Biology

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binary fission

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chromosome replication begins

one copy of the region moves to other end

replication finishes, plasma membrane grows inward and new cell wall is deposited

2 daughter cells result

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chromatin

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dna molecule

visible before division

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somatic cells

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46 chromsomes or two sets of 23

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gametes

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sperm and egg cell

have half as many chromosomes ad somatic cells

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genome

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complete dna sequence for an organism; contains complete set of instructions for organism

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chromosome when cell is not dividing

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in form of long, thin chromatin fiber

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chromosome after duplication

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chromosomes condense; each chromatin fiber becomes coiled and folded, making them shorter and thicker.

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eukaryotic cell cycle

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interphase+mitosis+cytokinesis

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interphase

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G1 phase

S phase

G2 phase

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where does most of the cellular growth occure in the eukaryotic cell cycle?

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G1 phase

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what happens in G2

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cells are preparing to enter cell division

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what is mitosis

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cell division

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cytokinesis

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splitting of cytoplasm

two separate cells

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prophase

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chromatin condense forming chromosomes

sister chomatids are joined at centromere

microtubules bind to kinetochore

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outcome of prophase

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nuclear membrane dissapears

nucleoli have disinegrated

sister chromatids are attached by kinetochores to microtubules from opposite poles

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mitotic spindle

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fibers of microtubules and proteins

assembly starts at centrosome

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metaphase

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chromosomes line up in the midplane of cell

chromosomes are highly condensed

2 types of microtubules(kinetichore and polar)

mitosis checkpoint

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anaphase

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sister chromatids seperate and are moved toward opposite poles

protein tethers at centromere bw the chromatids are broken

each sister chromatid can now be called a chromsome

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what does anaphase assure?

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that each daughter cell recieves one of the duplicate sets of chromosomes

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prometaphase

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some spindle microtubules attach to the kinetochores

motor proteins move the chromosomes towards the poles

kinetochore microtubules shorten behind moving chromomes

polar micro. lengthen

motor proteins on polar micro. push chrom. apart

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telophase

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essentially the reverse of prophase

mitotic spindle disinigrates; chromosomes decondense; nuclear membranes reform.

nucleoli reappear.

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cytokinesis in animal cells

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cleavage furrow.

begins in telophase

2 daughter cells form.

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cytokinesis in plant cells

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cell plate.

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cell plate

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developed from vesicles originated from the golgi

grow until reaches plasma membrane and then cells separate

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cell cycle

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events leading to replication of cells

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cell cycle control system

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cell-cycle checkpoints

genes encode molecules involved

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cell cycle checkpoints

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ensure all events of a particular stage have been completed before next stage begins

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key checkpoints in cell cycle

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G1-S checkpoint

G2-M checkpoint

metaphase-anaphase checkpoint(spindle checkpoint)

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meiosis (sexual reproduction)

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2 parents

genetic variation

adaptation to changing enviroments

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homologou chromosomes

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paired

similar shape size and centromere position

genetic info. for same traits

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ploidy

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number of sets of chromosomes in a cell

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haploid

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one set

gametes: egg and sperm

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autosome

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chromosome other than sex

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fetilization

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union of gametes to form zygote

diploid number is restored in fertilized egg

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polyploidy

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3n or more

rare in animals; mostly fatal in human

common in plasnts

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mitosis vs meiosis

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mitosis

-single nulcear division

-2 diploid daughter cells which are genetically identical to each other and original cell

meiosis

-diploid cell undergoes 2 nuclear divisions

-genetic rearrangement

-resulting in 4 genetically different haploid daughter cells

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meiosis

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reduces chromsome number (2n to n)

dna replicates once (interphase)

undergoes 2 divisions

four haploid nuceli

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prophase 1

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homologous chromosomes exchange segments by crossing over; nuclear envelope breaks down

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metaphase 1

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tetrad(new chromosome formed) line up in middle

tetrads held together at chiasmata (site of crossing over)

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anaphase 1

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homo. chromosomes seperate and move to opposite poles.

sister chromatids stay attached at their centromeres

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telophase 1

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one of each pair of homo. chromosomes is at each pole.

cytokinesis occurs

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prophase 2

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chromosomes condense again following brief period of interkinesis.

dna does not replicate again

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metaphase 2

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chromosomes line up along the cells midplane

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anaphase 2

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sister chromatids seperateand chromosomes move to opposite poles

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telophase 2

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nuclei form at opposite poles of each cell.

cytokinesis occurs

four haploid cells form.

animals-gametes

plants-spores

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synapsis

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during prophase 1

homologous chromosomes line up and become connected by a zipper like protein called synaptonemal complex

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crossing over

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occurs in prophase 1

enzymes break down and rejoin DNA molecules allowing paired homo chromosomes to exchange genetic material.

produces new combinations of genes(genetic recombination)

major source of genetic variation

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meitotic tetrad with 2 chiasmata

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metaphase 1

the 2 chiasmata are the result of seperate crossing over events

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chiasma

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location where two homologous chromatids previously crossed over

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genetic variations

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independent assortment

crossing over

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independent assortment

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maternal and paternal chromosomes of homo pairs seperate independently at anaphase 1

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crossing over

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exchange of DNA segments between maternal and paternal homo chromo. during prophase 1

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animal life cycles

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gametes-fertilization-zygote-multicellular diploid organism-meisis-gametes...

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gameteogenesis

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formation of gametes(meiosis)

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spermatogenesis

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male gametogenesis

4 haploid sperm cells per cell

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oogenesis

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female gametogenesis

one egg cell per cell

polar bodies

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trisomy 21

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down syndrome

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histones

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positively charged proteins in cell nucleus that connect to the negatively charger DNA

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nucleosomes

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repeating units of chromatin structure; each consisting of a length of DNA wrapped around a complex of 8 histone molecules.

adjacent nucleosomes are connected by a DNA linker region associated with another histone protein.

