* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Meiosis - TeacherWeb
Survey
Document related concepts
Point mutation wikipedia , lookup
Genomic imprinting wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Genetic engineering wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Genome (book) wikipedia , lookup
Designer baby wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Y chromosome wikipedia , lookup
Microevolution wikipedia , lookup
X-inactivation wikipedia , lookup
Transcript
Requires two parent cells from ◦ two separate organisms OR ◦ two sexually different parts of a single organism Produces offspring that are genetically different from either parent To make sex cells (gametes) Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote (fertilized egg) 2n = 6 1n =3 Is a zygote an example of a haploid or diploid cell? ◦ Diploid Before Meiosis occurs (similar to mitosis), DNA must Occurs in be replicated Interphase Occurs prior to division When does the replication of the chromosomes take place? ◦ During Interphase (sphase) Gene X Homologous chromosomes (a pair of chromosomes that carry alleles for the same traits) Sister Chromatids Diploid (2n): cells that have both sets of homologous chromosomes What are homologous chromosomes? - a pair of chromosomes that carry alleles for the same traits from mom from dad child too much! meiosis reduces genetic content The right number! Meiosis reduces the chromosome number by half Fertilization then restores the 2n (diploid) number Homologs separate Meiosis I Sister chromatids separate Meiosis II Diploid Haploid Spindle fibers Nucleus Early Prophase I (diploid) Late Prophase I Nuclear envelope Metaphase Anaphase Telophase I I I Early prophase I Late prophase I •Homologous chromosomes pair forming tetrads. •Crossing over occurs. •Chromosomes condense. •Spindle forms. •Nuclear envelope breaks down. Homologous chromosomes (each with sister chromatids) Join to form a TETRAD Called Synapsis How many chromatids are in a tetrad? - 4 Homologous chromosomes in a tetrad cross over each other Pieces of chromosomes or genes (alleles) are exchanged Produces genetic diversity in the offspring by creating new combinations of alleles. Crossing-over produces new combinations of alleles through independent assortment When does Crossing over happen? During Meiosis I - Homologous pairs of chromosomes align along the equator of the cell Homologous chromosomes separate and move to opposite poles. Sister chromatids remain attached at their centromeres. The nuclear envelopes reassemble. The spindle disappears. Cytokinesis divides cell into two. Meiosis I is also called ________ _________? Reduction Division - Gene X Only one homolog of each chromosome is present in the cell. Sister chromatids carry identical genetic information. Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. Prophase Metaphase II II Anaphase Telophase II 4 genetically II different haploid cells The nuclear envelope breaks down. The spindle forms. Chromosomes align along the equator of the cell. Equator Pole Sister chromatids separate and move to opposite poles. The nuclear envelope assembles. The chromosomes decondense. The spindle disappears. Cytokinesis divides cell into two. Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome One allele (variation) of each gene Compare mitosis with meiosis- what do you notice is similar? The stages have the same names Oogenesis or Spermatogenesis Occurs in the testes Two divisions produce 4 spermatids Spermatids mature into sperm Men produce about 250,000,000 sperm per day Primary Spermatocyte (diploid) Secondary spermatocyte (haploid) Spermatids (haploid) Occurs in the ovaries Two divisions produce 3 polar bodies that die, and 1 egg Polar bodies die because of unequal division of cytoplasm An immature egg is called an oocyte Starting at puberty, one oocyte matures into an ovum (egg) approximately every 28 days Primary Oocyte (diploid) Primary Polar Body (haploid) Secondary Oocyte (haploid) ootid Secondary oocyte Are the cells that result from Meiosis II diploid or haploid? They are haploid Mitosis Meiosis 2 Number of divisions 1 Number of daughter cells 2 4 Yes No Chromosome # Same as parent Half of parent Where Somatic (body) cells Sex (gamete) cells When Throughout life At sexual maturity Growth and repair Sexual reproduction Genetically identical? Role http://www.bbc.co.uk/schools/gcsebitesi ze/science/add_edexcel/cells/mitosisac t.shtml http://www.youtube.com/watch?v=iCL6d 0OwKt8