Explore how traits pass from parents to offspring through Mendel's experiments, predict crosses with Punnett squares, and get an introduction to evolution.
Gregor Mendel crossed tall and short pea plants and found that traits are inherited as distinct units (genes), with some versions being dominant over others.
In Mendel's pea plants, tallness (T) is dominant over shortness (t). What does "dominant" mean here?
A plant only needs one copy of the tall allele (T) to actually be tall — it masks the recessive short allele when both are present
A Punnett square predicts the possible genotypes of offspring from a genetic cross.
| T | t | |
|---|---|---|
| T | TT | Tt |
| t | Tt | tt |
Cross two Tt (tall, heterozygous) pea plants. What genotype ratio results?
1 TT : 2 Tt : 1 tt
From that same Tt × Tt cross, what is the phenotype (tall : short) ratio?
3 tall : 1 short, since TT and Tt both look tall
Evolution is the gradual change in inherited traits of a population over many generations, often driven by natural selection — organisms better suited to their environment are more likely to survive and reproduce.
If an environment suddenly gets colder, which individuals in a population are more likely to survive and pass on their genes — those with thicker or thinner fur?
Those with thicker fur, since it better suits the new, colder conditions
1. In pea plants, is tallness (T) dominant or recessive?
2. What genotype must a pea plant have to actually be short?
3. In a Tt × Tt cross, out of 4 possible offspring combinations, how many are genotype Tt?
4. What is the phenotype ratio in a Tt × Tt cross?
5. What is the term for the process where organisms better suited to their environment survive and reproduce more?