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Questions and Answers
What is the resulting ploidy of a zygote after fertilization?
What is the resulting ploidy of a zygote after fertilization?
- Haploid (n)
- Tetraploid (4n)
- Diploid (2n) (correct)
- Triploid (3n)
What is the primary function of meiosis in the life cycle of sexual organisms?
What is the primary function of meiosis in the life cycle of sexual organisms?
- To increase the number of diploid cells
- To maintain the chromosome number in each generation
- To facilitate mitosis and development
- To produce haploid gametes (correct)
How do offspring produced by sexual reproduction differ from their parents?
How do offspring produced by sexual reproduction differ from their parents?
- They are genetically different from their parents. (correct)
- They have the same genetic material as their parents.
- They are genetically identical to each other.
- They have no genetic variations.
What chromosome configuration is present in haploid cells?
What chromosome configuration is present in haploid cells?
Which stage of meiosis deals with the separation of homologous chromosomes?
Which stage of meiosis deals with the separation of homologous chromosomes?
What mechanism during meiosis contributes to genetic variation?
What mechanism during meiosis contributes to genetic variation?
What term is used to describe a cell with two sets of chromosomes?
What term is used to describe a cell with two sets of chromosomes?
Which type of organisms typically undergo meiosis?
Which type of organisms typically undergo meiosis?
What is the primary characteristic of the G0 phase in the cell cycle?
What is the primary characteristic of the G0 phase in the cell cycle?
Which of the following components is essential in forming an active complex that regulates the cell cycle?
Which of the following components is essential in forming an active complex that regulates the cell cycle?
How many pairs of sex chromosomes do humans possess?
How many pairs of sex chromosomes do humans possess?
What type of chromosomes are categorized as autosomes in human somatic cells?
What type of chromosomes are categorized as autosomes in human somatic cells?
Which species has the highest number of chromosomes in its body cells according to the given content?
Which species has the highest number of chromosomes in its body cells according to the given content?
How can homologous chromosomes be visualized?
How can homologous chromosomes be visualized?
What happens when cyclins and Cdk inhibitors (CKIs) form a complex?
What happens when cyclins and Cdk inhibitors (CKIs) form a complex?
What types of cells typically enter the G0 phase?
What types of cells typically enter the G0 phase?
What is the result when homologous chromosomes fail to separate during anaphase I?
What is the result when homologous chromosomes fail to separate during anaphase I?
When sister chromatids fail to separate during meiosis II, which abnormal gametic combinations can result?
When sister chromatids fail to separate during meiosis II, which abnormal gametic combinations can result?
What chromosomal condition is most commonly associated with Down syndrome?
What chromosomal condition is most commonly associated with Down syndrome?
What process involves the exchange of corresponding segments between non-sister chromatids?
What process involves the exchange of corresponding segments between non-sister chromatids?
At what stage of meiosis does nondisjunction occur if homologous chromosomes fail to separate?
At what stage of meiosis does nondisjunction occur if homologous chromosomes fail to separate?
How many distinct gametes can be produced from a species with n unique chromosomes?
How many distinct gametes can be produced from a species with n unique chromosomes?
What is the total chromosome number in a zygote produced when a normal gamete fertilizes an abnormal gamete with an extra chromosome?
What is the total chromosome number in a zygote produced when a normal gamete fertilizes an abnormal gamete with an extra chromosome?
During which phase of meiosis do homologous chromosomes align side by side?
During which phase of meiosis do homologous chromosomes align side by side?
In which population is Down syndrome most commonly observed?
In which population is Down syndrome most commonly observed?
How many possible combinations of chromosomes can a human produce during gamete formation?
How many possible combinations of chromosomes can a human produce during gamete formation?
What is a characteristic feature of individuals with Down syndrome?
What is a characteristic feature of individuals with Down syndrome?
What is formed during prophase I that contains homologous chromosomes?
What is formed during prophase I that contains homologous chromosomes?
What is a result of crossing over during prophase I?
What is a result of crossing over during prophase I?
What is one potential outcome of non-disjunction during meiosis?
What is one potential outcome of non-disjunction during meiosis?
Which of the following describes independent assortment?
