Lecture 10 Flashcards
Breaking Mendel’s laws
sometimes genes do not appear to behave as Mendel observed for his pea characters
- characters ‘blend’
- unexpected ratios
- unexpected phenotypes appear
Incomplete dominance
the gene for petal colour in carnations has two equally dominant alleles, this is codominance, if one dominant allele causes red petals and one white the heterozygous would be pink
Multiple alleles example
Blood groups
IA IB, (dominant)
IO (recessive)
IAIAB would be AB blood type as both are dominant
Sickle cell anaemia
William Warwick Cardozo pioneered the study of sickle cell anaemia
red blood cells are misshapen (break down quickly and block blood vessels)
it is an inherited disorder
Cause of sickle cell anaemia
An abnormal allele of Beta-globin has a single base substitution leading to the recessive genetic disease: sickle cell anaemia
Pleiotropy
a single gene has many different effects on the phenotype of an organism
Heterozygote advantage
in the case of sickle cell anaemia: carriers have a higher resistance to malaria, so this is advantageous and increases likelihood of allele being passed on
this is an example of balancing selection
Recessive lethality
where the recessive genotype is lethal and organisms die often in utero
Epistasis
one gene can mask the phenotype produced by a second gene: epistasis
Epistatic allele
allele doing the masking
Hypostatic allele
allele being masked
Recessive epistasis
where a recessive genotype is needed for the second gene to matter
