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Fun with Genes: Random Fertilisation and Punnett Squares

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Emi

12/09/2025

Biology

Genes and inheritance

Subjects

Biology

Inheritance, variation and evolution

Reproduction, the genome and gene expression

Sexual reproduction, meiosis and gamete formation

1,060

•

12 Sept 2025

•

3 pages

Fun with Genes: Random Fertilisation and Punnett Squares

user profile picture

Emi

@emimcmurtry_hdjd

Random fertilisation and genetic variation in meiosis play crucial roles... Show more

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Genes and Inheritance sexual reproduction involves the fusion and fertilisation of two gametes, which each Contain alleles that will be pass

Genetic Inheritance: Punnett Squares and Allele Dominance

This page delves into the concepts of genetic inheritance, focusing on how to determine offspring phenotypes using Punnett squares. It explains key genetic terms and provides an example to illustrate inheritance patterns.

Vocabulary:

  • Genotype: The combination of alleles an individual possesses for a particular trait.
  • Phenotype: The visible characteristics resulting from an individual's genotype.

The page introduces the concepts of dominant and recessive alleles:

  • Dominant alleles are always expressed, even if only one copy is present.
  • Recessive alleles are only expressed when two copies are present.

Definition:

  • Homozygous: When the two alleles for a trait are the same.
  • Heterozygous: When the two alleles for a trait are different, typically one dominant and one recessive.

An example is provided using eye color inheritance:

  • B represents the dominant allele for brown eyes
  • b represents the recessive allele for blue eyes

The page demonstrates how to use a Punnett square to predict offspring genotypes and phenotypes. In the given example:

  • Mother's genotype: bb (homozygous recessive, blue eyes)
  • Father's genotype: Bb (heterozygous, brown eyes)

Example: The Punnett square shows a 1:1 ratio of offspring genotypes:

  • 50% Bb (brown eyes)
  • 50% bb (blue eyes)

The concept of codominance is briefly introduced, where both alleles contribute to the phenotype.

Example: Red and white flowers producing pink offspring, demonstrating a blend of both parental phenotypes.

Genes and Inheritance sexual reproduction involves the fusion and fertilisation of two gametes, which each Contain alleles that will be pass

Sex Determination: Chromosomal Basis of Gender

This page focuses on the chromosomal basis of sex determination in humans, explaining how the 23rd pair of chromosomes determines an individual's biological sex.

Human body cells contain 23 pairs of chromosomes:

  • 22 pairs control various characteristics and look similar within each pair.
  • The 23rd pair carries sex-determining genes and looks distinctly different between X and Y chromosomes.

Highlight: Y chromosomes are significantly smaller than X chromosomes.

The page outlines the chromosomal composition of male and female gametes:

  • Female gametes (eggs) always contain an X chromosome.
  • Male gametes (sperm) can carry either an X or a Y chromosome.

A Punnett square is used to illustrate sex determination:

  • Mother contributes an X chromosome
  • Father contributes either an X or a Y chromosome

Example: The Punnett square demonstrates:

  • XY combination results in male offspring
  • XX combination results in female offspring

The outcome shows a 50:50 chance of having either a boy or a girl.

Highlight: The father's sperm determines the sex of the offspring, as it can carry either an X or Y chromosome, while the mother always contributes an X chromosome.

This page effectively explains how random fertilisation contributes to gender determination, linking back to the concept of genetic variation introduced earlier in the transcript.

Genes and Inheritance sexual reproduction involves the fusion and fertilisation of two gametes, which each Contain alleles that will be pass

Genes and Inheritance: DNA Structure and Genetic Variation

This page introduces the concept of sexual reproduction and its role in genetic variation. It explains the structure of DNA and its components, emphasizing the importance of random fertilisation in creating genetic diversity.

Random fertilisation is a crucial process in sexual reproduction that increases genetic variation. This occurs when billions of genetically different sperm have the potential to fertilise each egg, leading to a vast array of possible genetic combinations in offspring.

Highlight: Random fertilisation allows species to adapt to their environment over many generations, contributing to evolution.

The page provides a detailed illustration of DNA structure, including:

  • The cell nucleus containing chromosomes
  • DNA's double helix structure
  • The four DNA bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C)
  • Nucleotide composition (sugar molecule, phosphate group, and base)

Vocabulary: Nucleotide - A building block of DNA consisting of a sugar molecule, a phosphate group, and one of four nitrogenous bases.

The complementary base pairing A−TandC−GA-T and C-G is explained, showing how these specific pairings contribute to DNA's structure and function.

Definition: DNA DeoxyribonucleicacidDeoxyribonucleic acid - A polymer made up of many nucleotides joined together to form a long strand.

The page concludes by mentioning that every three bases in DNA code for an amino acid, which in turn join together to form proteins.



