154. In an ordered tetrad analysis, if the two genes are not linked, the ………… will be almost equal.
1. Parental ditype and non-parental ditype
2. Parental ditype and tetratype
3. Tetratype and non-parental ditype
4. Parental ditype, non-parental ditype and tetratype
Question
In an ordered tetrad analysis, if the two genes are not linked, the ………… will be almost equal.
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Parental ditype and non-parental ditype
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Parental ditype and tetratype
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Tetratype and non-parental ditype
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Parental ditype, non-parental ditype and tetratype
Detailed Explanation
Ordered tetrad analysis is a powerful genetic tool used to study genetic recombination and linkage between genes. It is particularly useful for examining the relationships between two genes to determine whether they are linked or assort independently.
What is Ordered Tetrad Analysis?
Ordered tetrad analysis involves the examination of four products (tetrads) resulting from a meiotic division. The four products are classified into different types based on the combination of alleles they carry, and these types help us determine the degree of genetic linkage between the genes involved. The four tetrad types are:
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Parental Ditype (PD): Tetrads that contain only the parental allele combinations.
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Non-parental Ditype (NPD): Tetrads that contain only recombinant allele combinations.
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Tetratype (T): Tetrads that contain a combination of parental and recombinant alleles.
Linkage and Independent Assortment
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Linked Genes: When two genes are linked, they are located close together on the same chromosome and tend to be inherited together. This results in a higher number of parental ditypes (PD) and fewer non-parental ditypes (NPD).
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Unlinked Genes: When two genes are not linked, they are located on different chromosomes or are far apart on the same chromosome. As a result, genes assort independently, and the distribution of tetrad types becomes more even, with the parental ditypes (PD) and non-parental ditypes (NPD) being almost equal in number.
Expected Outcome for Unlinked Genes
When the genes are not linked (i.e., they assort independently), the following relationships hold:
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Parental ditypes (PD) and Non-parental ditypes (NPD) will be nearly equal in number, as independent assortment means there is an equal probability of producing parental and recombinant allele combinations.
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Tetratypes (T) will also appear in significant numbers but will not be equal to parental ditypes or non-parental ditypes when the genes are unlinked.
Thus, the expected result in the case of unlinked genes is that the number of parental ditypes and non-parental ditypes will be almost equal.
Correct Answer and Explanation
The correct answer is:
1. Parental ditype and non-parental ditype
Explanation:
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When genes are not linked, the frequencies of parental ditypes (PD) and non-parental ditypes (NPD) will be approximately the same because the genes assort independently. This results in an equal distribution of these two types of tetrads. The tetratypes (T), which contain both parental and recombinant alleles, will also be present but will not match the distribution of PD and NPD.
Conclusion
Ordered tetrad analysis is a key method in genetics to determine whether genes are linked or assort independently. When two genes are not linked, the distribution of parental ditypes and non-parental ditypes will be almost equal, reflecting independent assortment. This principle helps in the mapping and understanding of genetic variation and inheritance patterns
