17.3.1

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

Classification of Living Organisms

1.1

Characteristics of Living Organisms

1.1.1MRS GREN1.1.2M.R.S.1.1.3G.R.E.N.
1.2

Concept and Uses of Classification Systems

1.2.1Classification1.2.2Linnaean Classification1.2.3Evolutionary Trees1.2.4Ancestors & DNA
1.3

Features of Organisms

1.3.1Dichotomous Keys1.3.2Kingdoms - Animals & Plants1.3.3Kingdoms - Fungi, Prokaryotes, Protoctista1.3.4Vertebrates1.3.5Anthropods1.3.6Plant Classification1.3.7Cellular Structures - Cells1.3.8Cellular Structures - Viruses
2

Organisation of the Organism

2.1

Cell Structure

2.1.1Animal Cells2.1.2Plant Cells2.1.3Properties of Prokaryotes2.1.4Cells & Tissues2.1.5Organs2.1.6Organ Systems2.1.7Organisms2.1.8Ciliated Epithelia2.1.9Sperm & Egg Cells2.1.10Red Blood Cells2.1.11Neurones2.1.12Root Hair Cells & Palisade Mesophyll Cells2.1.13Xylem
2.2

Size of Specimens

2.2.1Magnification2.2.2Microscopy2.2.3Orders of Magnitude2.2.4Microscopy - Calculations2.2.5Microscope Practical2.2.6Converting Measurements2.2.7End of Topic Test - Cells2.2.8Exam-Style Questions - Cell Structure & Microscopy
3

Movement Into & Out of Cells

3.1

Diffusion

3.1.1Diffusion3.1.2Factors Affecting Diffusion3.1.3Surface Area : Volume
3.2

Osmosis

3.2.1Osmosis3.2.2Osmosis Experiment3.2.3Osmosis in Plants3.2.4Osmotic Balance3.2.5Required Practical - Osmosis
3.3

Active Transport

3.3.1Active Transport3.3.2Transport in Cells3.3.3Carrier Proteins3.3.4Grade 9 - Cell Transport3.3.5End of Topic Test - Cell Transport3.3.6Exam-Style Questions - Substance Exchange
4

Biological Molecules

4.1

Biological Molecules

4.1.1Chemical Elements4.1.2Larger Molecules4.1.3Water4.1.4Testing for Biological Molecules4.1.5DNA4.1.6DNA Pairings
5

Enzymes

5.1

Enzymes

5.1.1Enzymes5.1.2Rate of Enzyme Action5.1.3Investigating Rate5.1.4Rate of Reaction - Calculations5.1.5End of Topic Test - Enzymes5.1.6Grade 9 - Enzymes
6

Plant Nutrition

6.1

Photosynthesis

6.1.1Photosynthesis6.1.2Photosynthesis - Plant Gas Exchange6.1.3Photosynthesis in Farming6.1.4Uses of Glucose6.1.5Ion Deficiency Conditions6.1.6Rate of Photosynthesis6.1.7Photosynthesis Experiments6.1.8Photosynthesis Equation6.1.9Photosynthesis - Calculations6.1.10Limiting Factors6.1.11Grade 9 - Photosynthesis Experiment6.1.12Exam-Style Questions - Photosynthesis
6.2

Leaf Structure

6.2.1Leaf Structure6.2.2Stomata6.2.3States of Stomata6.2.4Plant Tissues6.2.5Leaf Adaptations6.2.6End of Topic Test - Photosynthesis
7

Human Nutrition

7.1

Diet

7.1.1Diet7.1.2Vitamins & Minerals7.1.3Dietary Needs
7.2

Digestive System

7.2.1Digestive System7.2.2Steps of Digestion7.2.3Diarrhoea
7.3

Physical Digestion

7.3.1Physical Digestion - Human Tooth7.3.2Teeth Types7.3.3Tooth Diseases
7.4

Chemical Digestion

7.4.1Digestive Enzymes7.4.2Examples of Digestive Enzymes - Amylases7.4.3Examples of Digestive Enzymes - Proteases7.4.4Examples of Digestive Enzymes - Lipases7.4.5Chemical Digestion - Stomach7.4.6Exam-Style Questions - Digestive Enzymes7.4.7Pepsin & Trypsin
7.5

Absorption

7.5.1Small Intestine7.5.2Villi
8

Transport in Plants

8.1

Xylem & Phloem

8.1.1Plant Vessels8.1.2Specialised Plant Cells - Xylem
8.2

Water Uptake

8.2.1Water Uptake8.2.2Specialised Plant Cells - Root Hair8.2.3Exam-Style Questions - Transport in Plants
8.3

Transpiration

8.3.1Transpiration8.3.2Transpiration Tissues - Xylem8.3.3Rate of Transpiration8.3.4Measuring Transpiration
8.4

