5.1 Mendel and Heredity
Notes
Genetics is the study of heredity, how traits pass from parents to offspring. Gregor Mendel discovered its basic rules by breeding pea plants.
- A gene is a section of DNA that codes for a trait. Different versions of a gene are alleles.
- Each organism has two alleles for each gene, one from each parent.
- A dominant allele (capital letter, T) hides a recessive allele (lowercase, t).
- Law of segregation: the two alleles separate when gametes form, so each gamete gets one.
- Law of independent assortment: alleles for different genes are sorted into gametes independently.
- P generation = parents; F1 = their offspring; F2 = offspring of F1.
Practice
Mendel crossed pure tall pea plants with pure short plants. All the F1 plants were tall. What does this show?
The recessive short allele was hidden, then reappeared in the F2.
Which law states that each gamete carries only one allele for each gene?
The two alleles separate (segregate) when gametes form.
Different versions of the same gene, like purple-flower and white-flower versions, are called:
Alleles are alternate forms of one gene.
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