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Questions and Answers
What structure attaches sister chromatids to each other?
Which process produces four haploid cells?
What term describes one of a pair of chromosomes with the same gene sequence?
Which of the following statements about sister chromatids is true?
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What is the total number of chromosomes in a human somatic cell?
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What is the primary purpose of meiosis?
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At what stage in females does Meiosis II typically occur?
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How do homologous chromosomes differ from sister chromatids?
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Which process contributes to genetic variation during meiosis?
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What is the karyotype of a human individual?
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What is the primary outcome of crossing over during meiosis?
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During which phase of meiosis are homologous chromosomes separated?
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What does the Law of Independent Assortment state?
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What is the end result of meiosis I in terms of chromosome number?
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In which phase of meiosis does crossing over occur?
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How many viable gametes are produced by oogenesis?
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What role does the synaptonemal complex play during meiosis?
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What describes the outcome of meiosis II?
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Study Notes
DNA - Eukaryotes
- Found in the nucleus
- DNA is wound around histone proteins, which helps compact DNA into the nucleus.
- Chromatin: DNA in a loose, uncoiled form. Considered active.
- Chromosomes: Tightly coiled and condensed DNA. This occurs during cell division.
Chromosomes
- Chromatid: A single strand.
- Chromosome: Consists of two chromatids joined at the centromere.
- Centromere: The location on a chromosome where two chromatids are attached.
Homologous Chromosomes
- Homologous chromosomes are pairs of chromosomes that have the same genes, length, and centromere location.
- One chromosome from each pair comes from the father, and the other comes from the mother.
- Humans have 23 pairs of chromosomes (46 total).
- Autosomes: Any chromosome that is not a sex chromosome.
- Sex Chromosomes: The X or Y chromosomes.
Mitosis
- Sister chromatids separate.
- Sister chromatids are identical.
Sister Chromatids
- Two identical copies of the same chromosome.
- Formed by DNA replication and are attached by the centromere.
- During cell division, they are separated.
- Each daughter cell receives one copy.
Mitosis
- Eukaryotes
- Asexual
- DNA is replicated
- Produces 2 diploid cells.
Meiosis
- Eukaryotes
- Sexual
- 2 cell divisions
- Produces 4 haploid cells.
Meiosis I & II
Meiosis I
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Prophase I: Synapsis occurs to form a tetrad (crossing over). This contributes to variation.
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Metaphase I: Independent assortment occurs. This contributes to variation.
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Anaphase I: Homologous chromosomes segregate to opposite poles.
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Telophase I: Cytoplasm divides.
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Meiosis I starts with 2n, and ends with 1n.
Meiosis II
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Prophase II: Chromosomes condense.
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Metaphase II: Chromosomes line up at the middle of the cell.
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Anaphase II: Sister chromatids separate and move to opposite poles.
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Telophase II: Cytoplasm divides.
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Meiosis II starts with 1n and ends with 1n.
Homologues
- Meiosis I: Homologues (homologous chromosomes) are separated.
Sister Chromatids
- Meiosis II: Sister chromatids (are separated, similar to mitosis).
Crossing Over
- The exchange of genetic material between non-sister chromatids.
- This occurs during prophase I (meiosis I).
- Results in new combinations of alleles in daughter cells.
- Synaptonemal complex: Facilitates crossing-over between non-sister chromatids.
Variation
- Crossing Over: The exchange of genetic material between non-sister chromatids results in new allelic combinations.
- Independent Assortment: The random segregation of chromosomes during meiosis I contributes to genetic variation.
- Random fertilization: The random combination of sperm and egg during fertilization contributes to genetic variation.
Independent Assortment
- The law of independent assortment states that different genes and their alleles are inherited independently.
- Genes on a chromosome can rearrange themselves through crossing-over.
- Each gene is inherited independently.
Meiosis
- Gametogenesis: The production of sperm (spermatogenesis) and eggs (oogenesis), this occurs via meiosis.
- Sperm: Meiosis produces 4 equal sperm.
- Egg: Meiosis produces 3 polar bodies and one egg. This is an unequal division.
Summary
- Produces haploid cells (gametes), which are 1n.
- Genetic variation occurs via crossing over during Prophase I.
- Meiosis I is reduction division
- Meiosis II is equational division
- Males: Occurs at the start of puberty.
- Females: Meiosis I occurs before birth. Meiosis II occurs at puberty or fertilization.
Zygotes
- Zygote (2n) - A fertilized egg, it is diploid.
- Fertilization: The fusion of sperm (1n) and oocyte (1n) to form a zygote.
Human Chromosomes
- 23 pairs total: one from each parent.
- Karyotype: A complete set of chromosomes arranged in numerical order.
Learning Objectives
- Explain the process of meiosis.
- Explain why meiosis is important for sexual reproduction.
- Compare and contrast sister chromatids and homologous chromosomes.
- Describe the stages of meiosis.
- Differentiate between a zygote and a gamete.
- Compare and contrast mitosis and meiosis.
- Explain how crossing over occurs and how it contributes to genetic variation.
- Explain what a germ-line cell is and its role in gametogenesis.
- Explain how chromosomes are duplicated and separated during mitosis and meiosis.
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Description
This quiz covers essential concepts related to DNA and chromosomes in eukaryotic cells, including chromatin, homologous chromosomes, and the process of mitosis. Test your understanding of key terms such as chromatids, centromeres, and the role of histone proteins in DNA compaction. Perfect for biology students studying cell structure and division.
