GCSE Biology - DNA Part 2 - Alleles / Dominant / Heterozygous / Phenotypes and more! #64

Cognito

7 Jan 201904:15

Summary

TLDRThis video continues the discussion on DNA by explaining key genetic terms such as allele, dominant and recessive traits, homozygous and heterozygous, as well as genotype and phenotype. It describes how genes code for proteins, and how different versions of these genes, called alleles, determine traits. Using an example of fur color in mice, it shows how dominant and recessive alleles affect physical traits. The video also distinguishes between genotype, the genetic makeup, and phenotype, the observable characteristics, preparing viewers for the next topic on genetic diagrams.

Takeaways

🧬 Genes are segments of DNA that code for specific proteins, determining traits we develop.
👥 Traits can be influenced by a single gene or multiple genes interacting together.
🔄 Alleles are different versions of the same gene, which can lead to variations in traits.
👫 We inherit two alleles for each gene, one from each parent, which can be the same or different.
🎭 If both alleles are the same, the organism is homozygous for that trait, and if they are different, it's heterozygous.
🏆 In cases of heterozygosity, the dominant allele is expressed, while the recessive one remains unexpressed.
🐭 A mouse with one purple allele (dominant) and one green allele (recessive) will be purple.
🌈 The only way for the mouse to be green is if it inherits two green (recessive) alleles, which is homozygous recessive.
🧬 Genotype refers to the collection of alleles an organism has.
👀 Phenotype refers to the physical traits or characteristics expressed by the genotype, like fur color.

Q & A

What is an allele?
-An allele is a different version or form of the same gene. Each individual has two alleles for every gene, one from each parent.
How do dominant and recessive alleles affect traits?
-A dominant allele will always be expressed in an organism's appearance if present, while a recessive allele will only be expressed if both alleles are recessive.
What does it mean to be homozygous for a gene?
-Being homozygous means having two of the same alleles for a particular gene, either both dominant or both recessive.
What does it mean to be heterozygous for a gene?
-Being heterozygous means having two different alleles for a particular gene, one dominant and one recessive.
If a mouse is heterozygous for fur color with one purple allele (dominant) and one green allele (recessive), what color will the mouse be?
-The mouse will be purple because the purple allele is dominant and will be expressed over the recessive green allele.
What is the only way for a mouse to have green fur if green is the recessive allele?
-The mouse must have two green alleles (homozygous recessive) for green fur to be expressed.
What is the difference between genotype and phenotype?
-Genotype refers to the collection of alleles an organism has, while phenotype refers to the physical traits or characteristics that are expressed as a result of the genotype.
Can two mice with different genotypes have the same phenotype?
-Yes, a heterozygous mouse (one dominant, one recessive allele) and a homozygous dominant mouse (two dominant alleles) can both have the same phenotype, as the dominant trait will be expressed in both.
What is an example of a trait determined by a single gene?
-Fur color in mice and red-green color blindness in humans are examples of traits determined by a single gene.
Why are characteristics like height determined by multiple genes?
-Height is influenced by several genes that interact with each other, which is why people vary greatly in height. It is an example of a polygenic trait.

Outlines

00:00

🔬 Introduction to Genetic Terms

The video begins by introducing the continuation of the previous topic on DNA. It sets the stage for discussing various genetic terms such as alleles, dominant and recessive traits, homozygous and heterozygous conditions, and genotype and phenotype. All these terms are explained in relation to genes, which are segments of DNA that code for specific proteins, influencing the traits we develop.

🧬 Gene Inheritance and Its Impact on Traits

The paragraph explains that the characteristics we inherit are determined by our genes. While some traits, like fur color in mice or color blindness in humans, are controlled by a single gene, most characteristics result from the interaction of multiple genes. For example, height is influenced by many genes, which explains why people vary in size.

🔄 The Concept of Alleles: Different Versions of Genes

Here, the concept of alleles is introduced. Alleles are different versions of the same gene, coding for various forms of a protein. Since we inherit two copies of each gene, one from each parent, we have two alleles for each gene, which can be either the same or different. If they are the same, the organism is homozygous for that allele; if different, it is heterozygous.

🐭 Dominant vs. Recessive Alleles in Mice

This paragraph discusses how dominant and recessive alleles affect traits, using the example of fur color in mice. If a mouse has one allele for purple fur and another for green fur, the dominant allele (purple) will be expressed, making the mouse purple. The only way to have a green-furred mouse is if both alleles are for green fur (homozygous recessive). The purple allele will always be expressed if present, whether the mouse is homozygous or heterozygous for purple.

