Dihybrid Cross and Genetic Concepts

This video tutorial covers the topic of dihybrid crosses in A-level biology. It explains the concept of dihybrid inheritance, where two unlinked genes are independently inherited, leading to the characteristic 9:3:3:1 phenotypic ratio. The video discusses the importance of independent assortment during meiosis and provides key assumptions for solving genetic problems. It demonstrates how to use Punnett squares to predict outcomes of dihybrid crosses and includes example problems to illustrate these concepts.

What is the expected phenotypic ratio in a dihybrid cross when two unlinked genes are independently assorted?

• 3:1

• 9:3:3:1

• 1:1

• 2:1

Which of the following is assumed about a parent if not specified otherwise in a dihybrid cross?

• The parent is a hybrid.

• The parent is homozygous.

• The parent is heterozygous.

• The parent is a mutant.

What does the term 'wild type' refer to in genetics?

• A mutant allele

• An unknown genotype

• A recessive allele

• The normal or most common phenotype

In a Punnett square for a dihybrid cross, how many boxes are there?

• 16

• 8

• 4

• 12

When constructing a Punnett square, what is the significance of placing the dominant allele first?

• It simplifies the calculation of phenotypic ratios.

• It helps in identifying recessive traits.

• It is a convention to standardize genotype notation.

• It indicates the parent with the dominant trait.

In the alien example, what is the phenotype of an alien with a heterozygous genotype for fur color and eye color?

• Purple fur and blue eyes

• Red fur and green eyes

• Green fur and purple eyes

• Yellow fur and red eyes

What is the genotype of an alien with purple fur, given that purple is recessive?

• Homozygous dominant

• Heterozygous

• Homozygous recessive

• Unknown

In the tree frog example, what is assumed about a trait if it is not mentioned?

• It is wild type and dominant.

• It is heterozygous.

• It is a mutation.

• It is recessive.

How many different types of gametes can a heterozygous individual produce in a dihybrid cross?

• 1

• 2

• 3

• 4

In the tree frog example, what is the phenotype of the F1 generation?

• Green skin and green eyes

• Yellow skin and green eyes

• Red skin and blue eyes

• Blue skin and red eyes