23) Patterns of inheritance Flashcards
Define genotype
the genetic composition of an organism, which describes all the alleles it contains
Define phenotype
an organism’s observable characteristics, resulting from the interaction of genotype + environment
Define gene
length / section of DNA that codes for the production of a particular polypeptide
Define locus
the position on a chromosome of a particular gene
Define allele
a gene variant
Describe a dominant allele
expressed and affects the phenotype even with a recessive allele
represented by UPPER CASE LETTERS
Describe a recessive allele
only expressed when dominant allele is absent
Describe a codominant alleles
2 alleles that both contribute to the organism’s phenotype to an equal extent
Define heterozygous
having 2 different alleles of a gene
Define homozygous
having 2 identical alleles of a gene
Define monogenetic trait
a characteristic controlled by a single gene
What do gene mutations do?
alter nucleotide sequences in DNA
What is significant about genetic mutations in somatic cells?
they are not inherited but may result in cancer
Give 3 types of gene mutation
substitution
insertion
deletion
What happens in a substitution (point) mutation?
nucleotide exchanged
What happens in an insertion mutation?
extra nucleotide/s
What happens in a deletion mutation?
nucleotide/s removed
What is significant about insertion and deletion mutations?
alter all subsequent triplet codes (frameshift) so are more likely to result in major changes to translated polypeptide (non-function polypeptide)
Give 3 types of substitution mutation
silent
missense
nonsense
What happens in a silent mutation?
same amino acid appear in the sequence after translation due to the degeneracy of the genetic code
What happens in a missense mutation?
alters one amino acid in the primary structure of the polypeptide and is therefore, likely to disrupt tertiary structure and function
What happens in a nonsense mutation?
lead to stop codons in the mRNA, resulting in the length of the final polypeptide being shorter
What happens when a mutation benefits an organism?
natural selection acts to maintain the new gene variant in a population
Give 4 examples of genetic diseases
cystic fibrosis
phenylketonuria (PKU)
sickle cell anaemia
Huntington’s disease
Describe cystic fibrosis (5)
deletion mutation CFTR protein is non-function leading to production of thick sticky mucus infections, scarring in lungs faulty recessive allele locus = chromosome 7
Describe phenylketonuria (PKU) (4)
faulty recessive allele
locus = chromosome 12
prevents enzyme that breaks down phenylalanine from being made
those born with PKU often suffer from brain damage
Describe sickle cell anaemia (3)
substitution mutation in gene coding for beta-polypeptides in haemoglobin
locus = chromosome 11
amino acid valine added instead of glutamic acid
Describe Huntington’s disease (4)
insertion mutation on chromosome 4
dominant allele
>40 CAG triplets (greater number -> earlier symptoms begin, 30 years)
accumulation of protein fragments in the brain, reducing ability to talk, think and more
