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Summary Genetics Unit 1
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GeneticsThe cycle of cell growth and Division
Cell division – pre-existing cell divides to form two new cells
à enables organism to grow, reproduce + repair damaged tissues + organs
- New cells required for growth, replacement of cells + repair à synthesize of proteins,
lipids + carbs à replicates nuclear DNA Cytokinesis – division of cytoplasm. à each daughter
cell (genetically identical) nucleus contains one copy of replicated parent DNA
Cell cycle – period of growth followed by nuclear division (mitosis -asexual) and cytokinesis
- Zygote – adult (sperm + egg cells)
Transmission genetics – traits controlled by genes are transmitted through gametes.
Mutant strains – used in genetic crosses to map location and distance btw genes and chromosomes
Watson-crick model of DNA – genetic info stored and expressed
Recombinant DNA tech
• foundation for human genome project (info tech+ genetics)
• early 1970’s
• discovered restriction enzymes used by bacteria to cut the DNA of invading viruses can be used to
cut any type of organism’s DNA (at specific nucleotide sequence)
• inserted DNA fragments (produced by action of restriction enzymes into carrier DNA moleculesà
Vectors à forms recombinant DNA
• genomic library – complete haploid DNA contents of specific organism
Translational medicine – genetic findings directly translated into new+ improved methods of diagnosis and
treatment
Cardiovascular disease – elevated blood levels (bad cholesterol)
à low-density lipoprotein cholesterol
PCSK9 gene identified – mutant forms = high LDL cholesterol = familial hypercholesterolemia
à proteins binds to receptors on liver cells
Artificial selection of genetic variant from wild pop (horses, camels, oxen and wolves were domesticated)
- Aristotle’s extended Hippocrates thinking à male seme contains ‘vital heat” = produces offspring of
same form
Epigenesis – organisms developed from the fertilized egg by succession of developmental events that
transforms eggs into adult.
à conflicts with theory of preformation (fertilized egg contains complete miniature adult = homunculus)
à each step of development increases complexity of feature
à under the control and influence of many genes
à mutant phenotype = heterozygous trait
Cell theory
- Matthias schleiden + Theodor schwann
- all organisms composed of basic structural units (cells) = derived from pre-existing cells
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, - spontaneous generation – creating of living organisms form nonliving components = disapproved
by louis Pasteur)
- chromosomal theory of inheritance – heredity and development dependent on genetic info
residing in genes (in chromosome) = contributed to each gamete
Products of mitosis = genetic duplicates of dividing cell -
Daughter cells = genetic copies of parent cell
1. Master program of molecular checks and balances – ensures orderly + timely progression
2. DNA synthesis replicates each DNA chromosome into 2 copies (perfect fidelity)
3. Structural + mechanical web interwoven cables + motors of mitotic cytoskeleton that separates
the replicated DNA molecules precisely into daughter cell
- Meiosis – produces some cells that are genetically different from parent cell à produces
daughter nuclei (diff – one half the no. chromosomes the parental nucleus has)
Chromosomes are genetic units that are partitioned by mitosis
- Eukaryotes
- Hereditary info in nuclear genome + distributed among multiple, linear chromosomes
- Chromosomes – single, linear, double stranded DNA mol
- Chromosomes content of
cells o Two copies (diploid
(2n))
o Homologous chromosomes – 2 chromosomes of each pair in diploid cell à
same genes in same order in DNA of chromosome
DNA – supercoiled around protein o Haploid – one
copy of each type of chromosome (n) o Ploidy number
of chromosomes sets
- Packing of DNA in chromosome o DNA packed into shorter length of histones à small (+) (basic)
proteins that are complexed with DNA in eukaryote chromosomes
o histones bind to DNA by attraction o % types of histones (H1, H2A, H2B,
H3, H14) o Nonhistone proteins
o Chromatin – complex DNA + associated proteins
o Nucleosome – two mol of H2A, H2B, H3, H4 combine to form beadlike,
eight protein nucleosome core particles
o Linker – extends between one nucleosome and the next o 10-nm
chromatin fiber – 200 base pairs of DNAs o H1 – bring next level of
chromatin packing à binds both to nucleosome + to linker DNA
o 30-nm chromatin fiber – solenoid model o Euchromatin – loosely packed
regions
o Heterochromatin – densely packed regions (visible during nuclear
division)
- DNA à mRNA à protein
- NOR (nucleolus organizer region) – portions of DNA that encode rRNA
- Endosymbiont hypothesis – theory concerning the evolutionary origin of organelles
- Karyokinesis – genetic material is partitioned into daughter cells during nuclear division
à complex and need precision
1. Exactly replicated
2. Accurately partitioned
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, -
= 2 daughter nuclei (chromosome composition identical to that of parent cell)
à followed By cytoplasmic division (cytokinesis)
• LESS COMPLEX
• Require mechanism which partitioned into 2 parts
• Encloses new cell I distinct plasma membrane
Mitotic cell division
- Sister chromatids held together tightly by sister chromatid cohesion à proteins called cohesions
encircle sister chromatids à cohesion removed + chromatids separated.
