Lesson Notes By Weeks and Term v4 - SHS 1
THE HUMAN BODY AND HEALTH
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THE HUMAN BODY AND HEALTH
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: General Science
Class: SHS 1
Term: 2nd Term
Week: 20
Grade code: 3.4.1.LI.2
Strand code: 4
Sub-strand code: 1
Content standard code: 3.4.1.CS.2
Indicator code: 3.4.1.LI.2
Theme: RELATIONSHIPS WITH THE ENVIRONMENT
Subtheme: THE HUMAN BODY AND HEALTH
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This lesson explores the fascinating topic of heredity – how traits are passed down from parents to their children. We often hear people say, "You have your mother's eyes," or "You are tall like your father." But how does this actually happen? This lesson introduces the basic principles of genetics, discovered by Gregor Mendel, which provide a scientific explanation for these observations. Understanding these principles is not just about curiosity; it has very important real-world applications in Ghana, especially in understanding and managing inherited health conditions like Sickle Cell Disease, which affects many families in our communities.
This section breaks down the fundamental ideas you need to understand Mendelian genetics. A. Fundamental Vocabulary of Genetics Heredity: The passing of traits or characteristics from parents to offspring. Genetics: The scientific study of heredity and the variation of inherited characteristics. Trait: A specific characteristic of an individual, like height, eye colour, or blood type. Gene: A section of DNA that carries the instructions for a specific trait. Think of it as a recipe in a cookbook. For example, there is a gene for earlobe shape. Allele: Different versions or forms of a single gene. For the earlobe shape gene, there might be an allele for "detached earlobes" and an allele for "attached earlobes". We inherit one allele from each parent for every gene. We use letters to represent alleles. A capital letter represents a dominant allele, and a small letter represents a recessive allele. (e.g., E for detached, e for attached). B. Dominant and Recessive Alleles Dominant Allele: An allele that expresses its trait even when only one copy is present. It "masks" or overpowers the effect of the recessive allele. (Represented by a Capital Letter, e.g., T for tallness). Recessive Allele: An allele that only expresses its trait when two copies are present (i.e., when no dominant allele is there to mask it). (Represented by a Small Letter, e.g., t for shortness). C. Genotype and Phenotype
This is a crucial distinction. Genotype: The actual genetic makeup or combination of alleles an individual has for a trait. It's the "letter code". Examples: TT, Tt, tt. Phenotype: The observable physical characteristic of an individual that results from the genotype. It's what you can *see* or measure. Examples: Tall, Short.
| Genotype | Description | Phenotype | | :------- | :------------------------ | :------------- | | TT | Homozygous Dominant | Tall | | Tt | Heterozygous | Tall | | tt | Homozygous Recessive | Short | Homozygous: Having two identical alleles for a particular gene (e.g., TT or tt). This is also called "purebred". Heterozygous: Having two different alleles for a particular gene (e.g., Tt). This is also called a "hybrid" or a "carrier" in some contexts. D. The Punnett Square: A Tool for Prediction
The Punnett square is a simple diagram used to predict the possible genotypes of offspring from a cross between two parents.