other patterns of inheritance
In incomplete dominance, what does the heterozygote phenotype look like?
Intermediate / blended version of the two homozygous phenotypes (e.g., RW snapdragon).
Does crossing over occur between sister chromatids or non-sister chromatids?
Non-sister chromatids of homologous chromosomes.
In Griffith’s experiment, what happened when heat-killed S strain was mixed with live R strain and injected into mice?
Mice died, and live S strain bacteria were found in their blood.
What are the base pairing rules in DNA?
A pairs with T (2 H-bonds).
G pairs with C (3 H-bonds).
In Meselson and Stahl’s experiment, after one round of replication in N-14 medium, where was the DNA band?
One band at the center (intermediate density = hybrid N-15/N-14 DNA).
How does codominance differ from incomplete dominance at the molecular level?
Both alleles are transcribed into mRNA → both proteins accumulate without affecting each other → both traits appear separately (no blending).
What is the ploidy of a cell after Telophase I, before cytokinesis?
Haploid (N chromosomes) but each chromosome still has 2 sister chromatids (2N chromatids).
What key conclusion did Avery, MacLeod, and McCarty reach after using DNase, RNase, and protease?
DNA is the transforming substance (only DNase prevented transformation).
What did Rosalind Franklin’s Photo 51 reveal about DNA?
X-shaped pattern → helical structure.
Constant diameter → double helix.
10 bases per turn.
Why are Okazaki fragments formed on the lagging strand?
DNA polymerase synthesizes only 5′→3′.
On the lagging strand, template runs 5′→3′ away from fork → discontinuous synthesis.
A woman with type AB blood and a man with type O blood have a child. What possible blood types can the child have?
A (I^A i) or B (I^B i).
AB is impossible (no I^A I^B).
O is impossible (no ii).
In a cell with 3 pairs of homologous chromosomes (2n=6), how many possible combinations of chromosomes in gametes due to independent assortment alone?
2^n = 2^3 = 8 combinations.
Why did Hershey and Chase use radioactive ³⁵S and ³²P separately?
³⁵S labels protein (sulfur in methionine/cysteine).
³²P labels DNA (phosphorus in backbone).
To see which molecule enters bacteria during infection.
Explain why purines pair with pyrimidines.
Purine (two rings) + pyrimidine (one ring) = constant diameter (3 rings total).
Two purines would be too wide; two pyrimidines too narrow.
What is the role of telomerase in eukaryotic cells?
Adds short repeated DNA sequences to telomeres (ends of linear chromosomes) to prevent shortening during replication.
In Labrador coat color, the E/e gene controls pigment deposition, and B/b controls black vs. brown. What would be the phenotype of a dog with genotype bb Ee?
Brown (bb) with pigment deposited (Ee) → brown coat.
Explain why linked genes do not assort independently.
Linked genes are on the same chromosome close together → rarely separated by crossing over → usually inherited as a unit.
In Hershey-Chase, if they had found radioactivity inside bacteria in both ³⁵S and ³²P groups, what would that have suggested?
Both protein and DNA enter bacteria → cannot determine which is genetic material.
If a DNA sample is 28% adenine, what percentage is guanine?
A = T = 28% → A+T = 56% → G+C = 44% → G = 22%.
Compare transcription in prokaryotes vs. eukaryotes (two differences).
Prokaryotes: no nucleus, transcription & translation simultaneous, no RNA processing.
Eukaryotes: nucleus, transcription then RNA processing (capping, poly-A, splicing), then export.
In a species of flower, petal color shows incomplete dominance (R=red, W=white). A separate epistatic gene (S/s) determines whether any pigment is produced; ss prevents all pigment (white regardless of R/W). Cross two Rr Ss plants. What fraction of offspring will be red?
3/16 red.
Red requires: at least one R (RR or Rr) AND at least one S (SS or Ss) → (3/4 pigment) × (3/4 red among pigmented?) Wait carefully:
Pigment allowed: 3/4 (S_ ).
Among those, red = RR or Rr? Rr gives pink (incomplete dominance). Red = RR only → 1/4 of 3/4 = 3/16
In a test cross (AaBb × aabb), you observe 450 AaBb, 450 aabb, 50 Aabb, 50 aaBb. Are A and B linked? If so, what is the recombination frequency and arrangement (cis or trans)?
Yes, linked (parental types = 900, recombinants = 100).
Recombination frequency = 100/1000 = 10%.
Parental = AaBb and aabb → original arrangement was AB/ab (cis).
Griffith’s experiment did not prove DNA is the genetic material. Why not? What alternative explanation was still possible?
Transformation could have been caused by a non-DNA molecule (e.g., a protein, RNA, or other component) co-purifying with the S strain extract.
A 100 bp DNA molecule has 120 hydrogen bonds total. How many A-T and how many G-C pairs does it have?
Let x = # A-T (2 H-bonds each), y = # G-C (3 H-bonds each).
x + y = 100.
2x + 3y = 120.
Substitute: 2(100-y) + 3y = 120 → 200 + y = 120 → y = -80 → impossible.
A pre-mRNA has 4 exons and 3 introns. Alternative splicing can skip exon 2 and 3 only. How many different mature mRNA products can be made?
Possible exons included: Exon1 always, Exon4 always.
Exon2: include or skip (2 ways).
Exon3: include or skip (2 ways).
Total = 2 × 2 = 4 different mRNAs.