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)½ 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) ​(c) The following diagrams represents
The above diagrams represents
​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 ​(3mks)
How do identical twins and fraternal twins arise?
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  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
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
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;
K.C.S.E Biology Q & A - MODEL 2017PP2QN05
State how in-breeding leads to reduced hybrid vigour
answer
K.C.S.E Biology Q & A - MODEL 2017PP2QN05
State two advantages of using genetically modified varieties in bean farming.
answers
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
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;
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
K.C.S.E Biology Q & A - MODEL 2016PP2QN02
Differentiate between sickle cell anaemia and sickle cell trait.
ANSWERS
K.C.S.E Biology Q & A - MODEL 2016PP2QN02
How is sex determined in man?
ANSWERS
K.C.S.E Biology Q & A - MODEL 2015PP2QN03
A female with sickle cell trait marries a normal man. The allele for sickle cell is HbS and the normal allele is HbA. Determine the probability that their first born will have the sickle cell trait. Show your working..
ANSWERS
K.C.S.E Biology Q & A - MODEL 2015PP2QN03
State two examples of discontinuous variation.
ANSWERS
(i) Sex;
(ii) ABO blood group system/Rhesus factor; (iii) Ability to roll tongue; (iv) Free or attached earlobe; (v) Presence/ absence of hair in the nose! on the ear pinna; (vi) Finger prints; ability to taste PTC (phenythiocarbamide) PTV (phenylthio urea) (vii) Winglength in prosophila; (viii) Size of abdomen in drosophila; (ix) Eye colour in prosophila; (x) Smooth/wrinkled seed coats in pea plants; (xi) Green/yellow seed coats/seed coat colour in pea plants; (xii) Polymorphism/melanic and non melanic forms in moths. |
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