An Introduction to Mendelian Genetics | Biomolecules | MCAT | Khan Academy

Summary

This video script offers an introduction to Mendelian Genetics, explaining the significance of chromosomes and alleles in determining an individual's traits. It distinguishes between homozygous and heterozygous genotypes and dominant and recessive alleles, using blood type as an example. It also clarifies the difference between genotype and phenotype and demonstrates how a Punnett Square can predict offspring's genetic outcomes, illustrating inheritance patterns with hypothetical parents.

Takeaways

• 🧬 Human cells contain 46 chromosomes, with 23 inherited from each parent.
• 👩‍🔬 Chromosomes come in pairs, one from the mother and one from the father.
• 🔢 An allele is a section of a chromosome that codes for a specific gene.
• 🧑‍🤝‍🧑 Humans usually have two alleles for each gene: one from the mother and one from the father.
• 🅰 Blood type is determined by specific alleles, like A, B, and O.
• ⚖️ The terms homozygous and heterozygous refer to having identical or different alleles for a gene.
• 🥇 Dominant alleles, like A, overpower recessive alleles, like O.
• 🧬 Genotype refers to a person's genetic makeup, while phenotype refers to their physical traits.
• 📊 A Punnett Square helps predict possible genotypes and phenotypes of offspring.
• 👨‍👩‍👦 Allele combinations from parents determine the likelihood of certain traits, such as blood type.

Q & A

How many chromosomes do human cells typically contain?

Human cells typically contain 46 chromosomes.

How are the 46 chromosomes in human cells inherited?

23 chromosomes are inherited from a person's father and 23 from the mother.

What is the term used to describe a small section on a chromosome that codes for a specific gene?

The term used is 'allele'.

Why do we sometimes say humans have 23 pairs of chromosomes instead of 46?

It serves as a reminder that for each chromosome, we have a maternal and paternal copy.

What is the difference between homozygous and heterozygous individuals in terms of their alleles?

A homozygous individual has two identical alleles for a gene, while a heterozygous individual has two different alleles.

What does it mean for an allele to be dominant?

A dominant allele will be expressed in the phenotype if an individual has two different alleles.

What is the term for an allele that is not expressed when another, dominant allele is present?

The term is 'recessive allele'.

What is the difference between genotype and phenotype?

Genotype refers to an individual's genetic makeup, including the specific alleles they carry, while phenotype refers to the observable physical or biochemical traits expressed by those genes.

How can a Punnett Square be used to predict the genotypes of offspring?

A Punnett Square can be used to determine all possible combinations of alleles that offspring can inherit from their parents by aligning the alleles of each parent.

What is the expected blood type phenotype for a child with the genotype AO?

The child with the genotype AO will have blood type A as the A allele is dominant over the O allele.

If both parents have the genotype AO, what are the possible genotypes and phenotypes of their children?

The possible genotypes are AA, AO, and OO. The phenotypes will be blood type A for AA and AO, and blood type O for OO.