Cystic Fibrosis Inheritance
Genes and chromosome pairs:
- Gene; a length of DNA that codes for a protein
- Every cell (except sex cells) contain two copies of each gene, one from each parent
- Both copies have the same locus on each of the paired chromosomes
- 23 pairs of chromosomes; the chromosomes in each pair are called homologous chromosomes
- Cystic fibrosis is caused by a gene mutation that is passed from parent to offspring
Genotypes, Phenotypes and alleles:
- Mutation in the CF gene (the length of DNA that codes for the CFTR protein)
- CF gene occurs in two alternative forms or alleles
- Healthy gene = F / Non-functional protein = f
- FF – a person with two identical copies of the normal allele does have cystic fibrosis
- ff – a person with two copies of the mutated allele has cystic fibrosis
- Ff – A person with one normal allele and one mutated allele does not have cystic fibrosis but is a carrier and coud pass on the disease
- The alleles that a person has make up their genotype
- Homozygous genotype; both the same (ff/FF)
- Heterozygous genotype; different alleles (Ff)
- Characteristic caused by the genotype is the phenotype
Predicting the genotype of offspring:
- When gametes are produced, each egg or sperm has only one allele, f or F
- Punnett square; illustrates all the possible ways in which the two types of allele can combine, showing the possible genotypes of children
- Carriers (Ff) have some protection against typhoid
Inheritance of genetic diseases:
- Cystic fibrosis is a monohybrid inheritance; characteristics controlled by one gene
- Thalassemia; genetic disease cause by recessive alleles of a gene on chromosome 11
- Gene is involved in the manufacture of haemoglobin which carries oxygen round body
- Someone who is homozygous makes no haemoglobin, or non-functional haemoglobin – homozygous condition is often lethal
- Heterozygous conditions (advance) – have no symptoms but have protection against malaria
- Albinism, phenylketonuria and sickle cell anaemia are also called by single recessive alleles
- Achondroplasia is caused by a dominant allele
- A homozygote always dies
- Heterozygote – restricted growth
- Huntington’s diseae and the ability to taset PTC are also caused by dominant alleles
The work of Mendel:
- Carried out breeding experiments
- He established that a number of characteristics of the garden pea were determined by separate genes