Unit 1: HUMAN GENOME PROJECT

I. Introduction

• The Human Genome Project involved thousands of scientists globally collaborating to map the human genome between 1990 and 2003. 

• Approximately 20,500 genes and their locations were identified. 

• Scientists continue to explore the functions of these genes.

II. Medical Uses

• The project has identified approximately 1,800 genes associated with diseases, enabling various medical advancements:

1. Test for and Treat Genetic Disorders:

• Scientists were able to quickly identify the genes and alleles that are thought to have caused genetic disorders. Specific treatments are then given. 

2. Predict and Prevent Diseases:

• Understanding genetic predispositions allows for personalized preventive measures and early interventions.

• For example, heart disease is caused by a combination of genes alongside lifestyle factors so doctors can tailor their advice on diet and lifestyle to those who are more likely to get heart disease..

3. Create More Efficient Medication:

• Genetic variations influence treatment responses, facilitating the development of tailored medications for improved efficacy and fewer side effects.

• For example, in breast cancer, tests can be done to see whether a person will or won’t respond to a specific drug and which dosage is the most appropriate for them. 

III. Disadvantages

1. Potential Discrimination:

• Knowledge of genetic predispositions may lead to discrimination by employers and insurers, resulting in increased insurance costs and employment bias.

2. Psychological Stress:

• Awareness of genetic susceptibility to diseases can cause significant stress and anxiety.

3. Influence on Family Planning:

• Concerns about passing on genetic disorders may influence individuals' decisions regarding having children.

Unit 2: VARIATION AND ITS CAUSES (Genotypes and Phenotypes)

I. Key Terms

1. Genotype

• The collection of genes an organism inherits from its parents.

• Genetic makeup that determines traits.

• The genetic sequence of an organism in terms of the alleles present.

2. Phenotype

• The observable physical characteristics of an organism, determined by both genetic and environmental factors.

3. Variation

• Differences in phenotypes within a population.

• Allows populations to adapt and evolve.

• Essential for understanding life's diversity and applications in fields like medicine and agriculture.

4. Continuous Variation

•  Results in a range of phenotypes.

5. Discontinuous Variation

• Results in distinct phenotypes with no intermediates.

6. Genotypic Variation

• Differences in genotype

7. Phenotypic Variation

• Differences in expressed phenotypes.

8. Environmental Variation

• The differences in phenotype are caused by the environment.

• Hence, they are acquired characteristics

II. Reasons for Variation

1. Genes

• Inherited from parents, controlling many characteristics.

• For example, blood type is controlled by genes only, there is no environmental influence.

• Other examples of genetic phenotypes are natural eye colour and the ability to roll your tongue.

2. Environment

• External influences to the phenotype, such as accents.

3. Genes and Environment

• Most characteristics are influenced by both genes and environment.

III. Variation Between and Within Species

1. Between Species

• Significant differences.

• For example, a lion has a tail whereas a human does not.

2. Within Species

• More similarities, but still genetic variation exists due to mutations.

IV. Mutation and Variation

• Genetics Variation are differences in DNA code within a population and its due to mutations.

• Genetic Mutations are spontaneous changes in genetic material, sometimes affecting phenotype that results in trait alteration or disease.

V. Sexual Reproduction and Variation

1. Sexual Reproduction can also cause Variation

• Variation introduced through the mixing of maternal and paternal chromosomes during meiosis.

• Random fertilization of gametes contributes to genetic variation in offspring.

Unit 3: MITOSIS AND MEIOSIS

I. Mitosis

• Mitosis leads to the formation of two daughter cells which each have the same number of chromosomes as the parent cell.

• This is crucial for growth and tissue repair.

• It occurs through asexual reproduction.

• Predominant in tissues like skin and muscle cells.

• Part of the cell cycle, involving doubling of genetic material, alignment, separation, and formation of new cells.

Mitosis results in the production of two identical daughter cells,

II. Meiosis and Fertilization

• A division vital for sexual reproduction, producing four genetically unique daughter cells, each with half the number of chromosomes as the parent cell.

• Allows for the shuffling of genetic information from two parents, resulting in offspring that are genetically diverse.

• This diversity can increase the chances of survival and adaptation in changing environments.

1. Formation of Gametes

• Sperm and egg cells in animals, pollen and egg cells in plants.

2. Halving of Cell Number

• Original cell divides twice, yielding four haploid daughter cells, genetically distinct.

3. Production of Haploid Daughter Cells

• Unlike mitosis, meiosis yields four non-identical haploid daughter cells.

4. Fertilization Process

• Fusion of haploid gametes restores diploid chromosome number.

5. Human Fertilization

• Fusion of sperm and egg cells, resulting in a genetically diverse zygote.

6. Development into Embryo

• Zygote matures into an embryo, undergoing mitosis and differentiation.

III. Steps of Mitosis

1. Prophase

• The chromatin condenses into chromosomes and the spindle apparatus forms.

2. Metaphase

• The chromosomes align at the center of the cell.

