Monohybrid Inheritance
Overview
Why does a tall pea plant crossed with a dwarf one give all tall offspring, then dwarfs reappear in the next generation? Monohybrid inheritance is the study of how a single gene is passed on, and with one simple tool, the Punnett square, you can predict the offspring of a cross and state the exact ratios.
In this lesson you will master the language of genetics (genotype, phenotype, homozygous, heterozygous, dominant, recessive), read pedigree diagrams, and use Punnett squares to predict 3:1 and 1:1 ratios. For Extended you will work test crosses, codominance and the ABO blood groups, and sex-linked conditions such as red-green colour blindness.
Objectives
- Describe inheritance as the transmission of genetic information from generation to generation
- Describe genotype as the genetic make-up of an organism and in terms of the alleles present
- Describe phenotype as the observable features of an organism
- Describe homozygous as having two identical alleles of a particular gene
- State that two identical homozygous individuals that breed together will be pure-breeding
- Describe heterozygous as having two different alleles of a particular gene
- State that a heterozygous individual will not be pure-breeding
- Describe a dominant allele as an allele that is expressed if it is present in the genotype
- Describe a recessive allele as an allele that is only expressed when there is no dominant allele of the gene present in the genotype
- Interpret pedigree diagrams for the inheritance of a given characteristic
- Use genetic diagrams to predict the results of monohybrid crosses and calculate phenotypic ratios, limited to 1 : 1 and 3 : 1 ratios
- Use Punnett squares in crosses which result in more than one genotype to work out and show the possible different genotypes
- [Supplement] Explain how to use a test cross to identify an unknown genotype
- [Supplement] Describe codominance as a situation in which both alleles in heterozygous organisms contribute to the phenotype
- [Supplement] Explain the inheritance of ABO blood groups: phenotypes are A, B, AB and O blood groups and alleles are IA, IB and Io
- [Supplement] Describe a sex-linked characteristic as a feature in which the gene responsible is located on a sex chromosome and that this makes the characteristic more common in one sex than in the other
- [Supplement] Describe red-green colour blindness as an example of sex linkage
- [Supplement] Use genetic diagrams to predict the results of monohybrid crosses involving codominance or sex linkage and calculate phenotypic ratios
Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Monohybrid Inheritance. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- An organism with two identical alleles of a gene is described as: A. heterozygous B. homozygous C. recessive D. codominant Answer: B
- A cross between two heterozygous individuals (Bb x Bb) gives a phenotype ratio of: A. 1:1 B. 2:1 C. 3:1 D. 1:2:1 Answer: C
- A black mouse (Bb) is crossed with a brown mouse (bb). The expected phenotype ratio is: A. all black B. 3 black : 1 brown C. 1 black : 1 brown D. all brown Answer: C
- A person with blood group AB has the genotype: A. IA IO B. IB IO C. IA IB D. IO IO Answer: C
- Red-green colour blindness is more common in males because: A. the allele is dominant B. males have only one X chromosome, so a single recessive allele is expressed C. the gene is on the Y chromosome D. females cannot carry the allele Answer: B
Available on the Green Bridge App
Download the Green Bridge CBT app on your phone or computer to access full lesson notes, practice questions, and more.
Available on the Green Bridge App
Download the Green Bridge CBT app on your phone or computer to access full lesson notes, practice questions, and more.
Recommended Books
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