A cattle farmer in a tropical region keeps a herd of local breed cattle for beef production. The local breed is well adapted to the hot climate and resistan...

(a) The breeding method the farmer could use is crossbreeding. [1] This involves mating animals from two different breeds to combine desirable traits from each into the offspring.

(b) Three advantages of crossbreeding in this situation:

1. The F1 offspring may exhibit hybrid vigour (heterosis), performing better than either parent breed alone in traits such as growth rate, fertility, and disease resistance. [1]
2. The offspring may inherit disease resistance from the local breed and high growth rate from the temperate breed, creating animals that grow quickly while surviving in tropical conditions. [1]
3. The crossbred cattle may be better adapted to local conditions than purebred temperate cattle, combining heat tolerance and tick resistance from the indigenous breed with the superior meat production of the imported breed. [1]

(c) A three-generation selective breeding programme:

1. Generation 1: Cross a local cow (dam) with a temperate bull (sire) to produce F1 offspring. Using the local cow as the dam ensures calves are born in an adapted mother with good maternal instincts for the environment. [1]
2. Assessment of F1: Raise the F1 offspring and assess them for desirable traits such as growth rate, heat tolerance, and disease resistance. [1]
3. Selection of F1: Select the F1 animals that show the best combination of traits from both breeds for further breeding. [1]
4. Generation 2: Mate selected F1 animals together, or backcross to the local breed to reinforce adaptation traits, producing a second generation (F2 or backcross). [1]
5. Assessment and selection of G2: Again select only the offspring with the desired phenotype - those that combine fast growth, good meat yield, heat tolerance, and disease resistance. [1]
6. Generation 3 and beyond: Continue selecting and breeding the best animals over further generations until a consistent line is established that reliably expresses high growth rate, heat tolerance, and disease resistance together. [1]

(d) Why the farmer should avoid mating closely related offspring:

1. Mating closely related animals constitutes inbreeding. [1]
2. Inbreeding increases the probability of homozygous recessive alleles being expressed. Some recessive alleles carry harmful effects that are normally masked by dominant alleles in heterozygous individuals; inbreeding brings these to the surface. [1]
3. The result is inbreeding depression: reduced fertility, lower disease resistance, poor growth rates, and decreased vigour in the offspring [1] - the opposite of the hybrid vigour the programme is designed to achieve.

(e) Two types of record the farmer should keep:

1. Growth rate and weight gain records for each animal, to measure whether offspring are meeting the beef production targets set by the programme. [1]
2. Pedigree (parentage) records showing the sire and dam of each animal, to guide future mating decisions and avoid accidental inbreeding. [1]