Tiêu đề [ Q1W5 ] General Biology Transes.pdf ✅

CHAPTER 5 : MEIOSIS GBIO I S.Y. ‘23-24 SHS STEM S1Q1 WEEK 5 | CAMPBELL BIOLOGY 8TH ED. | CAMPBELL & REECE 05 MEIOSIS PPT & LECTURE CAMPBELL BIO 05 OVERVIEW : VARIATIONS ON A THEME Introduction to Meiosis ● Living organisms are distinguished by their ability to reproduce their own kind ● Genetics: the scientific study of heredity and variation ● Heredity: the transmission of traits from one generation to the next ● Variation: demonstrated by the differences in appearance that offspring show from parents and siblings 1.0 INHERITANCE OF GENES ● Genes: units of heredity; made up of segments of DNA - Passed to the next generation through reproductive cells called gametes (sperm and eggs). ● Gene locus/loci: Specific location of a gene on a certain chromosome. ● Most DNA is packaged into chromosomes ● One set of chromosomes is inherited from each parent. - One from the mother, and one from the father. 2.0 ASEXUAL VS. SEXUAL REPRODUCTION COMPARISON OF ASEXUAL AND SEXUAL REP. ASEXUAL SEXUAL One parent produces genetically identical offspring by mitosis. Two parents give rise to offspring that have unique combinations of genes inherited from the two parents. Undergoes mitosis. Undergoes both mitosis and meiosis. A clone is created, which is genetically identical to its parent. A genetically unique identical is created. 3.0 SETS OF CHROMOSOMES IN HUMAN CELLS ● Human somatic cells (any cell other than a gamete) have 23 pairs of chromosomes. ● The two chromosomes in each pair are called homologous chromosomes, or homologs. ● Homologous chromosomes are the same in: 1. Size 2. Shape 3. Genetic Material ADDITIONAL 3.0. Sets of Chromosomes Karyotype Refers to an ordered display of the pairs of chromosomes from a cell, such as the picture above. 3.1 THE SEX CHROMOSOMES ● The sex chromosomes are called X and Y. ● Human females have a homologous pair of X chromosomes (XX) ● Human males have one X and one Y chromosome ● The 22 pairs of chromosomes that do not determine sex are called autosomes. 4.0 THE SOMATIC AND SEX CELL (GAMETES) 4.1 THE HUMAN SOMATIC (BODY) CELL ● The 46 chromosomes in a human somatic cell are two sets of 23. - One from the mother and one from the father ● A diploid cell (2n) has two sets of chromosomes ● For humans, the diploid number is 46 (2n = 46) ● Each replicated chromosome consists of two identical sister chromatids. WONRIKA ON X | SHS STEM NOTES | CAMPBELL BIO 8TH ED. GENERAL BIOLOGY I SEM1 Q1 PAGE 1
CHAPTER 5 : MEIOSIS GBIO I S.Y. ‘23-24 SHS STEM S1Q1 WEEK 5 | CAMPBELL BIOLOGY 8TH ED. | CAMPBELL & REECE 4.2 THE HUMAN SEX CELL (GAMETES) ● A gamete (sperm or egg) contains a single set of chromosomes, and is haploid (n). ● For humans, the haploid number is 23 (n = 23). ● Each set of 23 consists of 22 autosomes and a single sex chromosome. ● In an unfertilized egg (ovum), the sex chromosome is X. ● In a sperm cell, the sex chromosome may be either X or Y. 5.0 FERTILIZATION IN THE HUMAN LIFE CYCLE ● Fertilization: union of gametes (the sperm and the egg). ● Zygote: refers to the fertilized egg and has one set of chromosomes from each parent ● The zygote produces somatic cells by mitosis and develops into an adult. ● At sexual maturity, the ovaries and testes produce haploid gametes. ● Gametes are the only types of human cells produced by meiosis, rather than mitosis. - Meiosis results in one set of chromosomes in each gamete ● Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number 5.0 MEIOSIS CYCLE ● Like mitosis, meiosis is preceded by the interphase. ● Meiosis takes place in two sets of cell divisions: 1. Meiosis I 2. Meiosis II ● The two cell divisions result in four daughter cells, rather than the two daughter cells in mitosis. ● Each daughter cell has only half as many chromosomes as the parent cell 5.1 INTERPHASE 5.2 MEIOSIS (ILLUSTRATION) WONRIKA ON X | SHS STEM NOTES | CAMPBELL BIO 8TH ED. GENERAL BIOLOGY I SEM1 Q1 PAGE 2
CHAPTER 5 : MEIOSIS GBIO I S.Y. ‘23-24 SHS STEM S1Q1 WEEK 5 | CAMPBELL BIOLOGY 8TH ED. | CAMPBELL & REECE WONRIKA ON X | SHS STEM NOTES | CAMPBELL BIO 8TH ED. GENERAL BIOLOGY I SEM1 Q1 PAGE 3
CHAPTER 5 : MEIOSIS GBIO I S.Y. ‘23-24 SHS STEM S1Q1 WEEK 5 | CAMPBELL BIOLOGY 8TH ED. | CAMPBELL & REECE 6.0 MEIOSIS I (MEIOSIS PHASE ONE) ● Division in meiosis I occurs in four phases: a. Prophase I b. Metaphase I c. Anaphase I d. Telophase I and cytokinesis 6.1 PROPHASE I ● Prophase I typically occupies more than 90% of the time required for meiosis. ● It is further subdivided into five stages: 1. Leptotene 2. Zygotene 3. Pachytene 4. Diplotene 5. Diakinesis FIVE STAGES OF PROPHASE I Leptotene ● Genetic material is further condensed into supercoiled duplicated chromosomes. Zygotene ● Duplicated chromosomes from the mother and father find their homologous pair to create pairs of homologous chromosomes. ● When they have found their pair, they attach or keep each other together. ● They bind the homologous pairs together through a set of proteins that glues or zips them together, known as the “synaptonemal complex.” ● The event where synaptonemal complex form is called “synapsis.” Pachytene ● The nonsister chromatids of each homologous pair overlap with each other due to synapsis. ● In crossing over, nonsister chromatids exchange DNA segments. ● Each pair of chromosomes forms a tetrad, a group of four chromatids (or bivalent, a group of two chromosomes). ● Chiasma/Chiasmata: X-shaped region where nonsister chromatids cross over. ● Crossing over is done to increase variation in your child’s genetic material. Diplotene ● The synaptonemal complex dissociates. Diakinesis ● The nuclear membrane & nucleolus fragments / dissociates. 6.2 METAPHASE I ● The tetrads align each other at the metaphase plate. 6.3 ANAPHASE I ● In anaphase I, pairs of homologous chromosomes separate. 6.3 TELOPHASE I AND CYTOKINESIS ● In the beginning of telophase I, each half of the cell has a haploid set of chromosomes; each chromosome still consists of two sister chromatids ● Cytokinesis usually occurs simultaneously, forming two haploid daughter cells. ● No chromosome replication occurs between the end of meiosis I and the beginning of meiosis II because the chromosomes are already replicated. 7.0 MEIOSIS II (MEIOSIS PHASE TWO) ● Division in meiosis II also occurs in four phases: e. Prophase II f. Metaphase II g. Anaphase II h. Telophase II and cytokinesis ● Meiosis II is very similar to mitosis. - See the discussion in Mitosis on Q1W4. ● At the end of meiosis II, there are four daughter cells, each with a haploid set of unreplicated chromosomes. WONRIKA ON X | SHS STEM NOTES | CAMPBELL BIO 8TH ED. GENERAL BIOLOGY I SEM1 Q1 PAGE 4