Honors Concept 3 Notes - Meiosis PDF

HONORS Our bodies have 2 types of cells: Somatic cells = Body cells – These are diploid (2n) – Ex. Blood cells, lung cells, muscle cells, heart cells, etc. Gametes = Sex cells – These are haploid (n) – Ex. Egg and sperm Our bodies have 2 types of cells: Diploid Cells =...

HONORS Our bodies have 2 types of cells: Somatic cells = Body cells – These are diploid (2n) – Ex. Blood cells, lung cells, muscle cells, heart cells, etc. Gametes = Sex cells – These are haploid (n) – Ex. Egg and sperm Our bodies have 2 types of cells: Diploid Cells = 2 full sets of chromosomes – (2n) – A set from mom and a set from dad – Ex. In human somatic cells, 2n = 46 Haploid Cells = 1 full set of chromosomes – (n) – Only one set that is a combination of chromosomes from mom and dad – Ex. Gametes = egg and sperm, n = 23  Our cells contain 2 types of chromosomes: Autosomes Karyotype = diagram that shows the – Carry traits that number and visual appearance of the make you who you chromosomes in a cell are – Ex. The 1st 22 pairs of chromosomes Sex chromosomes – Carry traits that make you who you are AND determine your biological sex – Ex. The 23rd pair of chromosomes (X or Y)  Background Babies can’t happen without pregnancy. Pregnancy can’t happen without fertilization. Fertilization can’t (naturally) happen without copulation. Copulation can’t result in offspring without an egg and a sperm. – So where do these cells come from??  Overview Meiosis: the process of cell division that makes gametes in the gonads (ovaries in females, testes in males). – Produces haploid sex cells (eggs in females and sperm in males) with half the number of chromosomes as diploid body cells. – Sexual reproduction can’t happen without meiosis!!  Sexual Reproduction Sexual reproduction = organisms that reproduce sexually (like humans) fuse the genetic information (gametes) from two parents to produce offspring that are a genetic mixture of both parents. Fertilization = the actual fusion of egg and sperm to form a zygote.  During sexual reproduction, the number of chromosomes is important!! MEIOSIS Duplicated chromosomes 2n Duplicated Meiosis I Duplicated chromosomes n n chromosomes Meiosis II Unduplicated Unduplicated chromosomes n n n n chromosomes  Remember… Homologous chromosomes = chromosome pairs that have the same types of genes – One from mom and one from dad Different from… Sister chromatids = 2 identical copies of the same chromosome  Meiosis I Purpose of Meiosis Meiosis is the process of creating gametes – sex cells that have HALF the normal number of chromosomes (only 1 set). – To do this, cell division happens twice. – Meiosis I: separation of Meiosis II homologous chromosomes A reduction from diploid duplicated chromosomes to haploid duplicated chromosomes. – Meiosis II: separation of sister chromatids Duplicated chromosomes from Meiosis I divide into individual chromosomes.  Before Meiosis I… Interphase = the growth phase of the cell cycle. 3 parts: – G1 phase = Gap 1 phase = cell grows and makes proteins – S phase = Synthesis phase = DNA replication occurs, doubling the number of chromosomes – G2 phase = Gap 2 phase = more cell growth and protein synthesis **At the end of interphase the cell has 2 duplicated copies of every chromosome!** Before Meiosis I… Remember how important S phase is!!!  Prophase I Nuclear membrane breaks down. Centrioles separate and make spindle fibers. Homologous chromosomes pair up & become visible. – Tetrad - cluster of 4 chromatids. Crossing over may occur between homologous chromosomes.  Crossing Over During Prophase 1 homologous chromosomes are lined up together. Sometimes chromosomes can cross over each other and get “tangled”. When this happens, they swap pieces of DNA. This process creates new combinations of genes – chromosomes that are “part mom/part dad”.  Metaphase I Homologous chromosomes are lined up in the middle of the cell in pairs.  Anaphase I Homologous chromosomes pairs separate, one chromosome (2 sister chromatids) pulled away to each side of the cell. Sister chromatids remain attached.  Telophase I and Cytokinesis Chromosomes gather at the poles. Nuclear membranes may reform. Cytokinesis = cytoplasm divides into 2 cells End result = 2 haploid daughter cells with duplicated chromosomes that are different from the sets in the original diploid cell.  Prophase II Nuclear membrane breaks down (if they reformed). Spindle fibers form and attach to the centromeres of the sister chromatids.  Metaphase II Sister chromatids line up in the middle of the cells single file.  Anaphase II Sister chromatids separate and are pulled away from each other to each side of the cells.  Telophase II and Cytokinesis Nuclear membranes form around each set of chromosomes. Spindle fibers dissolve. Cytokinesis = cytoplasm divides each cell into 2 cells. End result = 4 haploid daughter cells that are genetically unique.  Mitosis vs. Meiosis MITOSIS MEIOSIS What Creation of diploid Creation of haploid sex somatic cells cells When Females: before you are Throughout your life born; Males: throughout life Where Throughout body In ovaries and testes Why For growth and repair To make babies How PMAT once PMAT twice Result 2 identical diploid 4 unique haploid somatic cells gametes Type of Reproduction Asexual Sexual