Principle Inheritance and Variation PDF

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rrul,l.- ··,- AED L---;. co. 0 01\..l.' n.anu e f v e U.l.J c QJ e.. Ot- f\-LLL t t-t"P I e.. ru.l €,.lt · (l__O flE'- oto r1..,11·n a n~e -=- Fill"· e.r-, on 0 j(; o.. '."d ,~.,---_ ______. Ycllow.whllc u r and that with all the;1,e cessive a e es (aabbc will have the Qi e. 1-\ a.v e. E, ,. b> Broe.on , 10oci4 BrocO I' "MM arm··---- rkin colour. As expected the genotype with three dominant alleles cto /U I " 4 t , 1, bOd.'I I and three recessive alleles will have an Intermediates n colour. In thls 0 11 J l4t)., ( I' , u nder ym mec 1arusm of pleio · e , x- c..t'\romo&orn I =, ,-gd w m~ ,r y w yw on metabolic athwa s whi h c s.i c:a :a An example of this is the yellow.white yellow WhJte,mlnlaturc h um~ ~ e w easJ.Js causell -:..;.;,;;;~ ~ at codes for th e... ~ e ~h enyl alanine ht,droxvlase s e gene mu Uon. Titls ~fesls 1 F, generation itse lf t rough pheno~ypic express10n c h a racterised b ~ y.,,_ w· w m rel,ar;,henylalanine into tyrosine. As a resu o Ii 4 d. CL.I. c, 'I: Y I of ach a female has to 6e at leas fc s phenylalanine is accumulated and converted ~to phenvlpyruvic acid su unvlable In the later s e O d other dtµ:Jyatives. Accumulation of ,these In brain results in mental p -f,e.n~ l - phen1-1r~" thershouldbehaemopbillc( a dl!l!!,e of~ een Vict'o@ show§..- - a number fhae c etardfili!lll.{niese are also,excrets:d t)u-ough urine because of Its poor e. -o..ta.11°" 1-1.vr1.rc111 e.~/':, pe · ~-- ~rthP rllseas.i:. _ o.Cc.u.rrl ~alt, ome Unked re assemia : This Is also an au tosome-llnked recesslyil blood disease) ,..,.-. u r o. t"i on to.- Sickle-cell anaeJDlll · uu" ~ the O spring when ~::ca.-'-"'..:11ar mitted from parents to tlie offspring when botllthe partners are p-t,en td r p4-}-l.uvic v f> ~,/ Qc1'd (X) J be transmitted from parents ous). The disease is ected carrier for the gene (or heterozygous). The de ould be due_, + ~~:-t;,::~i\';:'1rui:;;:;;; et 5 t of -~ ~ - ate~ results uced rate ou · =-=-=-- Hb · b. and chain at make up s for Hb on of abnormal haemoglobin dlviduals \P£~9~7~~::,;~ · Heterozygous. 15 t anaemi which Is characteristic of the disease. are carrier of e sease as !here :'1111llallas1;e lass according to which chain of the haemoglobin 0 the mutant gene to ~e prog~ by tpP §J!bSUtJ1!!f>__. IrG)Thalassemia. production of a globin chain ls __.. q-O.J'C.G-T ~O~.i (Figure 5.15). The defect 1s cause alassemia, production of Bglgbio t,l,atjJ3 aftected. 0( - ThO..l i+,aJ,, :@ L °1 -1, onor lHBAi HB~~ l-l6B ted, the ntrolled r urs·due C.h-lb ic,;-Hj lckle-cell.ijc that the former ls a quantitative problem of synthesising too 1/ · in molecules while the latter is a qualitative problem of ,!sine; an incorrectl,r functiomn. ="" '-'> poff\r ···G1U··· ,u_J.U-QH'o(1 -GAG- ·· Sickle-cell Hb(S) gene.. ·CAC ·.1.. Normal Hb (A)gene.. -ere... · ·. e chromosomal disorders on the other hand are caused due to absence + o~'ol.i'C. kl. angemento es. mRNA t , mRNA · ·GUG·· · t - ~~~~~ ~:::.:c!~~~;:::;:~~...:;;=:::::;!..:::=~:::;.~:..:..: r examp e, cleresults ~U,Lt-ollA- c v~Ji ,~l~r gain of extra osome 21. ~-c}.~ e 'ssyndromeresultsduetolosso mosomein II. Pr ales Failure of oklnesls after telQ hase s e of cell division ~-1, 1 2 3 4 5 6 7 Val I His 2 · u · 3 4.~ 5 6 01 ,1! 7 anincreaselriawhoksetofchro~oso~~sinanorg:..nnm..nnn le 1,,.-,n..::::::r..:._,_,oldy. This condition ls-ofte J :i.-.it':ir ,.. HbApeptlde HbS peptide The total number of chromosomes in a normal human cell is 46 ·Figure 5.15 Micrograph of the red !ilood cells and the amino acid composition of the portion of /j-chaln of haemoglobin: (a) From a normal Individual; (b) From an 3 pairs). Out of these 22 pairs are~utosomes and one pair of S.3-?- with sickle-cell anaemia romosomes are sex chromosome. Sometimes. though rarely, either an ditional copy of a chromosome may be included in an individual or an '2 C\ \Wt:r{CJ. r,-, j) , - *fl0 Broad ilatface "'L ,,. ,, ·/ 1)(; ':, 1, no. l\ 1_,,.. l,\ RINCIPLES OF INHERITANCE AND VARIATION \ 1 l~ II. x.~ Flat bacl< ofheaa , ' " I - - - ~ 1 ~~- ,. ('h 1 i fi riu. (11 1 SUMMARY aim creas \ ! " l'tc.:;., Genetics ls a branch of biology which deals with principles of Inheritance '..... 