Cell Division, Genetics, and Meiosis

Comprehensive practice flashcards covering cell division, the cell cycle, mitosis, DNA molecular structure, chromosomes, karyotypes, meiosis phases, and gametogenesis.

What are the four primary biological reasons for cell division in organisms?

To form tissues, promote individual growth, repair damaged cells, and transfer information efficiently.

How is mitosis defined, and what is its cellular outcome?

The replication and division of the cell nucleus, where DNA is copied so that a single parent cell gives rise to two genetically identical diploid ($2n$) cells.

What is the structural role of centrioles and spindle fibres during cell division?

Centrioles are small cytoplasmic proteins that form spindle fibres, while spindle fibres are protein chains that guide chromosomes during cell division.

What major processes occur during interphase of the cell cycle?

As the longest time interval in a cell, the cell grows, synthesizes proteins, transports nutrients, and replicates its DNA during the $G_1$, $S$, and $G_2$ phases to prepare for division.

What cellular events take place during prophase of mitosis?

Chromosomes shorten and thicken, centromeres develop, the nuclear membrane dissolves, centrosomes migrate toward opposite poles, and spindle fibres begin to grow.

Which mitotic stage is depicted in this diagram, and what occurs during it?

Metaphase: chromosomes line up along the centre of the cell (equatorial plate), and spindle fibres attach directly to their centromeres.

What occurs during anaphase of mitosis?

Centromeres divide, and the separated chromosomes move toward opposite poles of the cell.

What key events occur during telophase of mitosis?

Chromosomes reach the opposite poles as the cell lengthens, spindle fibres dissolve, and a nuclear membrane reforms around each set of chromosomes.

How does cytokinesis differ between animal cells and plant cells?

Animal cells divide their cytoplasm by cleaving inward, whereas plant cells divide by developing a rigid cell plate.

What do the letters in the mnemonic "IPMATC" represent?

I – In between Phase (Interphase), P – Pairs (Prophase), M – Middle (Metaphase), A – Apart (Anaphase), T – Two (Telophase), and C – Cytokinesis.

What is cancer and what does metastasis refer to?

Cancer is uncontrolled, unregulated cell division; metastasis occurs when cancer cells break free from a tumour and enter tissues or the bloodstream to travel throughout the body.

What are the three statements that comprise the cell theory?

1) All living things are composed of one or more cells; 2) Cells are the smallest units of living organisms; 3) New cells come only from pre-existing cells by cell division.

What is the biological definition and primary role of DNA (deoxyribonucleic acid)?

A nucleic acid located in the nucleus of every cell that carries hereditary information across generations and whose sequence dictates the composition of proteins made by the cell.

Based on this structural diagram, what three components make up a single DNA nucleotide?

One deoxyribose sugar ($D$ or $S$), one phosphate group ($P$), and one nitrogenous base ($N.B.$, such as adenine, thymine, cytosine, or guanine).

What are the complementary base-pairing rules in a double-stranded DNA molecule?

Adenine always pairs with Thymine ($A - T$), and Guanine always pairs with Cytosine ($G - C$).

Why is DNA replication classified as semi-conservative?

Because each newly formed daughter DNA molecule retains half of the original parent strand as a template alongside half newly synthesized DNA.

What is the distinction between chromatin and chromatids?

Chromatin is the relaxed, unwound form of DNA in the nucleus (analogous to yarn), while a chromatid is a condensed, duplicated arm of a chromosome (analogous to a knitted scarf).

What is the chromosome composition and diploid number of a normal human somatic cell?

A diploid number of $46$ individual chromosomes ($2n = 46$), organized into $23$ pairs: $22$ pairs of autosomes and $1$ pair of sex chromosomes ($XX$ for females, $XY$ for males).

According to this diagram, what characteristics do homologous chromosomes share, and how do they differ?

They share the same length, centromere position, and banding patterns, but are not identical because they can carry different forms of the same gene called alleles.

What is a gene and what is an allele?

A gene is a specific sequence of DNA on a chromosome that governs the expression of a trait; an allele is a different version or form of that same gene.

How does asexual reproduction differ from sexual reproduction?

Asexual reproduction involves one parent producing genetically identical offspring (clones) via mitosis; sexual reproduction involves two parents producing genetically unique offspring via meiosis and fertilization.

What is a zygote, and how is it formed?

A diploid cell ($2n = 46$ in humans) formed through fertilization by the union of two haploid gametes (sperm and egg).

What specific events occur during Prophase I of meiosis, as shown in this diagram?

Chromosomes condense, homologous chromosomes pair up via synapsis to form tetrads, and non-sister chromatids cross over to exchange genetic segments.

How does Metaphase I of meiosis differ from mitotic metaphase?

In Metaphase I, homologous chromosome pairs (tetrads) line up along the equatorial plate together, whereas in mitotic metaphase, individual duplicated chromosomes line up single file.

Which meiotic stage is illustrated below, and which structures are separating?

Anaphase I: spindle fibres pull homologous chromosome pairs apart toward opposite poles, while sister chromatids remain joined at their centromeres.

What occurs during Anaphase II of meiosis?

Spindle fibres pull apart sister chromatids at their centromeres, moving them to opposite poles as individual chromosomes.

How do daughter cells produced by mitosis differ from those produced by meiosis in number and ploidy?

Mitosis produces $2$ diploid ($2n$) daughter cells genetically identical to the parent, whereas meiosis produces $4$ haploid ($n$) daughter cells that are genetically unique.

What sequence of cell stages occurs during human spermatogenesis?

Diploid spermatogonia ($2n$) differentiate into primary spermatocytes ($2n$), which undergo meiosis I to form $2$ secondary spermatocytes ($n$), followed by meiosis II to form $4$ haploid spermatids ($n$) that mature into flagellated sperm.

Why does oogenesis result in only one viable ovum instead of four?

Cytoplasm divides unequally during meiosis I and meiosis II, concentrating the nutrients into one large secondary oocyte/ovum and producing three non-viable polar bodies that degenerate.

At what developmental points does oogenesis pause in human females?

It begins before birth and pauses at prophase I; it resumes at puberty at metaphase I, pausing again at metaphase II until fertilization triggers anaphase II.

According to the principle of independent assortment ($2^n$), how many genetically distinct gametes can a human produce?

A human with $n = 23$ pairs of chromosomes can produce $2^{23}$, or $8{,}388{,}608$, genetically distinct gametes.

What three major mechanisms generate genetic variation during sexual reproduction?

1) Crossing over between non-sister chromatids in prophase I; 2) Independent assortment of maternal and paternal chromosomes in metaphase I; 3) Random fertilization of gametes.