BIO 30 UNIT C: Cell Division, Cell Cycle, Genetics, and Reproductive Strategies

Comprehensive review flashcards covering cell cycle phases, mitosis, meiosis, chromosomal abnormalities, cloning techniques, and plant reproductive life cycles based on BIO 30 lecture notes.

What are the four primary reasons why cells divide?

Growth (accumulating cytoplasm/organelles, overcoming surface area to volume limitations), maintenance (replacing worn out or dead cells), repair (regenerating damaged tissue), and reproduction (making new individuals).

Why does the surface area to volume ratio limit single-cell growth?

As a cell grows, its volume increases at a faster rate than its surface area, causing the surface area of the cell membrane to become inadequate for transport.

What is the structural composition of a nucleosome?

A nucleosome consists of molecules of DNA coiled around 8 histones.

What are the two states of eukaryotic genetic material and when does each appear?

Chromatin is the un-condensed state found during interphase, whereas chromosomes are distinct groupings of condensed chromatin visible under a microscope during cell division.

What are kinetochores and where are they located?

Kinetochores are proteins associated with the centromere where spindle fibers attach to the chromosome during cell division.

How is ploidy defined, and what are the specific haploid and diploid numbers for humans?

Ploidy is the number of chromosomes per cell; in humans, haploid ($n$) is $23$ chromosomes (found in germ cells/gametes) and diploid ($2n$) is $46$ chromosomes (found in somatic body cells).

What are three examples of polyploid plant species and their ploidy levels?

Banana is triploid ($3n$), potato is tetraploid ($4n$), and sugarcane is octoploid ($8n$).

What is the chromosomal composition of a normal somatic human karyotype?

A normal human karyotype contains $46$ chromosomes organized into $22$ pairs of homologous autosomes and $1$ pair of sex chromosomes ($XX$ or $XY$).

Where does mitosis occur and what type of daughter cells does it produce?

Mitosis occurs in somatic cells and produces two identical diploid daughter cells ($2n = 46$ chromosomes in humans).

Where does meiosis occur and what type of daughter cells does it produce?

Meiosis occurs in the gonads (ovaries and testes) and produces four haploid gametes ($n = 23$ chromosomes in humans), reducing the chromosome number by half.

What percentage of the cell cycle is spent in interphase versus cell division?

A cell spends approximately $90\%$ of its life in interphase and $10\%$ in cell division (mitosis and cytokinesis).

What occurs during the three stages of interphase: $G_1$, $S$, and $G_2$?

During $G_1$ (Gap 1/Growth 1), the cell grows rapidly and makes new organelles; during $S$ (Synthesis), genetic material is replicated; during $G_2$ (Gap 2/Growth 2), the cell undergoes further growth and preparation for cell division.

What major cellular changes happen during prophase of mitosis?

Chromatin condenses into distinct sister chromatids, the nuclear membrane and nucleolus disintegrate, centrioles in animal cells migrate to opposite poles, and the spindle apparatus forms from microtubules.

What is the structural difference between a centriole and a centrosome?

A centrosome is made up of two centrioles arranged at a right angle to one another; this is the region where spindle fibres form.

What occurs during metaphase of mitosis?

Spindle fibres attach to the kinetochores of sister chromatids and align the duplicated chromosomes single file along the equatorial plate (metaphase plate), with one sister chromatid facing each pole.

What occurs during anaphase of mitosis?

Centromeres divide, spindle fibres shorten, and sister chromatids are pulled apart to opposite poles of the cell, at which point the chromatids are officially called chromosomes.

What occurs during telophase of mitosis?

Chromosomes reach the opposite poles and unwind back into chromatin, spindle fibres break down and disappear, the nucleolus reappears, and a nuclear membrane reforms around each new set of genetic material.

How does cytokinesis differ between animal cells and plant cells?

In animal cells, an actin ring forms a cleavage furrow in the cell membrane that pinches the cytoplasm in two; in plant cells, a rigid cell wall prevents furrowing, so a cell plate forms between the two daughter nuclei instead.

What are the two major structural differences in plant cell division compared to animal cell division?

Plant cells do not contain centrioles (though they still form a spindle apparatus) and they form a cell plate rather than a cleavage furrow during cytokinesis.

What is the distinction between totipotent, pluripotent, and multipotent stem cells?

Totipotent cells can become any cell in the body plus placental cells (found up to the morula/16-cell stage); pluripotent cells can form all body cell types except placenta (found in blastocysts); multipotent cells can become more than one cell type but are more limited (e.g., adult and cord blood stem cells).

How are monozygotic (identical) twins formed compared to dizygotic (fraternal) twins?

Identical twins form when a cell breaks free from an early undifferentiated embryo and develops independently into a clone sharing the same DNA; fraternal twins result from two separate eggs being fertilized by two separate sperm and implanting simultaneously.

How was Dolly the Sheep cloned using nuclear transfer?

An adult cell taken from a sheep's udder was fused with an enucleated unfertilized egg using an electric shock; the fused cell divided normally by mitosis into an embryo, which was then implanted into the uterus of a foster mother.

Why is an animal produced via nuclear transfer, such as Dolly the Sheep, not a 100% identical clone of the nuclear donor?

Only chromosomal/nuclear DNA comes from the donor nucleus; mitochondrial DNA (mtDNA) is inherited from the cytoplasm of the enucleated egg cell.

Why is mitochondrial DNA inherited almost exclusively from the mother in multicellular animals?

An egg contains $100{,}000$ to $1{,}000{,}000$ mitochondria while a sperm contains only $10$ to $100$, or in some organisms, sperm mitochondria do not enter the egg upon fertilization.

What is therapeutic cloning and how does it differ from reproductive cloning?

