FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Chapter 11 Introduction To Genetics Section Meiosis

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Meiosis The Process That Separates The Genes So Each Gamete Gets Only 1 Set of Chromosomes

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Gamete A Specialized Cell Involved In The Process Of Sexual Reproduction (sperm, egg, pollen, etc.)

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Chromosome Number Drosophila (Fruit Fly)Drosophila (Fruit Fly) –Adult Has 8 Chromosomes 4 From The Male Parent4 From The Male Parent 4 From The Female Parent4 From The Female Parent –For A Total of 8 Homologous Chromosomes The 4 From The Male Has A Matching 4 Chromosomes From The Female

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Drosophila Karyotype

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Chromosome Number Drosophila Cells With 8 Chromosomes Are Diploid 2N = Both Sets of Chromosomes(8) 1N = One Set of Chromosomes(4) Haploid

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Chromosome Number Gametes Have Only 1N – Only 1 Set of Chromosomes Therefore, They Are Said To Be: Haploid

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Phases of Meiosis Key Concept: Meiosis Is A Process Of: Reduction Division In Which The Number Of Chromosomes Per Cell Is Cut In Half Through The Separation Of Homologous Chromosomes In A Diploid Cell.

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Phases of Meiosis Two Stages Meiosis I (Chromosomes Replicate) –A First Round of Cell Division Occurs Resulting In Two Haploid Cells Meiosis II (Chromosomes Don’t Replicate) –A Second Round of Cell Division Occurs Resulting In Four Haploid Cells

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Meiosis I NEXT Crossing Over Crossing Over !!! ONLY Happens Here !!! Notice Chromosome Alignment

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Meiosis I NEXT

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Meiosis I Meiosis I is Complete 1N Haploid Next Stop Meiosis II

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Meiosis II The Two (2) Cells Produced By Meiosis I now Enter A Second Meiotic DivisionThe Two (2) Cells Produced By Meiosis I now Enter A Second Meiotic Division NO Chromosome Replication OccursNO Chromosome Replication Occurs No Chromosome Replication Occurs…. Last Step Cytokinesis II

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Meiosis II Each Cell Now Has Half The Usual Number Of Paired Chromatids.Each Cell Now Has Half The Usual Number Of Paired Chromatids. During Metaphase II They Line Up Across The Center Of The CellDuring Metaphase II They Line Up Across The Center Of The Cell !! Finally !! 4 Haploid Gametes !! Finally !! 4 Haploid Gametes

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Oogenesis

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Spermatogenesis

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Gamete Formation Females At Birth The Ovary Already Contains All The Cells It Will Ever Have That Will Develop Into Eggs Males Spermatogenesis Occurs Constantly Throughout Life

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Comparing Mitosis & Meiosis Key Concept: Mitosis Results In The Production Of Two Genetically Identical Diploid Cells Meiosis Produces Four Genetically Different Haploid Cells

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Sex & Sex Chromosomes Do All Organisms Define Sex The Same Way? Do All Organisms Define Sex The Same Way?

FOOTHILL HIGH SCHOOL SCIENCE DEPARTMENT Sex & Sex Chromosomes MaleFemaleSpecies XXX Occurs in some insects like grasshoppers XYXX Drosophila, mammals and some plants XXXY birds, butterflies and some fishes YX organisms with alteration of generations (e.g., liverworts and vascular plants) XY Sporophytes