3. Extra-chromosomal inheritance can be detected by-
(1) Back cross (2) Test cross
(3) Reciprocal cross (4) Dihybrid cross
Introduction:
Extra-chromosomal inheritance refers to the transmission of genetic traits through cytoplasmic organelles like mitochondria and chloroplasts, rather than through nuclear chromosomes. Detecting such inheritance patterns requires specific genetic crossing techniques that help identify whether traits follow typical Mendelian inheritance or cytoplasmic transmission. Among the common genetic crosses—back cross, test cross, reciprocal cross, and dihybrid cross—one is particularly effective for detecting extra-chromosomal inheritance.
Explanation of Each Option:
-
Back Cross:
A back cross involves crossing an offspring (usually F1 hybrid) with one of its parents, either dominant or recessive. This cross helps study the inheritance pattern of a particular trait and confirm genotype. However, back cross alone cannot definitively detect extra-chromosomal inheritance as it is primarily used to analyze nuclear gene inheritance. -
Test Cross:
A test cross is a specific type of back cross where an individual showing the dominant phenotype is crossed with a homozygous recessive individual. This cross reveals whether the dominant phenotype is homozygous or heterozygous. Like the back cross, it mainly detects Mendelian nuclear gene patterns and is not effective in identifying extra-chromosomal inheritance. -
Reciprocal Cross:
In a reciprocal cross, the sexes of the parents are reversed in two crosses, e.g., male with trait A crossed to female with trait B and then female with trait A crossed to male with trait B. This cross is crucial for detecting extra-chromosomal inheritance because traits inherited from cytoplasmic organelles like mitochondria or chloroplasts show inheritance patterns dependent on the parent’s sex, often maternally inherited. Differences in traits between the reciprocal crosses indicate extra-chromosomal inheritance. -
Dihybrid Cross:
A dihybrid cross involves the inheritance of two different traits simultaneously and investigates their independent assortment. It is used to study Mendelian inheritance of nuclear genes but does not detect extra-chromosomal inheritance.
Correct Answer:
The correct option for detecting extra-chromosomal inheritance is (3) Reciprocal cross. This cross reveals differences in inheritance patterns based on the sex of the parent, highlighting whether traits are transmitted through cytoplasmic organelles rather than chromosomes.
Summary Table:
| Cross Type | Description | Use in Detecting Extra-chromosomal Inheritance |
|---|---|---|
| Back Cross | Cross offspring with one parent | No |
| Test Cross | Cross dominant phenotype with homozygous recessive | No |
| Reciprocal Cross | Reverse sexes in crosses | Yes (effective method) |
| Dihybrid Cross | Cross involving two traits simultaneously | No |
This explanation clarifies that reciprocal crosses are specifically valuable for detecting extra-chromosomal inheritance, distinguishing it from traditional nuclear gene inheritance demonstrated by back, test, or dihybrid crosses.
This SEO-friendly article uses the keyphrase “Extra-chromosomal inheritance detection,” with the meta description optimized for educational searches related to genetics and inheritance patterns, and the slug drawn from relevant keywords for clarity and search relevance.
