Explanation: Ploidy is defined as the number of complete sets of chromosomes within a cell, not exclusively the number of homologous chromosome pairs.

Explanation: Human somatic cells are typically diploid, containing 46 chromosomes arranged in 23 homologous pairs; gametes are haploid, containing 23 chromosomes.

Explanation: The term 'haploid' has both a general meaning (number of sets in a gamete) and a specific meaning (exactly one copy of each chromosome), so it does not *strictly* refer *only* to the latter.

Explanation: The term 'monoploid' is frequently employed as a less ambiguous descriptor for a single set of chromosomes, and it is often used interchangeably with the specific definition of 'haploid' that denotes exactly one copy of each chromosome.

Explanation: While the haploid number (n) often equals the monoploid number (x) in diploid organisms, this is not universally true, particularly in polyploid organisms where 'n' can be a multiple of 'x'.

Explanation: Gametes from a tetraploid organism can be considered haploid if they contain half the somatic chromosome number, even if that number represents more than one basic set (e.g., a tetraploid producing diploid gametes).

Explanation: Zygoidy describes the state where chromosomes are paired, facilitating meiosis; azygoidy refers to unpaired chromosomes.

Explanation: The 'chromosome number' refers to the total count of individual chromosomes, whereas the 'ploidy number' refers to the number of chromosome sets.

Explanation: Diploid cells are characterized by containing two complete copies of the genome, organized into homologous chromosome pairs.

Explanation: In cytogenetics, 'homoploid' signifies having the same ploidy level, in contrast to terms describing different ploidy states.

Explanation: Azygoidy refers to the state of unpaired chromosomes; zygoidy describes paired chromosomes ready for meiosis.

Explanation: The glossary defines the 'ploidy number' as the number of chromosome sets, whereas the 'chromosome number' refers to the total count of individual chromosomes.

Explanation: Ploidy fundamentally refers to the number of complete sets of chromosomes present in a cell's nucleus.

Explanation: The term 'monoploid' specifically denotes a cell containing exactly one complete set of chromosomes.

Explanation: Human somatic cells are diploid (46 chromosomes), while gametes are haploid (23 chromosomes).

Explanation: Monoploid is the term used to specifically denote a cell with exactly one copy of each chromosome.

Explanation: The glossary defines the 'chromosome number' as the total count of individual chromosomes within a cell.

Explanation: A cell with six complete sets of chromosomes is classified as hexaploid; heptaploid refers to seven sets.

Explanation: Ploidy levels can vary within a single mammalian organism; for instance, the liver is known to exhibit different ploidy levels in its cells.

Explanation: Aneuploidy is characterized by an abnormal number of individual chromosomes, not complete sets; it results in a chromosome number that is not an exact multiple of the haploid number.

Explanation: Down syndrome (Trisomy 21) is an example of aneuploidy, not euploidy, as it involves an extra copy of a single chromosome rather than a complete set.

Explanation: Polyploidy is a general term for having more than two sets of chromosomes; having exactly three sets is specifically termed triploidy.

Explanation: Endoreduplication is precisely the process by which a cell's genome is duplicated without subsequent cell division, thereby increasing the cell's ploidy level.

Explanation: Mixoploidy describes the coexistence of two or more cell lines with differing ploidy levels within a single organism, not just one abnormal cell line.

Explanation: Dihaploids are organisms derived from polyploids through chromosome reduction, resulting in a diploid constitution (2x), not double the haploid number (which would be 4x if starting from a tetraploid).

Explanation: Triploid organisms are typically sterile because the uneven number of chromosome sets (three) leads to improper segregation during meiosis, producing aneuploid gametes.

Explanation: Human heart cells commonly undergo endoreduplication, leading to a significant proportion of tetraploid and even octoploid nuclei in adults, thus they do not typically remain diploid.

Explanation: Tissue-specific polyploidy refers to variations in ploidy levels within particular tissues of an organism, not necessarily throughout the entire organism.

Explanation: Ploidy can vary within an organism, as exemplified by the mammalian liver, where different tissues may exhibit distinct ploidy levels.

Explanation: Aneuploidy is defined by the presence of an abnormal number of chromosomes, meaning the total is not an exact multiple of the haploid set.

Explanation: Down syndrome, characterized by an extra copy of chromosome 21, is a form of aneuploidy.

Explanation: Endoreduplication is the process where genome duplication occurs without cell division, resulting in polyploid somatic cells.

Explanation: Mixoploidy refers to the presence of multiple cell lines with varying ploidy levels within a single organism.

Explanation: Dihaploids and polyhaploids are generated through haploidisation, a process that reduces the chromosome set number.

Explanation: Triploid organisms are typically sterile because the uneven number of chromosome sets leads to improper segregation during meiosis.

Explanation: Polyploidy is a common phenomenon, particularly in plants, with approximately half of all known plant genera containing polyploid species.

Explanation: Changes in ploidy level are recognized as significant drivers of speciation, especially within plant and fungal lineages.

Explanation: Research indicates that polyploidy in plants is correlated with an increased propensity for invasiveness, potentially due to enhanced vigor and adaptability.

Explanation: The 'masking theory' posits that genes expressed in diploid tissues face less efficient natural selection, as deleterious recessive alleles can be masked by dominant alleles, unlike in haploid tissues.

