Inheritance: Dihybrid Crosses | A-level Biology | OCR, AQA, Edexcel

Summary

Key Points

• Dihybrid inheritance studies the simultaneous inheritance of two different genes or characteristics, each determined by a gene on a separate chromosome. 0:47
• In pea plants, seed color (yellow/green) and seed shape (round/wrinkled) are used as an example, with yellow and round being dominant traits. 2:18
• Pure breeding parents for a dihybrid cross would have genotypes like YYRR (yellow, round) and yyrr (green, wrinkled). 5:34
• When pure breeding parents are crossed, the F1 generation consists of offspring that are heterozygous for both traits (e.g., YyRr), and all display the dominant phenotypes (yellow and round). 9:10
• To produce the F2 generation, two individuals from the F1 generation are crossed. 10:33
• A Punnett square for the F2 generation, using the four gamete types from each parent, reveals a variety of genotypes. 10:57
• The F1 generation (YyRr) produces four types of gametes: YR, Yr, yR, and yr. 12:11
• This 9:3:3:1 phenotypic ratio is a consistent outcome for dihybrid crosses involving independently assorting genes, regardless of the specific traits studied. 14:56
• The F2 generation exhibits a phenotypic ratio of 9:3:3:1, meaning 9 parts are dominant for both traits, 3 parts are dominant for the first and recessive for the second, 3 parts are recessive for the first and dominant for the second, and 1 part is recessive for both traits. 15:10