Asexual Reproduction

Single parent – complete copy of DNA Offspring is identical to parent Prokaryotes Advantages: Disadvantages:

Types of Asexual Reproduction Binary fission – Fragmentation – Budding – Parthenogenesis -

Sexual Reproduction

Eukaryotes Two parents give genetic material to produce offspring that are genetically different from parents Gamete – Zygote – Germ cell – Somatic cell – Advantages /disadvantages of sexual reproduction

Chromosome Number Each chromosomes contains thousands of genes that control development and function of organisms. Humans have _____ (diploid) Mom gives ____ and Dad gives ____ (haploid) Chromosome reduction is MEIOSIS! Meiosis means reduction division – halves the number of chromosomes Diploid – 2n (human 2n=46) Haploid - n (human n=23)

Homologous Chromosomes Homologous chromosomes – similar in size, shape, and genes. A diploid cell contains pairs of chromosomes made up of two homologous chromosomes. One set comes from mom, and one set comes from dad.

Autosomes and Sex Chromosomes Autosomes – DO NOT determine sex of individual Sex Chromosomes – DETERMINE sex of individual MALE – XY (Mom donates the X, father donates the Y) FEMALE – XX (Mom donates the X, Father donates the other X)

Sex Chromosomes XX chromosome - female XY chromosome - male 9

Karyotype (Human)  Aorganized picture arranged in pairs by size  An organized picture of the chromosomes of a human arranged in pairs by size from largest to smallest.  P1-22 AUTOSOMES  Pairs 1-22 called AUTOSOMES  LSEX CHROMOSOMES  Last pair are SEX CHROMOSOMES 10 Male - XY

Human Chromosomes

Karyotype 12 Female - XX

Gamete Production

Interphase I mitosis  Similar to mitosis interphase.  CHROMOSOMES (DNA) S phase  CHROMOSOMES (DNA) replicate in the S phase chromosometwo identical SISTER CHROMATIDS CENTROMERES  Each duplicated chromosome consist of two identical SISTER CHROMATIDS attached at their CENTROMERES.  CENTRIOLE  CENTRIOLE pairs also replicate. 14

Interphase I visible  Nucleus and nucleolus visible. Nucleus nucleolus cell membrane chromatin 15

Meiosis Similar in many ways to mitosis Similar in many ways to mitosis Several differences however Several differences however Involves 2 cell divisions Involves 2 cell divisions Results in 4 cells with 1/2 the normal genetic information. Results in 4 cells with 1/2 the normal genetic information. Vocabulary: Vocabulary: Diploid (2N) - Normal amount of genetic material Diploid (2N) - Normal amount of genetic material Haploid (N) - 1/2 the genetic material. Haploid (N) - 1/2 the genetic material. Meiosis results in the formation of haploid cells. Meiosis results in the formation of haploid cells. In Humans, these are the Ova (egg) and sperm. In Humans, these are the Ova (egg) and sperm. Ova are produced in the ovaries in females Ova are produced in the ovaries in females Process is called oogenesis Process is called oogenesis Sperm are produced in the testes of males. Sperm are produced in the testes of males. Process is called spermatogenesis Process is called spermatogenesis Meiosis occurs in 2 phases: Meiosis 1 & Meiosis 2 Meiosis occurs in 2 phases: Meiosis 1 & Meiosis 2

Meiosis I (four phases)  Cell division chromosome number one-half.  Cell division that reduces the chromosome number by one-half.  Four phases  Four phases: a.Prophase I b.Metaphase I c.Anaphase I d.Telophase I 17 Prophase I

 Longest and most complex phase (90%).  Chromosomes  Chromosomes condense.  SynapsisHomologous chromosomes tetrad  Synapsis occurs - Homologous chromosomes come together to form a tetrad.  Tetrad two chromosomes four chromatids  Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids). 18

Non-Sister Chromatids- HOMOLOGS 19 Homologs contain DNA that codes for the same genes, but different versions of those genes Genes occur at the same loci

Meiosis I. Prior to division, amount of DNA doubles Prior to division, amount of DNA doubles

Overview of Meiosis

Prophase 1 During prophase 1 homologous chromosomes line- up along the metaphase plate During prophase 1 homologous chromosomes line- up along the metaphase plate Areas of homologous chromosomes connect at areas called chiasmata Areas of homologous chromosomes connect at areas called chiasmata

Crossing Over Segments of homologous chromosomes break and reform at similar locations. Segments of homologous chromosomes break and reform at similar locations. Results in new genetic combinations of offspring. Results in new genetic combinations of offspring. This is the main advantage of sexual reproduction This is the main advantage of sexual reproduction

Non-Sister Chromatids- HOMOLOGS 24 Homologs contain DNA that codes for the same genes, but different versions of those genes Genes occur at the same loci

Genetic Recombination nonsister chromatids chiasmata: site of crossing over variation Tetrad 25

