View
3
Download
0
Category
Preview:
Citation preview
Genetics ReviewPart I: Cell Division
Cell Cycle• The “life cycle” of a cell
o The M phase includes
mitosis and cytokinesis.
o Interphase accounts
for 90% of the cell
cycle.
DNA organized as chromosomes
• Before mitosis each chromosome is replicated in S phase.
o two sister chromatids
o chromatids connect at
the centromere.
• Mitosis will separate the chromatids into new cells.
Interphase
• Cell carries out its regular functions
• Grows, replicates organelles, replicates DNA
Prophase - early
• Chromatin becomes chromosomes
o sister chromatids
• mitotic spindle begins to form
o centrioles move to poles
• (animal only).
o Or Anchor to cell wall
• (plant only)
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 12.5b
Prophase – late (or prometaphase)
• Nucleus dissolves
• centrioles move to poles
• spindle attaches centromere (kinetochore) to centrioles.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 12.5c
Metaphase
• sister chromatids are all arranged at the metaphase plate.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 12.5d
Anaphase
• centromeres divide, separating the sister chromatids.
• these are pulled toward the pole.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 12.5e
Telophase• two nuclei begin to form
• DNA becomes less tightly coiled –back to chromatin.
• followed by Cytokinesis.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 12.5f
Cytokinesis in animals
• Division of the cytoplasm
• A cleavage furrow forms that pinches the cell in two
Cytokinesis in plants
• A cell plate made up of cell-wall components gradually forms in the middle of the cell.
Memory Tool• I = Rest and Replicate
• P = Appear
• M = Line up
• A = Pull apart
• T = Half and hide
**You need to be able to explain what happens with
the DNA, nuclear envelope, centrioles and spindle
fibers during each stage
Terminology
• Haploid (n) – contain one set of chromosomes (not
paired)o The 23 different kinds of chromosomes in humans
• Diploid (2n) – DNA is in homologous chromosome
form. Two sets of chromosomeso i.e., the 46 chromosomes of humans (23 pairs)
• Polyploid (more than 2n) – more than 2 sets of
chromosomes.
Cancer• Uncontrolled cell growth forms tumors
• Very little time in interphase
• Unspecialized cells – non-functional
• Metastasize as no adhesion to other cells
• A Mutation can affects the regulation of cell division
and thus uncontrolled mitosis, and cancer result
Cloning• Mitosis
• Budding (yeast)
• Vegetative propagation (plant runners)
• Identical twins (monozygotic)
• Adult stem cells e.g.: bone marrow produces blood
cells
• Embryonic stem cells from blastula inner mass are
totipotent (can produce entire organism)
• Blastula nucleus transplanted
Why form gametes (non-somatic cells)
• Diploid somatic (2n) �
Haploid Gamete (n)
• Union produces zygote
• Genetic recombination
of genes from both
parents for natural
selection
MeiosisKey Terms:� Homologous chromosomes� Tetrads� Synapsis� Crossing over� Segregation
General IPMAT & RALPHStill applies to the phases
Meiosis• Prophase 1 = crossing over
• Metaphase 1 = chromosomes line up side by side
• Only 1 interphase, no further growth or DNA
replication between Meiosis I and Meiosis II
• Meiosis 1 cells go from (2n) to (n) (still replicated in
sister chromatid form)
• Meiosis II cells go from replicated (n) to a single
copy (n)
Gametogenesis:
Nondisjunction
• Trisomy – 1 extra chromosome• Monosomy – 1 less chromosome
21
Comparison
Mitosis Meiosis
• Somatic cells
• 2 identical cells
produced
• 2n�2n or n�n
• No pairing or crossing
over of homologs
• For growth and repair
• Gonads
• 4 different cells
produced
• 2n�n
• Pairing of homologous
chromosomes
• Crossing over
• Produces gametes
Alternation of Generations• Some organisms alternate between sexual and asexual
reproduction
• You will be asked to either identify the areas of Mitosis and/or Meiosis or what structures are haploid or diploid
• Important Processes:o Fertilization = n + n → 2n
oMeiosis = 2n → n
oMitosis (maintains chromosome #)
• 2n → 2n or n → n
Genetics ReviewPart II: DNA and Molecular Genetics
DNA Structure
History• Only need to know Watson & Crick – deduced
structure of DNA (1953)
• Used x-ray diffractin pattern of Rosalind Franklin
DNA Composition
• Nucleotide = sugar, phosphate & nitrogen base
• 4 Nitrogen bases: Adenine, thymine, guanine, cytosine
• Antiparallel strands
• Sequence of bases on one strand determines sequence of other (A with T, C with G)
Base Pairing Rule
Example:• Species X has 20% Adenine in their DNA sample.
How much Cytosine do they have?
Central Dogma of Molecular Genetics….basics
• Replication
o DNA is copied (DNA→ DNA)
• Transcription
o A message is made from the DNA template (the gene is transcribed) (DNA→ mRNA)
• Translation
o mRNA is “read” and an amino acid sequence (protein) is
made (mRNA→ Protein)
DNA Replication• Each chromosome = long DNA strand, must be
replicated precisely
• During what phase of the cell cycle?
