KNEC KCSE BIOLOGY TOPICAL QUESTIONS AND ANSWERS

Explain why certain bacteria and other pathogens become resistance to drugs after some time

3/11/2021

(a) What is mutation? (2mks)

Mutation is a sudden/spontaneous change; in the genetic make up of an organism

(b) Explain why certain bacteria and other pathogens become resistance to drugs after some time. (2mks)

bacterial that survive the drug will undergo mutation: to produce bacteria which are resistance to the prevailing condition/drug. (2mks)

(c) Work out a cross between a Haemophiliac man married to a carrier woman for Haemophilia.
Use letter h to represent genes. (3mks)

(d) State the phenotypic ratio of the children. (1mk)

Phenotypic ratio :

1 male normal
1 male haemophiliac
1 female haemophiliac
1 female carrier

1 male normal:
1 male haemophiliac:
1 female haemophiliac:
1 female carrier: (1mk)

Comments

Define the term allele, Differentiate between a dominant gene and a recessive gene

30/10/2021

Comments

(a) Define the term allele (1mk)

Alternative forms of a gene controlling a particular characteristic

(b) Differentiate between a dominant gene and a recessive gene (2mks)

A dominant gene expresses itself in both its homozygous and heterozygous states; while a recessive gene can only express itself in homozygous state.

Comments

In an experiment a variety of garden peas having a smooth seed coat was crossed with a variety with wrinkled seed coat. All the seeds obtained in F1 generation had smooth seed coat. The F1 generation selfed. The total number is F2 generation was 7324.

16/9/2021

Comments

In an experiment a variety of garden peas having a smooth seed coat was crossed with a variety with wrinkled seed coat. All the seeds obtained in F1 generation had smooth seed coat. The F1 generation selfed. The total number is F2 generation was 7324.

(a) Work out the total number of wrinkled seeds in the F2 generation (2mks)

Â½ x 7324=1831 (2mks)

(b) Give an explanation to the absence of plants with smooth seedcoat in the F1 generation (1mk)

Gene for smooth seed coat is recessive /gene for wrinkled seed coat is dominant over that for smooth seed coat (1mk)

â€‹(c) The following diagrams represents

The above diagrams represents

â€‹Name the types of chromosomal mutations, X and Y (2mks)

X-Insertion
Y- inversion (2mks)

(d) Other than the above types of chromosomal mutations, name three other types of chromosomal mutations â€‹(3mks)

Deletion (3mks)
Translocation
Non-disjunction

Comments

How do identical twins and fraternal twins arise?

9/9/2021

Comments

How do identical twins and fraternal twins arise?

(i) Identical twins (2mks)
- Identical twins arise when a male gamete fertilizes the same ovum in an ovary and hence the similarity
(ii) Fraternal twins (2mks)
- Fraternal twins arise when male gametes fertilizes ova from different ovaries

Comments

Explain how the following occur during gene mutation

8/9/2021

Comments

Explain how the following occur during gene mutation

(i) Substitution (2mks)

Replacement of a portion of the gene with new portion

(ii) Insertion (2mks)

the addition of an extra base onto an existing DNA

Comments

The diagrams below show a pair of homologous chromosomes. Study them and answer the questions that follow

5/9/2021

Comments

The diagrams below show a pair of homologous chromosomes. Study them and answer the questions that follow

(i) State the phenomenon shown above (1mk)

Crossing over

(ii) What is the genetic significance of the phenomenon above? (2mks)

Variations; which may lead to new genetic fruits either advantages or disadvantages to the organism/may lead to evolution

Comments

K.C.S.E Biology Q & A - MODEL 2019PP2QN04

2/7/2020

Comments

K.C.S.E Biology Q & A - MODEL 2019PP2QN04

In cats, the gene for fur colour is sex-linked. Letter G represents the gene for ginger fur colour while letter B represents the gene for black fur colour in a given cat species. These genes are co-dominant. Heterozygous females have ginger and black patches of fur and their phenotype is described as tortoise-shell.

(a) With reference to the information given above, what is meant by the term co-dominance?
(b) Explain why male cats with a tortoise-shell phenotype do not usually occur.
(c) A tortoise-shell female was crossed with a black male. Determine the genotypes and phenotypes of the offspring.

answers

Comments

K.C.S.E Biology Q & A - MODEL 2018PP1QN18

1/7/2020

Comments

K.C.S.E Biology Q & A - MODEL 2018PP1QN18

A tall, light skinned lady with pimples on her face has long hair and limps.

(a) List two features which the lady has that are due to inheritance.
(b) Explain why most recessive genes are expressed phenotypically in male offspring of humans.

answers

(a) Height (tallness);
Long hair;
Skin colour (light);
(b) Most of the genes are sex-linked and are carried on the X - chromosomes; boys receive X chromosomes from the mother (and Y chromosomes from the father); if the X carries a recessive gene, it is more likely to be phenotypically expressed in boys;

Comments

State how in-breeding leads to reduced hybrid vigour

1/7/2020

Comments

K.C.S.E Biology Q & A - MODEL 2017PP2QN05

State how in-breeding leads to reduced hybrid vigour

answer

Chances of recessive/defective genes being combined increase,hence weaker offspring;

Comments

State two advantages of using genetically modified varieties in bean farming.

