ANSWERS TO BIOLOGY TOPICAL QUESTIONS –GENETICS

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1.         a)  BB;                                                                                                                        

            b) AA;

2.         a) Black mice are better adapted camouflage with the environment hence less are eaten by the

               owls compared to the white mice which are easily seen;                                                   

            b) Theory of natural selection;

3.         – Heterostly – stigma located above anthers;                                                             

            – Self  sterility or incompatibility – pollen grain from the same plant do not germinate

            – Protandry – Male parts mature before female parts;

            – Protogyny – Female parts mature before male parts;

4.         (a) Complete dominance is when an alliele completely surprises another intermediate fruits;

                Incomplete dominance is when heterozygous organisms show an intermediate trait;      

(b) Genetic recombination’s of alleles reading to variations; Independent assortment of

     chromosomes;

                Random fusion of gametes; mutations;

           Environment (may either enhance or suppress expression of a gene);

5.         (a) C-A – G – U – C _ A ;

            (b) – Stones genetic information (in a coded form);

                  – enables transfer of genetic information unchanged to daughter cells through replication);

         – Translates genetic information into characteristic of an organism 9thorugh protein synthesis);

6.         Ability to pollinate; response to stimuli (tactic) nastic or tropics); Ability to exploit localized nutrients an  ability to photosynthesize; Ability to disperse seeds/fruits, propagation;

7.         (a) Glucose;                                                                                                                           

            (b) The person was a sufferer of diabetes mellitus;

            (c) Pancrease;

8.         Continuous variation shows gradation in characteristic with intermediate; discontinuous shows distinct characteristics between organisms with no intermediate groupings;                        

9.         -mutation;                                                                                                                              

             -intermixing of genes already in the population through sexual reproduction recombination;

-crossing over during prophase of meosis I

-interdependent assortment of chromosomes, during metaphase of meosis I

10.       i) Substitution;                                                                                                                       

            ii) Deletion;

             iii) Inversion;

11.       i) C G G A T C T A G T G;                                                                                                   

            ii) C G G A U C U A G U G;

12.       a) Continuous ;                                                                                                                      

            b) Nutrition/ environment; genes;

13.       a) Father XHY ;                                                                                                                      

                Mother XHXh  ;                                                                                                                  

            b)         i) Genes found in the same chromosome and usually transmitted together;

                        ii) Across to determine an unknown genotype involving use of a recessive parent;

14.       a) Colour blindness; haemophilia;                                                                                         

                Sickle cell anaemia;

            b) Part of X chromosome has homologous portion on the Y chromosome therefore if the X has

                the recessive trait, it will show on the male phenotype ;                                                   

            c) The son inherits the X chromosome from the mother while the daughter inherits the

                X chromosome from the father;

15.       (a) Inversion    ;                                                                                                          

  • ustard gas;
  • ionizing radiation;
  • gamma rays;
  • X- rays ;

16.       (a) Ribonuclei acid /RNA                                                                                                      

             – Because it has uracil / presence of uracil;

17.       (a) Due to co-dominance /partial dominance/incomplete dominance/(Acc. equal dominance)

            (b) Red: 2Pink : white – 1: 2:1  (Acc. 1RR: 2RW: 1WW) mark as a whole;           

            (c)  Why women should drink extra milk;

           (i) Bore formation for infants  ;

           (ii) pressure on bladder by the enlarging uterus;

18.    a) Genes which are located on the sex- chromosomes and therefore are transmitted along with

them                                                                                                                           

                                 Example                      Haemophilia; colour blindness;

         b) Where more than two genes control a particular characteristic/ trait;

                                 Example                      ABO blood group system;

19.       a) Parental Genotype Rr, Rr   ;                                                                                              

            b) Red: white;

119/41; 41/41;

2.90: 1

3: 1;

20.       (i) Y – Chromosome-hairy  pinna, pre-mature  boldness;      ; (any one)      

            (ii) X – Chromosome- haemophilia (bleeders disease); colour blindness; (any one)

21.       The Gene that determine the growth of long hair on pinna is sex linked and an Y-chromosomes; V hence   can only be inherited by males as a single gene and it expresses itself out phenotypically

22.       Due to crossing over: that results in exchange of genetic materials between homologous

            chromosomes;                                                                                                                        

23.      (a) Co dominance/ incomplete dominance:                                                                

           (b) 1 Red flowered; 2 pink flowered; I white flowered:  for ratio for phenotype)

24.      (a) Albinism;                                                                                                              

            (b) Makes skin supple;

             – Kills bacteria/ a mild antiseptic;

25.       – Change in base sequence of the DNA;                                                                                p 1.

