Mendelian Genetics & Punnett Square Lab
Investigate inheritance patterns using Punnett squares. Cross parents with different genotypes, explore dominance patterns, analyze sex-linked traits, and compare predicted ratios to Mendel's classical results.
Guided Experiment: Monohybrid Cross and Dominance Patterns
What phenotypic ratio do you expect from crossing two heterozygous parents (Aa × Aa) under complete dominance? How does the ratio change under incomplete dominance?
Write your hypothesis in the Lab Report panel, then click Next.
Punnett Square
Controls
Monohybrid Cross Results
Where p = frequency of dominant allele, q = frequency of recessive allele
Data Table
(0 rows)| # | Cross Type | Parents | Genotypic Ratio | Phenotypic Ratio | Dominant % | Recessive % |
|---|
Reference Guide
Monohybrid Cross
A monohybrid cross involves a single gene with two alleles. The heterozygous cross Aa × Aa produces offspring in a predictable ratio.
A testcross (Aa × aa) reveals the genotype of an unknown parent by producing a 1:1 phenotypic ratio.
Dihybrid Cross
A dihybrid cross tracks two genes simultaneously. When both parents are double heterozygotes (AaBb × AaBb), independent assortment produces a 4×4 Punnett square with 16 cells.
Deviations from the 9:3:3:1 ratio may indicate gene linkage, epistasis, or other non-Mendelian patterns.
Incomplete & Codominance
Incomplete dominance produces a blended intermediate phenotype in heterozygotes. Example: red × white snapdragons produce pink offspring.
Codominance means both alleles are fully expressed simultaneously. Example: blood type where IᴬIᴮ individuals express both A and B antigens.
In both cases, the genotypic ratio (1:2:1) matches the phenotypic ratio, unlike complete dominance.
Sex-Linked Traits
Sex-linked (X-linked) traits are carried on the X chromosome. Males (XY) express the trait with only one copy of the recessive allele, while females need two copies.
A carrier mother (XᴬXᵃ) crossed with an unaffected father (XᴬY) produces 25% affected males, 25% carrier females, and 50% unaffected offspring.
Classic examples include color blindness and hemophilia, which appear more frequently in males because they have no second X chromosome to mask the recessive allele.