- Chromosome segregation – distribution of daughter chromosomes
- Clones – complex multicellular organism arose by mitosis from a single zygote - Grown in cell
cultures
Interphase extends from the end of mitosis to beginning of next mitosis
Stages
Interphase G1 phase
- Cell Grows
- Chromosome unduplicated with one DNA mol
- Determines whether cells divide rapidly or slowly
- Some cells stop dividing
- G0 – cells that are not destined to divide
- Internal regulatory controls ensure process is completed
S- phase
- DNA replication
- Duplication = two sister chromatids
- Unduplicated chromosome = one chromatid
- Duplicated chromosome = 2 sister chromatids (separated during M phase)
G2 Phase -
Brief gap
- 2 sister chromosomes
- Cohesins encircle each pair (aligns them tightly)
- Growth continues
- Prepares for mitosis (m-phase)
Mitosis
Prophase
- Chromosome condense into compact, rod like structures (tight alignment)
- Nucleolus becomes smaller + disappears
- Reduction RNA synthesis (centrosome has divided)
- Mitotic spindle - structure separates chromatids
- Begins to form spindle poles
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, - Sister chromatid are held together by cohesin (protein complex)
Prometaphase
- Nuclear envelope breaks down
- Microtubules attach two kinetochores of each chromosome
- Each sister chromatid has a region called the centromere (closely attached)
- Kinetochore forms on each chromatid at centromere
- kinetochore microtubules originating from spindle poles bind to kinetochores.
- Non-kinetochore microtubules – microtubules that do not attach to kinetochore.
- Cohesion degraded by enzyme (separase)
- Sister chromatids arms disjoin (except at centromere)
- Shugoshin protects cohesion from being degraded
Metaphase
- Spindle reaches final form
- Spindle microtubule moves chromosome into alignment at spindle midpoint (metaphase plate)
- Becomes aligned at spindle midpoint (held in position by opposing forces)
- Condensation complete – gives shape
- Forms karyotype of given species
Anaphase
- Enzyme (separase) activated + cleaves the cohesion rings
- Spindle separates sister chromatids + pulls them to opp poles
- Tension y spindle pulls kinetochore towards poles
- Shortest stage
- Disjunction occurs
à for complete disjunction to occur:
1. Shugoshin must be degraded reversing its protective roles
2. The cohesion complex holding the centromere of each sister chromosomes is then cleaved by
separase
3. Sister chromatids of each chromosome are pulled towards the opposite poles of the cell
=daughter chromosome
- Molecular motors us energy generated by hydrolysis of ATP = shorten spindle fibres
Telophase
- Spindle disassembles chromosomes at each spindle pole decondense
- Decondensation = nucleolus reappears
- RNA transcription continues
- New Nuclear envelopes forms
- 2 daughter nuclei (identical set of chromosomes
- Cytokinesis – division of cytoplasm
- Furrow – a groove = gridles the cell + gradually deepens + cuts cytoplasm into 2 parts
Plants – cell plate forms + grows laterally + divides cytoplasm = cell plate becomes middle lamella
- Chromosome unfolds + returns to interphase state
- G1 of following interphase = two daughter cells - genetic duplicates of parental cell that entered
mitotic division
- In animals – complete constriction of the cell membrane produces cell furrow characteristic if newly
divided cells
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