Question:
In general F\(_2\), F\(_3\) and the subsequent generations do not show segregation for a cytoplasmically inherited trait. This is because
In general F\(_2\), F\(_3\) and the subsequent generations do not show segregation for a cytoplasmically inherited trait. This is because
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Remember the rule for cytoplasmic inheritance: "Mom gives the mitochondria." Since the F1 generation gets all its cytoplasmic genes from one parent, there's no mix of alleles to segregate in later generations, unlike with nuclear genes which follow Mendelian rules.
Updated On: Sep 17, 2025
- The F\(_1\) individuals generally receive plasmagenes from one parent only.
- The F\(_1\) individuals generally receive nuclear genes from one parent only.
- The F\(_1\) individuals generally receive plasmagenes from both parents.
- The F\(_1\) individuals generally receive nuclear genes from both parents.
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
Cytoplasmic inheritance (also known as extranuclear or maternal inheritance) refers to traits controlled by genes located in organelles within the cytoplasm, such as mitochondria and chloroplasts. These are called plasmagenes. The question asks why these traits do not show Mendelian segregation in F\(_2\) and later generations.
Step 2: Detailed Explanation:
Mendelian segregation (e.g., the 3:1 ratio in F\(_2\)) occurs because nuclear genes from both parents are combined in the F\(_1\) zygote and then segregate during meiosis when the F\(_1\) individual produces gametes.
In contrast, during fertilization in most animals and plants, the male gamete (sperm or pollen) contributes almost no cytoplasm to the zygote. The zygote receives nearly all of its cytoplasm, and thus its mitochondria and chloroplasts, from the female gamete (the egg).
This means that the F\(_1\) individuals inherit their plasmagenes from only one parent, the mother. This is the basis of maternal inheritance.
Since the F\(_1\) individuals have plasmagenes from only one source, there are no alternative alleles (like there would be for nuclear genes in a heterozygote) to segregate during meiosis.
Consequently, all offspring in the F\(_2\), F\(_3\), and subsequent generations will have the same cytoplasmic genotype as the original maternal parent. No segregation is observed.
Step 3: Final Answer:
The lack of segregation is because the F\(_1\) generation inherits its cytoplasmic genes (plasmagenes) from a single parent (usually the mother). Option (A) correctly states this reason. Options (B) and (D) are incorrect as nuclear genes are received from both parents. Option (C) is incorrect as plasmagenes are typically received from only one parent.
Cytoplasmic inheritance (also known as extranuclear or maternal inheritance) refers to traits controlled by genes located in organelles within the cytoplasm, such as mitochondria and chloroplasts. These are called plasmagenes. The question asks why these traits do not show Mendelian segregation in F\(_2\) and later generations.
Step 2: Detailed Explanation:
Mendelian segregation (e.g., the 3:1 ratio in F\(_2\)) occurs because nuclear genes from both parents are combined in the F\(_1\) zygote and then segregate during meiosis when the F\(_1\) individual produces gametes.
In contrast, during fertilization in most animals and plants, the male gamete (sperm or pollen) contributes almost no cytoplasm to the zygote. The zygote receives nearly all of its cytoplasm, and thus its mitochondria and chloroplasts, from the female gamete (the egg).
This means that the F\(_1\) individuals inherit their plasmagenes from only one parent, the mother. This is the basis of maternal inheritance.
Since the F\(_1\) individuals have plasmagenes from only one source, there are no alternative alleles (like there would be for nuclear genes in a heterozygote) to segregate during meiosis.
Consequently, all offspring in the F\(_2\), F\(_3\), and subsequent generations will have the same cytoplasmic genotype as the original maternal parent. No segregation is observed.
Step 3: Final Answer:
The lack of segregation is because the F\(_1\) generation inherits its cytoplasmic genes (plasmagenes) from a single parent (usually the mother). Option (A) correctly states this reason. Options (B) and (D) are incorrect as nuclear genes are received from both parents. Option (C) is incorrect as plasmagenes are typically received from only one parent.
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