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Chapter 16: Genetics (Mutations: Change in DNA (Multiple mutation repair…
Chapter 16: Genetics
Mutations: Change in DNA
Smallest mutation=point mutation
single base converted to dif. base
Lost DNA=deletion
Several ways
short regions self complimentary strand
Added DNA=insertion
Variety of enzymes cut and rejoin DNA
Transposable elements
Readily Change position among chromosomes
Two Basic forms: transposons and insertion sequences
Insertion sequences
code for enzymes that cut and splice
Transposons
like insertion sequence, but much longer
codes for proteins not associate with transpostion
used for genetic analysis and engineering
backwards strand=inversion
Causes of Mutations: Mutagens
ex. Nitrous Acid, chemicals, wavelengths/rays
reacts with cytosine
converts cytocsine to Uracil
Multiple mutation repair enzymes exist
recognizes changes
Changes abnormal pairs
DNA polymerase sometimes arrives before
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Dihybrid Crosses
Two genes studied simultaneously
results depend on positions of genes
Genes on Separate Chromosomes: Independent Assortment
Independent Assortment: two genes on separate chromosomes
Genes move independently
during mitosis no way to tell which pole will receive which allele
In plants easy to obtain large numbers
In dihybrid cross: gene each gene showing complete dominance
Considering multiple genes doesn't effect inheritance
Crossing Over
during prophase I
synaptonemal complex formed
no preferential sites exist
farther apart=greater chance of cross over
Genes on the Same Chromosome: Linkage
If two genes close, usually don't indep. assort.
linked instead
several types heterozygote possible
most instructive cross includes doble homozygous recessive
rate of crossing-over directly related to spacing between genes
Replication of DNA
before mitosis or meiosis
S phase
Chromatin loosens
One strand cut
Bubble/Replicon
formed at seperation of strands
Nucleotides diffuse
NOT deoxyribonucleotides
Turned to primer RNA
Acs as substrates for DNA polymerase
enters&adds deoxy. nucleotides.
doubles DNA
DNA doesn't release from histones
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Monohybrid Crosses
Sexual reproduction between 2=cross
meitotic divisions before cross=reduce from diploid to haploid
both sex cells have complete set of genes
Monohybrid Crosses with Incomplete Dominance
Single Character analyzed
shape, color, height
Parents=parental generation
First generation of offspring=F1 or first filial generation
Homozygous: identical alleles Heterozygous: different alleles
Crossing Heterozygotes with Themselves
plants own pollen fertilizes eggs: selfing
also occurs plant w same genotype
Not all zygotes are same genetically
Punnett squares
predict probability of genotype and pheno type
