CELLULAR REPRODUCTION This is the making of cells --not necessarily making babies HEY YOU WANNA SPLIT? Ok!

Why do Cells Divide? 1. maintain surface area to volume ratio 2. growth of organism 3. repair damaged areas 4. replace worn out cells 5. pass on genetic information

2 Forms of Cellular Division Asexual Reproduction Sexual Reproduction

Asexual Reproduction production of new cells from one parent cell offspring cells identical to parent cell can make new cells or an entire organism

Asexual production of whole organisms 1. BINARY FISSION -cell divides into two equal cells -occurs in bacteria and blue-green algae and paramecia 2. SPORES -groups of cells form inside parent -cells burst out of parent and grow into new organisms -occurs in fungus and ferns

3. BUDDING -division into two unequal parts -smaller cell will then grow to size of parent -occurs in fungus (yeast) and hydras 4. VEGETATIVE PROPAGATION -part of the parent will break off and grow into a completely new organism -common in plants (spider plants, potatoes)

Asexual reproduction for growth, repair, and replacement of cells Terms To Know CHROMOSOME: structure that contains the DNA CHROMATIN: thin, stringy form of DNA where the molecule is relaxed and unwound into thread-like fibers

CENTROMERE: the point where sister chromatids are connected CHROMATID: the tightly wound, visible form of a chromosome SISTER CHROMATIDS: 2 identical chromosomes, the original and its copy Chromosome Structure

How many chromosomes do we have? 46- (23 pairs)- called the diploid number (2n=46) Where did these come from? Each Pair= 1 from mom & 1 from dad

Asexual reproduction for growth, repair, and replacement of cells Cells go through a cell cycle Then……… Cells split to form new cells and maintain chromosome number

BRAINTEASER If each cell has 46 chromosomes, what has to happen each time before a cell divides?

The Cell Cycle

Interphase stage of growth / preparation for division lasts about 21 hours DNA in Chromatin form 3 stages: G1, S, G2

Stages of Interphase G1- period of growth / development S (synthesis) duplicates DNA (chromosomes) –still in chromatin phase G2 duplicates cytoplasm and organelles

HOW DO CELLS DIVIDE? Answer= MITOSIS

Mitosis completes the cell cycle Prophase Metaphase Anaphase Telophase Cytokinesis

Prophase chromosomes become visible chromatids sister chromatids form (seen as X) microtubules form from a spindle at opposite ends of the cells spindle arises from centrioles nuclear envelope disappears

By the end of prophase… microtubules have attached to centromeres sister chromatids being pulled toward center of cell

Metaphase microtubules pull chromatids to center chromatids align along the center of cell

Anaphase Chromosomes split at centromeres microtubules pull apart chromosomes Chromosomes (chromatids) begin migrating to opposite ends of cell

Telophase Chromatids arrive at poles nuclear envelope reforms around chromatids chromatids unwind into chromatin spindle disintegrates cell membrane begins forming in center

Cytokinesis cell membrane finishes splitting the cell 2 daughter cells are formed cells will be slightly smaller than parent cell

TELOPHASE PROPHASE ANAPHASE METAPHASE nucleus cytoplasm one spindle pole one of the condensed chromosomes spindle equator microtubules organized as a spindle apparatus Plant Mitosis INTERPHASE

Animal Mitosis

METAPHASEANAPHASETELOPHASE INTERPHASE Fig. 9.5b, p. 153

Sexual Reproduction Key Facts sex cells are formed – called Gametes (Meiosis) fertilization results in offspring offspring exhibits traits of both parents

Points of Interest all cells contain 2 of each chromosome- 1 from mom and 1 from dad each of the pair carries identical genes variation exists in the outcome of the genes –example: eye color humans have 46 chromosomes (23 pairs) 22 pairs are called autosomes The 23 rd pair is the sex chromosomes (X and Y) Males= XY Females= XX

More Terms DIPLOID: the total number of chromosomes a species carries –often abbreviated as 2n –found only in parent cells HAPLOID: half the number of chromosomes for a species –often abbreviated as n –found in sex cells (egg/sperm) formed from meiosis

HOMOLOGOUS CHROMOSOME: 2 chromosomes which are the same (1 from mom 1 from dad) –Both found in diploid cells –often described as “homologues” GAMETE: the sex cell formed from meiosis –haploid condition –egg or sperm

MEIOSIS begins with the cell cycle 2 Phases –MEIOSIS I –MEIOSIS II Occurs only in Gonads- testes and ovaries Remember-Mitosis occurs in all other Somatic (body) cells Reduces the number of chromosomes by half

Interphase a stage of growth and preparation for division of nucleus DNA is in Chromatin form 3 stages: G1, S, G2 the DNA(chromosomes) does double

MEIOSIS I very similar to Mitosis stages include –Prophase I –Metaphase I –Anaphase I –Telophase I –Interkinesis**

Prophase I chromatin shortens and thickens into chromatids (sound familiar?) since there are 2 of each chromosome, the 2 homologous chromosomes pair up to form a TETRAD *(does not happen in Mitosis)

Brain Teaser You are the world’s leading tomato researcher. You have located the gene in a tomato’s DNA that produces lycopene, a natural chemical that helps fight heart disease. The gene is on chromosome 10. If a tomato has a diploid # (2n) of 24, how many tetrads will you have to search through during prophase 1 until you locate chromosome 10?

Metaphase I the tetrads will align along the center- similar to mitosis Different arrangements can be formed- see example on board

Anaphase I the tetrads break one of each chromosome and its sister chromatid will remain attached the sisters will migrate toward the poles

Telophase I cytoplasm will separate as in Mitosis the sisters remain attached at the centromere chromatids do not relax into chromatin

Interkinesis the DNA is not duplicated this is a period between 2 phases each cell has completed the first division each cell is haploid (n)

then…MEIOSIS II similar steps occur again except the cell is going to split the sister chromatids into two sets *no Interphase II stages include –Prophase II –Metaphase II –Anaphase II –Telophase II –Cytokinesis

but... in Anaphase II, the sister chromatids are split apart one of each migrates to opposite poles during Telophase II, the nucleus forms around the chromosomes (chromatids) chromatids relax into chromatin

Cell Division has finished the “daughter” cells produced are in the haploid condition 1 cell has now produced 4 haploid daughter cells they need to be finished

Formation of the Egg and Sperm In Females- OOGENESIS - formation of the egg –1 cell makes 4 daughter cells –only 1 daughter becomes the egg –cell division is not equal -3 become POLAR BODIES –all will be haploid

SPERMATOGENESIS - formation of sperm –1 cell makes 4 equal sized daughter cells –all 4 will be sperm –all will be haploid

Fertilization is not part of cell division occurs when an egg and sperm meet a ZYGOTE forms from the meeting the zygote is 2n- chromosomal number is restored

Function of Fertilization produces new offspring introduces mutations for survival increases variation in a population

Twins 2 Types Identical- always same sex- after being fertilized, zygote splits spontaneously and both begin dividing (MONOZYGOTIC) –Identical DNA Fraternal- 2 eggs are present to be fertilized- can be same or different sexes- appear different because DNA is different (DIZYGOTIC)