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Chapter 16: Genetics (Replications of DNA (S phase (DNA is doubled, during…
Chapter 16: Genetics
Replications of DNA
S phase
DNA is doubled
during cell cycle
replicon
small bubble
formed by separated DNA strands
semiconservative
DNA strand acts as template for complementary strand
each double helix
has one new molecule
has one old molecule
chromosomes
contains only a single DNA double helix
replication fork
#
where DNA uncoils and separates
runs into adjacent replicons
Mutations
effects
depend on nature, position, and extent
mostly harmful
somatic mutations
happen in cells that never lead to sex cells
causes
mutagen
ultraviolet light
X-rays
certain chemicals
many are man made
radiation from radioactive substances
insertions
can be caused by many methods
deletions
due to short regions of self-complementary sequence
transposable elements
insertion sequences
only a few thousand base pairs long
contain the genes that code for enzymes
transposons
like an insertion sequence
carry genes that code for proteins not associated with transposition
DNA Repair Processes
must not be perfect
must not be extremely efficient
Other Aspects of Inheritance
lethal alleles
can be difficult to detect
dormant lethal alleles would kill plant
maternal inheritance
uniparental inheritance
zygote obtains all genomes from one parent
plastid inheritance
responsible for certain types of variegation
in plants
presence of spots or sectors that are white, red, or orange
achlorophyllous plant
outcome depends on pollen and ovule parents
Multiple sets of chromosomes and gene families
polyploid
plants with more than two sets of chromosomes
can undergo meiosis
nondisjunction
change in chromosomes number per nucleus
paralogs
originated duplicates of a wild-allele
each will involve independently
gene family
may have up to 600 paralogs of
Monohybrid Crosses
crossing heterozygotes with themselves
selfing
plant's own pollen fertilizes its own eggs
plants can be crossed with another plant with the same genotype
Punnett square
shows a 1:2:1 ratio for inherited traits
discovered by Gregor Mendel
used Pea Plants
with dominance
incomplete
neither parental trait dominates the other
phenotype differs from both homozygous phenotypes
complete
dominant allele masks recessive allele
difficult to know the genotype is
test crosses
can reveal genotype
made on annual plants
results are usually unknown until the plant dies
multiple alleles
#
genes existing in many forms
concept of dominance's more complex
Dihybrid Crosses
genes on chromosomes
same
linkage
when genes are close together
separate
independent assortment
one gene moves separately from the other
crossing over
no preferential sites for this exist
will occur more the farther two genes are from each other
rate of crossing over
proportional to physical spacing between genes
measure between them in recombination percentages
centimorgan
map unit
Multiple Genes for One Character: Quantitative Trait Loci
determine what fraction of a phenotype is correlated with a particular gene
epistasis
multiple genes for each trait
pleiotropic effects
multiple phenotype effects of one mutation
