Genetics
- Monohybrid cross (Aa × Aa)
- genotypes 1 : 2 : 1, phenotypes 3 : 1
- Dihybrid cross
- phenotypes 9 : 3 : 3 : 1
- Hardy–Weinberg
- p + q = 1, p² + 2pq + q² = 1
- Independent genes
- multiply the probabilities
Biology: Genetics and Cell Biology: cram pack
Formula sheets, the key method steps for every topic and 4 practice problems, with full solutions at the back.
1Formulas and methods
2Practice problems
1.GeneticsMedium
Tall (A) is dominant over short (a), and round seeds (B) over wrinkled (b). The genes are on different chromosomes. For the cross AaBb × aaBb, what is the probability P that an offspring is short, round seeds?
AaBb × aaBb
P =
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives purple flowers (dominant) or white flowers; gene B gives round seeds (dominant) or wrinkled seeds. Click the one cell for an offspring that is homozygous for purple flowers and for round seeds.
AaBb × AaBb
- 1Ab × Ab
- 2Ab × AB
- 3Ab × ab
- 4Ab × aB
- 5aB × Ab
- 6aB × AB
- 7aB × ab
- 8aB × aB
- 9ab × Ab
- 10ab × AB
- 11ab × ab
- 12ab × aB
- 13AB × Ab
- 14AB × AB
- 15AB × ab
- 16AB × aB
3.Cell biologyMedium
Transcription produces:
- ADNA from RNA
- BmRNA from a DNA template
- CProtein from mRNA
- DDNA from DNA
4.Cell biologyHard
In eukaryotic mRNA processing, splicing removes:
- AThe poly-A tail
- BExons
- CIntrons
- DThe 5′ cap
3Solutions
1.Genetics
Answer: P = 0.375
Mendelian genetics: each parent passes on one allele of each gene, chosen at random. A Punnett square lists every combination of gametes, each equally likely. A dominant allele (capital letter) shows whenever it is present; a recessive one only in the homozygous form. Genes on different chromosomes are inherited independently, so their probabilities multiply.
Each gene on its own
P(short) = 0.5
P(round seeds) = 0.75
Multiply
P = 0.5·0.75 = 0.375
Answer
P = 0.375
2.Genetics
Answer: AB × AB
Punnett square: one parent's gametes run along the top, the other's down the side. Each cell joins the gamete above it with the gamete beside it, and every cell is equally likely. A recessive trait only shows when both alleles are recessive; for an X-linked trait, sons get their only X from the mother.
Genotype asked for
AABB
Gametes
A homozygous genotype needs the same gamete from both parents, so only one cell in the 16 fits.
AB × AB = AABB
Answer
Cell AB × AB → AABB
3.Cell biology
Answer: B · mRNA from a DNA template
Why this is the answer
RNA polymerase transcribes a DNA template strand into RNA; translation then makes protein at ribosomes.
Answer
B · mRNA from a DNA template
4.Cell biology
Answer: C · Introns
Why this is the answer
The spliceosome removes introns and joins exons; the 5′ cap and poly-A tail are added for stability and export.
Answer
C · Introns
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