1/7/2020

Comments

K.C.S.E Biology Q & A - MODEL 2017PP2QN05

State two advantages of using genetically modified varieties in bean farming.

answers

Higher yields;
Enhanced resistance to diseases/pests;
Early/faster maturity;
Enhanced resistance to harsh climatic conditions (drought/extremes in temperature);

Comments

K.C.S.E Biology Q & A - MODEL 2017PP2QN05

1/7/2020

Comments

K.C.S.E Biology Q & A - MODEL 2017PP2QN05

In beans, the gene for purple colour is dominant over the gene for white colour. A pure breeding bean plant with purple colour was crossed with a heterozygous bean plant.
Using the letter P to represent the gene for purple colour, work out the genotypic ratio of the offspring.

answer

Comments

K.C.S.E Biology Q & A - MODEL 2017PP1QN16

30/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2017PP1QN16

The following are text messages on a celiphone that represent gene mutation.

(a) Identify the type of gene mutation represented in each case
I
II
(b) State Mendel’s First Law.
(c) State two disadvantages of genetically modified plant products.

answers

a. I — Deletion;
II- Inversion;
b. The characteristics /traits of an organism are determined by internal factors/ genes (which occur in pairs). Only one of the genes can be carried in a gamete/ passed onto the next generation;
c. Most have lost most of the original (desirable) qualities e.g taste;
Poor/undesirable qualities are perpetuated through subsequent generations;
Products’ qualities are irreversible- can’t get original species/qualities;

Comments

Explain why people with sickle cell trait have an adaption survival advantage over normal individuals in malaria endemic regions.

30/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2016PP2QN02

Explain why people with sickle cell trait have an adaption survival advantage over normal individuals in malaria endemic regions.

ANSWERS

People with sickle cell trait are resistant to malaria; because the plasmodium cannot survive in sickle shaped red blood cells;

Comments

Differentiate between sickle cell anaemia and sickle cell trait.

30/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2016PP2QN02

Differentiate between sickle cell anaemia and sickle cell trait.

ANSWERS

Sickle-cell trait is heterozygous while sickle cell anaemia is a homozygous condition

Comments

How is sex determined in man?

30/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2016PP2QN02

How is sex determined in man?

ANSWERS

Males have two dissimilar chromosomes X and y/heterogametic;
Females have two similar chromosomes X and X/homogametic;
Male gamete/sperms have either X or y chromosome, while all ova have X chromosome;
if a sperm with X fuses with an ovum a female is formed and if a sperm with
fuses with an ovum a male is formed;

Comments

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​(a) What is mutation? (2mks)

(b) Explain why certain bacteria and other pathogens become resistance to drugs after some time. (2mks)

​(c) Work out a cross between a Haemophiliac man married to a carrier woman for Haemophilia. Use letter h to represent genes. (3mks)

​(d) State the phenotypic ratio of the children. (1mk)

​(a) Define the term allele (1mk)

(b) Differentiate between a dominant gene and a recessive gene (2mks)

In an experiment a variety of garden peas having a smooth seed coat was crossed with a variety with wrinkled seed coat. All the seeds obtained in F1 generation had smooth seed coat. The F1 generation selfed. The total number is F2 generation was 7324.

(a) Work out the total number of wrinkled seeds in the F2 generation (2mks)

(b) Give an explanation to the absence of plants with smooth seedcoat in the F1 generation (1mk)

â€‹(c) The following diagrams represents

â€‹Name the types of chromosomal mutations, X and Y (2mks)

(d) Other than the above types of chromosomal mutations, name three other types of chromosomal mutations â€‹(3mks)

Explain how the following occur during gene mutation

(i) Substitution (2mks)

(ii) Insertion (2mks)

​(i) State the phenomenon shown above (1mk)

​(ii) What is the genetic significance of the phenomenon above? (2mks)

K.C.S.E Biology Q & A - MODEL 2019PP2QN04

K.C.S.E Biology Q & A - MODEL 2018PP1QN18

State how in-breeding leads to reduced hybrid vigour

State two advantages of using genetically modified varieties in bean farming.

K.C.S.E Biology Q & A - MODEL 2017PP2QN05

K.C.S.E Biology Q & A - MODEL 2017PP1QN16

Explain why people with sickle cell trait have an adaption survival advantage over normal individuals in malaria endemic regions.

Differentiate between sickle cell anaemia and sickle cell trait.

How is sex determined in man?

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(a) What is mutation? (2mks)

(c) Work out a cross between a Haemophiliac man married to a carrier woman for Haemophilia.
Use letter h to represent genes. (3mks)

(d) State the phenotypic ratio of the children. (1mk)

(a) Define the term allele (1mk)

(i) State the phenomenon shown above (1mk)

(ii) What is the genetic significance of the phenomenon above? (2mks)