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Chapter 16 Genetics (Replication of DNA (each gene exists in two copies…
Chapter 16 Genetics
Replication of DNA
before mitosis or meiosis
during S phase
doubles amount of DNA
each gene exists in two copies
one on each of two chromatids
one goes to each daughter nucleus
anaphase
process
chromatin less compact
allow entry of replicating factors
One strand DNA double helix is cut
two strands separate
form replicon
aka small bubble
free nucleotides diffuse to regions of single stranded DNA
pair w/base
ribonucleotides
polymerized
primer RNA
10 nucleotides long
act as substrates for DNA-synthesizing enzyme
DNA polymerase
polymerase enters & adds deoxyribonucleotides onto the end of primer RNA
DNA acts as template
semiconservative replication
only adds to 3' end of growing nucleic acid
2 more items...
new pieces Primer RNA form Okazaki fragments
join 1st ones
DNA uncoils & separates
repilcation fork
ligated
Mutations
Causes
mutagen
certain chemicals
ultraviolet light
x-rays
radiation
deletions
short regions of self-complementary sequence
may form small loop
shorter than should be
DNA piece lost
transposable elements
pieces DNA readily change positions
two basic forms
insertion sequences
few thousand base pair long
contain genes that code for enzymes
involved in cutting
transposons
much longer
carries genes that code for proteins
insertion
DNA piece added
enzymes cut & rejoin DNA
repair processes
foreign DNA incorporated
Effects
depends on
nature
position
its extent
exon
gene code for protein active site is disrupted
cannot function
insertion
gene code for protein so long
cannot fold properly
mutation promoter region
inactivate a gene
cause to be active wrong time/place
point mutations
new codon
eliminate start codons
larger mutation
greater effects
Somatic Mutations
occur anytime in any cell
never lead to sex cells
somatic mutations
affect such small portion of the plant
not passed to offspring
might not result in altered phenotype
DNA Repair Processes
mechanisms recognize and remove mutations
recognize
mismatches
loops
other problems
minimize # of errors that occur
repair rate
must not be too efficient or ineffective
cause no variation or adaptation
mutations in repair enzymes
result in serious problems
changes in DNA
smallest is point mutation
inversion
DNA placed backwards
Monohybrid Crosses
Monohybrid Crosses w/ Incomplete Dominance
single character is analyzed & studied
much simpler
inheritance of other traits is not considered
parental generation
parents
first filial generation
F1
offspring
if they breed
F2 generation
homozygous
RR or rr
identical alleles for gene
heterzygous
Rr
two diff alleles for gene
incomplete dominance
neither parents dominate other
Crossing Heterozygotes w/ themselves
selfing
plants own pollen fertilizes own eggs
crossed w/plant w/same phenotype
instructive consequences
sperm & eggs contain
50% R allele
50% r
punnett square
explains proportions
one gamete in top and one on side
produces three types F1
Rr
RR
rr
Monohybrid Crosses w/ Complete Dominance
only half as much product of an enzyme is produced
enzyme functions only specific amount product synthesized
dominant
controls other trait
recessive
Test Crosses
used to discover genotype
traits w/ incomplete dominance
complete dominance
difficult to know genotype
unless shows recessive trait
involves plant in question & one that is homozygous recessive
gametes produced by homozygous recessive parent
carry recessive allele
pure-bred lines
homozygous recessive selfed & pure
useful & valuable
progeny exactly like them
Multiple Alleles
genes have many alleles
protein of average size
consists of 300 amino acids
coding portion portion of mRNA
must have 300 codons
each containing 3 nucleotides
gene exists in many forms
polymorphic
X1,X2,X3,X4
some altered protein structure
some normal enzyme activity
proper reaction carried out more slowly or not accurately controlled
Dihybrid Crosses
Genes on Separate Chromosomes: Independent Assortment
two genes are on separate chromosomes
alleles move independently
chromosomes duplicated during S phase
each has two copies of each allele
align on metaphase plate
chromosomes also pair with each other
anaphase
homologous chromosomes separate from each other
meiosis II
two chromatids seperate
4 hapliod cells
equal in numbers
Crossing-Over
two genes located far apart on same chromosome
crossing over occurs between them
during prophase I
after homologous chromosomes paried
synaptonemal complex formed
further apart two genes
greater possibility crossing over
can occur several times
Genes on the Same Chromosome: Linkage
close together on chromosome
do not undergo independent assortment
two genes are linked
recombinant chromosomes
formed from crossing over for homologous chromosomes
formed from recombination alleles
first two
parental type chromosomes
like parents
last two are recombinant types
measure using map unit
physical spacing
1% or centimorgan
approximately one million base pairs
two genes studied & analyzed simultaneously
results depend on position on chromosomes
diff chromosomes
alleles for one gene move independently of alleles for other gene
same chromosome
alleles for one gene chemically bound to alleles for other gene
move together
Multiple Genes for One Character: Quantitative Trait Loci
individual phenotypic traits
complex metabolic processes involving numerous enzymes
many separate genes affect any single trait
synthetic pathways involve @ least 4-5 intermediates
genes affect same trait
epistasis
having multiple genes for each trait
genes/other portions DNA associated w/such traits
extremely complex crosses
hundreds-thousands of progeny
pleiotrophic effects
multiple phenotype effects of one mutation
Other Aspects of Inheritance
Maternal Influence
biparental inheritance
alleles both parents are transmitted equally to progeny
uniparental inheritance
zygote obtains all its plastids & mitochondrial genomes from maternal parents
aka maternal inheritance
difficult to study
Mendelian ratios not produced
phenotypes not easily recognized
plastid genetics
alleles affecting chlorophyll synthesis
plastid inheritance
variegation
spots or sectors that diff colors on plant that otherwise green
cell mixture of plastid types
Lethal Alleles
presence can kill plant
most often recessive
fatal only if present in homozygouscondition
dominant would kill plant
rarely passed to offspring
difficult to detect
if effect occurs early
Multiple Sets of Chromosomes and Gene Families
plants tolerate triploid zygotes
triploid sporophyte develops
sterile
cannot undergo pairing of chromosomes during prophase I
odd ploidy
cells fail to undergo mitosis after S phase DNA replication
tetraploid
perfectly healthy
plants w/two or more sets of chromosomes
polyploid
can undergo meiosis
are fertile
nondisjunction
change in chromosome # per nucleus
chromosmes fail to disjoin
one daughter cell receives both copies
survives
tolerated in plants
result in triploid zygote
one daughter cell receives none
set similar genes
formed by duplication
gene family