Which of the following describes independent assortment?
What term is used to describe the point where crossing over occurs between homologous chromosomes?
What term is used to describe the point where crossing over occurs between homologous chromosomes?
What is the mean life expectancy of individuals with Trisomy 13 (Patau syndrome)?
What is the mean life expectancy of individuals with Trisomy 13 (Patau syndrome)?
Which of the following features is associated with Trisomy 18 (Edwards syndrome)?
Which of the following features is associated with Trisomy 18 (Edwards syndrome)?
What condition arises from multiple non-disjunctions involving sex chromosomes?
What condition arises from multiple non-disjunctions involving sex chromosomes?
Which of the following is NOT a characteristic of cancer cells?
Which of the following is NOT a characteristic of cancer cells?
What type of tumor remains at the original site and does not spread?
What type of tumor remains at the original site and does not spread?
What is one common cause of cancer related to cell cycle abnormalities?
What is one common cause of cancer related to cell cycle abnormalities?
How do unusual numbers of sex chromosomes affect genetic balance compared to autosomes?
How do unusual numbers of sex chromosomes affect genetic balance compared to autosomes?
What can excessive use of mitogens lead to in the context of cell division?
What can excessive use of mitogens lead to in the context of cell division?
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Study Notes
Cell Cycle and G0 Phase
- G0 phase is a resting stage where cells exit the cell cycle, ceasing division.
- This phase, also known as the quiescent stage, can last for long or indefinite periods.
- Differentiated cells, such as liver, nerve, and muscle cells, typically remain in G0 but may re-enter the cell cycle if needed.
Cell Cycle Controls
- The cell cycle is controlled by cyclins and cyclin-dependent kinases (Cdks).
- Various types of cyclins (G1, G1/S, S, G2, M) activate Cdks, forming active complexes.
- Cdk inhibitors (CKIs) and proteolysis are also crucial in regulating the cell cycle.
- Inactive complexes can form when cyclins, Cdks, and CKIs combine.
Chromosome Count in Species
- Indian muntjac deer: 6 chromosomes
- Koala: 16 chromosomes
- Opossum: 22 chromosomes
- Giraffe: 30 chromosomes
- Mouse: 40 chromosomes
- Human: 46 chromosomes
- Duck-billed platypus: 54 chromosomes
- Bison: 60 chromosomes
- Dog: 78 chromosomes
- Red viscacha rat: 102 chromosomes
Homologous Chromosomes and Karyotype
- A karyotype is created by staining and photographing chromosomes during metaphase of mitosis, arranging them by size.
- Humans possess 46 chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (X and Y).
- Male humans have one X and one Y chromosome, while females have two X chromosomes.
Sexual Reproduction and Gametes
- Human gametes are haploid (n = 23) and form through meiosis, which ensures the chromosome number remains stable across generations.
- Fertilization occurs when a haploid sperm unites with a haploid egg, resulting in a diploid zygote (2n = 46).
- Meiosis involves two divisions: Meiosis I and Meiosis II, producing haploid gametes.
Genetic Variation from Meiosis
- Meiosis introduces genetic diversity through processes like crossing over and independent assortment.
- Crossing over occurs during prophase I, where segments are exchanged between non-sister chromatids.
- Independent assortment in metaphase I allows for random orientation of homologous chromosome pairs, producing numerous combinations.
Nondisjunction in Meiosis
- Nondisjunction refers to the failure of chromosomes to separate properly during meiosis.
- Results in gametes with abnormal chromosome numbers, leading to conditions such as trisomy (extra chromosome) or monosomy (missing chromosome).
- Down syndrome (trisomy 21) results in 47 chromosomes and is characterized by facial features and developmental delays.
Cancer and Cell Cycle Abnormalities
- Cancer arises from mutations in the genome that affect protein expression and regulatory pathways.
- Cancer cells bypass normal cell cycle control, leading to excessive division and potential invasiveness.
- Tumors form as abnormal cell masses, with benign tumors remaining localized and malignant tumors spreading.
Key Cancer Types
- Benign tumors: non-invasive, remain at the original site.
- Malignant tumors: invasive, spread into neighboring tissues, disrupt organ function.
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