* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download meiosis
Segmental Duplication on the Human Y Chromosome wikipedia , lookup
Genomic library wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Genetic engineering wikipedia , lookup
Point mutation wikipedia , lookup
Genome evolution wikipedia , lookup
History of genetic engineering wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Genomic imprinting wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Gene expression programming wikipedia , lookup
Designer baby wikipedia , lookup
Genome (book) wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Y chromosome wikipedia , lookup
Microevolution wikipedia , lookup
X-inactivation wikipedia , lookup
MEIOSIS MEIOSIS • Genes: – Lined up on chromosomes – Chromosome = >1,000 genes MEIOSIS • Diploid and Haploid Cells – Chromosomes occur in pairs, 1 from male and one from female – Diploid = 2 of each kind of chromosome (2n) • Zygote – Haploid = 1 of each kind of chromosome (n) • Sperm or Egg (Gamete) MEIOSIS MEIOSIS • Homologous Chromosomes – Chromosomes matched in homologous pairs – Humans have 46 chromosomes (23 from egg, 23 from sperm) – 23 SETS of matching pairs of chromosomes MEIOSIS • Homologous Chromosomes – – – – – – – 2 chromosomes make matched pair Both carry same genes Genes exist at same location Similar length Centromere in same location Not always identical Can carry different alleles for same gene • Hair color location same, color different MEIOSIS MEIOSIS • Let’s review mitosis first! – What are the 4 phases? What happens in each? – Cell division produces new cells exactly like original cell MEIOSIS • Why can’t Mitosis be only means of cell division?? (DON’T WRITE!) – If pea plant, for example, produces 14 chromosomes – Gametes would each contain 14 chromosomes – Each offspring would have 28 – Offspring of next generation would have 56 – DOES NOT WORK!!! MEIOSIS • Meiosis: – – – – Sexual reproduction Production of gametes Reduction of chromosomes 2 Phases MEIOSIS • Sexual Reproduction: – Sperm (male gamete) and Egg (female gamete) fuse – Each gives 23 chromosomes to zygote = 46 total chromosomes in offspring MEIOSIS • Production of gametes: – BOTTOM LINE: Meiosis occurs in specialized body cells of each parent to produce gametes for sexual reproduction. MEIOSIS • Reduction of Chromosomes: – Allows for offspring to have same number of chromosomes as parents (not double) • Gametes (egg or sperm) with ½ number of chromosomes as parent’s body cells MEIOSIS • 2 Phases: 1. MEIOSIS I: Genetic Variation 2. MEIOSIS II: “Mitosis-Like” MEIOSIS • MEIOSIS I: INTERPHASE – Cell replicates chromosomes – Result: 2 identical sister chromatids held together by centromeres MEIOSIS • MEIOSIS I: PROPHASE I – Similar to Mitosis – DNA coils to form Chromosomes – Homologous chromosomes line up gene by gene along length • Tetrad: 2 homologous chromosomes w/ 2 sister chromatids each MEIOSIS • MEIOSIS I: PROPHASE I – TETRAD: 4 chromatids • Chromatids pair tightly • Crossing over: non-sister chromatids can break and exchange genetic information • Estimation: 2 or 3 crossovers • NEW GENETIC COMBINATION! MEIOSIS • MEIOSIS I: Metaphase I – Centromere attaches to spindle – Spindles pull tetrads into middle • Unique to meiosis • Tetrad = homologous pair of chromosomes MEIOSIS • MEIOSIS: Anaphase I – Begins as homologous chromosomes separate and move to opposite ends of cells • Each has two chromatids – Centromeres do not split • Why is this important? – Ensures that each new cell receives only 1 chromosome from each homologous pair MEIOSIS • MEIOSIS I: Telophase I – Spindle is broken down – Chromosomes uncoil – Cytoplasm divides 2 new cells – One of each chromosome per new cell • ANOTHER DIVISION IS NEEDED! WHY? MEIOSIS • MEIOSIS II: – Like Mitotic division – Phases: Prophase II, Metaphase II, Anaphase II, Telophase II – The only difference from mitotic division is that chromosomes do not replicate before they divide at centromeres. MEIOSIS MEIOSIS • Meiosis provides for genetic variation – Crossing over provides rearrangement of genes – Can happen anywhere at random on chromosome – Endless possibilities of different chromosomes • Genetic Recombination: reassortement of chromosomes and genetic information they carry by crossing over MEIOSIS MEIOSIS • Nondisjunction: – Caused when chromosomes do not separate properly in meiosis I – Chromosomes in tetrad move to one side of cell rather than separate – Two gametes are result: • 1 has extra chromosome • Other has missing chromosome MEIOSIS • Nondisjunction: – When zygote formed with an extra chromosome, condition called trisomy • Ex: In humans, having an extra Chromosome 21, zygote has 47 chromosomes instead of 46. This zygote develops into a baby with Down syndrome. – When zygote formed with a missing chromosome, condition called monosomy • Ex: In humans, a non-lethal monosomy zygote develops Turner syndrome. This results in a female that has only one x chromosome instead of two. MEIOSIS • Polyploidy: – Organisms with more than the usual number of chromosome sets – Rare in animals—causes death – Frequent in plants • Plants appear larger and healthier • Ex: Apples = triploid (3n) Wheat = hexaploid (6n) MEIOSIS