Metaphase I Shortest phase Tetrads align on the equator. Independent assortment occurs – chromosomes separate randomly causing GENETIC RECOMBINATION 26

Metaphase I Homologs line up at equator or metaphase plate OR 27

Question:  In terms of Independent Assortment -how many different combinations of sperm could a human male produce? 28

Answer  Formula: 2 n  Human chromosomes:2n = 46  n = 23  2 23 = ~8 million combinations 29

Anaphase 1 During anaphase 1, each homologous chromosome is pulled to opposite sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT BREAK. During anaphase 1, each homologous chromosome is pulled to opposite sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT BREAK. Nuclei may or may not reform following division. Nuclei may or may not reform following division. Cytokenesis may or may not occur. Cytokenesis may or may not occur.

Telophase I haploid chromosomes  Each pole now has haploid (1n) set of chromosomes.  Cytokinesis  Cytokinesis occurs and two haploid daughter cells are formed. 31

Telophase I 32 cytokinesis

Meiosis II DNA does not double DNA does not double Chromosomes randomly line-up along metaphase plate like regular mitosis. Chromosomes randomly line-up along metaphase plate like regular mitosis. During anaphase 2, CENTROMERES BREAK and each chromosome is pulled to opposite sides of the cell. During anaphase 2, CENTROMERES BREAK and each chromosome is pulled to opposite sides of the cell. Nuclei reform and cytokenesis usually occurs (although it is often unequal). Nuclei reform and cytokenesis usually occurs (although it is often unequal).

Telophase I haploid chromosomes  Each pole now has haploid (1n) set of chromosomes.  Cytokinesis  Cytokinesis occurs and two haploid daughter cells are formed. 34

Telophase I 35 cytokinesis

Meiosis II  No Interphase II or very short  **No DNA Replication  Remember: Meiosis II is similar to mitosis 36

Prophase II  Same as Prophase in mitosis  Nucleus & nucleolus disappear  Chromosomes condense  Spindle forms 37

Metaphase II Same as Metaphase in mitosis Chromosomes (not homologs) line up at equator 38

Anaphase II Anaphasemitosis  Same as Anaphase in mitosis  **SISTER CHROMATIDS separate 39

Telophase II  Same as Telophase in mitosis.  Nuclei and Nucleoli reform, spindle disappears  CYTOKINESIS occurs.  Remember: FOUR HAPLOID DAUGHTER cells are produced.  Called GAMETES (eggs and sperm) 40 1n Sperm cell fertilizes 1n egg to form 2n zygote

Telophase II 41

42

Variation  Also known as GENETIC RECOMBINATION  Important to population as the raw material for NATURAL SELECTION.  All organisms are NOT alike  Strongest “ most fit” survive to reproduce & pass on traits 43

Question:  What are the 3 sources of genetic recombination or variation? 44

Answer: 1. CROSSING OVER (prophase I) 2. INDEPENDENT ASSORTMENT (metaphase I) 3. RANDOM FERTILIZATION 45

Question: 20 chromosomes (diploid) chromosomes  A cell containing 20 chromosomes (diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes? 46

Answer:  10 chromosomes (haploid or 1n) 47

Haploid Diploid

Meiosis and Gamete formation Oogenesis Ovum and 3 polar bodies Un-equal distribution of the cytoplasm Spermatogenesis 4 sperm

Meiosis GAMETES (sperm or egg)  Sex cells divide to produce GAMETES (sperm or egg). HALF  Gametes have HALF the # of chromosomes. GONADS (testes or ovaries).  Occurs only in GONADS (testes or ovaries).  Male: SPERMATOGENESIS - sperm  Female: OOGENESIS - egg or ova 50

Spermatogenesis 2n=46 human sex cell diploid (2n) n=23 Meiosis I n=23 sperm haploid (n) Meiosis II 51

Oogenesis 2n=46 human sex cell diploid (2n) n=23 Meiosis I n=23 egg Haploid (1n) Meiosis II 52 Pol ar Bod ies (die )

Spermatogenesis & Oogenesis Egg/Ova 4 sperm

University of Arizona Biology Page iosis/main.html iosis/main.html Cell’s Alive

Karyotype 55 Female - XX

Fertilization spermegg zygote  The fusion of a sperm and egg to form a zygote. FERTILIZED EGG  A zygote is a FERTILIZED EGG n=23 egg sperm n=23 2n=46 zygote 56

Question: 40 chromatids chromosomes  A cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?  (Tricky! Think!) 57

Answer:  10 chromosomes 58

Multicellular Life Cycles LIFE CYCLE – events in the growth and development of an organism until it reaches sexual maturity. Most animals have a DIPLOID LIFE CYCLE During meiosis, germ cells undergo meiosis to produce haploid gametes. Fertilization – joining of 2 haploid cells to form a zygote which then undergoes mitosis to grow and develop into a new organism.

Haploid Life Cycle

Alternation of Generations