Translocation

8.4.1Translocation Tissues - Phloem8.4.2Translocation8.4.3End of Topic Test - Plant Transport
9

Transport in Animals

9.1

Circulatory Systems

9.1.1Circulatory Systems9.1.2Double Circulatory Systems
9.2

Heart

9.2.1Mammal Heart Function9.2.2Mammal Heart Structure9.2.3Heart Monitoring9.2.4Exercise Recovery9.2.5Heart Disease9.2.6Treatment of Heart Disease
9.3

Blood Vessels

9.3.1Types of Vessels - Arteries9.3.2Types of Vessels - Veins9.3.3Types of Vessels - Capillaries9.3.4Important Vessels9.3.5Lymphatic System9.3.6End of Topic Test - Circulatory System9.3.7Exam-Style Questions - Circulatory System
9.4

Blood

9.4.1Blood Components9.4.2Red Blood Cells9.4.3White Blood Cells9.4.4Platelets9.4.5Blood Clotting
10

Diseases & Immunity

10.1

Diseases & Immunity

10.1.1Health Issues10.1.2Causing Diseases10.1.3Preventing Infection10.1.4Human Defence Systems - Non-Specific Defences10.1.5Human Defence Systems - Immune Systems10.1.6Antibodies10.1.7Vaccination & Immunity10.1.8Passive Immunity10.1.9Viruses10.1.10End of Topic Test - Health & Disease
11

Gas Exchange in Humans

11.1

Gas Exchange in Humans

11.1.1Exchange Surface11.1.2Lung Gas Exchange11.1.3Alveoli11.1.4Breathing Process11.1.5Breathing Composition11.1.6Breathing & Exercise11.1.7Thorax
12

Respiration

12.1

Respiration

12.1.1Respiration Uses12.1.2Investigating Respiration12.1.3End of Topic Test - Respiration12.1.4Exam-Style Questions - Respiration During Exercise
12.2

Aerobic & Anaerobic Respiration

12.2.1Respiration Reactions12.2.2Oxygen Use & Debt12.2.3Aerobic and Anaerobic Respiration
13

Excretion in Humans

13.1

Excretion in Humans

13.1.1Excretion in Humans13.1.2Urea13.1.3Water Balance13.1.4Water in Urine13.1.5The Kidneys13.1.6Urine Production13.1.7Urinary System13.1.8Dialysis13.1.9Dialysis - Pros & Cons13.1.10Kidney Transplants13.1.11Kidney Transplants - Pros & Cons
14

Coordination & Response

14.1

Coordination & Response

14.1.1The Nervous System14.1.2Reflex Actions14.1.3Reflex Arc14.1.4Synapses14.1.5End of Topic Test - Nervous Control14.1.6Exam-Style Questions - Nervous System
14.2

Sense Organs

14.2.1Sense Organs14.2.2Eye Anatomy14.2.3Eye Function - Light14.2.4Eye Function - Focus14.2.5Eye Function - Detecting Colour
14.3

Hormones

14.3.1Hormones in Humans14.3.2Endocrine Glands14.3.3Nervous vs Endocrine14.3.4Adrenaline
14.4

Homeostasis

14.4.1Homeostasis14.4.2Regulating Internal Conditions14.4.3Control Systems14.4.4Negative Feedback14.4.5Thermoregulation14.4.6Thermoregulation - Hot and Cold14.4.7Thermoregulation - Skin14.4.8Thermoregulation - Sweating & Shivering14.4.9Thermoregulation - Hairs14.4.10Thermoregulation - Blood Vessels14.4.11Blood Glucose14.4.12Detecting Glucose14.4.13Type 1 Diabetes14.4.14End of Topic Test - Homeostasis & Hormones14.4.15Grade 9 - Hormonal Coordination
14.5

Tropic Responses

14.5.1Types of Tropisms14.5.2Auxins and Tropisms14.5.3Required Practical - Plant Hormones
15

Drugs

15.1

Drugs

15.1.1Antibiotics15.1.2Antibiotic Resistance15.1.3Resistant Bacteria
16

Reproduction

16.1

Asexual Reproduction

16.1.1Asexual Reproduction16.1.2Advantages of Asexual Reproduction
16.2

Sexual Reproduction

16.2.1Sexual Reproduction16.2.2Gametes vs. Zygotes16.2.3Advantages of Sexual Reproduction
16.3

Sexual Reproduction in Plants

16.3.1Flower Anatomy16.3.2Pollination Methods16.3.3Self-pollination & Cross-polination16.3.4Germination
16.4