Therapeutic cloning (embryo cloning) involves harvesting pluripotent stem cells from blastocysts or cord blood to grow differentiated tissues and study diseases, destroying the embryo, whereas reproductive cloning implants the embryo into a surrogate to generate a whole living organism.

How do telomeres behave differently in normal cells compared to cancer cells?

In normal cells, telomeres shorten in length each time a cell divides until the cell dies after a finite number of cycles; in cancer cells, telomeres do not shorten, allowing indefinite, uncontrolled division.

What is the difference between a benign tumor and a malignant tumor?

A benign tumor stays in one place and often eventually stops dividing, whereas a malignant tumor does not stop dividing and can metastasize (cells break off and spread to other parts of the body).

How do proto-oncogenes and anti-oncogenes (tumor suppressor genes) contribute to cancer when mutated?

A mutation in proto-oncogenes causes an increase in factors that promote cell growth, while a mutation in anti-oncogenes causes a decrease in factors that inhibit cell growth.

What is synapsis and what structure does it form during prophase I of meiosis?

Synapsis is the pairing of homologous chromosomes side by side, forming a structure called a tetrad consisting of four sister chromatids.

What is a chiasma and what genetic process occurs there?

A chiasma is the point of overlap where non-sister chromatids intertwine within a tetrad to exchange genetic segments during crossing over.

How does chromosome alignment in metaphase I of meiosis differ from metaphase in mitosis?

In metaphase I, homologous chromosomes line up side by side as pairs (tetrads) along the equatorial plate, whereas in mitosis, duplicated chromosomes line up single file.

What occurs during anaphase I of meiosis?

Spindle fibres shorten and homologous chromosome pairs separate to opposite poles in a process called segregation, splitting each tetrad into two double-stranded bivalents.

What is interkinesis?

Interkinesis is a short rest phase between meiosis I and meiosis II during which no DNA replication occurs.

Why is meiosis I called reduction division while meiosis II is called equational division?

Meiosis I reduces the chromosome number by half from diploid ($2n$) to haploid ($n$), whereas meiosis II separates sister chromatids without changing the chromosome ploidy number, mirroring mitosis.

What are the three main origins of genetic variation resulting from sexual reproduction?

1. Independent assortment of chromosomes at the equatorial plate during metaphase I; 2. Crossing over between homologous chromosomes during prophase I; 3. Random fertilization of an egg by a sperm.

How does cytokinesis differ between spermatogenesis and oogenesis?

Spermatogenesis divides cytoplasm equally to produce four functional haploid sperm, whereas oogenesis divides cytoplasm unequally, producing one large viable ootid (ovum) and three non-viable polar bodies that die and are reabsorbed.

What is non-disjunction and during which two specific meiotic phases can it occur?

Non-disjunction is the failure of chromosomes to separate properly; it occurs when homologous chromosomes fail to separate during anaphase I, or when sister chromatids fail to separate during anaphase II.

What are the chromosomal ploidy designations of gametes produced by non-disjunction?

One gamete will be missing a chromosome ($n - 1$, leading to monosomy after fertilization), while the other gamete contains an extra chromosome ($n + 1$, leading to trisomy after fertilization).

What is the chromosomal cause and karyotype of Down syndrome?

Down syndrome is caused by non-disjunction resulting in trisomy-21, giving the individual $47$ chromosomes instead of $46$.

What is the genetic cause and characteristic symptoms of Klinefelter syndrome?

Klinefelter syndrome is a trisomy-23 disorder characterized by an $XXY$ sex chromosome genotype; affected individuals are male at birth but produce less testosterone at puberty, leading to reduced muscle mass/body hair, enlarged breast tissue, broader hips, weak bones, and infertility.

What is the chromosomal profile and phenotypic presentation of Turner syndrome?

Turner syndrome is a monosomy disorder resulting in a female with a single $X$ chromosome ($X0$, $45$ total chromosomes), characterized by lack of sexual development (absent menstruation, infertility), a wide neck, drooping eyelids, and poor breast development.

How does amniocentesis compare to chorionic villus sampling (CVS) in terms of procedure and timing?

Amniocentesis extracts amniotic fluid containing fetal cells using a syringe between $14$ and $16$ weeks of pregnancy, while CVS samples placental chorionic villi cells and can be performed earlier, as early as $8$ weeks into pregnancy.

How do prokaryotes reproduce asexually and exchange genetic material?

Prokaryotes reproduce asexually via binary fission (chromosome replication, elongation, septum formation dividing cell every $20$ minutes in favorable conditions) and transfer genetic material sexually via conjugation through a bridging structure.

What is parthenogenesis?

Parthenogenesis is a form of reproduction in which an unfertilized egg develops directly into a new adult organism (e.g., in honeybee drones and whiptail lizards).

What is the difference between vegetative reproduction and fragmentation in plants?

Vegetative reproduction involves a new plant growing from creeping stems or runners (e.g., strawberries, trembling aspen), while fragmentation is the creation of a whole new individual from a broken plant piece or cutting.

In plant alternation of generations, what are the roles of the gametophyte and sporophyte stages?

The multicellular haploid ($n$) gametophyte produces haploid gametes through mitosis, while the multicellular diploid ($2n$) sporophyte produces haploid spores through meiosis.

Why are the generations in plant life cycles described as heteromorphic?

They are described as heteromorphic because the multicellular haploid gametophyte stage and the multicellular diploid sporophyte stage differ distinctly in their physical appearance and form.

What is the difference between self-fertilization and cross-fertilization in plants?

Self-fertilization occurs when the same individual produces both male and female gametes that fertilize each other, producing little genetic variation; cross-fertilization occurs when sperm from one individual fertilizes the egg of another individual, producing genetic variation.