1. Cellular Reproduction
Chapter 8
Winter 2015
Aultman

2. What Cell Reproduction Accomplishes
Production of new cells
“Daughter” cells are identical to each other and to their “Parent”
Chromosomes are duplicated and divided among the two daughters
A few genes are found in DNA in mitochondria and chloroplasts
Replaces damaged or lost cells
Permits growth
Increase in the number of cells
Allows for reproduction
Single-celled organisms – simple cell division
Multi-celled organisms – asexual or sexual

3. Sexual & Asexual Reproduction
Sea stars can grow new individuals from fragmented pieces
Growing a new plant from a clipping
Growth and maintenance of multicellular organisms
the lone parent and its offspring have identical genes
Sexual Reproduction
Two parents, each produces gametes (e.g. egg and sperm)
Offspring are a combination of the two genomes

4. Chromosomes most genes are located on chromosomes in the cell nucleus*
#/cell depends on the species
Chromosomes are
made of chromatin, fibers composed of roughly equal amounts of DNA and protein molecules and
not visible in a cell until cell division occurs
DNA in a cell is packed into an elaborate, multilevel system of coiling and folding
Histones are proteins used to package DNA in eukaryotes
Nucleosomes consist of DNA wound around histone molecules

5. Chromosome Duplication
results in two copies called sister chromatids containing identical genes
Two sister chromatids are joined together tightly at a narrow “waist” called the centromere
When the cell divides, the sister chromatids of a duplicated chromosome separate from each other
Once separated, each chromatid is
considered a full-fledged chromosome and
identical to the original chromosome

6. Cell Cycle A cell cycle is the ordered sequence of events that extend
from the time a cell is first formed from a dividing parent cell
to its own division into two cells
consists of two distinct phases:
interphase and
the mitotic phase
Most of a cell cycle is spent in interphase
performs its normal functions,
doubles everything in its cytoplasm, and
grows in size.

7. Mitosis Mitosis consists of four distinct phases: Figure 8.7, p 126
Prophase:
Chromosome duplication and thickening;
Mitotic Spindle Forms: football shaped structure of microtubules, guides the separation of two sets of daughter chromosomes
Metaphase: chromosomes line up along a central point
Anaphase: sister chromatids separate and move toward opposite poles
Telophase: nuclear membranes re-form; chromosomes uncoil

8. Cytokinesis Generation of two daughter cells Animal cells Plant cells
begins during telophase
divides the cytoplasm
different in plant and animal cells
Animal cells
known as cleavage
begins with the appearance of a cleavage furrow, an indentation at the equator of the cell
Plant cells
vesicles containing cell wall material collect at the middle of the cell
they fuse, forming a membranous disk called the cell plate

9. Cancer Cells: Growing Out of Control
Normal plant and animal cells have a cell cycle control system that consists of specialized proteins, which send “stop” and “go-ahead” signals at certain key points during the cell cycle
Cancer
a disease of the cell cycle
Involves mutations of one or more regulatory sites
Cancerous cells
Can form (solid) tumors or tumors
Benign: cells remain at their original site; grow slowly
Malignant: grow rapidly and often spread from their initial site through metastasis
Interrupt or interfere with normal body functions

10. Cancer Treatment May involve
radiation therapy, which damages DNA and disrupts cell division
chemotherapy, the use of drugs to disrupt cell division or target specific mutant genes
Surgery to remove the tumor

11. Meiosis Sexual Reproduction Homologous Chromosomes Depends on meiosis
offspring contain a unique combination of genes from the parents
All individuals of a single species have the same # and type of chromosomes
Homologous Chromosomes
matching pairs of chromosomes
can possess different versions (alleles) of the same genes
Human somatic cell has 46 chromosomes, 23 pairs
22 pairs of autosomes and 1 pair of sex chromosomes
XX or XY

12. Life Cycle of Sexual Organisms
Figure 8.12, page 131
the sequence of stages leading from the adults of one generation to the adults of the next
Fertilization results in a new zygotic cell that has one set of chromosomes from each parent
Offspring are unique, and not identical to either parent
Mitosis and cellular differentiation allow the zygote to grow into an adult

13. Meiosis Halves the Chromosome Number
Figure 8.13 Page 131; Figure 8.14 page
Somatic (body) cells are diploid: contain two sets, or one pair of each of the chromosomes; undergo mitosis
Reproductive cells undergo meiosis produce gametes that have only one chromosome of each type
Interphase
Each chromosome in a diploid cell is duplicated; 4 copies of each chromosome
Meiosis I
Homologous chromosomes separate
Results in return to 2x status
Meiosis II
Cells divide again
Each gamete 4 gametes, each with 1 copy of each chromosome
In humans: 22 autosomes and one sex chromosome

14. Genetic Variation
Offspring of sexual reproduction are genetically different from their parents and one another
Independent Assortment of Chromosomes
When aligned during metaphase I of meiosis, the side-by-side orientation of each homologous pair of chromosomes is a matter of chance
Every chromosome pair orients independently of all of the others at metaphase I
For any species, the total number of chromosome combinations that can appear in the gametes due to independent assortment is 2n, where n is the haploid number.
Humans: n=23; 8,388,608 different chromosome combinations possible in a gamete

15. Random Fertilization
A human egg cell is fertilized randomly by one sperm, leading to genetic variety in the zygote
If each gamete represents one of 8,388,608 different chromosome combinations, at fertilization, humans would have 8,388,608 × 8,388,608, or more than 70 trillion different possible chromosome combinations
Crossing Over
nonsister chromatids of homologous chromosomes exchange corresponding segments and
genetic recombination, the production of gene combinations different from those carried by parental chromosomes, occurs.

16. When Meiosis Goes Awry
mistakes can result in genetic abnormalities that range from mild to severe
Errors may alter chromosome number
Nondisjunction
Members of a chromosome pair fail to separate at anaphase
gametes have an incorrect number of chromosomes: 2n+1
Down Syndrome: An Extra Chromosome 21

17. Evolution Connection: The advantages of sex
Asexual reproduction conveys an evolutionary advantage when plants are
sparsely distributed and unlikely to be able to exchange pollen or
superbly suited to a stable environment.
Asexual reproduction also eliminates the need to expend energy
forming gametes and
copulating with a partner.
Sexual reproduction may convey an evolutionary advantage by
speeding adaptation to a changing environment or
allowing a population to more easily rid itself of harmful genes

18. Biology & Society: Komodo Dragons