Grade 12 Life Sciences Self-Study Guide

Introduction to the Self-Study Guide

• The declaration of COVID-19 as a global pandemic disrupted teaching and learning in South African schools.
• Many learners experienced reduced class time due to phased-in approaches and rotational attendance.
• The Department of Basic Education (DBE) collaborated with subject specialists to develop this Self-Study Guide.
• The guide aims to address content gaps, strengthen subject knowledge, and promote independent learning.
• The guide covers critical Grade 12 topics and skills to provide a foundation for further study.

How to Use This Self-Study Guide

• There are five Self-Study Guides covering all Grade 12 topics: DNA; Code of Life and Meiosis, Reproduction in Vertebrates, Human Reproduction, Endocrine System and Homeostasis, Genetics and Inheritance, Responding to the Environment: Humans and Plants and Evolution: Natural Selection and Human Evolution.
• Use this guide with the Life Sciences Mind the Gap Study Guide.
• Study content from the DBE Grade 12 Textbook, DBE Examination Guidelines 2021, and Mind the Gap.
• It focuses on answering questions in examinations.
• It includes exam techniques and tips (in italics).
• There's guidance on approaching question types, including terminology, graphs, tables, diagrams, genetics crosses, pedigree diagrams, calculations, and scientific investigations.
• Typical examination questions and solutions are provided at the end.

Genetics and Inheritance

• Focuses on DNA replication, chromosomes, and meiosis.
• Resources include Textbooks, Study Guides, Diagnostic reports, MTG, Past NSC, SC & Provincial Question Papers.

Key Concepts

• Concepts of inheritance
• Mendel’s principles of inheritance
• Monohybrid crosses
• Dihybrid crosses
• Sex determination
• Sex-linked inheritance
• Blood groups
• Genetic lineages and pedigree diagrams
• Genetic engineering
• Paternity testing

Terminology

• Albinism: Absence of skin pigmentation.
• Alleles: Versions of a gene at the same locus on a chromosome.
• Autosome: Any non-sex chromosome.
• Biotechnology: Using biological processes to improve human life.
• Clone: Genetically identical copy of an organism.
• Cloning: Creating genetically identical organisms using biotechnology.
• Co-dominance: Both alleles equally dominant; both expressed in the phenotype.
• Complete dominance: One allele dominant; masks the recessive allele in heterozygotes.
• Chromatin network: Tangled DNA threads in an inactive cell's nucleus.
• Chromosome: DNA thread carrying hereditary information (genes).
• Dihybrid cross: Cross involving two characteristics (e.g., seed shape and color).
• Dominant allele: Masks expression of the other allele; seen in homozygous (TT) and heterozygous (Tt) states.
• Gene: DNA segment coding for a specific characteristic.
• Gene mutation: Change in the DNA sequence.
• Genetic variation: Variety of genes resulting in new genotypes and phenotypes.
• Genotype: Genetic composition (e.g., BB, Bb, bb).
• Genome: The complete set of chromosomes in a cell.
• Gonosome: Chromosome pair responsible for sex determination.
• Haemophilia: Sex-linked disorder due to lack of blood-clotting factors.
• Heterozygous: Two different alleles for a trait (on the same locus).
• Homozygous: Two identical alleles for a trait (on the same locus).
• Incomplete dominance: Neither allele dominant; intermediate phenotype in heterozygotes.
• Locus: Gene's exact position on a chromosome.
• Mendel’s Law of Dominance: In crosses of homozygous organisms, the F1 generation displays the dominant trait, with heterozygotes exhibiting the dominant phenotype.
• Mendel's Law of Independent Assortment: "Factors" controlling characteristics are separate and independently sorted.
• Mendel’s Law of Segregation: An organism possesses two "factors" that separate, so each gamete has one.
• Monohybrid cross: Cross involving one characteristic (e.g., seed color).
• Mutation: Sudden change in the DNA sequence.
• Multiple alleles: More than two possible alleles for a gene locus (e.g., blood groups).
• Phenotype: External, physical appearance determined by genotype.
• Pedigree diagram: Chart showing inheritance of genetic disorders over generations.
• Population: Group of organisms of the same species living in the same habitat.
• Recessive allele: Suppressed by a dominant allele; only expressed in homozygous recessives (tt).
• Stem cells/meristematic cells: Undifferentiated cells capable of developing into any cell type.

Notes/Exam Tips/Techniques

• Chromatin is a tangled DNA structure in an inactive cell, while a chromosome is a DNA structure that carries hereditary information
• Genes code for particular characteristics, while alleles are versions of genes.
• A dominant allele is one that masks the expression of another allele with phenotypic effects, while a recessive allele is one that is only expressed when the dominant allele is absent.
• Phenotype is the observable characteristics or traits of an organism, while genotype is the genetic makeup
• Homozygous refers to when the allele that controls a single trait are identical on the same locus, whereas heterozygous refers to when the allele are different.

Mendel’s Laws of Inheritance

• Law of Segregation: Each organism has two "factors" that separate during gamete formation.
• Law of Dominance: When crossing contrasting homozygous organisms, F1 offspring exhibit the dominant trait.
• Law of Independent Assortment: Factors sort independently during gamete formation.

Format of a Genetic Cross

• P1: Parental generation (phenotype and genotype).
• Meiosis: Gamete formation (alleles segregate).
• Fertilization: Fusion of gametes (offspring genotype).
• F1: First filial generation (phenotype).
• Use the Punnett square to determine fertilization outcomes.

Monohybrid Crosses

• Complete Dominance: One allele masks the other (e.g., green pod color dominant over yellow).
• Incomplete Dominance: Neither allele fully dominant; intermediate phenotype (e.g., pink flowers from red and white parents).
• Co-dominance: Both alleles equally expressed (e.g., red and white coat color in cattle).

Sex Determination

• Humans have 22 pairs of autosomes and 1 pair of sex chromosomes (gonosomes).
• Males are XY, females are XX.

Sex-Linked Inheritance

• Genetic disorders linked to genes on sex chromosomes.
• X chromosome carries more genes than Y, X-linked traits are more common.
• Males only have one X chromosome and express X-linked traits more, even if recessive.
• Haemophilia is caused by a defect on in genes located on the X chromosome.

Blood Groups

• Multiple alleles (IA, IB, i) determine blood type.
• Notation for alleles are written as IA; IB and i only
• Blood types are A, B, AB, and O.
• Follow the 1-2-3-4 Rule.
• Inheritance displays co-dominance and complete dominance.

Dihybrid Crosses

• Involve two pairs of alleles for two characteristics.
• Alleles move independently into gametes (Law of Independent Assortment).

Pedigree Diagrams/Genetic Lineages

• Trace inheritance over generations.
• Identify sex-linked disorders (Haemophilia and Colour-blindness).
• Mark homozygous recessive individuals first.
• Work upwards from the last generation.

Mutations

• It is a sudden change in genetic composition.
• A gene mutation a change in nitrogenous bases or nucleotides, while chromosomal mutation is a change to the number of Chromosomes.

Genetic Engineering

• Manipulates biological processes to meet needs.
• Synthetic insulin is produced by genetically engineering technology
• Involves manipulation of genetic material
• Production, pest control, increased crop yields, and increased shelf-life are benefits.

Geneticallly Modified Organisms (GMO's)

• It is when genetic engineering alters the genome of cells for medical, industrial or agricultural purposes
• It can result in more productive crops, or help make new drugs.

Paternity Testing

• Uses blood grouping and DNA profiles. Blood Grouping: Child receives an allele from the mother and father while DNA Profiles compare the band to the parents to see if there are matches.