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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

Subjects

Biology

Inheritance, variation and evolution

Reproduction, the genome and gene expression

Sexual reproduction, meiosis and gamete formation

 

Biology

•

1,060

•

12 Sept 2025

•

3 pages

Fun with Genes: Random Fertilisation and Punnett Squares

user profile picture

Emi

@emimcmurtry_hdjd

Random fertilisation and genetic variation in meiosis play crucial roles in sexual reproduction, contributing to the diversity of offspring. This process involves the fusion of gametes, each carrying unique alleles, resulting in billions of potential genetic combinations. Random fertilisation genetic... Show more

Genes and Inheritance sexual reproduction involves the fusion and fertilisation of two gametes, which each Contain alleles that will be pass

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

Genetic Inheritance: Punnett Squares and Allele Dominance

This page delves into the concepts of genetic inheritance, focusing on how to determine offspring phenotypes using Punnett squares. It explains key genetic terms and provides an example to illustrate inheritance patterns.

Vocabulary:

  • Genotype: The combination of alleles an individual possesses for a particular trait.
  • Phenotype: The visible characteristics resulting from an individual's genotype.

The page introduces the concepts of dominant and recessive alleles:

  • Dominant alleles are always expressed, even if only one copy is present.
  • Recessive alleles are only expressed when two copies are present.

Definition:

  • Homozygous: When the two alleles for a trait are the same.
  • Heterozygous: When the two alleles for a trait are different, typically one dominant and one recessive.

An example is provided using eye color inheritance:

  • B represents the dominant allele for brown eyes
  • b represents the recessive allele for blue eyes

The page demonstrates how to use a Punnett square to predict offspring genotypes and phenotypes. In the given example:

  • Mother's genotype: bb (homozygous recessive, blue eyes)
  • Father's genotype: Bb (heterozygous, brown eyes)

Example: The Punnett square shows a 1:1 ratio of offspring genotypes:

  • 50% Bb (brown eyes)
  • 50% bb (blue eyes)

The concept of codominance is briefly introduced, where both alleles contribute to the phenotype.

Example: Red and white flowers producing pink offspring, demonstrating a blend of both parental phenotypes.

Genes and Inheritance sexual reproduction involves the fusion and fertilisation of two gametes, which each Contain alleles that will be pass

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

Sex Determination: Chromosomal Basis of Gender

This page focuses on the chromosomal basis of sex determination in humans, explaining how the 23rd pair of chromosomes determines an individual's biological sex.

Human body cells contain 23 pairs of chromosomes:

  • 22 pairs control various characteristics and look similar within each pair.
  • The 23rd pair carries sex-determining genes and looks distinctly different between X and Y chromosomes.

Highlight: Y chromosomes are significantly smaller than X chromosomes.

The page outlines the chromosomal composition of male and female gametes:

  • Female gametes (eggs) always contain an X chromosome.
  • Male gametes (sperm) can carry either an X or a Y chromosome.

A Punnett square is used to illustrate sex determination:

  • Mother contributes an X chromosome
  • Father contributes either an X or a Y chromosome

Example: The Punnett square demonstrates:

  • XY combination results in male offspring
  • XX combination results in female offspring

The outcome shows a 50:50 chance of having either a boy or a girl.

Highlight: The father's sperm determines the sex of the offspring, as it can carry either an X or Y chromosome, while the mother always contributes an X chromosome.

This page effectively explains how random fertilisation contributes to gender determination, linking back to the concept of genetic variation introduced earlier in the transcript.

Genes and Inheritance sexual reproduction involves the fusion and fertilisation of two gametes, which each Contain alleles that will be pass

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 Inheritance: DNA Structure and Genetic Variation

This page introduces the concept of sexual reproduction and its role in genetic variation. It explains the structure of DNA and its components, emphasizing the importance of random fertilisation in creating genetic diversity.

Random fertilisation is a crucial process in sexual reproduction that increases genetic variation. This occurs when billions of genetically different sperm have the potential to fertilise each egg, leading to a vast array of possible genetic combinations in offspring.

Highlight: Random fertilisation allows species to adapt to their environment over many generations, contributing to evolution.

The page provides a detailed illustration of DNA structure, including:

  • The cell nucleus containing chromosomes
  • DNA's double helix structure
  • The four DNA bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C)
  • Nucleotide composition (sugar molecule, phosphate group, and base)

Vocabulary: Nucleotide - A building block of DNA consisting of a sugar molecule, a phosphate group, and one of four nitrogenous bases.

The complementary base pairing A−TandC−GA-T and C-G is explained, showing how these specific pairings contribute to DNA's structure and function.

Definition: DNA DeoxyribonucleicacidDeoxyribonucleic acid - A polymer made up of many nucleotides joined together to form a long strand.

The page concludes by mentioning that every three bases in DNA code for an amino acid, which in turn join together to form proteins.

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.

Smart Tools NEW

Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines

Mock Exam
Quiz
Flashcards
Essay

Can't find what you're looking for? Explore other subjects.

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