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Explain each of the following: (i) The appearance of roan coat colour in Shorthorn cattle - Leaving Cert Agricultural Science - Question 7 - 2006
Question 7
Explain each of the following: (i) The appearance of roan coat colour in Shorthorn cattle. (ii) Lack of variation in plants that are propagated by cloning. (iii) ... show full transcript
Worked Solution & Example Answer:Explain each of the following: (i) The appearance of roan coat colour in Shorthorn cattle - Leaving Cert Agricultural Science - Question 7 - 2006
Step 1
(a)(i) The appearance of roan coat colour in Shorthorn cattle.
Answer
Roan coat color in Shorthorn cattle is a result of incomplete dominance. In this condition, both alleles (red and white) contribute to the phenotype of the heterozygous individual, leading to a blending of traits. As a result, the cattle exhibit a mixture of red and white hairs, creating the characteristic roan appearance.
Step 2
(a)(ii) Lack of variation in plants that are propagated by cloning.
Answer
Cloning produces genetically identical organisms since it involves asexual reproduction. This method does not introduce genetic variation because the offspring inherit the exact genetic material from the parent. Thus, any beneficial or detrimental traits are preserved in all clones, leading to a lack of diversity in the traits of the population.
Step 3
(a)(iii) Continuous variation in many characters associated with higher organisms.
Answer
Continuous variation is typically seen in polygenic traits, where multiple genes contribute to a single characteristic. Examples include height and skin color in humans. Because numerous alleles can combine in various ways, this results in a wide range of phenotypes rather than discrete categories. Environmental factors can also influence these traits further.
Step 4
(a)(iv) Why some defective phenotypes are more common in males than in females.
Answer
Defective phenotypes are often more common in males due to the presence of recessive genes located on the X chromosome. Males have only one X chromosome (XY), so if they inherit a recessive allele for a genetic disorder, they express the phenotype since there is no corresponding allele on the Y chromosome. In contrast, females have two X chromosomes (XX), providing a potential for masking the effect of a recessive allele.
Step 5
Step 6
(b)(ii) Describe the phenotypes of flowers produced when the seeds germinate and grow.
Answer
The phenotypes of the flowers produced from SsPp seeds will be:
- Straight stamen and plain petal (dominant)
- Straight stamen and striped petal
- Incurved stamen and plain petal
- Incurved stamen and striped petal Thus, the resulting phenotypic combinations will showcase both dominant and recessive traits.
Step 7
(b)(iii) What ratio of offspring phenotypes could result from a cross between the F1 hybrid plant in (ii) and a plant that is recessive for both traits?
Answer
The ratio of offspring phenotypes from a cross between an F1 hybrid (SsPp) and a plant homozygous recessive for both traits (sspp) would be 1:1:1:1. This means:
- 1 Straight stamen + plain petal
- 1 Straight stamen + striped petal
- 1 Incurved stamen + plain petal
- 1 Incurved stamen + striped petal.
Step 8
(c) Outline the significance of meiosis in reproduction.
Answer
Meiosis is significant in reproduction for several reasons:
- It reduces the chromosome number by half, producing haploid gametes (n) from diploid cells (2n).
- This reduction allows for the restoration of the diploid state at fertilization, ensuring the proper chromosome number in offspring.
- Meiosis also introduces genetic variation through crossing over and independent assortment, which contribute to the diversity of the population, enhancing adaptability and evolution.