Basic Mendelism Flashcards
Outline Pellegra
- Inherited but not genetic
- Caused by lack of vitamin B3 (niacin)
- Symptoms- inflamed skin, diarrhoea, dementia, mouth sores, blindness
Outline brachydactyly
- Autosomal dominant inheritance pattern
- Fingers/toes shorter than normal
- Types A to E
- Homozygotes die early in childhood
- One of first human pedigrees shows brachydactyly inheritance in Norwegian village in early C20
Outline Hapsburg lip
- Mandibular prognathism
- Extended chin and cross bite
- Result of inbreeding
- Autosomal dominant inheritance pattern
- House of Habsburg
- Pedigree of 409 people over 23 generations
- Possible as aristocrats have portraits painted, so it’s easier to diagnose
How does the study of dominant diseases differ to the study of recessive?
- Easier to study as genotype can always be worked out from phenotype
- Often disappear quickly if they’re harmful as they kill all carriers
- Everyone affected has one affected parent and it never skips a generation
What does the word pedigree come from?
French: Pied de grue
Crane’s foot
Outline achondroplasia
- Autosomal dominant inheritance pattern
- Bone growth disorder
- Causes disproportionate dwarfism
- Caused by mutation in FGFR3 gene
- Homozygotes die before/soon after birth
- 80% cases occurs as new mutation during early development
Outline Huntington’s disease
- Dominant, but comes on in later life
- Muscle weakness, depression, paralysis, death
- Short arm of chromosome 4- Huntingtin
- Repeat of CAG, number of repeats can change as passed on
- Result of duplication mutation
Outline cystic fibrosis
- Most common single gene abnormality in Europeans 1/2500
- Autosomal recessive inheritance
- 1/25 is a carrier in Europe
- Inability to pump fluids across membranes- fibrous cough
- Caused by CFTR mutation (CF transmembrane conductance regulator is a membrane chloride channel)
- Inbreeding
How can you calculate the number of possible gametes from the number of heterozygous loci (n)?
2^n
How can you calculate the number of F2 genotypes from the number of heterozygous loci (n)?
3^n
State Mendel’s first law
(law of segregation)
Two alleles at a locus segregate into separate gametes; half carrying one allele and the other half the other
State Mendel’s second law
(Law of independent assortment)
During the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other locus
Define zygote
Fertilised egg
Define homozygote
Has two copies of the same allele at a particular locus
Define heterozygote
Has two different alleles at a particular locus
Define recessive
An allele which has it’s effects masked by a dominant allele in heterozygotes
Define genotype
Genetic constitution that underlies the phenotype
Define phenotype
Physical appearance of an individual with a particular genotype
Define recombinant
New combinations of phenotypes not found in the parental generations.
Eg, wrinkled and yellow in Mendel’s peas
What is the phenotypic ratio of the F2 generation in a dihybrid cross?
9:3:3:1
What are the main applications of Mendel’s second law?
- Variation (allows natural selection)- Independent assortment can generate huge numbers of different genotypes by recombination
- DNA fingerprinting- highly variable and freely recombining loci generate unique combinations
- Agriculture- selective breeding, eg, short+productive rice recombinants
What are the implications for disease of Mendel’s second law?
- Bird and human influenza can combine in pig and give more virulent version
- Diff strains of HIV have combined to become resistant to antiviral drugs
