. There are t#o types of se- chromosomes1 6 and 4 chromosomes.ACUIED IRED TRAITS : -A trait of an organism #hich is (not inherited 'ut develops in response to the environment is called an ac7uired trait. E-ample1 %f a 'eetle does not get sufficient food for a considera'le time. The ac7uired traits oforganism cannot 'e passed on to their future generations.INHERITED TRAIT : -A trait of an organism #hich is caused 'y a change in its genes is called an inherited trait. EVOLUTION : - Evolution is the se7uence of gradual changes #hich tae place in the primitive organisms over millions of years in #hich ne# species are produced. EVIDENCES FOR EVOLUTION : -1. HOMOLOGOUS ORGANS PROVIDE EVIDENCE FOR EVOLUTION : - Those organs #hich have the same 'asic structure 'ut different functions are called homologous organs. E-ample1 the forelim's of a man& a li8ard 9reptile:& a frog 9amphi'ian:& a 'ird and a 'at 9mammal:.2. ANALOGOUS ORGANS PROVIDE EVIDENCE FOR EVOLUTION : - Those organs #hich have different 'asic structure 'ut have similar appearance and perform similar functionsare called analogous organs.!. FOSSILS PROVIDE EVIDENCE FOR EVOLUTION : - The remains of dead animals or plants that lived in the remote past are no#n as fossils.SPECIATION : - The process 'y #hich ne# species develop from the e-isting species is no#n as speciation.