3. Anaphase

• The chromosomes separate and move towards opposite poles of the cell.

4. Telophase

• A new nucleus forms around each set of chromosomes and the cell splits in two.

5. Cytokinesis

• The cytoplasm divides, creating two separate daughter cells.

IV. Steps of Meiosis

1. Prophase I

• The chromatin condenses into chromosomes and the spindle apparatus forms.

2. Metaphase I

• The chromosomes align at the center of the cell.

3. Anaphase I

• The chromosomes separate and move towards opposite poles of the cell.

4. Telophase I

• A new nucleus forms around each set of chromosomes and the cell splits in two.

5. Cytokinesis I

• The cytoplasm divides, creating two separate daughter cells.

6. Prophase II

• The chromatin condenses into chromosomes and the spindle apparatus forms.

7. Metaphase II

• The chromosomes align at the center of the cell.

8. Anaphase II

• The chromosomes separate and move towards opposite poles of the cell.

9. Telophase II

• A new nucleus forms around each set of chromosomes and the cell splits in two.

10. Cytokinesis II

• The cytoplasm divides, creating four separate daughter cells.

Unit 4: INHERITANCE

I. Definition

• Passing of genetic information from parent to offspring, determining traits.

• These traits can include physical characteristics, such as eye color and height, as well as behavioral traits and diseases.

II. Genes

• Units of genetic information about traits located on chromosomes. 

I. Mendel’s Experiments

• Mendelian genetics laid the groundwork for our understanding of inheritance.

• Mendel conducted experiments with plant breeding in the 19th century.

• He elucidated principles of dominance and monohybrid inheritance.

1. Monohybrid inheritance

• Single-gene inheritance of certain characteristics.

2. Mendel’s theory

• Proposed transfer of 'units' (later identified as genes) between organisms, influencing characteristics.

3. Pea Plant Experiments

• Studied traits like smooth and wrinkled peas to discern dominance.

• Smooth peas: dominant

• Wrinkled peas: recessive.

4. Posthumous Recognition

• Mendel's work gained appreciation later.

• Units (genes) correlated with chromosomes, laying groundwork for genetics.

• Linkage to DNA elucidated by subsequent discoveries.

II. Sex Determination

• Normal human cells contain 23 pairs of chromosomes, including one pair of sex chromosomes.

1. Autosomes 

• 22 pairs of autosomes control general traits.

2. Sex Chromosomes

• A chromosome is a structure in the nucleus of a cell that is made up of one condensed molecule of DNA.

• Structures containing genes within cells, humans have 46 chromosomes in pairs.

• Males have XY chromosomes.

• Females have XX chromosomes

• 1 pair of sex chromosomes determines gender..

III. Sex-Linked Characteristics

• Some traits are linked to the sex chromosomes, influencing their prevalence.

• Genes located on sex chromosomes (X or Y) influence inheritance, differing between males and females.

1. Colour Blindness

• Caused by a faulty allele on the X chromosome.

• Recessive allele (Only the recessive allele can be present if its characteristic is to be expressed), requiring two copies in females (Xn Xn) to manifest.

• Males need only one copy (Xn Y), making colour blindness more common in males.
  

2. Probability Calculation

• Utilize Punnett Squares, considering gender in the allele combinations.

• For instance, crossing Homozygous Dominant male (XDY) with Heterozygous female (XDXd).

a. XDXD

• A Homozygous dominant female

b. XDY

• A Homozygous dominant male

c. XDXd

• A Heterozygous female

d. AdY

• A Homozygous recessive man

• You can use these value to work out probabilities and ratios in the same way as above.

Unit 5: GENETIC DIAGRAMS

I. Punnett Squares (Gene Crosses)

• Punnett squares predict offspring phenotypes based on parental alleles, crucial for monohybrid inheritance.

• Single gene crosses follow monohybrid inheritance, facilitating prediction.

• Worked examples demonstrate probability and ratio determination for traits like hair color.

• Drawing Punnett squares involves placing parental alleles and combining them to predict offspring genotypes.

II. Codominance and Blood Groups

1. Codominance

• Both alleles of a gene are expressed equally in the phenotype.

• Neither allele is recessive so characteristics of both alleles are expressed.

2. Incomplete Dominance

• Both alleles contribute to the phenotype in a blended way.

3. 4 blood groups

• They are A, B, AB and O.

4. 3 different alleles for blood groups

• They are IA, IB and IO.

5. Codominant alleles

• IA and IB are codominant with each other so you have both alleles, both are expressed to give the blood group AB.

6. I° is recessive

• When you get two of these alleles, your blood group is O.

• If you get one of these alleles and say the other is IB, only IB will be expressed giving you the blood group B.

7. Use Punnett square to predict blood groups

• This can be done in the same way as recessive and dominant alleles but instead using the alleles IΑ, IB and I°.

III. Family Pedigrees

• Pedigrees illustrate inheritance patterns within families, useful for understanding genetic disorders.

