genetics and evolution notes
James Watson and Francis Crick:
Interpreted existing experimental data to unlock the DNA structure.
X-ray crystallography images by Maurice Wilkins and Rosalind Franklin indicated a helical pattern.
Watson and Crick pieced this information together to create a DNA model, completing it in February 1953, unveiling the double helix structure.
Rosalind Franklin:
Conducted crucial research on DNA's structure, contributing significantly to its understanding.
Learned X-ray diffraction techniques.
Worked independently on DNA, but misunderstandings and gender biases complicated her collaboration with Maurice Wilkins.
Photographed DNA using x-ray.
She came very close to solving the DNA structure between 1951 and 1953, but Crick and Watson published their findings first.
Franklin's work was published as a supporting article in the same journal issue.
Ongoing debate surrounds the credit due to Franklin for her role in discovering DNA's structure.
Genetic Mutations:
Mutations are changes in genetic material, which can occur in genes or at the chromosome level or in nucleic acids like RNA and DNA.
Changes can occur due to external factors (chemicals, radiation) or internal factors (errors during DNA replication in interphase).
Types of Mutations:
Gene Mutations:
Gene mutations can lead to the production of different proteins, affecting an organism's traits.
Types of gene mutations:
Substitution: Wrong base pairs up (e.g., A with G instead of A with T).
Insertion: Extra base(s) added.
Deletion: Base removed.
Insertions and deletions can cause frameshift mutations, altering protein synthesis.
Gene mutations are specific to individual genes.
Chromosome Mutations:
Types of chromosome mutations:
Duplication: Extra copies of genes generated, leading to extra copies of that chromosome.
Deletion: Genetic material breaks off from the chromosome.
Inversion: Broken chromosome segment is reversed and reattached.
Translocation: Fragment from one chromosome breaks off and attaches to another.
These mutations can have significant effects due to changes in gene number or arrangement.
Occurrence of Mutations:
Mutations can happen during DNA replication in interphase or other vulnerable times like meiosis.
Meiosis can result in nondisjunction, leading to too many or too few chromosomes in egg or sperm cells, potentially causing genetic disorders. ??????
Introduction to Mitosis
It is essential for growth and tissue repair.
Mitosis ensures that new cells are identical to the original ones.
Regulation of Cell Division
Cells do not continuously divide; this would lead to uncontrolled growth, similar to cancer.
The cell cycle includes interphase (growth and DNA replication) and mitosis (cell division).
Chromosomes condense DNA for efficient division.
Chromosome Replication
Before mitosis, chromosomes must be duplicated during interphase.
Despite duplication, chromosomes are counted by centromeres, leading to 46 chromosomes with 92 chromatids.
Mitosis Stages (PMAT)
Prophase (P): Chromosomes condense and become visible, while the nucleus is still present.
Metaphase (M): Chromosomes align in the middle of the cell, as the nucleus disassembles.
Anaphase (A): Chromosomes move towards opposite ends of the cell, aided by spindle fibers.
Telophase (T): Chromosomes reach opposite ends, and new nuclei begin to form.
Cytokinesis
Cytokinesis completes cell division by splitting the cytoplasm, resulting in two new, identical cells.
Introduction to Meiosis: Meiosis is a process that results in the formation of gametes (sperm and egg cells) and is responsible for genetic diversity. Unlike mitosis, which produces identical body cells, meiosis reduces the chromosome count by half.
Chromosome Count: Most body cells in humans have 46 chromosomes. However, human sperm and egg cells have 23 chromosomes each. When they combine during fertilization, the resulting fertilized egg has the normal 46 chromosomes.
Reduction Division: Meiosis is referred to as a reduction division because it starts with a cell containing 46 chromosomes and ends with four cells (gametes), each containing only 23 chromosomes.
Interphase: Meiosis begins with interphase, a stage where the cell grows, replicates its DNA, and carries out necessary processes. Chromosomes are duplicated during interphase.
Meiosis I: Meiosis involves two divisions, starting with Meiosis I.
Prophase I: Chromosomes condense and line up with their homologous pairs. Crossing-over occurs, allowing genetic information exchange between chromosomes.
Metaphase I: Chromosomes align in the middle of the cell in pairs.
Anaphase I: Chromosomes are pulled away to opposite sides of the cell.
Telophase I: Two newly formed nuclei are observed, resulting in two cells. Cytokinesis splits the cytoplasm.
Meiosis II: Meiosis continues with a second division.
Prophase II: Chromosomes condense, and spindles start to form. However, there are no homologous pairs or crossing-over.
Metaphase II: Chromosomes line up in a single file line in the middle.
Anaphase II: Chromatids are pulled away to opposite sides of the cell.
Telophase II: Nuclei reform, resulting in a total of four cells. Cytokinesis completes the division.
End Result of Meiosis: Meiosis in males produces four different sperm cells, each unique. In females, meiosis produces one egg cell and three polar bodies, but only one of these becomes a functional egg. This diversity in gametes contributes to genetic variation among siblings.
