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Mendelian Genetics & Inheritance

Predict how traits pass from parents to offspring. You will run monohybrid and dihybrid crosses, handle non-Mendelian and X-linked patterns, read pedigrees, and use recombination frequencies to map linked genes.

Study this chapter in PrepMed (free)

What this chapter covers

• Alleles & Monohybrid Crosses. Every genetics problem starts with vocabulary and a Punnett square, and the MCAT also loves conditional probability.
• Dihybrid Crosses & Independent Assortment. Two-gene crosses are solved fastest by treating each gene separately and multiplying probabilities.
• Non-Mendelian Patterns & X-Linkage. Incomplete dominance, codominance, epistasis, and X-linked traits each change the expected ratio in a predictable way.
• Reading Pedigrees. Pedigree questions ask you to name the inheritance mode and compute carrier risk from a chart.
• Linkage & Recombination Frequency. Recombination data let you turn offspring counts into distances on a chromosome, a favorite calculation.

Key points to know

• Segregation: each gamete gets one allele of each gene
• Aa × Aa gives 3:1 phenotypes and 1:2:1 genotypes
• Independent assortment applies to unlinked genes
• n heterozygous genes make 2ⁿ gamete types
• Incomplete dominance: blended heterozygote, 1:2:1 in F2
• Codominance: both alleles show (AB blood)
• Unaffected parents + affected child = recessive
• Every generation affected, vertical = dominant

Try a practice question

Which statement best describes Mendel's law of segregation?

1. Alleles of different genes are inherited independently
2. The two alleles of a gene separate into different gametes
3. Dominant alleles always mask recessive alleles
4. Each gamete receives two alleles for every gene

Common questions

24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.