GCSE Biology - DNA Part 2 - Alleles / Dominant / Heterozygous / Phenotypes and more! #64
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
🔬 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
💡Dominant
💡Recessive
💡Homozygous
💡Heterozygous
💡Gene
💡Genotype
💡Phenotype
💡Protein
💡Trait
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.
Transcripts
today's video is sort of a continuation
of our last video on dna
and we're going to take a look at a
whole bunch of different terms to see
what an allele is
and what the differences are between
dominant and recessive
homozygous and heterozygous and also
genotype and phenotype
now all of these terms are related to
genes
and remember a gene is just a segment of
dna that codes for a particular type of
protein
together these genes we inherit
determine the characteristics that we go
on to develop
sometimes these traits are determined by
a single gene
like the ones that code for fur color
and mites
and red green color blindness in humans
more often though our characteristics
are determined by several different
genes that interact with each other
for example there are loads of genes
that code for height
which is one of the reasons why we're
all different sizes
if we look back at the definition of a
gene you'll notice that it codes for a
particular type of protein
the reason i say type of protein is that
there are often multiple forms of the
same protein
and so there'll be a different genetic
code for each of those forms
and we call these different codes
alleles
so you can think of alleles as different
versions of the same gene
because we have two copies of every gene
one from each of our parents it means
that we'll have two alleles of each gene
and these could both be the same allele
or they could be two different alleles
if they were the same we'd say they were
homozygous for that allele
whereas if they were different we would
be heterozygous
this brings a bit of a problem though
say we had a mouse that was heterozygous
for fur color
with one allele coding for purple fur
and the other for green fur
what color would our mouse be
well it's not going to be a mix of the
two
instead one of the alleles will be
dominant
and the other one will be recessive
and it's always a dominant one that gets
expressed
so if the purple allele was dominant to
the green allele
which would make that green allele
recessive
then our heterozygous mouse would be
purple
this means that the only way to have a
green mouse is if both of its alleles
were for green fur
which we would call homozygous recessive
on the other hand the purple allele will
always be expressed when it's present
regardless of whether the mouse is
heterozygous or homozygous for the
purple allele
now the last two terms that we need to
cover are genotype and phenotype
the genotype is basically the entire
collection of alleles that we have
so if we take the three mice that we
used before
the heterozygous mounts the homozygous
dominant and the homozygous recessive
one
we would say that they all have
different genotypes because they have
different alleles and so different
genetic codes
however your phenotype
is the characteristics that you get from
your genotype
so as both the heterozygous mouse and
the homozygous dominant mouse are purple
we would say that they have the same
phenotype
even though they had different genotypes
meanwhile because our homozygous
recessive mouse is green rather than
purple it has a different phenotype
as well as a different genotype
anyway that's it for this video in our
next one we're going to take a look at
genetic diagrams
so cheers for watching and we'll see you
soon
you
Посмотреть больше похожих видео
Genetics vocabulary | Inheritance and variation | Middle school biology | Khan Academy
An Introduction to Mendelian Genetics | Biomolecules | MCAT | Khan Academy
Introduction to Cytogenetics (Filipino) Genes Alleles Chromosomes
Co-dominance and Incomplete Dominance | Biomolecules | MCAT | Khan Academy
Genetics - Mendelian Experiments - Lesson 2 | Don't Memorise
Genotypic Ratios and Phenotypic Ratios for Punnett Squares
5.0 / 5 (0 votes)