Nondisjunction: Sometimes, chromosomes do not separate correctly during meiosis, leading to conditions like Down syndrome. Scientists study these events to understand genetic disorders better.
Your notes provide a comprehensive overview of meiosis, explaining the stages and their significance in producing genetically diverse gametes.
Sexual Reproduction: Many organisms pass their genes to their offspring through sexual reproduction, which involves the union of two gametes to form a genetically unique embryo.
Gametes and Meiosis: Gametes, which are sperm and egg cells, are formed through a process called meiosis. The cells undergoing meiosis are called germline cells.
Diploid and Haploid Cells: In diploid organisms, germline cells have two copies of each chromosome. Meiosis reduces the chromosome count, resulting in haploid gametes, each with one copy of each chromosome.
Life Cycle of Germline Cells: Germline cells go through stages similar to mitosis, including interphase (G1, S, and G2). DNA is duplicated during the S phase, resulting in sister chromatids.
Meiosis Division Events: There are two cell division events during meiosis.
Meiosis I: It results in two unique daughter cells, each with half the DNA content of the parent germline cells.
Meiosis II: This stage results in four unique haploid cells, each with one copy of each chromosome. These haploid cells are the gametes used in sexual reproduction.
Prophase I: DNA condenses into chromosomes, and sister chromatids join at the centromere. Synapsis occurs, leading to crossing-over, where genetic material is exchanged. This contributes to genetic diversity.
Metaphase I: Synapsed chromosomes align randomly at the cell's equator, creating different combinations in each meiosis event.
Anaphase I: Homologous chromosomes separate and migrate to opposite poles, but sister chromatids remain attached.
Telophase I and Cytokinesis: The cell divides into two daughter cells, each undergoing Meiosis II.
Meiosis II: Similar to mitosis, this stage involves Prophase II, Metaphase II, Anaphase II, and Telophase II, followed by cytokinesis. The key difference is that daughter cells have only one copy of each homologous chromosome.
Gametes Formation: Meiosis II results in four unique haploid cells, which are the gametes used in sexual reproduction. These gametes can fuse to form a diploid embryo.
Genetic Diversity: Crossing-over during Prophase I and random alignment during Metaphase I contribute to genetic diversity among offspring. Siblings, except for twins, are not genetically identical.
Cytokinesis and Final Outcome: Cytokinesis following Meiosis II leads to four unique haploid cells, which are gametes. Two gametes (one from each parent) can fuse to produce a diploid embryo. The embryo then grows through cycles of mitosis.
These notes provide a comprehensive overview of meiosis and its role in generating genetic diversity in sexual reproduction.
James Watson and Francis Crick:
Interpreted existing experimental data to unlock the DNA structure.
X-ray crystallography images by Maurice Wilkins and Rosalind Franklin indicated a helical pattern.
Watson and Crick pieced this information together to create a DNA model, completing it in February 1953, unveiling the double helix structure.
Rosalind Franklin:
Conducted crucial research on DNA's structure, contributing significantly to its understanding.
Learned X-ray diffraction techniques.
Worked independently on DNA, but misunderstandings and gender biases complicated her collaboration with Maurice Wilkins.
Photographed DNA using x-ray.
She came very close to solving the DNA structure between 1951 and 1953, but Crick and Watson published their findings first.
Franklin's work was published as a supporting article in the same journal issue.
Ongoing debate surrounds the credit due to Franklin for her role in discovering DNA's structure.
Genetic Mutations:
Mutations are changes in genetic material, which can occur in genes or at the chromosome level or in nucleic acids like RNA and DNA.
Changes can occur due to external factors (chemicals, radiation) or internal factors (errors during DNA replication in interphase).
Types of Mutations:
Gene Mutations:
Gene mutations can lead to the production of different proteins, affecting an organism's traits.
Types of gene mutations:
Substitution: Wrong base pairs up (e.g., A with G instead of A with T).
Insertion: Extra base(s) added.
Deletion: Base removed.
Insertions and deletions can cause frameshift mutations, altering protein synthesis.
Gene mutations are specific to individual genes.
Chromosome Mutations:
Types of chromosome mutations:
Duplication: Extra copies of genes generated, leading to extra copies of that chromosome.
Deletion: Genetic material breaks off from the chromosome.
Inversion: Broken chromosome segment is reversed and reattached.
Translocation: Fragment from one chromosome breaks off and attaches to another.
These mutations can have significant effects due to changes in gene number or arrangement.
Occurrence of Mutations:
Mutations can happen during DNA replication in interphase or other vulnerable times like meiosis.
Meiosis can result in nondisjunction, leading to too many or too few chromosomes in egg or sperm cells, potentially causing genetic disorders. ??????
Introduction to Mitosis
It is essential for growth and tissue repair.
Mitosis ensures that new cells are identical to the original ones.
Regulation of Cell Division
Cells do not continuously divide; this would lead to uncontrolled growth, similar to cancer.
The cell cycle includes interphase (growth and DNA replication) and mitosis (cell division).
Chromosomes condense DNA for efficient division.
Chromosome Replication
Before mitosis, chromosomes must be duplicated during interphase.