Sexual Reproduction in Humans

16.4.1Human Reproductive Systems - Male16.4.2Human Reproductive Systems - Female16.4.3Human Gametes - Sperm Cells16.4.4Human Gametes - Egg Cells16.4.5Human Gametes - Egg vs. Sperm16.4.6Pregnancy16.4.7Pregnancy Health16.4.8Birth - Labour16.4.9Birth - Breast-feeding
16.5

Sex Hormones in Humans

16.5.1Puberty16.5.2Menstruation16.5.3Menstrual Cycle16.5.4Menstrual Hormones16.5.5Baby Planning16.5.6Infertility16.5.7Fertility Treatments Pros & Cons16.5.8End of Topic Test - Reproductive Hormones16.5.9Exam-Style Questions - Hormones & Contraception
16.6

Sexually Transmitted Infections

16.6.1HIV
17

Inheritance

17.1

Chromosomes, Genes & Proteins

17.1.1Genome17.1.2Genome Diagram17.1.3Gene Expression17.1.4DNA Pairings17.1.5Protein Synthesis17.1.6Synthesis Process
17.2

Mitosis & Meiosis

17.2.1Cell Division17.2.2Stem Cells17.2.3Meiosis
17.3

Monohybrid Inheritance

17.3.1Alleles17.3.2Phenotype17.3.3Sex Determination17.3.4Monohybrid Inheritance17.3.5Punnett Square17.3.6Blood Groups17.3.7Sex-linked Disorders17.3.8Cystic Fibrosis17.3.9Cystic Fibrosis - Punnett Square17.3.10Cystic Fibrosis - Pedigree Diagram17.3.11Test Crosses17.3.12End of Topic Test - Genes & Inheritance
18

Variation & Selection

18.1

Variation

18.1.1Variation18.1.2Continuous & Discontinuous Variation18.1.3Mutations18.1.4Sickle Cell Symptoms18.1.5Sickle Cell & Malaria18.1.6Sickle Cell Inheritance
18.2

Adaptive Features

18.2.1Adaptive Features18.2.2Plant Adaptations
18.3

Selection

18.3.1Natural Selection18.3.2Evolution18.3.3Antibiotic Resistance18.3.4Selective Breeding18.3.5Selective Breeding Process18.3.6Uses of Selective Breeding18.3.7Grade 9 - Evolution18.3.8End of Topic Test - Variation & Evolution
19

Organisms & Their Environment

19.1

Energy Flow

19.1.1Energy Flow
19.2

Food Chains & Food Webs

19.2.1Food Chains & Webs19.2.2Decomposers19.2.3Trophic Levels19.2.4Pyramids of Biomass19.2.5Editing Food Chains19.2.6Reasons for Energy Wastage19.2.7Transfer Efficiency19.2.8Exam-Style Questions - Biomass19.2.9End of Topic Test - Food and Trophic Levels
19.3

Nutrient Cycles

19.3.1Importance of Cycling19.3.2Carbon Cycle19.3.3Peat Bog19.3.4Water Cycle19.3.5Nitrogen Cycle19.3.6Nitrogen Cycle & Microorganisms
19.4

Populations

19.4.1Ecosystems19.4.2Population Growth Factors19.4.3Population Growth19.4.4Human Population19.4.5Grade 9 - Ecosystems19.4.6End of Topic Test - Ecosystems
20

Human Influence on Ecosystems

20.1

Food Supply

20.1.1Food Supply & Modern Technology20.1.2Food Supply & Modern Technology Drawbacks20.1.3Food Supply & Populations20.1.4Causes of Famine20.1.5Declining Fish Stock
20.2

Habitat Destruction

20.2.1Habitat Destruction20.2.2Deforestation20.2.3Exam-Style Questions - Deforestation
20.3

Pollution

20.3.1Humans & Waste20.3.2Nuclear Waste20.3.3Land Pollution20.3.4Waste Production - Plastics20.3.5Air Pollution20.3.6Greenhouse Effect20.3.7Global Warming20.3.8Eutrophication
20.4

Conservation

20.4.1Conservation20.4.2Reasons to Conserve Biodiversity20.4.3Renewable Resources20.4.4Recycling20.4.5Sustainability20.4.6Sewage Treatment20.4.7Sustainable Fishing20.4.8Sustainable Forest20.4.9Endangered Species20.4.10Causes of Endangering
21

Biotechnology & Genetic Modification

21.1

Biotechnology & Genetic Modification

21.1.1Bacteria in Biotechnology
21.2

Biotechnology

21.2.1Yeast in Biotechnology21.2.2Enzymes in Biotechnology21.2.3Penicillin
21.3

Genetic Modification

21.3.1Genetic Modification21.3.2Genetic Modification - Process21.3.3Genetic Modification - Controversy21.3.4Pros & Cons of Genetic Modification

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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Meiosis

Phenotype