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7. (a) Explain four of the following terms, as used in genetics; mutation, sex linkage, diploid, multiple alleles, back-crossing - Leaving Cert Agricultural Science - Question 7 - 2008
Question 7
7. (a) Explain four of the following terms, as used in genetics; mutation, sex linkage, diploid, multiple alleles, back-crossing. (b) The gender of offspring is de... show full transcript
Worked Solution & Example Answer:7. (a) Explain four of the following terms, as used in genetics; mutation, sex linkage, diploid, multiple alleles, back-crossing - Leaving Cert Agricultural Science - Question 7 - 2008
Step 1
Explain four of the following terms, as used in genetics; mutation, sex linkage, diploid, multiple alleles, back-crossing.
Answer
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Mutation: A mutation is a change in the genetic code of an organism. It can occur naturally or due to environmental factors, resulting in variants in traits.
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Sex Linkage: This refers to genes that are located on the sex chromosomes (X or Y). Traits linked to the X chromosome may exhibit different expression patterns in males and females due to their chromosomal differences.
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Diploid: Diploid refers to cells that contain two sets of chromosomes, one from each parent. In humans, this is represented as 2n.
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Multiple Alleles: This describes a situation where a single gene has more than two alleles, allowing for a variety of phenotypes. For example, blood type in humans is dictated by one gene with multiple alleles (A, B, O).
Step 2
The gender of offspring is determined by the male parent in mammals. Illustrate this statement in terms of chromosomes.
Answer
In mammals, the male has XY chromosomes while the female has XX chromosomes. The male parent contributes either an X or a Y chromosome:
- If the male contributes an X chromosome, the offspring will be female (XX).
- If the male contributes a Y chromosome, the offspring will be male (XY).
This shows that the gender of the offspring is indeed determined by the male parent.
Step 3
Suggest why all the offspring were broad-leaved.
Answer
All the offspring were broad-leaved due to the presence of a dominant allele for broad leaves from the red-flowered snapdragon. In genetic terms, broad leaf is an allele that expresses itself over the narrow leaf trait, leading all offspring to exhibit the broad-leaved phenotype.
Step 4
Step 5
List the phenotypes that may result from a cross between two plants heterozygous for both traits.
Answer
From a cross between two heterozygous plants (BbRr x BbRr) for broad leaves and pink flowers, the potential phenotypes are:
- Broad Red
- Broad Pink
- Narrow Red
- Narrow Pink
- Narrow White
- Broad White (assuming incomplete dominance allows for these combinations).