NESA Biology Cell Replication

Both spermatogenesis and oogenesis are forms of meiosis that result in the production of haploid gametes ($n$) from diploid germ cells ($2n$).

Spermatogenesis begins at puberty and continues throughout life, whereas oogenesis begins during fetal development, arrests, and resumes at puberty.

Both processes begin with diploid stem cells (spermatogonia and oogonia) that differentiate into diploid primary spermatocytes and oocytes before undergoing meiosis.

Uracil is found in RNA, where it pairs with adenine. In DNA, thymine replaces uracil.

Guanine pairs with cytosine via three hydrogen bonds, not with adenine.

Cytosine pairs with guanine via three hydrogen bonds, not with adenine.

Incorrect. DNA repair involves identifying and fixing damaged DNA strands, whereas PCR is designed to synthesize new copies of a DNA template rather than fix errors.

Incorrect. Transcription is the cellular process of synthesizing RNA from a DNA template, while PCR synthesizes new DNA strands.

Incorrect. Translation is the process of building proteins from an mRNA template at the ribosome, which is entirely different from the DNA amplification performed in PCR.

This describes the function of DNA helicase, which unwinds the double helix by breaking hydrogen bonds between base pairs.

This describes the function of DNA ligase, which joins DNA fragments (such as Okazaki fragments) together to form a continuous strand.

RNA primers are synthesized by the enzyme primase, not DNA polymerase, to initiate DNA synthesis.

This is the percentage of guanine, which pairs equally with cytosine. Adenine pairs with thymine, so it will have a different percentage.

This represents the combined total percentage of both adenine and thymine ($100\% - 56\% = 44\%$), not adenine alone.

This is the combined total percentage of cytosine and guanine ($28\% + 28\% = 56\%$) in the DNA molecule.

Incorrect. This is half of the haploid number, but gametes contain the full haploid set of chromosomes, not half of it.

Incorrect. This is the diploid number ($2n=48$), which represents the chromosome count in somatic (body) cells, not reproductive sperm cells.

Incorrect. This is an arbitrary number that does not relate to the haploid ($n=24$) or diploid ($2n=48$) chromosome counts of an orangutan.

While spermatogenesis occurs in the testes, the production of a single functional gamete with polar bodies is the outcome of oogenesis, not spermatogenesis.

Spermatogenesis occurs in the testes, not the ovaries; furthermore, the process occurring in the ovaries (oogenesis) typically results in only one functional gamete.

This option describes the process of oogenesis, which occurs in the ovaries and results in one functional egg cell and non-functional polar bodies.

Incorrect. The geep receives 27 chromosomes from the sheep and 30 from the goat, making its total chromosome count 57, not a haploid number of 29.

Incorrect. The total chromosome count is determined by adding the haploid numbers of the parents ($27 + 30 = 57$), not 52.

Incorrect. This is the sum of the parents' diploid numbers ($54 + 60 = 114$). Fertilization involves the fusion of haploid gametes, not diploid cells.

This describes the function of initiator proteins or origin recognition complexes, which bind to specific DNA sequences to recruit helicase to the origin of replication.

Adding complementary nucleotides to synthesize the new DNA strand is the function of DNA polymerase, not helicase.

Joining DNA fragments (such as Okazaki fragments) by sealing nicks in the sugar-phosphate backbone is the role of DNA ligase.

Proofreading (II) occurs after the new DNA strand is synthesized, not at the beginning of the replication process.

DNA must uncoil (I) before it can unzip (IV), and proofreading (II) occurs after synthesis (III), not before.

DNA synthesis (III) requires the DNA to be uncoiled (I) and unzipped (IV) first in order to expose the template strands.

This is incorrect because neither process occurs during meiosis II. Meiosis II involves the separation of sister chromatids, whereas crossing over and independent assortment involve homologous chromosomes during meiosis I.

This is incorrect because independent assortment occurs during metaphase I of meiosis I, not meiosis II. During meiosis II, sister chromatids separate, but the random assortment of homologous pairs has already taken place.

This is incorrect because crossing over occurs during prophase I of meiosis I, not meiosis II. By the time meiosis II begins, homologous chromosomes have already been separated into different cells.

Incorrect. Mitosis is specifically the division of the nucleus in eukaryotes, while binary fission occurs in prokaryotes which do not have a nucleus.

Incorrect. The pairing of homologous chromosomes is a key feature of meiosis, not mitosis or binary fission.

Incorrect. Both binary fission and mitosis are forms of cell division that result in the production of two genetically identical daughter cells.

While DNA does contain a deoxyribose sugar, uracil is a nitrogenous base found exclusively in RNA, replacing the thymine found in DNA.

Although guanine is a nitrogenous base found in DNA, ribose is the sugar backbone of RNA. DNA contains deoxyribose sugar instead.

Adenine is a base found in DNA, but ribose is the sugar found in RNA. The sugar in a DNA molecule is deoxyribose.

This is incorrect. Complementary bases are held together by hydrogen bonds, not nitrogen bonds, which do not exist in this context.

This is incorrect. Phosphodiester bonds form the strong sugar-phosphate backbone of the DNA strand, which must remain intact while the two strands are separated.

This is incorrect. The phosphate-based bonds connecting adjacent nucleotides make up the structural backbone of the DNA strand and are not broken to separate the strands.