Transcript Cystic fibrosis and genetic definitions

Genes
and
Cystic
Fibrosis
Gene
Gene: A sequence of bases in DNA (sometimes RNA) that codes
for one polypeptide (protein). Genes are found in the same loci on
chromosomes.
e.g. the human CFTR gene codes for the CFTR protein.
Locus
Locus, (plural loci): The position of a gene on a
chromosome.
e.g. the human CFTR gene is located on the long
arm (q) of human chromosome 7 . (7q31.2)
Locus of gene
CFTR Protein
CFTR protein: This protein is 1480 amino acids in length.
The protein forms a chloride channel in the membranes of
cells that line the passageways of the lungs, liver, pancreas,
intestines, reproductive tract, and skin
Allele
Allele: Genes which code for the same characteristic and have the
same loci; but which express the characteristic differently.
e.g. The gene for CFTR has many alleles and the protein it
codes for is 1480 amino acids long. The f allele is one of the
commonest and having two copies of this mutation (ff),
(inherited from both parents,) is the leading cause of cystic
fibrosis .
Gene Mutation
Mutation: A change in the sequence of bases in DNA. There are
three main types: deletion, addition and substitution. A change in
the base sequence may lead to a change in the amino acid sequence
and to the shape and functioning of the protein the gene codes for.
One of the commonest alleles of the CFTR gene f (DF508) is
caused by a specific mutation, a deletion of three base pairs
(TTT). This codon codes for phenylalanine at the 508th position
of the protein. Having two copies of this mutation (ff), (inherited
from both parents,) is the leading cause of cystic fibrosis
Chromosome
Chromosome: Thread like structures found in the nucleus
of Eukaryotic cells. They are composed of DNA, histone
and non histone protein. The histone proteins help to
package the DNA
e.g. Human Chromosome 7 is one of the 23 pairs of chromosomes in humans.
People normally have two copies of this chromosome. Chromosome 7 spans
more than 158 million base pairs and represents between 5 and 5.5 percent
of the total DNA in cells. The estimated number of genes varies. But is likely
to be between 1,000 and 1,400 genes.
DNA interactive, Genome, Chromosome packing and Chromosome tour
Chromosome Packing
Short region of DNA double helix
2 nm
‘Beads on a string’ chromatin chain
11 nm
Packed nucleosomes
30 nm
Section of extended chromosome
300 nm
Condensed section of
metaphase chromosome
700 nm
Entire metaphase chromosome
1400 nm
Human
The Metaphase
X and Y Chromosome
Chromosomes
Homologous Chromosomes
An Address Book Analogy
Homologous chromosomes
chromosomes:are
Chromosomes
with
the same
types of
genes
Homologous
like an address
book.
All address
books
in the
same
however
the alleles in these loci may be different.
have
twoloci,
things
in commen:
pair
i.Homologous
They havechromosomes
the same letters
D,inZ,prophase
F, Q etc.1 of meiosis and exchange
genes
in iscrossing
over. Theychromosomes
then segregate
independently
one another.
(this
like homologous
having
the same of
genes)
ii. All address books have their letters in the same order A, B C, D, E, etc.
(this is like each gene in a homologous chromosome having the same
locus.)
However no two address books are identical, why?.
Because the names and addresses put in may be different.
(two homologous may have different alleles in the same locus)
Human
Karyotype
Homozygous
Homozygous: An organism that has the same alleles for a
particular gene (characteristic).
e.g. In Humans homozygous individuals with alleles ff
will have Cystic fibrosis. Whereas homozygous individuals
with the alleles FF will not.
Heterozygous
Heterozygous: An organism that has the two different
alleles of the same gene (characteristic).
e.g. In Humans heterozygous individuals with alleles Ff
will be normal, but carry a cystic fibrosis allele.
Dominance
Dominance: When one gene/allele masks or prevents the
expression of another.
e.g. In humans the allele F is dominant to f . Heterozygous
individuals Ff will be normal, but carry a cystic fibrosis
gene.
Recessive
Recessive: When one gene/allele is masked or prevented
from expression by another.
e.g. In humans the allele f is recessive to F. Heterozygous
individuals Ff will be normal, but carry a cystic fibrosis
gene.
Genotype
Genotype: The genetic makeup of an organism, the genes it
possess.
e.g. In humans normal individuals may have the genotype FF
or Ff whereas genotype ff will produce individuals who suffer
from cystic fibrosis.
Phenotype
Phenotype: The observable characteristics of an organism.
A product of interactions between the genotype and the
environment.
e.g. In humans individuals with the genotype FF or Ff have a
normal phenotype .
Cystic Fibrosis Genetics
Parents Phenotype
Parental genotype
Gametes
Normal Father
Ff
F or
Normal Mother
Ff
F or
f
Gametes from Mother
Gametes
from
Father
F
f
F
FF
Ff
f
Ff
ff
f
Cystic Fibrosis Pedigree Diagrams
Cystic Fibrosis Pedigree Diagrams
Explain how Frank could
have inherited CF from
James and Margaret, who
do not have CF?
Alibinism Pedigree Diagrams