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Questions and Answers
What is the primary function of histones in relation to chromosomes?
What is the primary function of histones in relation to chromosomes?
During which phase of the cell cycle is the genome copied in preparation for cell division?
During which phase of the cell cycle is the genome copied in preparation for cell division?
Which of the following best defines a genome?
Which of the following best defines a genome?
In what state are chromosomes most visible under a microscope?
In what state are chromosomes most visible under a microscope?
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What characterizes diploid cells compared to haploid cells?
What characterizes diploid cells compared to haploid cells?
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What is the primary purpose of the G1/S checkpoint in the cell cycle?
What is the primary purpose of the G1/S checkpoint in the cell cycle?
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During which phase of the cell cycle does DNA replication occur?
During which phase of the cell cycle does DNA replication occur?
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What structural protein is responsible for holding sister chromatids together during mitosis?
What structural protein is responsible for holding sister chromatids together during mitosis?
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Which of the following correctly describes the cell's condition before entering mitosis?
Which of the following correctly describes the cell's condition before entering mitosis?
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What distinguishes haploid cells from diploid cells?
What distinguishes haploid cells from diploid cells?
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What is the correct order of phases within interphase?
What is the correct order of phases within interphase?
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What happens to the genome during the S phase?
What happens to the genome during the S phase?
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How long does the G2 phase typically last in the cell cycle?
How long does the G2 phase typically last in the cell cycle?
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What is the role of microtubules during prometaphase in mitosis?
What is the role of microtubules during prometaphase in mitosis?
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What occurs during anaphase that ensures equal segregation of chromatids?
What occurs during anaphase that ensures equal segregation of chromatids?
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In which stage of mitosis does the nuclear membrane re-form around each set of chromosomes?
In which stage of mitosis does the nuclear membrane re-form around each set of chromosomes?
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Which statement best describes the function of the centrosomes during mitosis?
Which statement best describes the function of the centrosomes during mitosis?
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What distinguishes diploid cells from haploid cells in terms of chromosome number?
What distinguishes diploid cells from haploid cells in terms of chromosome number?
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In the context of the cell cycle, which phase directly precedes cytokinesis?
In the context of the cell cycle, which phase directly precedes cytokinesis?
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What is a primary purpose of meiosis in the context of sexual reproduction?
What is a primary purpose of meiosis in the context of sexual reproduction?
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How do chromosomes behave during metaphase?
How do chromosomes behave during metaphase?
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Study Notes
Medical Genetics Lecture Notes
- Course: Medical Genetics
- Institution: UDS School of Medicine
- Department: Biochemistry and Molecular Medicine
- Instructor: Jennifer Suurbaar
- Year: 2023/2024
Lecture 1 & 2
- Topics covered: Introduction to genetics, medical genetics, history of genetics, physical basis of genetics (cells, chromosomes, terminology), cell division (cell cycle, mitosis, meiosis, gametogenesis, sex determination)
Introduction to Medical Genetics
- Focuses on the role of genes in health and disease
- Aims to understand genetic factors contributing to various medical conditions
- Identifies genetic disorders
- Explores diagnostic techniques
- Seeks therapies for genetic diseases
Overview of the History of Genetics
- Pre-1860: Discoveries of cells, the nucleus, a miniature human in sperm (homonculus), the theory of epigenetics, observed cell structure, single lens microscope (Leeuwenhoek), description of cell nucleus, Brownian motion of particles, mitosis in cells, and the term "protoplasm".
- 1860-1900: Mendelian traits and observation of chromosomes (Mendel's pea plant experiment), German embryology (fusion of sperm and egg forming a zygote). Walther Flemming’s use of aniline dyes to view chromosomes, and the hypothesis that chromosomes are individual structures with continuity from one generation.
- 1900-1944: Chromosome theory and sex linkage (the role of chromosomes). Thomas Hunt Morgan and Drosophila melanogaster as a model genetic system, Mendel's rules of inheritance, genes producing traits like white eyes. the location of genes on the X chromosome, mutation, and bacteria showing genetic systems and phenotypes.
- 1944-Present: DNA, RNA and molecular genetics. Oswald Avery, Alfred Hershey, Martha Chase’s work on DNA as genetic material; James Watson, Francis Crick, Structure of DNA; recombinant DNA molecule construction (Paul Berg); Haemophilus influenzae sequenced. Advancement and techniques like DNA sequencing, CRISPR gene editing, and rapid advancement in personalized medicine.
Cell Division
- Cell division is the fundamental aspect of growth, development, and tissue maintenance.
- During cell division, each daughter cell needs an exact copy of the mother cell's contents.
