28 Questions
During which phase of cell division do the chromosomes line up in the middle of the cell?
Metaphase
Which phase of cell division involves the separation and movement of sister chromatids to opposite poles of the cell?
Anaphase
What is the phase of cell division where the nuclear envelope reforms around the separated daughter chromosomes?
Telophase
Which phase of cell division involves the spindle fibers attaching to the kinetochores of chromosomes?
Prometaphase
In which phase of cell division does the cleavage furrow form to divide the cytoplasm into two daughter cells?
Cytokinesis
When do the chromosomes condense and become visible during cell division?
Prophase
At which phase of cell division does the nuclear envelope break down and disappear?
Prophase
Which stage of mitosis involves the fragmentation of the nuclear envelope?
Prometaphase
What defines metaphase in mitosis?
Alignment of chromosomes at the metaphase plate
Which phase involves the physical splitting of sister chromatids into individual chromosomes?
Anaphase
In which phase of mitosis does the cleavage furrow start to form?
Telophase
What is the main function of telophase in mitosis?
Division of the cytoplasm
During which stage of cell division is the nuclear envelope forming again?
Telophase
During which phase of cell division do the sister chromatids separate and move towards opposite poles of the cell?
Anaphase
In which phase of cell division does the plasma membrane pinch inward, physically dividing the cell into two separate daughter cells?
Cytokinesis
Which stage of cell cycle involves the alignment of chromosomes at the equatorial plane of the cell?
Metaphase
When do the daughter chromosomes actively move apart in cell division?
During Anaphase
What phase of cell division marks the start of chromosome replication?
Prometaphase
Which phase of cell division involves the completion of replication and subsequent pinching of the plasma membrane?
Telophase
What process occurs after Anaphase in cell division to physically divide the cell into two daughter cells?
Cytokinesis
During metaphase I of meiosis, what aligns at the metaphase plate?
Both maternal and paternal homologs
How does crossing over contribute to genetic variation?
By exchanging genetic material between nonsister chromatids
What is the average number of crossover events that occur per chromosome pair in human meiosis?
1-2
What is the result of chromosomal nondisjunction during Meiosis I?
Both members of a homologous pair go to one pole
What condition results from trisomy 21?
Down syndrome
Which type of sex chromosome abnormality can still yield 'femaleness'?
Presence of multiple X chromosomes
What type of chromosomal alteration involves the repeat of a chromosome segment?
Duplication
Which type of chromosomal alteration results in the reversal of a chromosome segment?
Inversion
Study Notes
Cell Division and Reproduction
- Cell division is a continuum of dynamic changes that result in the growth and reproduction of an organism.
- It involves the preparation for cell division, mitosis, and cytokinesis.
Mitosis and Cytokinesis
- Mitosis is the division of the nucleus and consists of four stages: prophase, metaphase, anaphase, and telophase.
- Cytokinesis is the division of the cytoplasm and completes the mitotic phase.
Meiosis
- Meiosis is a type of cell division that produces haploid gametes in diploid organisms.
- It consists of meiosis I and meiosis II, resulting in four genetically unique haploid gametes.
- Meiosis reduces the chromosome number by half, from diploid to haploid.
Homologous Chromosomes
- Humans have 46 chromosomes, forming 23 pairs of homologous chromosomes.
- Homologous chromosomes are matched in length, centromere position, and staining pattern.
- Sister chromatids are pairs of homologous duplicated chromosomes.
Life Cycle
- An organism's life cycle is the sequence of stages leading from adults of one generation to adults of the next.
- Humans, many animals, and plants are diploid, with all somatic cells containing pairs of homologous chromosomes.
- Gametes (eggs and sperm) are haploid, with a single set of chromosomes.
Meiosis Reduces Chromosome Number
- Meiosis reduces the chromosome number from diploid to haploid.
- Meiosis consists of two consecutive cell divisions, resulting in four haploid gametes.
Origins of Genetic Variation
- The behavior of chromosomes during meiosis and fertilization contributes to genetic variation.
- Three mechanisms contribute to genetic variation: crossing over, independent assortment of chromosomes, and random fertilization.
Independent Assortment of Chromosomes
- Each pair of chromosomes independently aligns at the metaphase plate.
- The number of combinations for chromosomes packaged into gametes is 2n.
- In humans, there are over 8 million possible combinations of chromosomes.
Crossing Over
- Genetic recombination occurs through crossing over, exchanging corresponding segments between nonsister chromatids of homologous chromosomes.
- Crossing over increases genetic variability.
Nondisjunction
- Nondisjunction is the failure of chromosomes or chromatids to separate normally during meiosis.
- It can occur during meiosis I or meiosis II, resulting in abnormal gametes and altered chromosome numbers.
Trisomy 21
- Trisomy 21 involves the inheritance of three copies of chromosome 21, resulting in Down syndrome.
- Symptoms include characteristic facial features, short stature, heart defects, and developmental disabilities.
Abnormal Numbers of Sex Chromosomes
- Sex chromosome abnormalities seem to be less severe than autosomal abnormalities.
- A single Y chromosome is enough to produce "maleness," while the absence of a Y chromosome yields "femaleness."
Alterations of Chromosome Structure
- Chromosome breakage can lead to rearrangements, producing genetic disorders or cancer.
- There are four types of alterations in chromosome structure: inversion, deletion, duplication, and reciprocal translocation.
Test your knowledge on the phases of cell division, including interphase, mitotic phase (mitosis and cytokinesis), and the dynamic changes that occur during each stage.
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