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wilsonc13
11/12/2025
Biology
Biology - DNA, Genes, Chromosomes & Alleles
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11 Dec 2025
•
Understanding DNA, Genes, Chromosomes, and Alleles
wilsonc13
@wilsonc13
1 / 3
DNA Structure and Basics
Your body contains roughly 2 metres of DNA packed into every single cell - that's absolutely mental when you think about it! This DNA (Deoxyribonucleic Acid) lives in the nucleus and has a twisted ladder shape called a double helix, made from a sugar-phosphate backbone with nitrogen base pairs forming the rungs.
Here's where it gets interesting: humans have 46 chromosomes arranged in 23 pairs. Most cells are diploid (containing all 46 chromosomes), but sex cells like sperm and eggs are haploid (containing only 23). This setup is essential for reproduction since two haploid cells combine to create a new diploid organism.
Genes are specific sections of DNA on chromosomes that code for particular characteristics - think of them as individual recipes in your genetic cookbook. With roughly 700 genes per chromosome, your genome (entire genetic material) contains thousands of instructions that make you uniquely you.
Key Point: The four nitrogen bases - Adenine pairs with Thymine, and Cytosine pairs with Guanine - form the genetic code that determines every trait you possess.
DNA Double Helix Structure
The double helix structure is basically two twisted strands connected by hydrogen bonds between nitrogen bases. Each strand consists of repeating units called nucleotides, which contain a phosphate group, deoxyribose sugar, and one of four nitrogen bases (adenine, thymine, cytosine, guanine).
The sugar-phosphate backbone forms the outer edges of the DNA ladder, whilst the nitrogen bases pair up in the middle like rungs. This pairing follows strict rules: A always bonds with T, and C always bonds with G - remember this as it's crucial for DNA replication and protein synthesis.
Chromosomes are essentially DNA that's been tightly coiled and packed up, like winding a really long piece of string into a compact bundle. This coiling allows metres of DNA to fit into the tiny nucleus of each cell without getting tangled.
Remember: One gene represents a section of DNA that codes for a specific protein or characteristic - it's like having one recipe within a massive cookbook.
Genes and Alleles
Alleles are different versions of the same gene - imagine having multiple recipes for chocolate cake, each slightly different. You inherit one allele from each parent, creating pairs that determine your characteristics through dominant and recessive interactions.
Dominant alleles (written with capital letters like B) only need one copy to show their effect, whilst recessive alleles (written with lowercase letters like b) need two copies to be expressed. This explains why you might have your dad's brown eyes even though your mum has blue eyes - brown is typically dominant over blue.
Your genotype refers to the actual letter combinations you possess (like Bb or BB), whilst scientists use terms like homozygous (same alleles: BB or bb) and heterozygous (different alleles: Bb) to describe these combinations. Some traits like eye colour involve polygenic inheritance, where multiple genes work together to create the final result.
The 23 pairs of homologous chromosomes mean you've got maternal and paternal versions of each chromosome, giving you genetic diversity whilst maintaining the essential instructions for life.
Top Tip: Remember that you need two recessive alleles for a recessive trait to show up - this is why some characteristics can skip generations in families.
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
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This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
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Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
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Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Understanding DNA, Genes, Chromosomes, and Alleles
wilsonc13
@wilsonc13
DNA is essentially the instruction manual inside every cell in your body that determines everything from your eye colour to your height. Understanding DNA, genes, and alleles is crucial for grasping how traits are passed from parents to children and... Show more
DNA Structure and Basics
Your body contains roughly 2 metres of DNA packed into every single cell - that's absolutely mental when you think about it! This DNA (Deoxyribonucleic Acid) lives in the nucleus and has a twisted ladder shape called a double helix, made from a sugar-phosphate backbone with nitrogen base pairs forming the rungs.
Here's where it gets interesting: humans have 46 chromosomes arranged in 23 pairs. Most cells are diploid (containing all 46 chromosomes), but sex cells like sperm and eggs are haploid (containing only 23). This setup is essential for reproduction since two haploid cells combine to create a new diploid organism.
Genes are specific sections of DNA on chromosomes that code for particular characteristics - think of them as individual recipes in your genetic cookbook. With roughly 700 genes per chromosome, your genome (entire genetic material) contains thousands of instructions that make you uniquely you.
Key Point: The four nitrogen bases - Adenine pairs with Thymine, and Cytosine pairs with Guanine - form the genetic code that determines every trait you possess.
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DNA Double Helix Structure
The double helix structure is basically two twisted strands connected by hydrogen bonds between nitrogen bases. Each strand consists of repeating units called nucleotides, which contain a phosphate group, deoxyribose sugar, and one of four nitrogen bases (adenine, thymine, cytosine, guanine).
The sugar-phosphate backbone forms the outer edges of the DNA ladder, whilst the nitrogen bases pair up in the middle like rungs. This pairing follows strict rules: A always bonds with T, and C always bonds with G - remember this as it's crucial for DNA replication and protein synthesis.
Chromosomes are essentially DNA that's been tightly coiled and packed up, like winding a really long piece of string into a compact bundle. This coiling allows metres of DNA to fit into the tiny nucleus of each cell without getting tangled.
Remember: One gene represents a section of DNA that codes for a specific protein or characteristic - it's like having one recipe within a massive cookbook.
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Genes and Alleles
Alleles are different versions of the same gene - imagine having multiple recipes for chocolate cake, each slightly different. You inherit one allele from each parent, creating pairs that determine your characteristics through dominant and recessive interactions.
Dominant alleles (written with capital letters like B) only need one copy to show their effect, whilst recessive alleles (written with lowercase letters like b) need two copies to be expressed. This explains why you might have your dad's brown eyes even though your mum has blue eyes - brown is typically dominant over blue.
Your genotype refers to the actual letter combinations you possess (like Bb or BB), whilst scientists use terms like homozygous (same alleles: BB or bb) and heterozygous (different alleles: Bb) to describe these combinations. Some traits like eye colour involve polygenic inheritance, where multiple genes work together to create the final result.
The 23 pairs of homologous chromosomes mean you've got maternal and paternal versions of each chromosome, giving you genetic diversity whilst maintaining the essential instructions for life.
Top Tip: Remember that you need two recessive alleles for a recessive trait to show up - this is why some characteristics can skip generations in families.
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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Most popular content: Genes
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Students love us — and so will you.
4.9/5
App Store
4.8/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user