y5 bio: cluster 5 (cell and nuclear division + inheritance)

what is the main role of mitosis in eukaryotes?

to produce two genetically identical diploid daughter nuclei for cell proliferation, growth, tissue repair, and asexual reproduction.

what occurs during the S-phase of interphase prior to mitosis or meiosis?

DNA replication occurs, producing identical sister chromatids held together at the centromere.

what are the four phases of mitosis in sequential order?

prophase, metaphase, anaphase, and telophase.

what happens during prophase of mitosis?

chromatin condenses into distinct chromosomes, spindle microtubules form, and the nuclear membrane breaks down.

what is the role of microtubules and kinetochores during metaphase?

kinetochores attach chromosomes to spindle microtubules at the centromere, aligning chromosomes along the cell equator.

what occurs during anaphase of mitosis?

spindle fibers shorten, pulling separated sister chromatids to opposite poles of the cell.

how does cytokinesis differ between animal and plant cells?

animal cells divide via an actin ring forming a cleavage furrow, whereas plant cells construct a cell plate formed by fusing Golgi vesicles.

what is unequal cytokinesis and where does it occur in human biology?

unequal distribution of cytoplasm resulting in one large cell and smaller polar bodies, occurring during human oogenesis.

how do you calculate the mitotic index of a tissue micrograph?

divide the number of cells displaying visible chromosomes (in mitosis) by the total number of observed cells.

what is the function of cyclins in cell cycle regulation?

cyclins bind to cyclin-dependent kinases (CDKs) to activate them, triggering specific events at cell cycle checkpoints (G1, G2, and M).

how do proto-oncogenes and tumor suppressor gene mutations lead to cancer development?

mutated proto-oncogenes become overactive oncogenes (stimulating division), while mutated tumor suppressor genes lose cell cycle control, leading to uncontrolled proliferation.

what is the difference between a primary tumor, secondary tumor, and metastasis?

a primary tumor forms at the original site, metastasis is the spread of cancer cells through blood/lymph, forming secondary tumors elsewhere.

why is meiosis I referred to as a reduction division?

it reduces the chromosome number from diploid (2n) to haploid (n) by separating homologous chromosomes.

what is a bivalent (tetrid) and when does it form?

a pair of homologous chromosomes formed during prophase I of meiosis.

what occurs during crossing over in prophase I and what is its consequence?

non-sister chromatids exchange DNA segments at chiasmata, producing recombinant chromatids and increasing genetic variation.

how does independent assortment generate genetic diversity in meiosis?

homologous chromosome pairs align randomly at the metaphase plate in metaphase I, creating 2^n possible gamete combinations.

what is non-disjunction and what condition can it cause?

the failure of homologous chromosomes or sister chromatids to separate properly during anaphase I or II, causing aneuploidy such as trisomy 18 (Edward’s syndrome) and 21 (Down syndrome).

what is an allele?

a specific alternative sequence/form of a gene at a particular chromosomal locus.

what is the difference between phenotype and genotype?

genotype is the specific allele combination of an organism, while phenotype is the observable physical or biochemical trait.

what pattern of inheritance is demonstrated by ABO blood groups?

codominance between Ia and Ib alleles, both being completely dominant over the recessive I allele.

why do sex-linked recessive traits (like hemophilia) affect males more frequently than females?

males are hemizygous (XY) and need only one copy of the recessive allele on the X chromosome to express the condition.

what are linked genes?

genes located close together on the same chromosome that do not assort independently during meiosis.

how can you identify recombinant offspring in a dihybrid cross involving linked genes?

recombinants display combination phenotypes different from either parent and occur in much lower frequencies than parental types.

what phenotypic ratio is expected in a test cross of a dihybrid heterozygote with unlinked genes vs linked genes?

unlinked genes yield a 1:1:1:1 ratio, whereas linked genes produce a higher proportion of parental phenotypes and fewer recombinants, at 9:3:3:1 ratio.

what is polygenic inheritance and what type of variation does it produce?

a single trait controlled by two or more unlinked additive genes, resulting in continuous variation (e.g., human height or skin color).

how does the environment influence polygenic phenotypes?

environmental factors (e.g., nutrition, sun exposure) act on continuous phenotypic variation, smoothing out discrete genetic categories.

what is the purpose of a chi-squared test in genetics?

to determine whether observed offspring phenotypic counts differ significantly from expected Mendelian inheritance ratios.

how do you calculate degrees of freedom (df) for a genetic chi-squared test?

df = n - 1, where n is the total number of phenotypic categories being compared.

what does it mean if a calculated x^2 value is greater than the critical value at p = 0.05?

the difference between observed and expected results is statistically significant, rejecting the null hypothesis (suggesting gene linkage or selection).