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?

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.

Mentions mitochondrial DNA (mt-DNA) as a distinct genetic material used to trace lineages, showing mtDNA is a recognizable hereditary component.

A student could combine this with the standard fact that mtDNA is inherited via the egg to infer that replacing mtDNA in the egg or early embryo might prevent transmission.

Explains that parents produce specialised gametes (eggs and sperm) that carry halves of genetic material and join to form a new cell, highlighting the distinction between pre-fertilization (egg) and post-fertilization (zygote) stages.

By noting the egg is a distinct manipulable gamete, a student could see why a technique applied to the egg before fertilization (spindle transfer) differs from one done after fertilization (pronuclear transfer).

Describes how germ cells take one chromosome from each pair and how fertilization restores the full chromosome set, illustrating the biological difference between processes acting on gametes versus on the fertilized cell.

A student could extend this to reason that interventions can be targeted either at germ cells (pre-fertilization) or at the combined cell (post-fertilization) to alter hereditary material passed on.

Refers to 'rules of heredity' governing how traits are inherited, providing a general framework that hereditary diseases follow predictable transmission patterns.

A student could apply these rules plus the specific maternal nature of mtDNA to evaluate whether manipulating the egg or embryo could interrupt predictable transmission of mitochondrial disease.

States the principle 'Prevention is better than cure,' which supports the idea of preventive medical interventions to stop disease transmission rather than treating disease after onset.

A student could use this policy/ethical guideline together with biological clues to justify investigating preventive techniques applied before or shortly after fertilization to avoid inheritable mitochondrial disease.

Mentions mitochondrial DNA (mt-DNA) studies used to trace prehistoric migrations, highlighting mt-DNA as a distinct genetic marker.

A student could combine this with the basic fact that mtDNA is often used to trace maternal lineages (because it is transmitted in a particular way) to investigate whether mtDNA — and thus mitochondrial diseases — show maternal-only inheritance.

Explains the general rule that nuclear chromosomes come one each from mother and father and that germ cells carry one chromosome of each pair.

By contrasting this biparental nuclear inheritance with mt-DNA as a separate entity, a student could explore whether mitochondria/mtDNA follow the same biparental pattern or an exception (e.g., maternal-only transmission).

States the general rule that both father and mother contribute practically equal amounts of genetic material to the child for most traits.

A student can use this general rule as a baseline and then look for exceptions (like organelle genomes) to test if mitochondrial traits deviate from equal parental contribution.

Describes how gametes carry half the parent's genetic material and combine to give a full nuclear genome.

A student could use this description of nuclear gamete contribution to ask whether mitochondrial genomes are included in that gametic mixing or are transmitted by a different mechanism (e.g., predominantly via egg cytoplasm).