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Form 4 Biology Genetics Questions and Answers

In this session, we are going to solve several Form 4 Biology questions on genetics. All questions are exam quality and very suitable for those preparing for KCSE exam.

Lessons (33)

• 1.    State the function of Deoxyribonucleic acid (DNA) molecule.
  1m 12s

• 2.    In an experiment, black mice were crossed and the offspring were black and brown. The gene for black colour is dominant over that of brown colour. Using letter B to represent the gene for black colour and b to represent the gene for brown colour, (a) Work out the genotypes of F1 generation. (b) What is the phenotype ratio of the offspring?
  4m 31s

• 3.    In a breeding experiment, plants with red flowers were crossed. They produced 123 plants with red flowers and 41 with white flowers. (a) Identify the recessive character. Give a reason. (b) What was the genotype of the parent plants that gave rise to the plants with red and white flowers? (c) If the white flowers were selfed, what would be the genotypes of their offspring?
  4m 26s

• 4.    In a family with four children, three were found to have normal skin pigmentation while one was an albino. Using letter A to represent gene for normal skin pigmentation and ‘a’ to represent the gene for albinism, (a) What are the genotypes of the parents? (b) Work out the genotype of (i) Normal pigmentation (ii) The albino child. (c) What is the probability that the fifth child will be an albino?
  3m 47s

• 5.    In an investigation, plants with red flowers were crossed with plants with white flowers. All the plants in the F1 generation had pink flowers. (a) Give a reason for the appearance of pink flowers in the F1 generation. (b) If the plants of F1 generation were selfed, state the phenotypic ratio of the F2 generation.
  3m 15s

• 6.    Name three types of chromosomal mutations.
  0m 40s

• 7.    Tallness in pea plants is due to a dominant gene. Two tall pea plants were crossed and their F1 generations were in the ration of 3 tall: 1 short. Using letter T to represent the gene for tallness and t for shortness, give the (a) (i) Genotype of the parents (ii) Gamete of the parents (iii) Genotype ratio of the F1 generation. (b) What is meant by the term testcross in genetic studies?
  4m 52s

• 8.    State two characters that researchers select in breeding programme.
  0m 56s

• 9.    Give an example of a sex – linked trait in humans on:Y – CHROMOSOME. X – CHROMOSOME.
  0m 49s

• 10.    (a) What is meant by the term sex linkage? (b) Name two sex linked traits in humans. (c) In Drosophila Melanogaster, the inheritance of eye colour is sex linked. The gene of red eye is dominant. A cross was made between a homozygous red eyed female and a white eyed male. Work out the phenotypic ratio of F1 generation. (Use R to represent the gene for red eyes)
  4m 19s

• 11.    A cross between a red flowered plant and white flowered produced plants with pink flowers. Using letter R to represent the gene for red colour and W for white colour, (a) What were the parental genotypes (b) Workout a cross between F1 plants. (c) Give the: (i) Phenotypic ratio of F1 plants. (ii) Genotypic ratio of F2 plants.
  5m 39s

• 12.    In a garden with plants of same species, 705 plants had red flowers while 224 had white flowers. (a) Work out the ratio of red to white flowered plants. (b) (i) Using letter R to represent the dominant gene, work out a cross between F1 offspring and a white flowered plant. (ii) What is the genotypic ratio from the cross in b (i) above? (c) What is meant by the term allele?
  5m 26s

• 13.    (a) Name two disorders in human caused by gene mutation. (b) Describe the following chromosomal mutations: (i) Inversion. (ii) Translocation. (c) In mice, the allele for black fur is dominant to the allele for brown fur. What percentage offspring would have brown fur from a cross between heterozygous black mice? Show your working. Use letter B to represent the allele for black colour.
  9m 30s

• 14.    (a) What is meant by the term allele? (b) Explain how the following occur during gene mutation: (i) Deletion. (ii) Inversion. (c) What is test – cross?
  4m 40s

• 15.    In maize, the gene for purple colour is dominant to the gene for white colour. A pure breeding maize plant with purple grains was crossed with heterozygous plant. (a) (i) Using letter G to represent the gene for purple colour, work out the genotype ratio of the offspring. (ii) State the phenotype of the offspring. (b) What is genetic engineering? (c) What is meant by hybrid vigour?
  4m 28s

