Monohybrid Cross Explained

Summary

This video explains the concept of a monohybrid cross, where two heterozygous parents are crossed to predict offspring genotypes and phenotypes for a single gene. Using pea plants as an example, it highlights how yellow is dominant and green is recessive. The video walks through a Punnett square to show that the offspring will have a 1:2:1 genotype ratio and a 3:1 phenotype ratio, with about 75% producing yellow peas and 25% producing green peas. This is a fundamental example of Mendelian genetics.

Takeaways

• 🌱 A monohybrid cross involves two heterozygous parents with respect to a single gene.
• 🧬 Each parent in a monohybrid cross carries two different alleles for the gene.
• 🍀 'Mono' refers to one gene, while 'hybrid' refers to the mixing of different alleles.
• 🌿 Pea plants are a classic example for explaining monohybrid crosses, where pea color (yellow or green) is determined by two alleles.
• 💛 The yellow pea color is dominant, while the green pea color is recessive.
• ⚖️ The offspring's genotype ratio in a monohybrid cross is typically 1:2:1 (homozygous dominant : heterozygous : homozygous recessive).
• 🌻 The phenotype ratio in a monohybrid cross is typically 3:1, with yellow peas being more common than green peas.
• 🧪 If you complete a monohybrid cross with 100 offspring, approximately 75 will have yellow peas, and 25 will have green peas.
• 📊 The 3:1 phenotype ratio indicates that both parents are heterozygous.
• 🔍 The script introduces fundamental principles of Mendelian genetics and suggests exploring further topics like dihybrid and test crosses.

Q & A

What is a monohybrid cross?

A monohybrid cross is a mating event between two parents that are heterozygous for a single gene, meaning each parent carries two different alleles for that gene.

What does 'mono' and 'hybrid' mean in the context of a monohybrid cross?

'Mono' refers to the single gene being considered, and 'hybrid' refers to the fact that each parent has two different alleles for that gene.

Can you provide an example of a monohybrid cross using pea plants?

Yes, a classic example is using pea plants with two possible pea colors: yellow (dominant) and green (recessive). The cross involves heterozygous plants for these traits.

What are the possible genotypes for the offspring of a monohybrid cross?

The possible genotypes for the offspring are homozygous dominant, heterozygous, and homozygous recessive.

How can you predict the genotypes and phenotypes of the offspring in a monohybrid cross?

By setting up a Punnett square, you can predict the genotypes and phenotypes of the offspring, showing a 1:2:1 ratio for genotypes and a 3:1 ratio for phenotypes.

What is the expected phenotype ratio for the offspring of a monohybrid cross involving pea plants?

The expected phenotype ratio is 3:1, with 3/4 of the offspring having the dominant phenotype (yellow peas) and 1/4 having the recessive phenotype (green peas).

If you were to create 100 offspring from a monohybrid cross, what would be the expected numbers of each phenotype?

You would expect around 75 yellow pea-producing plants and 25 green pea-producing plants.

Why might you not get the exact expected numbers in a real monohybrid cross experiment?

Variability in the actual breeding process and random chance can lead to deviations from the expected numbers, although the ratios should still hold true over a large number of offspring.

What does a 3:1 offspring phenotype ratio suggest about the parents in a monohybrid cross?

A 3:1 phenotype ratio suggests that both parents are heterozygous for the gene in question.

Can you provide more information on dihybrid crosses and test crosses?

Yes, dihybrid crosses involve two genes, and test crosses are used to determine the genotype of an individual when its phenotype is known, which can be explored in further videos.

What is the significance of the 1:2:1 genotype ratio in a monohybrid cross?

The 1:2:1 genotype ratio is significant because it reflects the expected distribution of genotypes in the offspring when two heterozygous parents are crossed, following Mendel's laws of inheritance.