Inheritance
Overview
You share about 99.9% of your DNA with every other human on the planet, yet no two people (apart from identical twins) are genetically the same. The tiny differences in that remaining 0.1% account for everything from eye colour and blood group to your risk of certain diseases. Understanding how traits pass from parent to offspring - and how populations change over time - is one of the most powerful ideas in biology.
This lesson takes you from the structure of DNA through to Darwin's theory of evolution. You will learn how genes code for proteins, how alleles produce variation, how to predict the outcome of genetic crosses using Punnett squares, and why antibiotic resistance is a modern example of natural selection in action.
Objectives
- Understand that the genome is the entire DNA of an organism and that a gene is a section of a molecule of DNA that codes for a specific protein
- Understand that the nucleus of a cell contains chromosomes on which genes are located
- Describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G)
- Understand that an RNA molecule is single stranded and contains uracil (U) instead of thymine (T)
- Describe the stages of protein synthesis including transcription and translation, including the role of mRNA, ribosomes, tRNA, codons and anticodons
- Understand how genes exist in alternative forms called alleles which give rise to differences in inherited characteristics
- Understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, and genotype
- Understand the meaning of the term codominance
- Understand that most phenotypic features are the result of polygenic inheritance rather than single genes
- Describe patterns of monohybrid inheritance using a genetic diagram
- Understand how to interpret family pedigrees
- Predict probabilities of outcomes from monohybrid crosses
- Understand how the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male
- Describe the determination of the sex of offspring at fertilisation, using a genetic diagram
- Understand how division of a diploid cell by mitosis produces two cells that contain identical sets of chromosomes
- Understand that mitosis occurs during growth, repair, cloning and asexual reproduction
- Understand how division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes
- Understand how random fertilisation produces genetic variation of offspring
- Know that in human cells the diploid number of chromosomes is 46 and the haploid number is 23
- Understand that variation within a species can be genetic, environmental, or a combination of both
- Understand that mutation is a rare, random change in genetic material that can be inherited
- Understand how a change in DNA can affect the phenotype by altering the sequence of amino acids in a protein
- Understand how most genetic mutations have no effect on the phenotype, some have a small effect and rarely do they have a significant effect
- Understand that the incidence of mutations can be increased by exposure to ionising radiation and some chemical mutagens
- Explain Darwin's theory of evolution by natural selection
- Understand how resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lead to infections being difficult to control
Mind map
This topic is mapped out so you can see how the ideas connect.
Open the mind map in the app
Flashcards
Quick recall practice on the facts this topic is tested on.
Practise these cards in the app
Lesson Note
Complete Note Available on the Green Bridge App
Get the Green Bridge CBT app on your phone or computer for the complete IGCSE library: past papers, mark schemes, mind maps, flashcards and audio lessons.
Lesson Evaluation
Congratulations on completing the lesson on 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.
- What is the complementary DNA base pair for cytosine? A) Adenine B) Thymine C) Guanine D) Uracil Answer: C
- How many chromosomes are found in a human gamete? A) 46 B) 23 C) 44 D) 92 Answer: B
- Which type of cell division produces genetically identical cells? A) Meiosis B) Mitosis C) Binary fission D) Fertilisation Answer: B
- Two heterozygous parents (Bb) are crossed. What proportion of offspring are expected to show the recessive phenotype? A) 0% B) 25% C) 50% D) 75% Answer: B
- Which of the following can increase the rate of mutation? A) A balanced diet B) Regular exercise C) Exposure to ultraviolet radiation D) Drinking water Answer: C
Work through these questions in the app
Work through these questions in the app
Recommended Books
Practice Mock Questions
Want to practice mock questions on Inheritance? Download the Green Bridge CBT app to access mock questions and full practice assessments for this topic.
Download The App On Google Playstore
Everything you need to excel in your exams