26.       (i) Sudden and spontaneous change in structure of chromosome and DNA which is inherited 

           (ii) Chemical ionizing radiations, Uv light, extreme temperature or some virus       

27.       (a) GCCTATG – DNA          

                  GCCUAUG- MRNA      

(b) Ribosome;

28.       a) Parental phenotype             Pink flight feathers     X         White flight feathers

               Parental genotype               XRxr                            X                      XrY

              Parental gametes

                 Fusion

                 F1 genotypes                     

            b) incomplete;

            c)         i) Ribonucleic acid;

                        ii) has uracil base;

                        ii) – 3;

  • There are three codons;

29.       A – XhY;

            B – XHY;

            F – XHXh;   

                          XH     Xh;      X                Xh;Y;

(c) Albinism; sickle cell anaemia; colour blindness; chondrodystrophic dwarfism;

30.       (i)  Father        Mother

                XHY             XHYH

   Since father cannot have the recessive gene ad fail to be affected. The mother must be a carrier

    on her second X chromosome for a male son to be haemophiliac.

            (ii) Parental phenotypes mother carrier, father normal          

  Parental genotypes XHXh       XHY

31.       a) the two genes that control flower colour ,that is the gene  for  red  flowers and the

                one  for white are  codominate;                                                                                                      b)  F₁  phenotype    pink flowers            pink flowers

            F₁   genotype         RW           X          RW ;

             Gameter                R   W                     R   W ;

             Fussion

            F₂ genotypes        RR  RW                 RW   WW ;

             F₂ phenotypes      red 

                                     Flowered    pink                  white  flowered ;

                                                         Flowered

c)genotypic ratio= 1RR:2RW:1WW/RR:RW:WW=1:2:1 ;

            Phenotypic ratio=1 red  flowered:2 pink flowered:1white  flowered ;

            Notes: i) there must be  cross on genotype

                        ii) gameter should  be circled

d) recessive gene expressed it self only  underlined homozygous condition while dominant gene expresses  it self in both homozygous  and heterozygous  conditions;

32.       (a) (i) Male and female flowers are separate hence cross pollination is made possible.       

            (ii) 1 Yellow       : 3 Purple                                                                                                    

                        Rej.: 15 yellow  : 45 Purple

F1 genotype  

 (b) Let letter T represents purple maize grai

P1  

                 Let letter t represent yellow maize grain

Parental phenotype:    Purple                                                  Yellow Genotype:                   TT                                            x                      tt Gametes:  

             (c) Gene for purple grain;                                                                                                     

            (d) (i) Finger prints are used to identify criminals;                                                                                 (ii) Blood groups are used to settle parental disputes

Parental gametes

Fusion;

F1 offspring;

            c) All Rhesus positive/ all RhDRhd;

            (d) None

35.       – By keeping their mouth open/panting; to lose heat over surface area of the tongue by evaporation;                                                                                                                                    

-Basking; to gain heat by conduction;

– Shivering; to generate heat through increased metabolism;

– Physical activity (e.g. running); to generate heat through metabolism;

– Hibernation; to increase metabolism;

– Putting on warm clothes when it is cold; to retain the heat energy;

– Reduction of physical activity; to reduce the metabolic rate;

– Migratory behaviour to cooler environment; to reduce the body temperature;

– Moving into water when it is hot; to cool the body;

– Staying around fire place; to gain heat by convection;

– Taking hot drinks; to warm the body;

36.       a) Parental genotypes                                                                                                             

                        i) Woman/ OX –           AO

                        ii) Man/ O –                 BO

            b

 AO
BABBO
OAOOO

         c) Cases of disputed paternity settlement

              – Determining compatible blood groups in blood transfusion

            d)         i) Corresponding complementary DNA strand          GAA;

                        ii) Corresponding RNA          CUU

            iii) Nitrates/ sulphites/ hydroquinone/ gamma/ beta/ alpha/ x-rays/ UV light/ hydrogen peroxide

37.       let R rep. gene  for Red flowers                                                                                             

                W.rep  gene  for white  flowers

 a) parental phenotype Pink flowered                         Pink flowerd

          genotype          gametes

;

       red                                 pink                                white

  b) phenotypic ratio 1Red:2Pink:1White;

                 genotypic ratio: 1RR:2RW:1WW;

 c) 2 x 480;=240

                

