Mitosis Stages
During prophase the chromosomes
Condense and become visible
How many daughter cells does mitosis produce compared to meiosis?
Mitosis - 2, Meiosis - 4
During which phase of meiosis does crossing over occur, and what is the result of this process?
Crossing over occurs in Prophase I, when homologous chromosomes exchange DNA segments. This creates new allele combinations.
What is the primary purpose of interphase in the cell cycle?
To allow the cell to grow, carry out normal functions, and prepare for division
Which type of cell produces sperm or eggs?
Germ Cell
What is happening in this stage of Mitosis?
Replicated chromosomes are moved to the middle of the cell (metaphase)
What kind of cell does both mitosis and meiosis start with?
Diploid (2n)
Why does meiosis I reduce the chromosome number (ploidy) from diploid to haploid?
Because homologous chromosome pairs separate during Anaphase I, each daughter cell receives only one chromosome from each pair.
During which stage of interphase is DNA replicated?
The S phase (Synthesis phase)
Is most of your body mostly made of somatic or germ cells?
Somatic Cells
In a diploid cell with 12 chromosomes, how many chromosomes will each daughter cell have after mitosis?
Each daughter cell will have 12
Which type of reproduction creates offspring identical to the parent without needing a mate?
Asexual reproduction (mitosis)
Why are no two haploid cells produced by meiosis genetically identical, even if they come from the same parent cell?
Because of crossing over in Prophase I and independent assortment in Metaphase I. Each gamete receives a unique mix of maternal and paternal chromosomes.
What enzyme unwinds the DNA double helix at the start of replication?
Helicase
What is the ploidy level of gametes produced by germ cells?
Haploid
In what phase do nuclear envelopes re-form around each set of chromosomes?
Telophase
During which division are cells more likely to have the wrong number of chromosomes due to nondisjunction?
Meiosis - specifically when homologous chromosomes fail to separate
What major event distinguishes meiosis II from meiosis I, and why does meiosis II not further reduce ploidy?
Meiosis II separates sister chromatids, not homologous pairs. Since the cells entering meiosis II are already haploid, this division does not change ploidy.
Why is DNA replication described as “semiconservative”?
Because each new DNA molecule contains one original (parental) strand and one newly synthesized strand.
Which type of mutation is heritable?
Germline Mutation
Why does DNA replication have to occur before mitosis, in interphase?
Mitosis sends one copy of each chromosome to each daughter cell, so it can't occur unless replication has already made the copies.
Why does meiosis include crossing over while mitosis does not?
Meiosis increases genetic variation in offspring & mitosis does not
You are shown two micrographs. Identify the stage shown in each image, what is happening to the chromosomes, and explain the key difference between the two stages.
Image A is Metaphase I. Homologous chromosomes are paired and aligned, they will separate, reducing ploidy.
Image B is Metaphase II. Individual chromosomes , sister chromatids will separate next
Key difference: Metaphase I involves homologous chromosome pairs, Metaphase II involves only sister chromatids.
During DNA replication, the leading and lagging strands are synthesized differently. Explain why the lagging strand is built in short fragments and what are they called?
Because DNA polymerase can only synthesize DNA in the 5’ to 3’ direction, the lagging strand must be built discontinuously in short segments called Okazaki fragments.
Which cells experience crossing over?
Germ Cells