Answer: Mendel's monohybrid crosses involve the inheritance of a single trait, while dihybrid crosses involve the inheritance of two different traits. The ratios of progeny expected in the F2 generation depend on the specific genotypes of the parents and follow certain patterns based on the principles of inheritance.
Step-by-step explanation:
Mendel's monohybrid and dihybrid crosses are important concepts in the study of genetics. Let's start with monohybrid crosses.
A monohybrid cross involves the inheritance of a single trait. For example, let's consider the cross between two pea plants: one with round seeds (RR) and the other with wrinkled seeds (rr). In this case, the round seed trait is dominant (R) and the wrinkled seed trait is recessive (r).
When these two plants are crossed, all the offspring in the F1 generation will have round seeds because the dominant trait masks the recessive trait. So, all the F1 progeny will have the genotype Rr, where R represents the dominant allele and r represents the recessive allele.
Now, if we cross two F1 plants (Rr x Rr), we move on to the F2 generation. In this generation, the Punnett square can be used to predict the possible genotypes and phenotypes of the offspring.
In the Punnett square, we write the possible alleles from each parent along the top and left side of the square. In this case, both parents have the genotype Rr. When we combine the alleles, we get the possible genotypes of the offspring: RR, Rr, Rr, and rr.
Based on the law of segregation, there is a 25% chance of getting an individual with the genotype RR (round seeds), a 50% chance of getting an individual with the genotype Rr (round seeds), and a 25% chance of getting an individual with the genotype rr (wrinkled seeds).
Regarding the phenotypes, individuals with the genotypes RR and Rr will have round seeds, while individuals with the genotype rr will have wrinkled seeds. So, the ratio of round-seeded to wrinkled-seeded plants in the F2 generation is 3:1.
Now, let's move on to dihybrid crosses.
A dihybrid cross involves the inheritance of two different traits. Let's consider a cross between two pea plants: one with yellow round seeds (YYRR) and the other with green wrinkled seeds (yyrr). In this case, the yellow seed color (Y) is dominant over green (y), and the round seed shape (R) is dominant over wrinkled (r).
When these two plants are crossed, all the offspring in the F1 generation will have yellow round seeds because the dominant traits mask the recessive traits. So, all the F1 progeny will have the genotype YyRr.
Now, if we cross two F1 plants (YyRr x YyRr), we move on to the F2 generation. The Punnett square can be used to predict the possible genotypes and phenotypes of the offspring.
In the Punnett square, we write the possible alleles from each parent along the top and left side of the square. In this case, both parents have the genotype YyRr. When we combine the alleles, we get the possible genotypes of the offspring.
Based on the law of independent assortment, there is a 9:3:3:1 ratio of the four possible phenotypes in the F2 generation.
- 9 individuals will have the genotype YYRR and exhibit the yellow round seed phenotype.
- 3 individuals will have the genotype YyRR or YYRr and exhibit the yellow round seed phenotype.
- 3 individuals will have the genotype YYrr or YyRr and exhibit the yellow wrinkled seed phenotype.
- 1 individual will have the genotype yyrr and exhibit the green wrinkled seed phenotype.