IGCSE Biology Paper-3: Specimen Questions with Answers 253 - 254 of 358
Passage
Coat color in cattle is inherited in a very similar way to blood groups in humans. The gene for coat color has two codominant alleles:
CB which is the allele for brown coat
CW which is the allele for white coat.
Table shows the genotypes and phenotypes of different coat colors seen in a herd of cattle.
| genotype | phenotype |
| CBCB | brown |
| CWCW | white |
| CBCW | roan |
Question 253 (1 of 5 Based on Passage)
Write in Short
Short Answer▾A farmer crossed several roan colored cows with a roan colored bull.
Complete the genetic diagram to show the ratio of expected phenotypes among the offspring.
Explanation
Question 254 (2 of 5 Based on Passage)
Write in Short
Short Answer▾A farmer has a herd of cows that produce milk. The farmer wants to improve the milk yield of the herd by using artificial selection (selective breeding) . The farmer buys semen (fluid containing sperm) to inseminate the cows artificially.
(i) Describe how the farmer could improve the milk yield of the cows using artificial selection.
Explanation
Artificial selection is the process by which humans use animal breeding to selectively develop phenotypic traits (characteristics) by choosing which typically animal males and females will sexually reproduce and have offspring together.
Steps of Artificial Selection
- Breeder decide trait or characteristic of interest.
- Breed the choices together (artificial insemination used)
- Choose offspring with ideal characteristics to mate
- Repeat for many generations
- The allelic frequency for the characteristic increases.
- Decide what type of selection is occurring in the population
- Selective, Directional, Disruptive
In order to achieve the cow yielding higher milk directional selection is used as it pushes mean of the frequency of the selected individual in one direction.