• Help identify carriers and predict probabilities of offspring inheriting the disease.

1. Cystic fibrosis is a recessive disease

• A recessive disease where carriers are heterozygous.

2. If they are heterozygous, they will be carriers of the disease

• This means that they don’t have the disease but it can still be passed down the family.

3. If they are homozygous dominant, they won’t have the disease or be carriers

• You can tell that the cystic fibrosis allele isn’t dominant because Katie has the disease when neither of her parents had the disease – they were carriers. The carriers have the genotype Ff.

• You can predict the probability of the newborn baby having cystic fibrosis. As both parents are carriers of the disease, there is a 25% chance the baby will have the disease (genotype ff), 25% they will be unaffected (genotype FF) and a 50% chance that they will be a carrier (genotype Ff). Try drawing a punnett square for this and see if you get the same probabilities.

Unit 6: GENES AND INHERITANCE

I. Definition of Terms

1. Gamete

• Sex cell containing half the normal number of chromosomes (haploid).

2. Gene

•  DNA segment coding for a specific protein or characteristic.

3. Allele

• Variant form of a gene that influences trait variation.

4. Dominant

• Allele is always expressed in an organism.

5. Homozygous

• Two identical alleles, either dominant or recessive.

6. Heterozygous

• One dominant and one recessive allele present.

II. Genetic Inheritance

• Transmission of genetic information from one generation to the next.

• Most traits involve multiple genes rather than single-gene inheritance.

• Specific characteristics may be controlled by a single gene, like red-green color blindness and fur color in mice.

1. Hair Colour

• Hair color demonstrates genetic inheritance terminology.

• Dominant allele for dark hair, recessive for light hair.

• Homozygous dominant individuals have dark hair, homozygous recessive individuals have light hair.

• Heterozygous individuals have dark hair due to dominance of the dark hair allele.

2. Dominant and Recessive Inheritance 

• Interaction of genes determining trait expression.

3. Polygenic Inheritance 

• Traits determined by multiple genes.

Unit 7: ASEXUAL AND SEXUAL REPRODUCTION

• Reproduction is one of the essential (biological) processes of life as it promotes continuation of species by producing offspring.

• It occurs not only between human and animals, but also in every single one of our cells.

• There are two different types of reproduction and they are present for different purposes.

I. Asexual Reproduction

• Occurs via mitosis, creating genetically identical clones.

• Requires only one parent cell, resulting in offspring that are clones of the parent without gametes or fertilization.

• Examples include bacteria, fungi, single-celled organisms, and some plants and animals.

II. Sexual Reproduction

• Involves two individuals of different sexes contributing genetic information through mating.

• Results in offspring with a unique combination of genetic material from both parents.

• Fusion of nuclei of two gametes forms a zygote, leading to genetically different offspring.

• Requires meiosis to form gametes (sperm and egg cells in animals, pollen and egg cells in flowering plants).

• Some organisms can reproduce both sexually and asexually, enhancing species survival.

• Some examples include:

1. Malaria Parasite

• Reproduces asexually in humans and sexually in mosquitoes.

2. Fungi 

• Reproduce asexually through budding and sexually through spore formation.

3. Plants

• Strawberry plants reproduce sexually via seeds and asexually via runners.

• Daffodils reproduce sexually through seeds and asexually through bulb division.

Unit 8: SEXUAL REPRODUCTION: PROS AND CONS

I. Advantages of Sexual Reproduction

1. Variation in offspring

• Genetic material mixing leads to genetically diverse offspring and provides survival advantages.

• Variation provides survival advantages through natural selection.

• Selective breeding in crop production enhances desired characteristics.

II. Disadvantages of Sexual Reproduction

1. Resource cost

• Sexual reproduction, involving meiosis and the need for a mate, is time and energy-intensive.

• Fewer offspring produced due to the complexity and resource demands of the process.

2. Dependency on mating

• Requires two parents, necessitating finding a mate.

• Difficulties may arise if organisms are isolated or need to travel far to find a mate.

Unit 9: ASEXUAL REPRODUCTION: PROS AND CONS

I. Advantages of Asexual Reproduction

1. Requires only one parent

• Asexual reproduction is efficient as it only involves one parent, eliminating the need to find a mate.

• Saves time and energy compared to sexual reproduction.

2. Quicker process

• Asexual reproduction is faster than sexual reproduction, as it only involves mitosis.

• Meiosis, required for sexual reproduction, is a longer process.

3. Produces clones

• Offspring produced through asexual reproduction are genetically identical to the parent.

• Favourable traits in the parent can be quickly passed on to offspring, enhancing survival.

• Rapid production of advantaged offspring.

II. Disadvantages of Asexual Reproduction

1. Lack of variation

• Asexual reproduction does not result in genetic variation as there is no transfer of genetic material.

• Offspring may not be well-suited to changing environments, increasing susceptibility to disease.

2. Risk of Overpopulation

• Due to its efficiency, asexual reproduction can lead to overpopulation if left unchecked.