Theory question 104
Mendelian Inheritance(a)(i) What is a gene? (ii) Differentiate between the terms genotype and phenotype.
(b) Explain the following terms: (i) hybrid; (ii) pure breeding; (iii) nucleotide.
(c) In garden pea seeds, smooth seed coat is dominant over rough seed coat. With the aid of a genetic diagram, determine the result expected if a homozygous rough pea is crossed with a smooth seed coat plant whose parents were rough coated.
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(a)(i) A gene is a unit of inheritance, a section of DNA on a chromosome that controls a particular characteristic.
(ii) Genotype is the genetic make-up (set of alleles) of an organism; phenotype is its observable features, produced by the genotype together with the environment.
(b)(i) Hybrid: offspring of a cross between two genetically different parents (e.g. heterozygous Tt).
(ii) Pure breeding: an organism that is homozygous for a trait and always produces offspring like itself when bred with a similar one.
(iii) Nucleotide: the unit of a nucleic acid, made of a pentose sugar, a phosphate group and a nitrogenous base.
(c) Let S = smooth, s = rough. The smooth plant had rough (ss) parents, so it must be Ss. Cross: ss × Ss; gametes s and S, s; offspring Ss and ss; result: 1 smooth : 1 rough (50% smooth, 50% rough).
First work out the smooth parent's genotype from its rough parents.