MEIOSISGENETICSCAMBELL & REECE 2012 CHAPTER 13
INTRODUCTION TO MEOISIS
SOMATIC CELLS HAVE 23 HOMOLOGOUS CHROMOSOMES HALF FROM THE FATHER: PATERNAL HALF FROM THE MOTHER: MATERNAL SEX CHROMOSOMES ARE KNOWN AS GONOSOMES OR X
AND Y X AND Y DIFFER IN GENETIC COMPOSITION AND IN SIZE
HOMOLOGOUS CHROMOSOMES
HOMOLOGOS CHROMOSOMES ARE SIMILAR IN LENGTH, CENTROMERE POSITION AND GENETIC LOCATION (LOCUS)
DIFFERENT VERSIONS OF A GENE ARE CALLED ALLELES AND CAN BE FOUND IN THE SAME LOCUS ON PATERNAL AND MATERNAL CHROMOSOMES
WHAT IS MEOISIS
ALL HUMANS AND MOST PLANTS HAVE DIPLOID (2n) CHROMOSOMES
MEOISIS IS THE HALVING OF THE NUMBER OF CHROMOSOMES TO HAPLOID (n)
MEOISIS OCCURS IN THE SEX ORGANS TO PRODUCE GAMETES THAT WILL MATURE INTO AN EGG CELL OR A SPERM CELL
FERTILIZATION IS THE FUSION OF GAMETES
INTERPHASE ONE
IN THE CELL THERE IS A BUILD UP OF ENERGY DNA REPLICATION STARTS
PROPHASE 1
NUCLEOMEMBRANE AND NUCLEOLUS STARTS TO DISAPPEAR
THE CENTRIOLI MOVE TO OPPOSITE POLES
CROSSING OVER
CROSSING OVER IS THE PROCESS WHEREBY THE HOMOLOGOUS CHROMOSOMES TOUCH AT POINTS CALLED CHIASMATA
THIS INCREASES THE GENETIC VARIATION OF THE GAMETES
METAPHASE 1
CENTRIOLI REACH POLES SPINDLE FIBRES FORM BETWEEN THEM HOMOLOGOUS CHROMOSOMES REACH POLES
EQUOTORIAL PLANES ATTACHED TO SPINDLE FIBRES
KINETOCHORE OF CENTROMERE ATTACH TO SPINDLE FIBRES
ANAPHASE 1
DUPLICATED CHROMOSOMES MOVE TO ONE PART OF THE CELL
SPINDLE FIBRES AND CENTRIOLI CONTRACT
TELOPHASE 1
THE CYTOPLASM WILL FORM AN INVAGINATION AND UNGERGO CYTOKENISIS
THE NUCLEOMEMBRANE AND NUCLEOLUS REAPPEAR
TWO DAUGHTER CHROMOSOMES FORM THAT ARE HAPLOID
PROPHASE 2
NUCLEAR MEMBRANE AND NUCLEOLUS DISAPPEAR CENTRIOLI MOVES TOWARDS THE POLES
METAPHASE 2
INDIVIDUAL DUPLICATED CHROMOSOMES ATTACH TO SPINDLE FIBRES
ANAPHASE 2
DAUGHTER CHROMATIDS MOVE TO THE POLES OF THE CELLS
TELOPHASE 2
FOUR NEW CELLS WITH HAPLOID NUMBER OF CHROMOSOMES
THESE CAN MATURE TO FORM SERM CELLS AND EGG CELLS