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Mendle's principle of inheritance

1860s

heredity

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heritable factors: now genes

transfer of characteristics (traits) from parent to offspring

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genetics

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the science of heredity and variation in living organisms

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gregor mendel

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father of modern genetics

used pea plants to study inheritance of traits

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P generation(P1)

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parental generation

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F1 generation

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first generation

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F2 generation

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second generation

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phenotype

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physical appearance of an organism with respect to a specific trait

or

expression of an organisms genes

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genotype

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genetic makeup of an organism

combination of alleles

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gene

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segment of DNA that serves as a unit of heredity

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locus (loci)

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location of a particular gene on a chromosome

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alleles

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alternative versions of a gene

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dominant allele

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dominates over others

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recessive allele

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no phenotypic expression in the presence of a dominant allele

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homozygous alleles

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pair of identical alleles

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heterozygous

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having a pair of unlike alleles

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hybrid

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result of pure lines crossed

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monohybrid cross

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cross between individuals that are both heterozygous for the gene that you are following

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mendel's hypothesis or model

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1. alleles account for variation in inherited characteristics

2. for each trait, an organism inherits 2 alleles; one from each parent

3. alleles: dominant is expressed over recessive

4. law of segregation

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law of segregation

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during segregation of chromosomes in anaphase (meiosis) gametes only carry one allele for each inherited trait

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monohybrid cross results

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3:1 phenotype(color) ratio

1:2:1 genotype(allele) ratio

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test cross

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reveals the genotype of the dominant parent, or at least give some idea of the probable genotype

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mendel's law of independent assortment

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dihybrid cross

meiosis 1

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dihybrid cross

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individuals are both heterozygous for 2 different traits phenotype ratios of 9:3:3:1

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varitaions on mendel's laws

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1. incomplete dominance

2. codominance

3. multiple alleles

4. pleiotrophy

5. gene interactions

6. polygenic inheritance

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incomplete dominance

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heterozygote with intermediate phenotype between the 2 homozygous parents

dominance has no true meaning here

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codominance

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the heterozygote expresses characteristics of both alleles

each allele is distinctly expressed

example: ABO human blood type

three alleles of a single gene type

mutliple alleles

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pleiotrophy

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single gene locus

many variations

affects many aspects of the phenotype: multiple characteristics(traits)

seen with many diseases(sickle cell disease)

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gene interactions

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two or more genes interact to produce a novel (new) phenotype

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epistasis

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type of gene interaction

one gene influences the phenotype that is controlled by the second gene

preventing or masking any effects of alleles at the second gene

no novel phenotype is produced here

one gene is dependent on the presence of one or more modifier genes

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albinism

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epistatic

dominant allele expresses pigment of skin colr; homozygous recessive, masks the expression of pigment, regardless how many other alleles are present(even dominant)

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polygenic inheritence

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two or more genes have additive effects on a single characteristic

they usually are measured traits(quantitative)

--height, skin color, body form

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sex chromosomes

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all individuals require an X

X-female

Y- determines male

X and Y are not true homologous

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in male, X from mother contains what?

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active genes

male is neither homo or heterozygous

said to be hemizygous

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pure breeding plants make up the

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P1 generation

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when mendel crossed true breeding tall plants with true breeding short, the offspring were the...

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F1 generation

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homologous

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corresponding chromosomes from the opposite-sex parent

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independent assortment

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alleles of unlinked loci are randomly distributed to gametes

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karyotype

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chromosomal composition of an individual

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haploid

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one set of chromosomes per nucleus

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diploid

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two sets of chromosomes per nucleus

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fredrick griffith

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discovered genetic role of DNA in 1928

mice experiment

called it transformation

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mice experiment

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2 strands of bacteria: S-caused disease(pathogenic), R-not cause disease(non-patho.)

mice injected with S die, injected with R survive.

kills pathogenic bacteria with heat and mix its parts with living nonpathogenic bacteria and then injects it back into mice.

some of mice die

finds living S cell in the blood.

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transformation

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change in genotype and phenotype due to the assimilation of external DNA by the cell.

found in mice experiment

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bacteriophage

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virus that infects and kills bacteria; made of essentially DNA and protein.

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james watson and francis crick 1953

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molecular model for DNA

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DNA replication

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making copies of itself

happens in interphase, specifically S phase

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mechanism of DNA replication

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1.helical DNA must first untwist

2.copies its new strands

3.semiconservative

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semiconservative

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each strand works as a template for making a complementary strand

results in 2 new DNA molecules:

each one has old strand from parent molecules and a newly synthesized strand

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where does it begin on the double helix?

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origin of replication: forking point

both directions

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why can new strand only grow in the 5' to 3' direction?

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the daughter strand can be synthesized in one continuous piece by a DNA polymerase working from the 3 prime end

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anzymes add_________to a growing strand.

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nucleotides

-DNA polymerase

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how is the other strand made?

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new daughter strand is synthesized in short pieces as the fork opens up.

another enzyme called DNa ligases links the pieces together into a single DNA strand.

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lagging strand

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3' to 5' forms discontinuously

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Okazaki fragments

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short seperated DNA fragments (100-2000 nucleotides)

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leading strand

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grows continuously 5'-3' end of the old strand

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DNA ligase

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joins leading and lagging strands of DNA

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DNA polymerase

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fixes most mistakes

removes incorrect nucleotide and replaces it with the correct one

DNA repair

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mismatch repair system

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mistakes not removed by DNA poly. but by special enzymes that recognize the mistake and remove it; DNA poly. then fills in the correct nucleotide.