1n1 and its practices. Progeny resembling the parents In morphological and ' , " r111 ; I \ I, I n physiological features has attracted the attention of many biologists... r.r. " Mendel was the first to study this phenomenon systematically. While I ~; ti 1, s tudying th e pattern of inheritance in pea plants of contrasting "\ \ characters. Mendel proposed the principles of lnherttance, which are ( r ' :;;:: i;;J J. ;, I. jpday referred to as 'Mendel's Laws of Inheritance'. He proposed that ' I', lbe ·factors' (la ter named as genes) regulating the characters are found ~-- "-,, I - In pairs known as a ll eles. He observed that the expression of the " A representnttve figure showing an individual inflicted With characters in the offspring follow a definite pattern In different-first Figure 5. 16 syndrome and the corresponding chromosomes of the !ndiv, generations IF,). second (F2) and so on. Some characters are dominant j over others. The dominant characters are expressed when factors are 1n heterozygous condition (Law of Dominance). The recessive characters are only expressed in homozygou s condition s. The characters n~ver Individual may lack one of any one blend in heterozygous condition. A recessive character that was not chromosomes. These situations are known aa expressed ln heterozygous conditon may be expressed again when it becomes homozygo,us._ Hence, characters segregate wh!le formation of or monosomy of a chromosome, r esp ectively,: gametes (Law of Segregat[2n). situation leads to very serious consequ Not all characters show true dominance. Some characters show tndlvldual. Down's syndrome. Tomer' Incomplete, and some show co-domtn,ance. When Mendel studied the /' Kllnefelter's syndrome are common inheritance of two characters together, lt was found that the factors / chromosomal disorders. ind epende ntly assort a nd combine In all permutations a nd combinations (Law of Independent Assortment). Different combinations Down's Syndrome ; Th of gametes are theoretically represented In a square tabular form known Is the presence of as 'Punnett Square·. The factors (now known as gene) on chromosomes regula ting the characters are called the genotype and the physical. ·i1f, thromosome numbe~ 1 I expression of the chraracters ls called phenotype. was first described by After knowing that the genes are located on the chromosomes, a affected indlvtdual Is short.---·-· __ good correlation was drawn between Mendel's laws : segregation and ~ - furrowed tongue a n· assortment of chromosomes during meiosis. The Mendel's laws were (b) (Figure 5. 16). Palm Is broad extended in the form of 'Chromosomal Theory of.Inheritance' Later, it (a) ~ - Physica l,. P ccs.,_ === y.;c.. c:..:l was found that Mendel's law of independent assortment does not hold. true for the genes that were located on the same chromosomes. These Tall s tature Short s tature and development.ls retarded. genes were called as 'linked genes·. Closely located gen es assorted with feminised underdeveloped together. and distantly located genes, due to recombination. assorted w-~-- __._ ___ _ Kllnefelter's S character feminine character caused due to th,.. t'.' independently. Linkage maps, therefore, corresponded to arrangement chromosome resulting tnt - - - - -,';M of genes on a chromosome. Figure 5.17 Diagrammatic represe- Many genes were linked to sexes also. and called as sex-linked Such an indlvidual has ove genes. The two sexes (male and female) were found to have a set of ntation of genetic disorders due to sex however. the femlnln~~l~p~~nt (d«- ·-:'111 chromosomes whi ch were common, and another set which was chromosome composition In humans : ~- (a) Klinefelter Syndrome; (b) Turner's of breast, I.e.. Gynaecomastla) Is also different. The chromosomes which were different in two sexes were (Figure 5.17 a ). Such individuals are stedl n a m ed as sex chromosomes. The remaining set was named as ·. :~~--= Syndrome autosomes. In humans, a normal female has 22 pairs of autosomes Turner's Syndrome : Such a disorder lsn u and a palr of sex chromosomes (XX). A male has 22 pairs of autosomes -.... tothe,~. e.{45with XO,~uch. ~ e a s ovaries a re rudlmentary besides other features lni and a pair of sex chromosome as XY. In chicken. sex chromosomes In male are zz. and in females are VN. · (·im Mutation ls defined as chan ge in the genetic material. A point J a c k o f ~ F l gure 5.17b). mutation ls a change of a single base pair In DNA. Sickle-cell anemia ls caused due fo change of one base In the gene cocling for beta-chain of 'it* hemoglobin. Inheritable mutations can be studied by gener ating a pedigree of a fam!ly. Some mutations Involve changes In whole set of