Fl generation               Award for punnet Square and genotypes

(b) (i) IBB : 2Bb: lbb 

                        (1 mark for ratio, 1 mark Par genotype)

                (ii) 3 B lack: I brown         

                (iii) 24;

39.       (a) Homologous structures:

                 Structures of common embryonic origin modified to perform different functions;         

                  Example: Eye structure in man and octopus/ wings in birds and insects (I mark)

                  Analogous structures Example

(b) They undergo mutations: resulting in new forms that rcsis selection resistant to drugs;

 (c ) (i) Failure of chromosomes to separate during anaphase I resulting in gametes

           with an extra  chromosome and others with less chromosomes: (I mark)

            (ii) Downs syndrome / Klinefelters syndrome/ Turners syndrome: any I ( 1mk)

40.       a) Homologous structures have a common embryonic origin but are modified to   

Perform different functions; while analogous structures have different embryonic origin but are modified to perform similar functions;

            b) Nictitating membrane; post anal tail; body hair;

41.       a) Pentadactyl limb structure of mammals; beaks of birds; feet of birds;                            

b) – Missing links between fossils because some parts or whole organisms were not fossilized

                – Some parts were distorted during fossilization hence may give wrong impression

            of structures;

– Some structures have been destructed by geological activities;

42.       Camouflage is the conceal/ element of identity of an organism by resembling the color    

of the environment while mimicry is the imitation of non- living organisms to conceal identity

43.       Light energy splits water molecules; into hydrogen ions and oxygen atoms;                       

44.       (a) Caecum/ Rumen/ pauch;                                                                                      

            (b)  Closes to prevent food from moving up the oesophagus;

45.       (a) – the soft bodied organisms fail to fossilize;

           – Human activities interfere with fossilization;

Earth movements e.g. volcanic eruptions interfere with fossilization; (mark any first2 pts

        (b) – They resembled from neck downwards;

             -They walked upright;

         – The shape of the skull suggested they were able to speak;

46.       a i)vestigial structures are those structures that have ceased  to be functional over along

     period of time and hence reduced  in  sizes

              ii)-appendix;

            -caecum

              -coccyx or tail/tail bone;

             – Nictitating membrane/semi – lunar fold at the corner of the eye;

             -ear muscles

             – Body hair;

            b) Disease causing organism mutates; and became resistant;

47.       Struggle for existence –environmental pressure on the population in order to survive;       

Survival for the fittest-advantageous variations an individual possesses to make it survive;

48.       Secretion of antidiuretic hormone; rearbsorption of salts at the loop of Henle;                  

49.       -Divergent evolution refers to a  situation where by organisms that are believed to have

 had a common ancestral origin have homologous  structures which have been modified to suit       different environments;

50.       a) Allows survival of organisms with better qualities / traits / characteristics; eliminates

organisms  with unfavorable characteristics/ traits;                                                  

            b) Divergent;

51.       Evidence does not support Larmarks theory                                                 

Acquired characteristics are not inherited/;

             Inherited characteristics are found in reproductive cells ;                

52.       (a) Vestigial structures                                                                                                           

                 (i) Are those structures that have ceased to be functional over a long period of time hence      

                      reduced in size;

                (ii) Appendix/coccyx/tail/ nictitating membrane semilun fold at the corner of the   

                 eye/caecum/ear muscles, body hairs;

            (b) Disease causing micro-organisms mutate and become resistant;

53.       a) The gradual emergence of complex life forms from pre-existing simple forms over along

      period of time        ;                                                                                              

         b) Nature selects those organisms with structures that are well adapted to survival in

             the environment. These structures are passed to their offspring; organisms with structures    

           that  are poorly adapted perish ;

54.       The insecticide kills most of the insects when introduced; those that survive; give rise to a new

generation of flies that are resistant to insecticide.                                                                

55.       – Most organisms especially soft-bodied ones do not form fossils;                                       

             – Most fossils have not yet been discovered;

             – Exposed fossils are usually destroyed by physical and chemical weathering;

– Earth movements e.g. volcanicity, earthquakes, tsunami do destroy fossils;

– Most animals are prayed upon;

56.       -Fossil records/paleontology   ;                                                                                              

  -Comparative anatomy/taxonomy;

  -Comparative embryology;

 -Geographical distribution;

 -Cell biology;

 -Comparative cellulogy/immunology; (award 1st three 3mks)