4.3.1

Alleles

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Alleles

Alleles are different forms of the same gene. Humans have pairs of every gene and in one gene, each half of the pair may have different alleles. People's characteristics are determined by the alleles that they have. Alleles can either be dominant or recessive:

Dominant Alleles

Dominant Alleles

  • A dominant allele is always expressed, regardless of the identity of the other allele.
  • It only needs one copy present to be expressed (BB or Bb).
  • It is represented by a capital letter, e.g. B.
  • If B is the allele for brown eyes:
    • When a person has a copy of the B allele, they will have brown eyes, no matter what other allele is present.
Recessive Alleles

Recessive Alleles

  • A recessive allele is only expressed if the other allele is also recessive.
  • It is represented by a lowercase letter e.g. b. It needs two copies to be present to be expressed (bb).
  • If b is the allele for blue eyes:
    • A person can only have blue eyes if both of their alleles are b.
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1

The Nature & Variety of Living Organisms

1.1

Characteristics of Living Organisms

1.1.1MRS GRENC1.1.2M.R.S.1.1.3G.R.E.N.C.
1.2

Variety of Living Organisms

1.2.1Types of Cells1.2.2Properties of Prokaryotes1.2.3Structure of Eukaryotic Cells1.2.4Organisms: Animals & Plants1.2.5Other Kingdoms1.2.6Pathogens1.2.7Viruses
2

Structure & Functions in Living Organisms

2.1

Organisation Structure

2.1.1Cells2.1.2Tissues2.1.3Organs2.1.4Organ Systems2.1.5Organisms2.1.6Animal cells2.1.7Plant cells2.1.8Cell Differentiation2.1.9Stem Cells2.1.10Uses of Stem Cells2.1.11Disadvantages of Stem Cells2.1.12End of Topic Test - Cell Types & Structures2.1.13Exam-Style Questions - Cells2.1.14Diffusion2.1.15Factors affecting Diffusion2.1.16Surface Area to Volume Ratio2.1.17Diffusion - Experiment2.1.18Osmosis2.1.19Required Practical - Osmosis2.1.20Active Transport2.1.21Transport in Cells2.1.22End of Topic Test - Cell Transport2.1.23Grade 9 - Cell Transport2.1.24Exam-Style Questions - Substance Exchange
2.2

Biological Molecules

2.2.1Chemical Elements2.2.2Larger Molecules2.2.3Required Practical - Food Testing2.2.4Enzymes2.2.5Rate of Enzyme Action2.2.6Investigating Effect of pH on Amylase2.2.7Grade 9 - Enzymes
2.3

Nutrition

2.3.1Photosynthesis2.3.2Photosynthesis Equation2.3.3Factors affecting Rate of Photosynthesis2.3.4Photosynthesis - Calculations2.3.5Investigating Photosynthesis2.3.6Testing Leaves for Starch2.3.7Grade 9 - Photosynthesis Experiment2.3.8Exam-Style Questions - Rate of Photosynthesis2.3.9Leaf Adaptations2.3.10Ion Deficiencies2.3.11Human Diet2.3.12Vitamins and Minerals2.3.13Dietary Needs2.3.14Human Digestive System2.3.15Peristalsis2.3.16Villi2.3.17Digestive Enzymes2.3.18Amylase2.3.19Protease2.3.20Lipase2.3.21Bile2.3.22End of Topic Test - Enzymes & Nutririon2.3.23Exam-Style Questions - Enzymes & Digestion
3

Organism Functions

3.1

Respiration

3.1.1Respiration3.1.2Aerobic and Anaerobic3.1.3Investigating Respiration3.1.4End of Topic Test - Respiration
3.2

Gas Exchange

3.2.1Guard Cells & Stomata3.2.2States of Stomata3.2.3Plant Gas Exchange3.2.4Human Thorax3.2.5Breathing Process3.2.6Gas Exchange in Lungs3.2.7Exchange Surfaces3.2.8Alveoli3.2.9Breath Composition3.2.10Exercise and Breathing3.2.11Smoking
3.3

Transport

3.3.1Surface Area to Volume Ratio3.3.2Exchange Surfaces3.3.3Examples of Exchange Surfaces3.3.4Root Hair Cells3.3.5Transpiration3.3.6Rate of Transpiration3.3.7Measuring Transpiration3.3.8Xylem3.3.9Translocation3.3.10Blood Components3.3.11Plasma3.3.12Red Blood Cell3.3.13Platelets3.3.14The Immune System3.3.15Antibodies3.3.16Vaccination3.3.17Types of Blood Vessel3.3.18Blood Vessels - Arteries3.3.19Blood Vessels - Veins3.3.20Blood Vessels - Capillaries3.3.21Function of the Heart3.3.22Structure of the Heart3.3.23Heart Rate3.3.24Heart Disease3.3.25Double Circulatory System3.3.26Important Blood Vessels3.3.27End of Topic - Transport3.3.28Exam-Style Questions - The Heart
3.4

Excretion

3.4.1Excretion3.4.2Kidneys3.4.3Urine Production3.4.4Urinary System3.4.5Nephron3.4.6Water in Urine
3.5

