Question map
In the context of hereditary diseases, consider the following statements : 1. Passing on mitochondrial diseases from parent to child can be prevented by mitochondrial replacement therapy either before or after in vitro fertilization of egg. 2. A child inherits mitochondrial diseases entirely from mother and not from father. Which of the statements given above is/are correct?
Explanation
The correct answer is Option 3 (Both 1 and 2). This is based on the biological mechanisms of mitochondrial inheritance and advanced reproductive technologies.
- Statement 1 is correct: Mitochondrial Replacement Therapy (MRT) aims to prevent the transmission of mitochondrial diseases. It can be performed through Pronuclear Transfer (after fertilization, where nuclei are transferred from the mother’s zygote to a donor zygote) or Maternal Spindle Transfer (before fertilization, where the nuclear DNA is removed from the mother’s egg and inserted into a donor egg).
- Statement 2 is correct: In humans, mitochondria are inherited exclusively from the mother. During fertilization, the sperm's mitochondria are typically located in the tail, which is either lost or destroyed by the egg's cytoplasm (autophagy) upon entry. Therefore, mitochondrial DNA (mtDNA) mutations are passed down solely through the maternal line.
Since both statements accurately describe the clinical application of MRT and the biological reality of uniparental inheritance, Option 3 is the right choice.
PROVENANCE & STUDY PATTERN
Guest previewThis question is a classic 'Science in Context' trap. While technically nuclear DNA can cause mitochondrial issues, the context of MRT (Three-parent baby) restricts the scope to mitochondrial DNA (mtDNA). The strategy is to read statements as a coherent narrative: Statement 1 (the cure) only makes sense if Statement 2 (the cause) is true.
This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.
- Statement 1: In the context of hereditary mitochondrial diseases, can mitochondrial replacement therapy prevent transmission of mitochondrial diseases from a parent to their child?
- Statement 2: In the context of hereditary mitochondrial diseases, does mitochondrial replacement therapy include procedures performed both before fertilization (spindle transfer) and after fertilization (pronuclear transfer) during IVF to prevent disease transmission?
- Statement 3: In the context of hereditary mitochondrial diseases, are mitochondrial diseases inherited entirely from the mother with no paternal contribution?
- Explicitly states MRT can be used to prevent inheritance of mitochondrial diseases caused by variants in mitochondrial DNA.
- Explains the biological rationale (mitochondria are passed via the egg), which underlies how MRT can prevent transmission.
- Clarifies the scope and limitation of MRT by noting it does not prevent diseases caused by variants in nuclear DNA.
- Helps specify that MRT prevents transmission only for mtDNA-based (not nuclear DNA–based) mitochondrial diseases.
- Summarizes the purpose of MRT as enabling prospective parents to avoid passing down mitochondrial diseases to their children.
- Frames MRT as a reproductive technique explicitly aimed at reducing transmission of certain serious mitochondrial conditions.
Explains that specialised reproductive cells (gametes) carry genetic material and that offspring get genetic material via gametes.
A student can combine this with the external fact that mitochondria (and their DNA) are primarily transmitted via the egg cytoplasm to reason that altering the egg's cytoplasm (as in mitochondrial replacement) could change mitochondrial inheritance.
Notes that each baby gets a mix of genetic information from both parents through gametes and that gametes determine inherited traits.
Use the idea that traits depend on gamete contents to infer that replacing the egg's mitochondrial content might prevent transmission of maternal mitochondrial variants.
States the general rule that both parents contribute genetic material and rules govern inheritance of traits.
A student could apply the concept of inheritance rules to consider a special case (non-nuclear inheritance) where only one parent's cytoplasmic elements are passed on, and therefore targeted replacement might alter transmission.
Poses the question of how equal genetic contribution is ensured, highlighting that mechanisms of gamete formation determine what is passed on.
From this, a student may reason that because gamete formation/mechanisms control inheritance, interventions at the gamete/egg level (mitochondrial replacement) could influence what is transmitted.
Provides an example where an intervention (condom) reduces transmission of disease during sexual activity.
As an analogy, a student could extrapolate that medical interventions exist that can prevent biological transmission, prompting investigation into whether a parallel intervention (mitochondrial replacement) could prevent hereditary transmission.
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