17. Inheritance (Part 2) (Cambridge IGCSE Biology 0610 for exams in 2023, 2024 and 2025)

Summary

This educational video provides a comprehensive overview of inheritance according to the Cambridge IGCSE Biology syllabus. It covers essential concepts such as genes, alleles, genotypes, and phenotypes, explaining how traits are passed from parents to offspring through Punnett Squares. The video details monohybrid inheritance, test crosses, and pedigree diagrams, while also introducing co-dominance in blood group inheritance and sex linkage, particularly with color blindness. By the end, viewers gain a solid understanding of how genetic traits are inherited, along with practical examples and applications.

Takeaways

• 😀 Inheritance is the process of passing genetic information from one generation to the next.
• 😀 A gene is a segment of DNA that instructs the creation of a specific protein affecting traits.
• 😀 Alleles are different versions of a gene, with individuals having two copies inherited from each parent.
• 😀 The genotype represents an organism's genetic makeup, while the phenotype reflects observable traits.
• 😀 Homozygous individuals have two identical alleles for a gene, whereas heterozygous individuals have two different alleles.
• 😀 Dominant alleles are expressed in the phenotype if present, while recessive alleles only show their effect if both alleles are recessive.
• 😀 Monohybrid inheritance studies the transmission of a single trait from parents to offspring, often illustrated using Punnett Squares.
• 😀 A test cross can determine an unknown genotype by crossing it with a homozygous recessive individual.
• 😀 Codominance occurs when both alleles contribute to the phenotype, as seen in blood group inheritance.
• 😀 Sex-linked traits, like color blindness, are often more common in males due to their single X chromosome.

Q & A

What is inheritance in genetics?

Inheritance is the transmission of genetic information from one generation to the next.

What is a gene?

A gene is a section of DNA that provides instructions for making a specific protein, which influences a particular characteristic.

What are alleles?

Alleles are variations of the same gene. Each individual has two alleles for each gene, one inherited from each parent.

What is the difference between genotype and phenotype?

Genotype refers to the genetic makeup of an organism, including all of its genes, while phenotype refers to the observable features or traits of an organism.

What is the significance of homozygous and heterozygous genotypes?

Homozygous genotypes have two identical alleles (e.g., BB or bb), while heterozygous genotypes have two different alleles (e.g., Bb). This distinction influences how traits are expressed.

How are dominant and recessive alleles defined?

A dominant allele is expressed if present in the genotype, while a recessive allele is only expressed when no dominant allele is present.

What is monohybrid inheritance?

Monohybrid inheritance is the study of how a single trait or characteristic is passed from parents to offspring, often illustrated using a Punnett square.

What does a Punnett square represent?

A Punnett square is a tool used to determine the possible combinations of alleles in offspring, allowing calculation of ratios of different genotypes and phenotypes.

What is a test cross, and why is it used?

A test cross involves crossing an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype based on the offspring's phenotypes.

What are pedigree diagrams and their purpose?

Pedigree diagrams are charts used to track how a specific trait or disease is passed through generations in a family, helping to predict the chances of inheriting genetic disorders.

What is codominance, and can you provide an example?

Codominance occurs when both alleles in heterozygous organisms contribute to the phenotype. An example is blood group inheritance, where IA and IB are co-dominant alleles.

How does sex linkage affect inheritance patterns?

Sex-linked traits are controlled by genes located on sex chromosomes, making them more common in one sex than the other. For example, red-green color blindness is more prevalent in males.