Cell Cycle:

Reason for Division

• As cells increase in volume, the surface area decreases and demand for material resources increases which limits surface size.

Cell Cycle:

Surface Area to Volume

Ratio

Smaller cells have a more favorable surface area to volume ratio for exhange of materials with the environment (diffusion, etc.).

High surface area is favorable.

Ex. 6:1 is better than 6:5

Cell Cycle:

Cell cycle switches between...

Cell Cycle:

Interphase has 3 phases

1. Growth (G1)
2. Synthesis of DNA (S)
3. Preparation for mitosis (G2)

Cell Cycle:

During mitosis, what

are spindle fibers

responsible for?

During mitosis duplicated chromosomes line up in the center with spindle fibers attached to help pull them apart.  

Duplicated chromosomes are pulled apart by spindle fibers.

Cell Cycle:

Cytokinesis

the division of cytoplasm and

reformation of cell membrane

Animal cell - pinches in (cleavage) using microfilaments

Plant cell - form cell plate reforms cell wall

Cell Cycle:

Checkpoints

Checkpoints are internal controls that direct the cell cycle.

Internal (enzymes and promoting factors) and external signals (growth factors) provide stop and go signs at the checkpoints

Example: Mitosis-promoting factor (MPF)

Cell Cycle:

Cancer

• Cancer results from disruptions in the cell cycle control 
• too much division, defective tumor suppressor genes, overactive genes
• disruptions are a result of DNA damage to proto-oncogene (regulatory gene)
• which makes products such as cyclins and cyclin-dependent kinases (CDKs)

Cell Cycle:

Cells spend different amounts of time in interphase or division.

Nondividing cells may exit the cell cycle

OR

hold at a particular stage in the cell cycle.

Cell Cycle:

Mitosis is used for ... 

Animals use mitosis

for growth and repair.

Plants use mitosis to

make gametes and

for growth and repair.

Cell Cycle:

Mitosis usually beins with one cell...

Makes 2 identical cells or clones

Maintains chromosome number

1n -> 1n   Or   2n -> 2n

Cell Cycle:

Meiosis

Meiosis occurs after interphase.

It takes diploid cells and reduces the chromosome number to haploid.  2n -> 1n

Cell Cycle:

Homologous Chromosomes

During meiosis, homologous chromosomes are paired (one from mom and one from dad) and line up in the center of the cell randomly.  The homologues are pulled apart and separated in meiosis I.

A second division occurs in which the duplicated chromosomes are pulled apart.

Cell Cycle:

Variation

Mendel's Laws:

Law of Dominance

One allele will be expressed over another

Ex. Aa -> If big A is purple, it will be seen over little a which is white.

Mendel's Laws

Mendel's Laws:

Law of Segregation

Mendel's Laws:

Law of Independent Assortment

Alleles assort independently during meiosis IF they are on separate chromosomes

(i.e. AaBb can make gametes AB, Ab, aB, or ab)

Probability, Patterns, and Exceptions to Mendel's Rules:

Product Rule 

Probability, Patterns, and Exceptions to Mendel's Rules:

Autosomal vs. Sex-linked

autosomal = on a non-sex-determining chromosome

(one of the first 22 chromosomes)

sex-linked = on a sex-determining chromosome

(23^rd chromosomes)

Probability, Patterns, and Exceptions to Mendel's Rules:

Monohybrid cross

• one trait
• 3:1 ratio if Aa x Aa
• 1:1 ratio if Aa x aa
• 4:1 ratio if AA x Aa or AA x aa or aa x aa

Probability, Patterns, and Exceptions to Mendel's Rules:

Dihybrid cross

• two traits
• 9:3:3:1 genotypic ratio if AaBb x AaBb
• test cross 1:1:1:1 (AaBb x aabb)

Probability, Patterns, and Exceptions to Mendel's Rules:

Thomas Hunt Morgan

Experimented w/ fruit flies

and X-linked traits

1. Male = heterozygous XY; Y chromosome is very small in mammals and fruit flies w/ few genes
2. Female = homozygous XX
3. Single gene mutations on X chromosome cause disease such as hemophilia or colorblindness
4. Sex limited traits are dependent on sex of individual like milk production or male patterned baldness

Probability, Patterns, and Exceptions to Mendel's Rules:

Incomplete Dominance

red x white -> pink

Both protein products are expressed and blended

Probability, Patterns, and Exceptions to Mendel's Rules:

Codominance

red x white -> red and white

Both protein products are equally expressed 

Ex. type AB blood

Probability, Patterns, and Exceptions to Mendel's Rules:

Epitasis

Probability, Patterns, and Exceptions to Mendel's Rules:

Linked genes

• genes on same chromosome that are inherited together
• can be unlinked by crossing over
• Recombination frequency calculated by recombinants divided by total
• Used for chromosome mapping
• Genes farther apart cross over more often

Probability, Patterns, and Exceptions to Mendel's Rules:

Genes and their environments

• phenotypes affected by environment
• Siamese cat
• flower color w/ soil pH
• seasonal color in artic animals
• human height and weight 

Probability, Patterns, and Exceptions to Mendel's Rules:

Polygenic

• continuous variation
• many genes affect one trait
• for example height and color

Human Genetics:

Karyotype

22 pair autosomes and 1 pair sex chromosomes

46 chromosomes total

Human Genetics:

Chromosomal Mutations

(occur during gamete formation)

1. deletion, inversion, addition of genes as a result of crossing over mistakes
2. chromosomal number abnormalities
• nondisjunction is failure of chromosomes to separate at anaphase of meiosis