5. Genetics & Inheritance

1. Core Content

Introduction

Mention of Mendel as the father of genetics

Concepts in inheritance

Chromatin and chromosomes

Genes and alleles

Dominant and recessive alleles – The Law of Dominance

Phenotype and genotype

Homozygous and heterozygous

Monohybrid crosses

Format for representing a genetics cross

Mendel's Principle of Segregation

Types of dominance:

• Complete dominance – one allele is dominant and the other is recessive, such that the effect of the recessive allele is masked by the dominant allele in the heterozygous condition

• Incomplete dominance – none of the two alleles of a gene is dominant over the other, resulting in an intermediate phenotype in the heterozygous condition

• Co-dominance – both alleles of a gene are equally dominant whereby both alleles express themselves in the phenotype in the heterozygous condition

Genetics problems involving each of the three types of dominance

Proportion and ratio of genotypes and phenotypes

Sex determination

22 pairs of chromosomes in humans are autosomes and one pair of chromosomes are sex chromosomes/gonosomes

Males have XY chromosomes and females have XX chromosomes

Differentiate between sex chromosomes (gonosomes) and autosomes in the karyotypes of human males and females

Representation of a genetic cross to show the inheritance of sex

Sex-linked inheritance

Sex-linked alleles and sex-linked disorders

Genetics problems involving the following sex-linked disorders:

• Haemophilia

• Colour-blindness

Blood grouping

Different blood groups are a result of multiple alleles

The alleles (refer to exam guidelines) in different combinations result in four blood groups

Genetics problems involving the inheritance of blood type

Dihybrid crosses

Mendel's Principle of Independent Assortment

Dihybrid genetics problems

Determination of the proportion/ratio of genotypes and phenotypes

Genetic lineages/pedigrees

A genetic lineage/pedigree traces the inheritance of characteristics over many generations

Interpretation of pedigree diagrams

Mutations

Definition of a mutation

Effects of mutations: harmful mutations, harmless mutations and useful mutations

Mutations contribute to genetic variation

Definition of gene mutation and chromosomal mutation

Mutations lead to altered characteristics in each of the following genetic disorders:

• Haemophilia – absence of blood-clotting factors

• Colour-blindness – due to absence of the proteins that comprise either the red or green cones/photoreceptors in the eye

• Down syndrome – due to an extra copy of chromosome 21 as a result of non-disjunction during meiosis

Genetic engineering

Genetic engineering uses biotechnology to satisfy human needs:

• Stem cell research – sources and uses of stem cells

• Genetically modified organisms – brief outline of process (names of enzymes involved are not required) and benefits of genetic modification

• Cloning – brief outline of process and benefits of cloning

Paternity testing

The role of each of the following in paternity testing:

• Blood grouping

• DNA profiles

Genetic links

Mutations in mitochondrial DNA used in tracing female ancestry