Theory question 103
Chromosomes, DNA and Sex Linkage(a) Define the following terms:
(i) gene; (ii) gene mutation.
(b) Name two structures each of plants and animals where the following processes take place:
(i) mitosis; (ii) meiosis.
(c) State four advantages a farmer may hope to derive in cross-breeding two different breeds of cows.
(d) State three applications of the knowledge of genetics in medicine.
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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 and is passed from parents to offspring.
(ii) A gene mutation is a sudden, permanent change in the structure of a gene (its DNA), which may be inherited.
(b)(i) Mitosis – plants: root tip, shoot tip (apical meristem), cambium; animals: skin (Malpighian layer), bone marrow, wounded tissue, embryo.
(ii) Meiosis – plants: anthers, ovules (ovary); animals: testes, ovaries.
(c) Any four: higher milk yield; more and better meat; faster growth/early maturity; resistance to disease; tolerance of heat or poor feed; increased fertility; hybrid vigour.
(d) Any three: genetic counselling of couples (e.g. sickle cell); prevention of hereditary diseases; blood transfusion matching (blood groups); settling disputed paternity (blood groups, DNA tests); organ transplant matching; gene therapy; production of drugs such as insulin by genetic engineering.
Name actual organs for (b).