110 Mendel 2 Testcross, Dihybrid Cross

Summary

This video explains Mendel's principles of inheritance, starting with key genetic terms like genotype and phenotype. It covers the concept of homozygous and heterozygous alleles, as well as Mendel's test cross method for determining an unknown genotype. The video further delves into Mendel's laws of inheritance, including the Law of Segregation and the Law of Independent Assortment, demonstrated through monohybrid and dihybrid crosses. Mendel’s experiments reveal how genes assort independently and the resulting genetic ratios, providing a foundation for modern genetics.

Takeaways

• 😀 Genotype refers to the genetic makeup of an individual, specifically the set of alleles inherited for a gene.
• 😀 Phenotype refers to the physical appearance or observable traits of an individual, determined by their genotype.
• 😀 A **homozygous** individual has two identical alleles for a gene, while a **heterozygous** individual has two different alleles.
• 😀 **Homozygous dominant** individuals have two copies of the dominant allele, while **homozygous recessive** individuals have two copies of the recessive allele.
• 😀 A **test cross** is used to determine the genotype of a dominant phenotype by crossing it with a homozygous recessive individual.
• 😀 In a **monohybrid cross**, Mendel observed a 3:1 ratio of dominant to recessive phenotypes in the F2 generation, showing dominant-recessive inheritance.
• 😀 Mendel’s **dihybrid cross** examined two traits at the same time (seed color and shape), revealing a **9:3:3:1** ratio in the F2 generation.
• 😀 **Independent assortment** occurs when the alleles of two different genes segregate independently during gamete formation, creating four possible allele combinations.
• 😀 Mendel’s **Law of Segregation** states that each gamete carries only one allele for each inherited characteristic, inherited randomly from each parent.
• 😀 Mendel’s **Law of Independent Assortment** asserts that the segregation of one gene’s alleles does not affect the segregation of another gene’s alleles.
• 😀 By applying the test cross and observing inheritance patterns, Mendel confirmed that traits assort independently and follow predictable ratios in offspring.

Q & A

What is the definition of a genotype?

A genotype is the genetic makeup of an individual, specifically the set of alleles an individual has for a particular gene.

What is the difference between homozygous dominant and homozygous recessive?

Homozygous dominant means having two copies of the dominant allele (e.g., uppercase P), while homozygous recessive means having two copies of the recessive allele (e.g., lowercase p).

What does heterozygous mean in terms of genotype?

Heterozygous refers to having two different alleles for a gene, one dominant and one recessive (e.g., uppercase P and lowercase p).

What is a phenotype?

A phenotype is the physical appearance or observable traits of an individual, which can also include behaviors. In this case, it refers to flower color (purple or white).

How can Mendel determine whether a purple flowered plant is homozygous dominant or heterozygous?

Mendel used a test cross, crossing the purple flowered plant with a homozygous recessive white flowered plant. The offspring's phenotypes help determine the genotype of the purple flowered plant.

What are the possible outcomes of a test cross if the unknown purple plant is homozygous dominant?

If the unknown plant is homozygous dominant, all offspring from the test cross will be heterozygous and have purple flowers.

What happens in the test cross if the unknown purple flowered plant is heterozygous?

If the unknown plant is heterozygous, half of the offspring will have purple flowers (heterozygous) and the other half will have white flowers (homozygous recessive).

What is a dihybrid cross and how is it different from a monohybrid cross?

A dihybrid cross looks at two traits at once, while a monohybrid cross focuses on one trait. For example, Mendel's dihybrid cross involved seed color and seed shape.

What is the principle of independent assortment in genetics?

The principle of independent assortment states that the alleles of one gene segregate independently of the alleles of another gene during gamete formation, meaning that the inheritance of one trait does not affect the inheritance of another.

What did Mendel conclude from his dihybrid cross regarding the inheritance of traits?

Mendel concluded that alleles for different traits assort independently during gamete formation, as evidenced by the 9:3:3:1 ratio observed in the offspring of his dihybrid cross.