Cellular Reproduction, Mitosis, and Meiosis

Flashcards covering cell division, the cell cycle, mitosis, meiosis, checkpoints, genetic variation, and chromosomal abnormalities from Chapters 6 and 7.

What is the biological distinction between somatic cells and reproductive cells?

Somatic cells form the body of an organism, whereas reproductive cells are sex cells (gametes) responsible for reproduction.

In sexually reproducing organisms, what distinct functions do mitosis and meiosis serve?

Meiosis is used for reproduction to produce gametes (eggs and sperm), whereas mitosis is used for organismal growth, development, and tissue maintenance/repair.

What are the genetic characteristics of the daughter cells produced by mitotic cell division?

Mitosis produces two daughter cells that are genetically identical both to each other and to the original parent cell.

What specific events take place during the $G_1$, $S$, and $G_2$ subphases of interphase?

During $G_1$, the cell undergoes cell growth and protein synthesis; during $S$ phase, DNA replication and replication of the centrosome occur; during $G_2$, the cell carries out further growth and protein synthesis.

What are sister chromatids and where are they held together tightly prior to division?

Sister chromatids are two duplicated copies of a chromosome carrying identical genes that are joined tightly together at the centromere.

What occurs during prophase of mitosis?

Chromosomes condense and become visible, spindle fibers emerge from centrosomes, the nuclear envelope breaks down, and the nucleolus disappears.

What specific events characterize prometaphase during mitosis?

Chromosomes continue to condense, kinetochores appear at the centromeres, mitotic spindle microtubules attach to kinetochores, and centrosomes move toward opposite poles.

How are chromosomes organized during metaphase of mitosis?

Chromosomes line up along the metaphase plate with the mitotic spindle fully developed, centrosomes at opposite poles, and each sister chromatid attached to a spindle fiber originating from opposite poles.

What mechanical and biochemical actions drive chromosome movement in anaphase of mitosis?

Cohesin proteins binding the sister chromatids break down, allowing sister chromatids (now called chromosomes) to be pulled toward opposite poles, while non-kinetochore spindle fibers lengthen to elongate the cell.

What key cellular events take place during telophase of mitosis?

Chromosomes arrive at opposite poles and begin to decondense, nuclear envelope material surrounds each set of chromosomes, and the mitotic spindle breaks down.

Based on this diagram, how does cytokinesis fundamentally differ between animal cells (a) and plant cells (b)?

In animal cells, an actin contractile ring constricts the plasma membrane to form a cleavage furrow that deepens to pinch the cell in two; in plant cells, Golgi vesicles coalesce at the former metaphase plate to form a cell plate that grows outward to fuse with the cell walls.

What is the $G_0$ phase of the cell cycle, and when do cells enter it?

The $G_0$ phase is an alternate quiescent state entered by cells not actively preparing to divide, which can be either a temporary condition until triggered to re-enter $G_1$ or a permanent state.

What cellular conditions are evaluated at the $G_1$, $G_2$, and $M$ checkpoints?

Integrity of DNA is assessed at the $G_1$ checkpoint; proper chromosome duplication is assessed at the $G_2$ checkpoint; and attachment of each kinetochore to a spindle fiber is assessed at the $M$ checkpoint.

According to this diagram, how does normal p53 protein function compare to mutated p53 in response to cellular damage?

Normal p53 arrests the cell cycle to allow DNA repair or triggers apoptosis if damage is irreparable; mutated p53 fails to arrest the cycle, permitting damaged cells to continue dividing and potentially become cancerous.

How do radiation therapy and chemotherapy function to treat cancer?

Radiation therapy targets and damages DNA to disrupt cell division, whereas chemotherapy uses specialized drugs systemically to disrupt cell division.

Based on this figure, what is the definition of an allele?

An allele is a different version or form of the same gene located at the same locus on homologous chromosomes (such as the form for blue eyes versus brown eyes).

What are the two unique genetic outcomes of meiosis?

Meiosis reduces the amount of genetic material in gametes by halving chromosome number (producing haploid cells) and produces gametes with unique combinations of alleles.

When does chromosome replication occur in cells undergoing meiosis?

Each chromosome replicates during the $S$ phase of interphase prior to entering meiosis.

What occurs during crossing over in prophase I of meiosis, and what are recombinant chromosomes?

Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes at chiasmata; chromosomes bearing a new combination of maternal and paternal sequences are termed recombinant.

According to this diagram, how do kinetochore attachments and chromosome separations differ between meiosis I and meiosis II?

In prometaphase I, microtubules attach to the fused kinetochores of homologous pairs, separating homologs in anaphase I while sister chromatids stay joined; in prometaphase II, microtubules attach to individual kinetochores of sister chromatids, pulling sister chromatids apart in anaphase II.

What is the formula for calculating chromosome combinations in gametes due to independent assortment, and how many combinations exist for humans ($n = 23$)?

The total number of combinations is $2^n$ (where $n$ is the haploid number); for humans with $n = 23$, there are $2^{23} = 8{,}388{,}608$ different chromosome combinations per gamete.

What are the three distinct mechanisms by which sexual reproduction generates genetic variation among offspring?

The three mechanisms are crossing over (prophase I), independent assortment and shuffling of homologous chromosomes (metaphase I), and random fertilization of an egg by a sperm.

How many potential chromosome combinations can result from random fertilization in human reproduction?

Because each gamete represents one of $8{,}388{,}608$ possible combinations, fertilization can produce $8{,}388{,}608 \times 8{,}388{,}608$, or more than $70\text{ trillion}$ possible chromosome combinations in the resulting zygote.

How do mitosis and meiosis differ in daughter cell number, ploidy level, and genetic identity?

Mitosis results in two diploid daughter cells that are genetically identical to the parent cell, whereas meiosis results in four haploid daughter cells that are genetically distinct.

What types of chromosomes are shown in this micrograph, and what is the standard chromosomal makeup of a human cell?

This shows the human sex chromosomes ($X$ and $Y$); human somatic cells contain $46$ chromosomes total ($23$ pairs), consisting of $22$ pairs of autosomes and $1$ pair of sex chromosomes ($XX$ in females, $XY$ in males).

Based on this figure, what is nondisjunction and how do gamete products differ if it occurs in meiosis I versus meiosis II?

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate; nondisjunction in meiosis I yields $100\%$ abnormal gametes ($n+1$, $n+1$, $n-1$, $n-1$), whereas nondisjunction in meiosis II yields two normal ($n$, $n$) and two abnormal gametes ($n+1$, $n-1$).

What genetic condition is identified by the red box in this karyotype, and what causes it?

The karyotype displays trisomy 21 (Down syndrome), which is characterized by the presence of three copies of chromosome 21 resulting from nondisjunction.

How does maternal age correlate with the risk of having a child with trisomy 21 (Down syndrome)?

The incidence of trisomy 21 increases dramatically and sharply with advanced maternal age, particularly rising after age $35$ to $40$.