Genetics Overview 🧬

Genetics is the study of the mechanisms involved in the control, transmission, and expression of inherited characteristics. 📚

Variation 🌈

Variation refers to the differences in characteristics among organisms of the same species. There are two types of variation:

Continuous Variation 📏

Definition: Characteristics that exhibit many intermediate forms between two extremes. 🌟

Examples: Height, complexion, and body mass/size in humans. 👤

Causes:

• Control by many genes (polygenic inheritance). 🧬
• Influence of environmental factors (e.g., diet, climate). 🌍

Discontinuous Variation 🚫

Definition: Characteristics that fall into distinct groups with no intermediate forms. ❌

Examples: Sex, blood groups, and eye color in humans. 👁️

Causes:

• Control by one or few genes. 🔬
• Lack of environmental influence. 🌤️

Chromosomes and Genes 🧬

Chromosomes: DNA threads found in the nucleus responsible for storing inherited information in the form of genes. 📦

Each species has a fixed number of chromosomes:

• Somatic Cells: Diploid number (2n). 👥
• Gametes: Haploid number (n). 🥚

Types of Chromosomes 🧬

Sex Chromosomes: Determine the sex of the individual. 🚻

Autosomes: Non-sex chromosomes. ⚙️

Nuclear Division 🔄

Nuclear division is the process through which new cells (daughter cells) are formed from existing cells (parent cells). There are two types of nuclear division:

Mitosis 🔁

Produces two genetically identical diploid daughter cells from one diploid parent cell. 👶

Stages of Mitosis:

• Prophase: Chromosomes become visible; spindle fibers appear; nuclear membrane disappears. 🔍
• Metaphase: Chromosomes align along the cell equator. ➡️
• Anaphase: Sister chromatids are pulled apart to opposite poles. ↔️
• Telophase: Chromatids arrive at poles, unwind, and nuclear membranes reappear. 🏁

Importance of Mitosis: Growth, regeneration, asexual reproduction, and maintenance of genetic stability. 🌱

Meiosis ⚖️

A reduction division that produces four genetically different haploid daughter cells from one diploid parent cell. Involves two divisions (Meiosis I and Meiosis II). 🔄

Importance of Meiosis: Formation of gametes and contribution to genetic variation. 🌍

Monohybrid Inheritance 🧬

Monohybrid inheritance involves the study of one characteristic controlled by a single gene. 🔍

Key Genetic Terms:

• Chromosome: DNA thread wrapped in protein carrying inherited information. 📜
• Gene: Segment of DNA controlling a specific characteristic. 🧬
• Allele: Alternative form of a gene. 🔄
• Genotype: Genetic composition of an organism. 🧬
• Phenotype: Outward expression of the genotype. 🌟
• Dominant Allele: Expressed in phenotype. 💪
• Recessive Allele: Overridden by a dominant allele. 🔒
• Homozygous: Organism with identical alleles. 👥
• Heterozygous: Organism with different alleles. ⚖️

Mendel’s Experiments 🧑‍🔬

Mendel used garden peas for his experiments because they have a short life cycle and exhibit contrasting characteristics. 🌱

Experiment 1: Crossed homozygous tall plants with homozygous short plants, resulting in all tall offspring (F1 generation). 🌾

Experiment 2: Allowed F1 plants to self-pollinate, resulting in a phenotypic ratio of 3 tall to 1 short in the F2 generation. 📊

Back Cross (Test Cross) 🔄

A test cross involves crossing an organism with a dominant phenotype with a homozygous recessive organism to determine its genotype. 🔍

Blood Group Inheritance 🩸

Human blood type is controlled by three alleles: IA, IB, and IO. 🩸

• Genotype: IAIA - Group A 🅰️
• IAIO - Group A 🅰️
• IBIB - Group B 🅱️
• IBIO - Group B 🅱️
• IAIB - Group AB 🆎
• IOIO - Group O ⭕

Sex Inheritance 🚻

Sex determination in humans is controlled by the X and Y sex chromosomes. XX indicates a female, while XY indicates a male. 👩‍🦰👨‍🦰

Sex Linkage 🔗

Non-sex genes located on sex chromosomes are known as sex-linked genes. Examples include haemophilia and red-green color blindness. 🧬

Mutations ⚠️

A mutation is a sudden change in the structure of a gene or the number of chromosomes. 🔄

• Gene Mutations: Changes in the chemical structure of a gene (e.g., albinism, sickle cell anemia). ⚗️
• Chromosome Mutations: Changes in the number of chromosomes (e.g., Down syndrome). 🔢

Selection 🌱

Selection is the process by which environmental pressures eliminate some individuals while allowing the fittest to survive. 🌍

• Natural Selection: Driven by environmental factors. 🌦️
• Artificial Selection: Human-induced (e.g., selective breeding). 👩‍🌾

Genetic Engineering 🛠️

Genetic engineering involves transferring genes between organisms, which can be of the same or different species. 🔄

Example: Human insulin production by transferring the gene for insulin into bacteria. 🦠