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Transcript
BELL WORK Current Event Complete the following tasks: 1. Read the Current Event – New Chemistry May Cure Human Cancers 2. Answer the Questions – What facts about cells did scientists use to design their treatment – How did it work? Week of April 21, 2014 HOMEWORK Friday, April 25, 2014 • MP3 Recording – – – – Meiosis – Mitosis Comparison Listen to Recording Take Quiz and Print for Credit Put in Folder • BioFlix – Finish – Place in Folder • Folders – Complete – after Karyotyping Lab next week Friday Agenda • Vocabulary Quiz • BioFlix Meiosis – Animation – Tutorials – Worksheet • Absent? – See Me for Details Meiosis Basic Notes Just Add Note Cards Meiosis Parent cell – chromosome pair Chromosomes copied 1st division - pairs split 2nd division – produces 4 gamete cells with ½ the original no. of chromosomes Reduction Division THE STAGES OF MEIOSIS: Meiosis I : Separates Homologous Chromosomes • Interphase – Each of the chromosomes replicate – The result is two genetically identical sister chromatids which remain attached at their centromeres Interphase I • Nucleus and nucleolus visible. chromatin nuclear membrane cell membrane nucleolus Prophase I - Synapsis Homologous chromosomes sister chromatids Tetrad sister chromatids Homologous Chromosomes • Pair of chromosomes (maternal and paternal) that are similar in shape and size. • Homologous pairs (tetrads) carry genes controlling the same inherited traits. • Each locus (position of a gene) is in the same position on homologues. • Humans have 23 pairs of homologous chromosomes. 22 pairs of autosomes 1 pair of sex chromosomes Homologous Chromosomes eye color locus eye color locus hair color locus hair color locus Paternal Maternal Karyotype • A method of organizing the chromosomes of a cell in relation to number, size, and type. Humans have 23 Sets of Homologous Chromosomes Each Homologous set is made up of 2 Homologues. Homologue Homologue Autosomes (The Autosomes code for most of the offspring’s traits) In Humans the “Autosomes” are sets 1 - 22 Sex Chromosomes The Sex Chromosomes code for the sex of the offspring. ** If the offspring has two “X” chromosomes it will be a female. ** If the offspring has one “X” chromosome and one “Y” chromosome it will be a male. In Humans the “Sex Chromosomes” are the 23rd set XX chromosome - female XY chromosome - male Boy or Girl? The Y Chromosome “Decides” Y chromosome X chromosome Sex Chromosomes “Sex Chromosomes” …….the 23rd set 23 This person has 2 “X” chromosomes… and is a female. Interphase I • Nucleus and nucleolus visible. chromatin nuclear membrane cell membrane nucleolus Prophase I • This is a crucial phase for mitosis. • During this phase each pair of chromatids don’t move to the equator alone, they match up with their homologous pair and fasten together (synapsis) in a group of four called a tetrad. • Extremely IMPORTANT!!! It is during this phase that crossing over can occur. • Crossing Over is the exchange of segments during synapsis. Prophase I spindle fiber aster fibers centrioles Metaphase I • The chromosomes line up at the equator attached by their centromeres to spindle fibers from centrioles. – Still in homologous pairs Metaphase I OR metaphase plate metaphase plate Anaphase I • The spindle guides the movement of the chromosomes toward the poles – Sister chromatids remain attached – Move as a unit towards the same pole • The homologous chromosome moves toward the opposite pole – Contrasts mitosis – chromosomes appear as individuals instead of pairs (meiosis) Anaphase I Telophase I • This is the end of the first meiotic cell division. • The cytoplasm divides, forming two new daughter cells. • Each of the newly formed cells has half the number of the parent cell’s chromosomes, but each chromosome is already replicated ready for the second meiotic cell division Cytokinesis • Occurs simultaneously with telophase I – Forms 2 daughter cells • Plant cells – cell plate • Animal cells – cleavage furrows • NO FURTHER REPLICATION OF GENETIC MATERIAL PRIOR TO THE SECOND DIVISION OF MEIOSIS Telophase I Meiosis II : Separates sister chromatids • Proceeds similar to mitosis • THERE IS NO INTERPHASE II ! Prophase II • same as prophase in mitosis Metaphase II • same as metaphase in mitosis metaphase plate metaphase plate Anaphase II • same as anaphase in mitosis • sister chromatids separate Telophase II • Same as telophase in mitosis. • Nuclei form. • Cytokinesis occurs. • Remember: four haploid daughter cells produced. gametes = sperm or egg Telophase II One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes. In humans, n = 23 and 223 = 6,000,0000. That’s a lot of diversity by this mechanism alone. Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment. The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis Mitosis The first (and distinguishing) division of meiosis Boy or Girl? The Y Chromosome “Decides” Y chromosome X chromosome Boy or Girl? The Y Chromosome “Decides” ANY QUESTIONS? EXTRA SLIDES Meiosis – division error Chromosome pair Meiosis error - fertilization Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’. In humans this often occurs with the 21st pair – producing a child with Downs Syndrome 21 trisomy – Downs Syndrome Can you see the extra 21st chromosome? Is this person male or female?