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