Fiche de révision : Alleles and Inherited Traits

📋 Course Outline

1. Alleles and Inheritance
2. Homozygous and Heterozygous States
3. Dominant and Recessive Traits
4. Genotype and Phenotype
5. Punnett Squares

📖 1. Alleles and Inheritance

🔑 Key Concepts & Definitions

• Allele : A version of a gene found at a particular position on a chromosome.

★ Must-know

• An individual inherits two alleles for a gene, with one allele coming from each parent.

Further detail

• Alleles help determine which eye-colour trait an individual obtains when the parents have different eye colours, such as blue and brown.

💡 Memory Hook

Two parental alleles meeting at the same chromosome position

📖 2. Homozygous and Heterozygous States

🔑 Key Concepts & Definitions

• Homozygous : When the two alleles are the same.
• Heterozygous : When the two alleles are different.

📝 Essential Points

📌 Homozygous and heterozygous describe whether the two alleles for a trait are the same or different, respectively.

💡 Memory Hook

Homozygous means same; heterozygous means different

📖 3. Dominant and Recessive Traits

🔑 Key Concepts & Definitions

• Dominant Trait : Needs only one copy of an allele to be visible in an individual's appearance.
• Recessive Trait : A trait that is dominated by a dominant trait.

📝 Essential Points

• Dominant traits are represented by capital letters, whereas recessive traits are represented by lowercase letters.

💡 Memory Hook

One dominant copy is visible, whereas a recessive trait is dominated

📖 4. Genotype and Phenotype

🔑 Key Concepts & Definitions

• Genotype : A combination of allelic symbols representing the alleles for a trait.
• Phenotype : The physical expression of a trait or characteristic.

💡 Memory Hook

Genotype is the allelic combination; phenotype is its physical expression

📖 5. Punnett Squares

🔑 Key Concepts & Definitions

• Punnett Square : Shows all the combinations of genes that offspring could inherit and the likelihood of inheriting those genes.

📝 Essential Points

• To use a Punnett square, combine the alleles inherited from the two parents to determine the possible gene combinations of their offspring and the likelihood of each combination.

• The course asks students to calculate the possibility of a child having red hair when a heterozygous brown-haired man has a child with a woman carrying a recessive red-hair trait.

💡 Memory Hook

Parents' alleles → possible offspring combinations → likelihood