- The mother cell replicates the nucleus into two, one for each daughter cell.
- The nucleus contains the genome (DNA) which is copied.
Cell Cycle & Mitosis
- Mitosis is responsible for growth, development, and tissue maintenance.
- Cell cycle is the life of a single cell, involving tissue repair and cell replacement.
- Stages include G1 (prepares to duplicate genome), S (duplicates genome), G2 (prepares for mitosis), and M (mitosis and cytokinesis).
- Checkpoints in the cell cycle ensure that damaged cells do not continue.
Interphase (before Mitosis)
- The extended period between cell divisions
- Three distinct stages: G1, S, and G2 phases
- G1: Cell growth, prepares for DNA duplication
- S: DNA duplication; the genome is copied
- G2: Cell prepares for division, checks for DNA damage
Mitosis Stages
- Prophase: DNA compacts, visible under microscope, centrosomes move to opposite poles, and the mitotic spindle forms
- Prometaphase: The nuclear envelope breaks, chromosomes attach to spindle microtubules
- Metaphase: Chromosomes align along the metaphase plate (center of the cell)
- Anaphase: Sister chromatids separate and migrate to opposite poles
- Telophase: New nuclear envelopes form around the separated chromosomes
After mitosis
- Each new daughter cell contains an identical genome (no loss of DNA) to the mother cell.
Meiosis
- Crucial for sexual reproduction, producing haploid cells (gametes).
- Key event: Genetic diversity among offspring
- Involved in the shuffling of genetic information of two parents
Meiosis Similarities to Mitosis
- Both go through the cell cycle interphase.
- Cytokinesis occurs after both mitosis/meiosis I, and meiosis II.
- Resulting in four non-identical haploid gametes (egg or sperm)
Meiosis I Stages
- Prophase I: Chromosomes compact, homologous chromosomes pair up next to each other (synapsis), and crossing over (exchange genetic material) occurs
- Metaphase I: Homologous chromosome pairs align at the equatorial plate
- Anaphase I: Homologous pairs separate, but sister chromatids remain together
- Telophase I: New nuclei form; Cytokinesis produces two cells
Meiosis II Stages
- Prophase II: Chromosomes condense in each of the two haploid cells from Meiosis I
- Metaphase II: Chromosomes align at the equatorial plate
- Anaphase II: Sister chromatids separate and move to opposite poles
- Telophase II: New nuclei form and Cytokinesis occurs, forming four haploid gametes
Interkinesis
- Brief stage between meiosis I and meiosis II
- DNA replication does not occur during interkinesis.
Independent Assortment
- Random distribution of alleles during meiosis
- Randomness generates genetic variability in gametes
Meiosis in Animals (Gametogenesis)
- Gametes arise from primordial germ cells during embryonic life.
- Germ cells are the stem cells of the species.
- Meiosis is used to produce sperm or eggs, which are haploid and carry half the genetic information of a diploid cell.
Sex Determination
- Sex of the offspring is determined at fertilization.
- Female mammals have two X chromosomes.
- Male mammals have one X and one Y chromosome
- Sex of the offspring is determined by the male parent
Sex Determination Syndromes of Humans
- Turner Syndrome, Klinefelter Syndrome, Triple X Syndrome
Basic Principles of Heredity (Lecture 3 & 4)
- Topics: Mendelian Genetics, Gregor Mendel's History, Basic genetic terminology, Monohybrid crosses, Using genetics to predict offspring of the parent.
Mendel's Laws of Inheritance
- Law of Dominance: In a cross of pure contrasting traits, only one form of the trait appears in the next generation.
- Law of Segregation: During gamete formation, alleles responsible for a trait separate from each other.
- Law of Independent Assortment: Alleles of different traits distribute independently into gametes.
Exceptions to Mendel's Laws
- Multiple Allelic Traits (e.g., ABO blood types)
- Codominance
- Pleiotropy (one gene affects multiple traits)
Probability & Genetics
- Probability in genetics uses Punnett squares to predict possible genotypes and phenotypes of offspring.
- Probabilities range from 0 to 1 (0= event will not occur, 1= event is certain to occur).
- Rules for independent events (product rule) and disjoint events (sum rule).
Pedigree Analysis
- Method to track the expression/prevalence of traits across family generations.
- Key Assumptions: Complete penetrance and rare-in-population traits.
Modes of Inheritance
- Inheritance patterns are tracked based on dominant/recessive and sex-linked traits (X-linked and Y-linked).
Exceptions to Mendelian inheritance
- Some characteristics are influenced by interactions of other genes/environmental factors in addition to the gene itself.
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