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Questions and Answers
During which phase of cell division do the chromosomes line up in the middle of the cell?
During which phase of cell division do the chromosomes line up in the middle of the cell?
- Metaphase (correct)
- Prophase
- Telophase
- Anaphase
Which phase of cell division involves the separation and movement of sister chromatids to opposite poles of the cell?
Which phase of cell division involves the separation and movement of sister chromatids to opposite poles of the cell?
- Prometaphase
- Anaphase (correct)
- Cytokinesis
- Telophase
What is the phase of cell division where the nuclear envelope reforms around the separated daughter chromosomes?
What is the phase of cell division where the nuclear envelope reforms around the separated daughter chromosomes?
- Telophase (correct)
- Metaphase
- Prophase
- Cytokinesis
Which phase of cell division involves the spindle fibers attaching to the kinetochores of chromosomes?
Which phase of cell division involves the spindle fibers attaching to the kinetochores of chromosomes?
In which phase of cell division does the cleavage furrow form to divide the cytoplasm into two daughter cells?
In which phase of cell division does the cleavage furrow form to divide the cytoplasm into two daughter cells?
When do the chromosomes condense and become visible during cell division?
When do the chromosomes condense and become visible during cell division?
At which phase of cell division does the nuclear envelope break down and disappear?
At which phase of cell division does the nuclear envelope break down and disappear?
Which stage of mitosis involves the fragmentation of the nuclear envelope?
Which stage of mitosis involves the fragmentation of the nuclear envelope?
What defines metaphase in mitosis?
What defines metaphase in mitosis?
Which phase involves the physical splitting of sister chromatids into individual chromosomes?
Which phase involves the physical splitting of sister chromatids into individual chromosomes?
In which phase of mitosis does the cleavage furrow start to form?
In which phase of mitosis does the cleavage furrow start to form?
What is the main function of telophase in mitosis?
What is the main function of telophase in mitosis?
During which stage of cell division is the nuclear envelope forming again?
During which stage of cell division is the nuclear envelope forming again?
During which phase of cell division do the sister chromatids separate and move towards opposite poles of the cell?
During which phase of cell division do the sister chromatids separate and move towards opposite poles of the cell?
In which phase of cell division does the plasma membrane pinch inward, physically dividing the cell into two separate daughter cells?
In which phase of cell division does the plasma membrane pinch inward, physically dividing the cell into two separate daughter cells?
Which stage of cell cycle involves the alignment of chromosomes at the equatorial plane of the cell?
Which stage of cell cycle involves the alignment of chromosomes at the equatorial plane of the cell?
When do the daughter chromosomes actively move apart in cell division?
When do the daughter chromosomes actively move apart in cell division?
What phase of cell division marks the start of chromosome replication?
What phase of cell division marks the start of chromosome replication?
Which phase of cell division involves the completion of replication and subsequent pinching of the plasma membrane?
Which phase of cell division involves the completion of replication and subsequent pinching of the plasma membrane?
What process occurs after Anaphase in cell division to physically divide the cell into two daughter cells?
What process occurs after Anaphase in cell division to physically divide the cell into two daughter cells?
During metaphase I of meiosis, what aligns at the metaphase plate?
During metaphase I of meiosis, what aligns at the metaphase plate?
How does crossing over contribute to genetic variation?
How does crossing over contribute to genetic variation?
What is the average number of crossover events that occur per chromosome pair in human meiosis?
What is the average number of crossover events that occur per chromosome pair in human meiosis?
What is the result of chromosomal nondisjunction during Meiosis I?
What is the result of chromosomal nondisjunction during Meiosis I?
What condition results from trisomy 21?
What condition results from trisomy 21?
Which type of sex chromosome abnormality can still yield 'femaleness'?
Which type of sex chromosome abnormality can still yield 'femaleness'?
What type of chromosomal alteration involves the repeat of a chromosome segment?
What type of chromosomal alteration involves the repeat of a chromosome segment?
Which type of chromosomal alteration results in the reversal of a chromosome segment?
Which type of chromosomal alteration results in the reversal of a chromosome segment?
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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.
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