The correct option is
D. a homozygote.
Explanation of the Correct Answer
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Definition of Homozygote: A homozygote is an organism that has two identical alleles for a particular gene. This means that for a specific trait, both copies of the gene (one inherited from each parent) are the same. For example, if we consider a gene that determines flower color, a homozygous organism could have two alleles for red flowers (RR) or two alleles for white flowers (rr).
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Genetic Makeup: In genetics, alleles are different forms of a gene that can exist at a specific locus (position on a chromosome). When an organism has two identical alleles (like AA or aa), it is classified as homozygous for that trait. This is important because homozygous organisms will consistently express the same phenotype (observable characteristics) for that trait.
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Importance in Genetics: Understanding whether an organism is homozygous or heterozygous (having two different alleles, such as Aa) is crucial in predicting inheritance patterns, especially in breeding experiments and genetic studies. Homozygous individuals can produce offspring with predictable traits, while heterozygous individuals can produce a mix of traits.
Explanation of Incorrect Options
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A. a heterozygote: This option is incorrect because a heterozygote has two different alleles for a gene (e.g., Aa). This means that the organism carries two variations of a gene, which can lead to different expressions of a trait. For example, if A represents a dominant allele and a represents a recessive allele, the heterozygote (Aa) will express the dominant trait.
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B. a hybride: This term is often used to describe the offspring resulting from the crossbreeding of two different species or varieties. While hybrids can be heterozygous (having different alleles), the term does not specifically refer to the genetic makeup of having identical alleles. Therefore, it is not the correct answer in this context.
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C. an allelomorph: This term is synonymous with "allele" and refers to the different forms of a gene. It does not describe the genetic makeup of an organism. An allelomorph can be either homozygous or heterozygous, depending on whether the alleles are identical or different. Thus, this option does not answer the question about having one pair of identical genes.
Summary of Key Points
- A homozygote has two identical alleles for a specific gene, leading to consistent expression of traits.
- A heterozygote has two different alleles, resulting in a mix of traits.
- The term hybride refers to offspring from different species or varieties, not specifically to genetic identity.
- Allelomorph is another term for allele and does not indicate whether the alleles are identical or different.
Revision Summary
- Homozygote: Organism with identical alleles (e.g., AA or aa).
- Heterozygote: Organism with different alleles (e.g., Aa).
- Hybride: Offspring from different species or varieties, not a specific genetic term.
- Allelomorph: Another term for allele, does not specify genetic identity.