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Page 1: Genetics Exam 1 Study Guide

1) Linkage in Drosophila a. Only consider males because the considered trait is on the X chromosome. There can be

no recombination in the fathers of the F2 since they are XY and XY don’t crossover … that would lead to issues.

b. Determine the parental genotypes – these are the most frequently appearing. c. Determine the DCOs – these are the least frequently appearing d. Compare parentals with DCOs and whatever changes in both is the middle gene. e. Given the middle gene apply the formulas for map distance. f. Coefficient of interference is observed DCO events divided by calculated DCO events

i. Calculated DCO events: multiply gene distances by total number of chromosomes

ii. 1-C = interference

g. Gene to centromere distance: ( 12 ) (2nd seg. )

total

h. Gene-gene distance: NP+ 1

2(T )

total2) Inheritance

a. Sex-influenced inheritance b. 9:3:3:1 and 3:1 ratios indicate simple Mendelian explanations

3) Probability

a. 4) Chi-squared analysis

a.b. If p<0.05 then the variation seen in the data from the expected values is due to

something other than chance or experimental error c. Null hypothesis: variation is due to chance

Page 2: Genetics Exam 1 Study Guide

d. Reject null5) Recessive epistasis

a. A recessive allele if present covers up another recessive allele

Extranuclear inheritance

1) Organelle heredity a. mtDNA is transmitted through the maternal gamete … passed on by mothers … b. chloroplast DNA is transmitted either way

2) Maternal effect – expression of maternal nuclear genotype during gametogenesis and early development – may have a strong influence on phenotype

3) Infectious heredity – symbiotic or parasitic association with a microorganism 4) Maternal effect on phenotype – nuclear gene products are stored in egg and transmitted

through the OOPLASM TO THE OFFSPRING … CELL CYTOPLASM TO OFFSPRING. 5) Unifying theme: cell cytoplasm to offspring.

a. Defined as extranuclear inheritance 6) Heteroplasmy – variation in genetic content of organelles 7) Endosymbiotic theory – mitochondria and chloroplasts arose independently about 2 billion

years ago from free-living protobacteria

Extranuclear inheritance lecture

1) Three most common forms? a. Chloroplast DNA

i. Does not use modified genetic codeii. Commonly carries duplicated sequences

b. mtDNA i. Disorganized

ii. Long linear stretch – contains coding informationiii. Mitochondrial genome also have small plasmid like structures; circles,

fragments, etc. 2) Suppressive petite yeast mutants

a. MT mutants where aerobic respiration is halted b. Results from deletions in mtDNAc. Can survive because anaerobic respiration is unaffected d. Still survive in small colonies e. Helps demonstrate mt in yeast is inherited from both parents (not just the mom)f. Can suppress intact mtDNA because mutant mtDNA can replicate more quicklyg. Heteroplasmic – single cell with multiple mitochondria – some are one genotype, other

are other genotypes 3) Endosymbiotic theory suggests that

a. Mitochondria and chloroplasts have systems of transcription and translation different from that of the nucleus

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b. Does not suggest protobacterial cells were engulfed by PHOTOSYNTHETIC HOST CELLS. c. But mitochondria and chloroplasts do have systems of transcription and translation that

differ from that of the nucleus4) How do maternal effect mutations differ from EC inheritance?

a. Mutations are not expressed in the F2 but often times expressed in the F3b. Egg sets up developmental axis that affects the development of the offspring c. Shell coiling

i. Patterened by a single maternal effect locus? ii. Mechanism where the direction of shell coiling in the offspring is regulated by

the mother? iii. Cleavageiv. Microtubules or spindle fibers v. Altered microtubule dynamics; embryo axis is being set up.


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