Coordination & Response

3.5.1Homeostasis3.5.2Regulating Internal Conditions3.5.3Coordinated Responses3.5.4Types of Tropisms3.5.5Auxin and Phototropism3.5.6Nervous System3.5.7Synapses3.5.8Reflex Actions3.5.9Reflex Arc3.5.10Sense Organs3.5.11The Eye3.5.12Eye - Focusing3.5.13Eye - Adapting to Light3.5.14Thermoregulation3.5.15Sweating and Shivering3.5.16Thermoregulation - Blood Vessels3.5.17Exam-Style Questions - Homeostasis3.5.18Endocrine Glands3.5.19Hormones3.5.20Nervous vs Endocrine3.5.21Adrenaline3.5.22Glucose3.5.23Puberty3.5.24Menstruation3.5.25Menstrual Cycle3.5.26Menstrual Hormones3.5.27Grade 9 - Hormonal Coordination3.5.28End of Topic Test - Coordination & Response
4

Reproduction & Inheritance

4.1

Reproduction

4.1.1Asexual Reproduction4.1.2Sexual Reproduction4.1.3Gamete vs Zygote4.1.4Plant Reproduction4.1.5Flower Anatomy4.1.6Germination4.1.7Pollination4.1.8Pollination Methods4.1.9Male Reproductive System4.1.10Female Reproductive System4.1.11Pregnancy4.1.12Exam-Style Questions - Sexual Reproduction
4.2

Genetics

4.2.1Cell Division4.2.2Meiosis4.2.3Genome4.2.4Genome Diagram4.2.5DNA4.2.6RNA4.2.7Protein Synthesis4.2.8Synthesis Process4.2.9End of Topic Test - Reproduction & Genetics
4.3

Variation

4.3.1Alleles4.3.2Phenotype4.3.3Monohybrid Inheritance4.3.4Punnett Square4.3.5Sex Determination4.3.6Codominance4.3.7Cystic Fibrosis Punnett Square4.3.8Cystic Fibrosis Pedigree Diagram4.3.9Variation4.3.10Mutations4.3.11Natural Selection4.3.12Evolution4.3.13Resistant Bacteria4.3.14End of Topic Test - Variation4.3.15Grade 9 - Evolution4.3.16Exam-Style Questions - Cystic Fibrosis
5

Ecology

5.1

Ecosystems

5.1.1Ecosystems5.1.2Resources5.1.3Interdependence5.1.4Growth Factors5.1.5Assessing Ecosystems5.1.6Quadrats5.1.7Required Practical5.1.8Exam-Style Questions - Sampling5.1.9Energy Flow5.1.10Food Chains5.1.11Trophic Levels5.1.12Decomposers5.1.13Pyramids of Biomass5.1.14Transfer of Biomass5.1.15Reasons for Wastage5.1.16End of Topic Test - Food and Trophic Levels5.1.17Recycling Materials5.1.18Carbon Cycle5.1.19Exam-Style Questions - Carbon Cycle5.1.20Nitrogen Cycle5.1.21The Nitrogen Cycle and Microorganisms5.1.22End of Topic Test - Ecosystems5.1.23Grade 9 - Ecosystems
5.2

Human Impacts

5.2.1Waste Management5.2.2Eutrophication5.2.3Air Pollution5.2.4Deforestation5.2.5The Greenhouse Effect5.2.6Greenhouse Gases5.2.7Global Warming5.2.8End of Topic Test - Human Impacts5.2.9Exam-Style Questions - Air Pollution
6

Biological Resources

6.1

Food Production

6.1.1Intensive Farming - Crop Yield6.1.2Intensive Farming - Ion Deficiency6.1.3Intensive Farming - Pest Control6.1.4Intensive Farming - Fish Farming6.1.5Microorganisms in Food6.1.6Factors Affecting Microorganism Growth6.1.7Industrial Fermentation6.1.8Selective Breeding6.1.9Selective Breeding Process6.1.10Uses of Selective Breeding6.1.11Exam-Style Questions - Selective Breeding
6.2

Genetic Engineering

6.2.1Genetic Engineering6.2.2Uses of Genetic Engineering6.2.3Producing Human Proteins in Bacteria6.2.4Tissue Culture6.2.5Uses of Tissue Culture6.2.6Artificial Animal Cloning6.2.7Exam-Style Questions - Mitosis & Cloning

Practice questions on Alleles

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    Roberto inherits an allele for brown eyes (B) from one parent and an allele for blue eyes (b) from the other parent. What can you infer about Roberto's eye colour?Multiple choice
  2. 2
    A family study reveals that a certain trait follows a pattern where it appears in every generation, regardless of the specific pairing of alleles. What type of allele is most likely responsible for this pattern?Multiple choice
  3. 3
    During a genetic counselling session, parents are informed that they both carry the recessive allele for a genetic disorder. What is the probability that their child will express this disorder?Multiple choice
  4. 4
    Danielle carries a recessive allele (c) for a genetic trait. To evaluate the potential expression of this trait, what other information do you need?Multiple choice
  5. 5
    A geneticist explains that a person has a Bb genotype for a particular trait. What is the most likely outcome for the expression of this trait?Multiple choice
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End of Topic Test - Reproduction & Genetics

Phenotype