📊 Genotype vs. Phenotype Explained

The final key terms, genotype and phenotype, are explained. Genotype refers to the complete set of alleles an organism possesses, while phenotype is the physical expression of these alleles. In the example of the three mice (heterozygous, homozygous dominant, and homozygous recessive), they have different genotypes, but two of them (heterozygous and homozygous dominant) share the same purple phenotype. The green mouse, with a homozygous recessive genotype, has a different phenotype.

👋 Conclusion and Preview of the Next Video

The video concludes with a brief summary of the topics covered and a teaser for the next video, which will explore genetic diagrams. The presenter thanks the viewers for watching and encourages them to stay tuned for future content.

Mindmap

Keywords

💡Allele

An allele is a variant form of a gene. In the video, alleles are described as different versions of the same gene, which may code for different traits. For example, one allele could code for purple fur in a mouse, and another could code for green fur. Each organism inherits two alleles for each gene, one from each parent.

💡Dominant

A dominant allele is one that is expressed when present, even if there is only one copy. In the video, the purple fur allele is described as dominant, meaning that a mouse with at least one purple allele will have purple fur, regardless of the other allele's code.

💡Recessive

A recessive allele is only expressed when both alleles are the same, meaning the individual must be homozygous for that allele. In the video, the green fur allele is recessive, so a mouse would need two green alleles (homozygous recessive) to have green fur.

💡Homozygous

Homozygous refers to having two identical alleles for a particular gene. In the video, if a mouse has two purple fur alleles (homozygous dominant) or two green fur alleles (homozygous recessive), it is said to be homozygous. This determines whether traits like fur color are consistently expressed.

💡Heterozygous

Heterozygous means having two different alleles for a gene. The video explains that a heterozygous mouse for fur color would have one allele for purple fur and one for green fur. In this case, the dominant allele (purple) would determine the mouse’s fur color.

💡Gene

A gene is a segment of DNA that codes for a specific protein, which contributes to the organism's traits. The video emphasizes that genes are inherited from both parents and together, they determine characteristics like fur color in mice or red-green color blindness in humans.

💡Genotype

The genotype is the combination of alleles that an organism possesses for a specific gene or set of genes. In the video, the different genotypes (heterozygous, homozygous dominant, and homozygous recessive) of the mice lead to either purple or green fur, but these genotypes reflect the underlying genetic code.

💡Phenotype

Phenotype refers to the observable physical traits or characteristics that result from an organism's genotype. The video explains that while a heterozygous and a homozygous dominant mouse might have different genotypes, they would share the same phenotype—purple fur—since the dominant allele is expressed.

💡Protein

Proteins are molecules coded by genes that perform various functions in the body. In the video, it is mentioned that genes code for proteins, and different alleles result in different forms of a protein, which ultimately leads to variations in traits such as fur color or height.

💡Trait

A trait is a characteristic that is determined by genes and can be observed in an organism. The video explains that traits, such as fur color in mice or color blindness in humans, are influenced by the interaction of multiple genes or, in some cases, by a single gene.

Highlights

Introduction to the continuation of DNA concepts from a previous video, focusing on allele, dominant and recessive traits, homozygous and heterozygous, and genotype and phenotype.

Genes are segments of DNA that code for specific proteins, which collectively determine the traits we develop.

Some traits, like fur color or red-green color blindness, are determined by a single gene, while most traits, like height, are influenced by multiple genes.

Alleles are different versions of the same gene, and we inherit two alleles for each gene, one from each parent.

When both alleles are the same, the organism is homozygous for that allele, but when they are different, the organism is heterozygous.

In heterozygous organisms, one allele is dominant and the other is recessive, meaning the dominant allele will be expressed.

Example: If a mouse is heterozygous for fur color, with one purple allele (dominant) and one green allele (recessive), the mouse will have purple fur.

For a recessive trait, like green fur in the mouse example, to be expressed, the organism must be homozygous recessive (both alleles for green fur).

The dominant allele is always expressed, regardless of whether the organism is homozygous or heterozygous for that dominant allele.

Genotype refers to the complete set of alleles that an organism has, representing its genetic code.

Phenotype describes the physical traits or characteristics that result from an organism's genotype.

Even though different genotypes may exist (e.g., heterozygous vs. homozygous dominant), organisms with the same phenotype may share similar physical traits.

Homozygous recessive organisms, like a green-furred mouse, will have both different genotypes and phenotypes compared to heterozygous or homozygous dominant organisms.

The video clarifies how genotype and phenotype relate but differ, using color examples to illustrate how alleles influence appearance.

Preview of the next video in the series, which will cover genetic diagrams and provide further exploration of genetics.