MITOSIS
What phase of mitosis is characterized by chromosomes lining up at the center of the cell?
Metaphase
Reasoning: Chromosomes align at the metaphase plate before separation.
What is the main purpose of meiosis?
To produce haploid gametes for sexual reproduction
Reasoning: Meiosis reduces chromosome number by half to maintain species chromosome number after fertilization.
Which process produces genetically identical cells?
Mitosis
Reasoning: Produces clones (genetically identical cells), barring mutation.
What is the definition of an allele?
An allele is a version of a gene
Reasoning: Same gene locus can have different DNA sequences (variants).
What tool is commonly used to predict the probability of offspring genotypes?
Punnett square
Reasoning: A grid model used to predict genotype probabilities from parental gametes.
A mistake occurs during meiosis that causes gametes to have too many or too few chromosomes.
Name this process and explain one possible consequence for inheritance.
Failure of homologous chromosomes (Meiosis I) or sister chromatids (Meiosis II) to separate properly → gametes with abnormal chromosome number (aneuploidy). Possible consequence: disorders such as trisomy (e.g., Down syndrome) or monosomy; often miscarriage.
What structure pulls sister chromatids apart during mitosis?
Spindle fibers (mitotic spindle / microtubules)
Reasoning: Spindle microtubules attach to kinetochores and move chromatids.
What phase of meiosis is responsible for increasing genetic variation through crossing over?
Prophase I
Reasoning: Homologous chromosomes pair (synapsis) and crossing over occurs, increasing variation.
Which process results in four daughter cells?
Meiosis
Reasoning: One diploid cell → four haploid cells after two divisions.
What does it mean for an organism to be heterozygous?
Heterozygous means two different alleles (e.g., Aa)
Reasoning: One allele from each parent; alleles differ.
In a monohybrid cross of Aa × Aa, what percentage of offspring are expected to be homozygous recessive?
25% (1 out of 4) are aa
Reasoning: Aa × Aa yields AA, Aa, Aa, aa (1:2:1 genotype ratio).
In what phase of mitosis do sister chromatids separate?
Anaphase
Reasoning: Sister chromatids separate and move to opposite poles.
How is Meiosis I different from Meiosis II?
Meiosis I separates homologous chromosomes; Meiosis II separates sister chromatids
Reasoning: Meiosis I is the reduction division (2n → n); Meiosis II resembles mitosis.
Name one similarity between mitosis and meiosis.
Similarities: DNA replicates once before division; uses spindle fibers; has PMAT phases
Reasoning: Both are nuclear division processes with shared cell machinery.
What is the difference between genotype and phenotype?
Genotype = allele combination; Phenotype = expressed trait
Reasoning: Phenotype is what you observe; genotype is the genetic makeup behind it.
What is incomplete dominance, and how is it different from complete dominance?
Incomplete dominance: heterozygote is intermediate (blended) phenotype; complete dominance: heterozygote matches dominant phenotype
Reasoning: The heterozygote phenotype is the key difference.
A cell has 46 chromosomes before mitosis. How many chromosomes will each daughter cell have after mitosis, and why?
46 chromosomes in each daughter cell
Reasoning: Mitosis preserves chromosome number; sister chromatids separate so each new nucleus receives one complete set.
Why are gametes haploid? Explain using chromosome number.
Gametes are haploid so fertilization restores diploid number
Reasoning: If gametes were diploid, chromosome number would double every generation.
Explain why meiosis, but not mitosis, contributes to genetic diversity.
Meiosis increases variation via crossing over + independent assortment
Reasoning: Homologous recombination and random alignment in metaphase I create unique gametes.
Define dominant and recessive in terms of allele expression.
Dominant: expressed in heterozygote; Recessive: expressed only when two recessive alleles present (in complete dominance)
Reasoning: Dominant masks recessive in Aa; recessive shows in aa.
Describe codominance and give a biological example.
Codominance: both alleles are fully expressed in the heterozygote (e.g., AB blood type)
Reasoning: You see both traits at once, not blended.
Why is mitosis important for multicellular organisms? Give one biological reason.
Growth, repair, and replacement (also asexual reproduction in some organisms)
Reasoning: Mitosis makes genetically identical somatic cells needed for body maintenance.
A species has a diploid number of 12. How many chromosomes are in each gamete after meiosis? Explain.
6 chromosomes in each gamete
Reasoning: Diploid number 12 means n = 6; meiosis halves the number.
During which process do homologous chromosomes pair up, and why does this matter biologically?
Homologous pairing occurs in meiosis (Prophase I); it matters because it enables crossing over and proper segregation
Reasoning: Pairing allows recombination and helps ensure each gamete gets one homolog, reducing errors.
Why can two parents with a recessive trait produce a child with the same recessive trait? Use allele combinations in your explanation
Two recessive parents are aa × aa, so all offspring are aa (recessive trait)
Reasoning: Each parent can only pass “a,” so offspring must be “aa.”
Why do Punnett squares show probability rather than certainty?
Punnett squares show probability because meiosis and fertilization involve random assortment and random union of gametes