C H A P T E R 1 3

SEXUAL LIFE CYCLES: MEIOSIS

LEARNING TARGET 1I C A N E X P L A I N H O W O F F S P R I N G A C Q U I R E G E N E S F R O M P A R E N T S B Y I N H E R I T I N G

C H R O M O S O M E S .I can distinguish between asexual and sexual reproduction.

WHERE DO YOUR GENES COME FROM?

• Ever wonder where you got your traits from?• And where they got their traits from?

WHAT’S A GENE?

• A segment of DNA which codes for a protein

• Can code for an enzyme, a structural protein or a regulatory protein

• This determines an organism’s traits

• More next unit…

ASEXUAL REPRODUCTION

• No gametes produced• One parent• Prokaryotes – binary

fission• Single-celled eukaryotes

• Yeast – budding• Amoeba – binary fission

• Simple multicellular eukaryotes • Hydra – budding

• Complex multicellular eukaryotes - regeneration• Sea stars • Planaria

SEXUAL REPRODUCTION

• Gametes produced by meiosis

• Two parents• Direct contact not

required• Plants: pollination strategies

vary• Animals: release of gametes

into environment (aquatic)

LEARNING TARGET 2I C A N D I S T I N G U I S H B E T W E E N T H E F O L L O W I N G P A I R S O F T E R M S :

Somatic cell and gameteAutosome and sex chromosomeDiploid and haploidZygote and fertilization

IMPORTANT VOCABULARY

• Somatic cell• Body cell

• Gamete• Reproductive cell (sperm or egg)

• Diploid• Contains 2 sets of homologous chromosomes (2n)

• Haploid• Contains 1 set of homologous chromosomes (n)

Diploid Haploid

IMPORTANT VOCABULARY, CONT.

• Zygote• Fertilized egg

• Fertilization• Union of sperm and

egg cells in sexual reproduction

• Autosome• Chromosome 1-22

(everyone has)

• Sex chromosome• Chromosome 23

(XX = female, XY= male)

LEARNING TARGET 3I C A N E X P L A I N H O W H A P L O I D A N D D I P L O I D C E L L S D I F F E R F R O M E A C H O T H E R .

I can state which cells in the human body are diploid and which are haploid.

HAPLOID VS. DIPLOID

• Somatic cells are diploid• Only gametes are haploid – why?

LEARNING TARGET 4I C A N E X P L A I N H O W M E I O S I S G E N E R A T E S H A P L O I D D A U G H T E R C E L L S F R O M D I P L O I D P A R E N T C E L L S .

I can list the phases of meiosis I and meiosis II and describe the events characteristic of each phase.I can describe what homologous chromosomes are.I can explain how the spindle fiber separates either homologous chromosomes of sister chromatids.I can recognize the phases of meiosis from diagrams or micrographs.I can explain how genetic recombination occurs.

STEPS OF MEIOSIS

• Meiosis I• Interphase• Prophase I• Metaphase I• Anaphase I• Telophase I

• Meiosis II• Prophase II• Metaphase II• Anaphase II• Telophase II

1st division of meiosis separates homologous pairs

2nd division of meiosis separates sister chromatids*just like mitosis*

DNA replication

HOMOLOGOUS CHROMOSOMES

• Paired chromosomes• Both chromosomes carry a pair of genes

• Control same inherited characters• Homologous = same information

Chromosome 17

SPINDLE FIBERS AND CHROMOSOME MOVEMENT

LEARNING TARGET 5I C A N C O M PA R E A N D C O N T RA S T M I T O S I S , M E I O S I S I A N D

M E I O S I S I I .

MITOSIS VS. MEIOSIS I VS. MEIOSIS II

LEARNING TARGET 6I C A N E X P L A I N H O W I N D E P E N D E N T A S S O R T M E N T , C R O S S I N G O V E R A N D R A N D O M F E R T I L I Z A T I O N C O N T R I B U T E T O G E N E T I C V A R I A T I O N I N S E X U A L LY R E P R O D U C I N G

O R G A N I S M S .

INDEPENDENT ASSORTMENT

• Random orientation of homologues at metaphase plate during metaphase I

• Independent assortment in humans produces 223 (8,388,608) different combinations

CROSSING OVER

• During Prophase I• Homologous pairs swap pieces of chromosome• Sister chromatids intertwine and cross over each other• Breakage and re-fusing of DNA• Creates completely new combinations of traits in the next

generation

RANDOM FERTILIZATION

• Random ovum fertilized by a random sperm• Any 2 parents will produce a zygote with over 70

trillion (223 x 223) diploid combinations

LEARNING TARGET 7I C A N E X P L A I N W H Y H E R I TA B L E VA R I AT I O N I S C R U C I A L T O D A RW I N ’ S T H E O RY O F E V O LU T I O N BY N AT U RA L S E L E C T I O N .

SEXUAL REPRODUCTION CREATES VARIABILITY

• Allows us to maintain both genetic similarity and differences

• Why is this significant to evolution by natural selection?