Explanation: Polyploidy is considered a principal mechanism driving speciation and evolutionary diversification in plants and fungi.

Explanation: The 'ploidy nutrient limitation hypothesis' proposes a complex relationship, suggesting that while haploidy may be favored under certain nutrient limitations, higher ploidy can also be advantageous under specific conditions.

Explanation: Polyploidization occurring within the germline is a significant, albeit not universally common, mechanism that can directly lead to the formation of polyploid species.

Explanation: The '2R hypothesis' posits that early vertebrate ancestors underwent *two* rounds of whole genome duplication, not just one.

Explanation: The 'masking theory' suggests less efficient selection in *diploid* tissues, where recessive alleles can be masked, not in haploid tissues.

Explanation: Triploidy is a common agricultural technique employed to generate seedless fruits, such as watermelons and bananas, by inducing sterility.

Explanation: Polyploidy is highly prevalent in plants, with approximately half of all known plant genera containing polyploid species.

Explanation: Ploidy changes are considered significant drivers of speciation, particularly in plants and fungi, by altering genetic makeup and reproductive compatibility.

Explanation: The 'masking theory' posits that natural selection is less efficient on genes expressed in diploid tissues due to the masking effect of dominant alleles.

Explanation: Polyploidy in plants is correlated with an increased likelihood of becoming invasive.

Explanation: The '2R hypothesis' posits that early vertebrate ancestors underwent two rounds of whole genome duplication.

Explanation: Many fungi and primitive plants, such as mosses, spend the majority of their life cycle in the haploid stage, unlike more evolved plants which are predominantly diploid.

Explanation: Haplodiploidy is indeed a sex-determination system where females arise from fertilized diploid eggs and males from unfertilized haploid eggs.

Explanation: Allopolyploids arise from hybridization between individuals of *different* species, not the same species.

Explanation: Polytene chromosomes, notably found in the salivary glands of fruit fly larvae, are indeed known to exhibit extremely high ploidy levels, reaching up to 1024-fold.

Explanation: Homoploid hybridization results in offspring with the same ploidy level as the parents, differing from polyploid speciation which involves a change in chromosome set number.

Explanation: In the common potato (*Solanum tuberosum*), which is tetraploid, the haploid number (n=24) is twice the monoploid number (x=12), not half.

Explanation: The *Xenopus* genus indeed demonstrates a remarkable 'ploidy series,' encompassing species that range from diploid to dodecaploid.

Explanation: Polyploidy in bacteria such as *Deinococcus radiodurans* is indeed associated with enhanced resistance to environmental stressors like radiation and desiccation, likely due to improved DNA repair capabilities.

Explanation: The 'Brassica triangle' is a classic example of *allopolyploidy*, involving hybridization between different species followed by chromosome doubling, rather than homoploid hybridization.

Explanation: The fern genus *Ophioglossum* is renowned for its exceptionally *high* ploidy levels, leading to some of the highest chromosome counts observed in eukaryotes.

Explanation: Retroviruses are considered diploid when they possess two copies of their RNA genome per virion; having only one copy would be haploid.

Explanation: For common wheat (*Triticum aestivum*), the haploid number (n=21) is a multiple (3x) of its monoploid number (x=7), not lower.

Explanation: In many social insects exhibiting haplodiploidy, males are haploid (developing from unfertilized eggs) and females are diploid (developing from fertilized eggs).

Explanation: The common potato (*Solanum tuberosum*) is tetraploid; its haploid number (n=24) is twice its monoploid number (x=12), not equal.

Explanation: This statement is correct: a hexaploid species with a monoploid number of 11 would have 6 sets * 11 chromosomes/set = 66 chromosomes, as exemplified by *Sequoia sempervirens*.

Explanation: Both humans and fruit flies are diploid organisms, but humans possess a total of 46 chromosomes, whereas fruit flies have only 8.

Explanation: Common wheat is hexaploid (6x) with x=7. Its haploid gametes contain three sets (n=3x), thus n=21.

Explanation: Many plants and fungi exhibit alternation of generations, cycling between haploid and diploid life stages.

Explanation: Haplodiploidy is a prevalent sex-determination system among social insects such as ants, bees, and termites.

Explanation: Allopolyploids arise from hybridization events between individuals belonging to distinct species.

Explanation: Polytene chromosomes found in fruit flies can exhibit extremely high ploidy levels, reaching up to 1024-fold.

Explanation: Homoploid hybridization results in new species formation without altering the ploidy level of the parental organisms.

Explanation: The *Xenopus* genus exhibits a 'ploidy series' with species spanning diploidy to dodecaploidy.

Explanation: Polyploidy in bacteria and archaea is typically associated with *enhanced* DNA repair efficiency and environmental resistance, not reduced efficiency.

Explanation: The 'Brassica triangle' serves as a prime example of allopolyploidy, involving hybridization between different species followed by chromosome doubling.

Explanation: The term 'ploidy' is derived from the Ancient Greek word '-plóos', meaning '-fold', not 'many'.

Explanation: Eduard Strasburger, a prominent botanist, coined the terms 'haploid' and 'diploid' in 1905.

Explanation: The term 'ploidy' derives from the Greek '-plóos' ('-fold') and '-eides' ('form or likeness').

Explanation: Eduard Strasburger is credited with coining the terms 'haploid' and 'diploid' in the early 20th century.