2.5 Flashcards
Cystic fibrosis occurs because people with CF have a faulty version of a protein called CFTR that transports
Chloride ions across cell membranes
Cystic fibrosis is an inherited disorder that affects
Plasma membranes
CFTR is coded for by a gene on
Chromosome 7
A gene is a
Length of DNA that occupies a specific position on a chromosome
A locus is a
Specific position on a chromosome
Each gene codes for a
Specific protein or polypeptide
A particular gene may have more than one form that is slightly different from the others in its sequence of nucleotide bases - these different forms of genes are called
Alleles
The allele that codes for cystic fibrosis has
3 nucleotides missing
The three missing nucleotides code for one amino acid, so this means that the faulty CFTR protein has one
Amino acid missing
(CF) this missing amino acid is very significant. Without it the CFTR protein folds up into a different tertiary structure, resulting in a protein that will
Not function
Human DNA is arranged in the form of
Chromosomes
Human body cell contains 23 pairs of chromosomes, making
46 in all
A gamete contains one set of 23 chromosomes. This means that every individual receives one set of chromosomes from
Their mother and one from their father
Every individual has two genes that code for CFTR, however, the two
Alleles may be the
Same or different
If an individual has 2 identical alleles of a gene, they are said to be:
Homozygous for that gene
If the alleles are different, they are said to be
Heterozygous
An allele is said to be dominant if it is always expressed in the
Phenotype
Phenotype =
The characteristics of an organism resulting from its alleles
The allele for the normal CFTR protein can be identified with the symbol:
F
Allele for normal CFTR protein is
Dominant
The allele for the faulty version of CFTR is
Recessive
Faulty CFTR allele can be identified with symbols
f
Faulty CFTR allele means that it is only expressed in the phenotype of an individual if
Two copies of the allele are present
The genotype of an individual is their
Genetic make up
The genotype tells you the
Alleles they carry
A person with the genotype Ff is
Heterozygous for the cystic fibrosis gene
A person who is FF or ff is
Homozygous
Heterozygous = do not have CF because the normal allele is
Dominant
2 people who are heterozygous for the CFTR gene may have child with CF this is because a person who is heterozygous passes on only one of their alleles into each gamete. If the child inherits one faulty CFTR allele from each parent then they will develop
CF
Sometimes we say that heterozygous individuals who will not have CF but could pass on CF to their own children are
Carriers of cystic fibrosis
Monohybrid inheritance involves a cross between individuals in which only a
Single gene is being considered
Cystic fibrosis is an example of a
Monohybrid cross
