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
âName the types of chromosomal mutations, X and Y (2mks)
Y- inversion (2mks)
(d) Other than the above types of chromosomal mutations, name three other types of chromosomal mutations â(3mks)
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.
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.
(a) Height (tallness);
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;
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.
The following are text messages on a celiphone that represent gene mutation.
(a) Identify the type of gene mutation represented in each case
(b) State Mendel’s First Law.
(c) State two disadvantages of genetically modified plant products.
a. I — Deletion;
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;
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