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 black fur (dominant) or white fur. Click the one cell for an offspring that is shows both white flowers and white fur.
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
The Golgi apparatus mainly:
- AModifies, sorts and packages proteins for transport
- BBreaks down old organelles and engulfed bacteria with enzymes
- CReplicates DNA
- DProduces ATP
4.Cell biologyHard
In damaged tissue, cells swell, their membranes burst and the area becomes inflamed. Which type of cell death is this?
- ANecrosis
- BApoptosis
- CSenescence
- DMitosis
3Solutions
1.Genetics
Answer: P = 0.125
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) = 0.25
P(round seeds) = 0.5
Multiply
P = 0.25·0.5 = 0.125
Answer
P = 0.125
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: A · Modifies, sorts and packages proteins for transport
Why this is the answer
The Golgi modifies proteins (e.g. glycosylation) and sorts them into vesicles for secretion, membranes or lysosomes.
Answer
A · Modifies, sorts and packages proteins for transport
4.Cell biology
Answer: A · Necrosis
Why this is the answer
Necrosis is uncontrolled death with swelling, membrane rupture and leakage of contents that trigger inflammation. Apoptosis is orderly shrinkage into apoptotic bodies that are removed quietly.
Answer
A · Necrosis
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