• Location?
• Enzymes involved:
o Helicase – opens DNA Strands
o DNA Polymerase – adds new nucleotides to growing strand
• Semi-conservative replication
Biotechnologies: PCR• Polymerase Chain Reaction
• Making millions of copies of a DNA sample using
laboratory equipment, heat resistant polymerase
enzyme and nucleotide supply• Cause replication to happen at a very rapid rate
• Used for DNA analysis
Transcription:• Occurs in nucleus
• One side of DNA
• DNA to mRNA
• RNA – Uracil, ribose,
single stranded
• Enzyme: RNA
Polymerase
• Amino acid chain = polypeptide chain = Protein
• Protein functions: hormones, enzymes, antibodies, structures
• Function of a protein is COMPLETELY dependent on its shape
• Shape is determined by sequence of amino acids which is determined by sequence of mRNA codons• Sequence of mRNA codons determined by base sequence of DNA in the
gene
• Defective (mutant) or missing gene = altered protein function
Translation (cytoplasm) one gene = one protein
RNA• Messenger – mRNA
• Transfer - tRNA
Process of Translation:• A ribosome moves along the mRNA, tRNAs
sequentially bring in the appropriate amino acids
which are then bonded together in a polypeptide
chain (protein)
• The tRNAs are then free to pick up another amino
acid in cytoplasm
• When ribosome reads a stop codon on the mRNA,
the amino acid chain is released as a protein and
the ribosome releases the mRNA
For the Details…
Mitochondrial DNA
• mtDNA
• Small number of bases (70 000 versus 6 billion in
genome)
• Mitochondria is from mother exclusively
• Trace lineage maternally
Mutations• Gene mutation – DNA sequence altered
• Chromosome – missing portions or entire
chromosome leads to huge alterations
• Mutagens – spontaneous error, radiation chemicals
• Types of mutations: substituition, deletion, insertion…
Types of mutations
Genetic Engineering• DNA can be artificially recombined in the lab to
have specific gene combinations and
characteristics
• Requires:
o Restriction Enzymes – cut DNA (scissors)
oDNA Ligase – glues backbone back together
• Can produce transgenic organisms that contain
foreign DNA. Why?....o Bacteria can make human proteins (insulin)
o Modify plants to withstand disease, harsh conditions
o Animals with increased growth or to serve as organ donors.
DNA
Gel Electrophoresis• Separation of DNA fragments based on size
• Restriction Enzymes cut DNA
• Apply to gel, electric current
• Smaller fragments move farther/faster
• Paternity testing, gene presence, court evidence
Genetics ReviewPart III: Classical Genetics (Mendel & Beyond)
Genes – Units of Heredity
Heredity
• Genes – determine a protein and hence a trait
• Polygenic – 2 or more genes determine some traits
e.g.: height, intelligence
• Genome – all the genes of an organism in DNA
• Alleles – forms of a gene
• Law of Dominance
o Dominant
o Recessive
o Homozygous (pure)
o Heterozygous (hybrid, carrier)
Law of Segregation
Pairs of alleles separate during meiosis
Phenotype and Genotype
What it looks likeWhat alleles it carries
Testcross• To determine the genotype of a dominant
phenotype
• Unknown mated with HOMOZYGOUS RECESSIVE
• If all offspring are dominant the parent is pure =
homozygous dominant
• If ANY offspring are recessive the parent is
heterozygous
Law of Independent Assortment
• Genes on separate chromosomes assort
independently (randomly) during gamete formation
Dihybrid Cross
Steps to Solving a dihybrid Question:
Alternatively…
Incomplete Dominance Codominance
• Alleles are equally
dominant and create a
blend
• Use superscript symbols
instead of capital and
small letters
• Both alleles are
expressed in the
heterozygote
• Use same superscript
symbols as incomplete
dominance
Multiple Alleles – blood groups
Blood Groups• The diploma often asks questions about blood groups
o Multiple alleles for ABO
• 4 phenotypes: A, B, AB, O
o Dominant/recessive for + or –
• 2 phenotypes + or -
o Codominance for MN group
• 3 phenotypes: MM, MN or NN
• Sometimes questions are dihybrid crosses, sometimes
“What offspring are possible from parents”, etc
Epistasis• One gene affects the expression of another gene
• E.g.: Coat color
Sex-linked Traits
• If traits are carried on the
X Chromosome (most):
o Only female carriers
o Never passed from father to
son
• If carried on the Y
chromosome (rarely):
o Only affect males
o Passed from father to sonNote: males and females are already considered so don’t multiply by half when answering question
Linked Genes
Gene Mapping
Pedigrees
Pedigree AnalysisPossible modes of inheritance you need to identify, interpret,
calculate probabilities
• Autosomal – equal male and female
o Dominant – affected child has affected parent
o Recessive – 2 unaffected parents have affected child
• X-linked – more males
o Dominant – no transmission from father to son, affected
males produce only affected daughters
o Recessive – affected female has affected father
• Y-linked – only males, from father to son
Recommended