Despite duplication, chromosomes are counted by centromeres, leading to 46 chromosomes with 92 chromatids.
Mitosis Stages (PMAT)
Prophase (P): Chromosomes condense and become visible, while the nucleus is still present.
Metaphase (M): Chromosomes align in the middle of the cell, as the nucleus disassembles.
Anaphase (A): Chromosomes move towards opposite ends of the cell, aided by spindle fibers.
Telophase (T): Chromosomes reach opposite ends, and new nuclei begin to form.
Cytokinesis
Cytokinesis completes cell division by splitting the cytoplasm, resulting in two new, identical cells.
Introduction to Meiosis: Meiosis is a process that results in the formation of gametes (sperm and egg cells) and is responsible for genetic diversity. Unlike mitosis, which produces identical body cells, meiosis reduces the chromosome count by half.
Chromosome Count: Most body cells in humans have 46 chromosomes. However, human sperm and egg cells have 23 chromosomes each. When they combine during fertilization, the resulting fertilized egg has the normal 46 chromosomes.
Reduction Division: Meiosis is referred to as a reduction division because it starts with a cell containing 46 chromosomes and ends with four cells (gametes), each containing only 23 chromosomes.
Interphase: Meiosis begins with interphase, a stage where the cell grows, replicates its DNA, and carries out necessary processes. Chromosomes are duplicated during interphase.
Meiosis I: Meiosis involves two divisions, starting with Meiosis I.
Prophase I: Chromosomes condense and line up with their homologous pairs. Crossing-over occurs, allowing genetic information exchange between chromosomes.
Metaphase I: Chromosomes align in the middle of the cell in pairs.
Anaphase I: Chromosomes are pulled away to opposite sides of the cell.
Telophase I: Two newly formed nuclei are observed, resulting in two cells. Cytokinesis splits the cytoplasm.
Meiosis II: Meiosis continues with a second division.
Prophase II: Chromosomes condense, and spindles start to form. However, there are no homologous pairs or crossing-over.
Metaphase II: Chromosomes line up in a single file line in the middle.
Anaphase II: Chromatids are pulled away to opposite sides of the cell.
Telophase II: Nuclei reform, resulting in a total of four cells. Cytokinesis completes the division.
End Result of Meiosis: Meiosis in males produces four different sperm cells, each unique. In females, meiosis produces one egg cell and three polar bodies, but only one of these becomes a functional egg. This diversity in gametes contributes to genetic variation among siblings.
Nondisjunction: Sometimes, chromosomes do not separate correctly during meiosis, leading to conditions like Down syndrome. Scientists study these events to understand genetic disorders better.
Your notes provide a comprehensive overview of meiosis, explaining the stages and their significance in producing genetically diverse gametes.
Sexual Reproduction: Many organisms pass their genes to their offspring through sexual reproduction, which involves the union of two gametes to form a genetically unique embryo.
Gametes and Meiosis: Gametes, which are sperm and egg cells, are formed through a process called meiosis. The cells undergoing meiosis are called germline cells.
Diploid and Haploid Cells: In diploid organisms, germline cells have two copies of each chromosome. Meiosis reduces the chromosome count, resulting in haploid gametes, each with one copy of each chromosome.
Life Cycle of Germline Cells: Germline cells go through stages similar to mitosis, including interphase (G1, S, and G2). DNA is duplicated during the S phase, resulting in sister chromatids.
Meiosis Division Events: There are two cell division events during meiosis.
Meiosis I: It results in two unique daughter cells, each with half the DNA content of the parent germline cells.
Meiosis II: This stage results in four unique haploid cells, each with one copy of each chromosome. These haploid cells are the gametes used in sexual reproduction.
Prophase I: DNA condenses into chromosomes, and sister chromatids join at the centromere. Synapsis occurs, leading to crossing-over, where genetic material is exchanged. This contributes to genetic diversity.
Metaphase I: Synapsed chromosomes align randomly at the cell's equator, creating different combinations in each meiosis event.
Anaphase I: Homologous chromosomes separate and migrate to opposite poles, but sister chromatids remain attached.
Telophase I and Cytokinesis: The cell divides into two daughter cells, each undergoing Meiosis II.
Meiosis II: Similar to mitosis, this stage involves Prophase II, Metaphase II, Anaphase II, and Telophase II, followed by cytokinesis. The key difference is that daughter cells have only one copy of each homologous chromosome.
Gametes Formation: Meiosis II results in four unique haploid cells, which are the gametes used in sexual reproduction. These gametes can fuse to form a diploid embryo.
Genetic Diversity: Crossing-over during Prophase I and random alignment during Metaphase I contribute to genetic diversity among offspring. Siblings, except for twins, are not genetically identical.
Cytokinesis and Final Outcome: Cytokinesis following Meiosis II leads to four unique haploid cells, which are gametes. Two gametes (one from each parent) can fuse to produce a diploid embryo. The embryo then grows through cycles of mitosis.
These notes provide a comprehensive overview of meiosis and its role in generating genetic diversity in sexual reproduction.