• 16.    (a) What is meant by non – disjunction? (b) Give two examples of continuous variation in humans.
  1m 46s

• 17.    A pea plant with round seeds was crossed with a pea plant that had wrinkled seed, the gene for round seeds is dominant over that for wrinkled seeds. Using letter R to represent the dominant gene, state: (a) The genotype of parents if plant with round seed was heterozygous. (b) The gametes produced by the round and wrinkled seed parents. (c) The genotype and phenotype of F1 generation.
  5m 18s

• 18.    (a) What is meant by the following terms: (i) Hybrid vigour, (ii) Polyploidy? (b) State two causes of chromosomal mutations.
  4m 12s

• 19.    When the offspring of purple and white flowered pea plants were crossed, they produced purple and white flowered plants in the ratio of 3:1. Using letter H to represent the gene for purple colour; (a) State the genotype of: (i) Parents (ii) F1 generation. (b) Work out the cross between plants in the F1 generation. (c) Account for the colour of the flowers in plants of the F1 generation.
  3m 16s

• 20.    State two advantages of hybrid vigour.
  0m 27s

• 21.    (a) What is meant by the term non – disjunction? (b) Give an example of genetic disorder caused by: (i) Non – disjunction (ii) Gene mutation.
  1m 59s

• 22.    When the pure breeding black guinea pigs were crossed with pure breeding white guinea pigs, the offspring had a coat with black and white patches. (a) Using letter G to represent the gene for black coat colour and letter H for white coat colour, work out the genotypic ratio of F2. (b) State the phenotypic ratio of F2. (c) (i) Name the term used when two alleles in heterozygous state are fully
  4m 59s

• 23.    (a) Differentiate between the following terms: (i) Dominant gene and recessive gene, (ii) Continuous variation and discontinuous variation. (b) What would be the expected results from a test cross?
  5m 49s

• 24.    In humans, hairy ears are controlled by a gene on the Y chromosome. (a) Using letter YH to represent the chromosome carrying the gene for hairy ears, work out a cross between a hairy eared man and his wife. (b) (i) What is the probability of the girls having hairy ears? (ii) Give a reason for your answer in (b) (i) above. (c) Name two disorders in humans that are determined by sex linked genes
  3m 25s

• 25.    What is the probability of a couple with blood group AB getting a child with blood group AB? Show your working.
  1m 33s

• 26.    In a certain plant species which is normally green, a recessive gene for colour (n) causes the plants to be white in colour. Such plants die at an early age. In the heterozygous state, the plants are pale green in colour but grow to maturity. (a) Give a reason for the early death of the plants with homozygous recessive gene. (b) If a normal green plant was crossed with pale green plant, what
  4m 28s

• 27.    (a) What is meant by the term sex – linked genes? (b) Name two sex linked traits in human beings.
  2m 17s

• 28.    In an investigation, a variety of pea plants grown from seeds with smooth coats were crossed with plants grown from seeds with wrinkled coats. All the seeds obtained in the first filial (F1) generation had smooth seed coats. (a) Using the letter R to represent the gene for smooth seed coat, work out the genotype of the F1 generation. Show your working. (b) If the F1 generation was selfed
  5m 16s

• 29.    Differentiate between phenotype and genotype as used in genetics.
  2m 37s

• 30.    State three structural differences between DNA and RNA.
  2m 43s

• 31.    (a) How is sex determined in man? (b) (i) Differentiate between sickle cell anaemia and sickle cell trait. (ii) Explain why people with sickle cell trait have an adaptive survival advantage over normal individuals in malaria endemic regions.
  2m 35s

• 32.    The following are text messages on a cell phone that represent gene (a) Identify the type of gene mutation represented in each case I and II. (b) State Mendel’s First Law. (c) State two disadvantages of genetically modified plant products.mutation.
  4m 10s

• 33.    Below are photographs of two dogs. Explain the possible reason for the difference in the length of their fur.
  0m 52s