Thebiotutor.com A2 Biology OCR Unit F215: Control, genomes and environment Module 1.2 Meiosis and variation Answers

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1 Theiotutor.com A2 Biology OCR Unit F215: Control, genomes nd environment Module 1.2 Meiosis nd vrition Answers Andy Todd 1

2 1. () (i) gene length of DNA; codes for (specific), polypeptide / protein / RNA; 1 llele lterntive form of gene; found t, locus / prticulr position on, chromosome; 1 ssume llele refers to cot colour llele (cot colour) gene / lleles, only on X chromosome; A no (cot colour), gene / llele, on Y chromosome mle cts, XY / only hve one X chromosome; mles hve only one (cot colour) llele / cnnot hve two (cot colour) lleles; need lck nd ornge lleles for tortoiseshell colour; 2 () prentl genotypes C r C r C w C w ; gmetes C r, C w ; F 1 genotypes nd phenotypes 1 mrk: F 1 genotypes (ll) C r C w F 1 phenotypes (ll) pink; F 2 genotypes nd phenotypes 1 mrk: gmetes C r, C w C r, C w ; F 2 genotypes C r C r C r C w C r C w C w C w F 2 phenotypes red pink (pink) white; F 2 rtio 1:2:1; ccept other symols if key given. ccept r nd w s symols without key. 6 (c) (i) 65; 10; 65; (iii) ; (or other suitle working) ; 2 mrks for correct vlue if no working shown ecf for oth mrks ut clculted vlue must e to three deciml plces 2 support, figure lower thn / figure lower thn criticl vlue; R support on its own. ecf pplies if vlue in is incorrect 1 [16] Andy Todd 2

3 2. nmed chrcteristic; nmed environmentl fctor; (mrk first nswer only) 2 [2] i) crossing over; tret chism(t) s neutrl 1 prophse; 1 (iii) hve different, lleles/se sequence of DNA; A sister chromtids hve sme lleles/non sister hve different lleles 1 [] 4 two different genes represented in ech gmete ie Q or q nd R or r; four correct comintions ie Q nd R, Q nd r, q nd R, q nd r; 2 [2] 5 () linkge (two or more) genes / loci, on sme chromosome; R lleles do not ssort independently (in meiosis) / inherited together; crossing over reciprocl exchnge of portions of, chromtids / DNA; A swpping lleles etween (pternl nd mternl) homologous chromosomes; A ivlent in prophse I (of meiosis); 2 Andy Todd

4 () nthers removed (efore mturity) (to produce mle sterility); mle sterilistion; genetic or, PGS / hormone pollen trnsferred y hnd; plnts isolted; flowers gged (efore nd fter pollintion); (c) (i) R chnce lone chnce fertilistion; chnce re picking 50 offspring; chnce re other trits ffecting survivl; AVP; e.g. position effect, different gene interctions ffecting expression, effect of crossing over on numers of other clsses 1 wrd two mrks if correct nswer (16%) is given without working recognition of recominnt clsses; 2 100; 200 =16%; 2 (iii) 1,2 A B ;; A (AB)() ()() oth chromtids per chromosome shown; 4 crossover shown; 5 result of crossover shown; 6 most / 84%, gmetes A B nd [ ]; A AB nd 7 = prentl; 8 few / 16%, gmetes A nd B [ ]; A A nd B 9 = recominnt; 10 ref 16 mp units prt / close together; 6 [15] Andy Todd 4

5 6 mrking points 1,6 nd 9 must e linked to correct sttements s to wht is tking plce in these stges to gin the mrk. 1 prophse 1 ; 2 synpsis / homologous chromosomes pir up / ivlents form ; crossing over ; 4 chism(t) occur ; 5 DNA / lleles, exchnged ; A linked genes seprted ; 6 metphse 1 ; 7 independent / rndom, ssortment ; 8 ivlents line up on equtor, independent of ech other / rndomly ; 9 metphse 2 ; 10 independent ssortment of chromtids ; 11 chromosome muttion ; 12 nmed exmple ; e.g. non-disjunction 1 AVP ; e.g. ref to non-sister / non-identicl, chromtids. 7 QWC cler well orgnised using specilist terms ; wrd the QWC mrk if four of the following re used in correct context prophse, metphse, homologous, ivlent, chism, crossing over, independent ssortment 1 7 (i) Q, S, P, N, M, R ; 1 ccept correct nmes of stges Q ; A prophse 1 M ; A nphse 2 Q / S ; A prophse 1 / metphse 1 S ; A metphse 1 R ; A telophse 2 5 (iii) DNA repliction ; synthesis of proteins / nmed protein ; A trnscription / trnsltion synthesis of memrne ; synthesis of, orgnelle(s) / nmed orgnelle ; respirtion ; AVP ; e.g. centrioles replicte ; 2 [8] Andy Todd 5