Lecture 7 and 8 Flashcards
What is the theory of pangensis?
Seeds are produced by all body parts, collected in reproductive organs and transmitted to offspring
Who proposed the theory of pangenesis?
Hippocrates (400B.C.)
What is the theory of preformationism?
Sex cells contain fully developed homunculus (mini human)
What were the two theories surrounding preformationism?
Spermists: homunculus found in sperm
Ovists: homunculus resides in egg
What is the blending theory of inheritence?
Hereditary traits are malleable, blending together through generations
What plant did Mendel work with?
Peas: Pisum satvium
Why peas?
Easy to handle, grow well, self fertilise or cross fertilise, short generation time, lots of offspring, discrete traits, pure bred strains exist
What were the basic ratios in Mendel’s experiments:
F1: all the same
F2: 3:1 ratio
What did Mendel’s data suggest?
Particulate theory of inheritance
What is Mendel’s first law?
Law of segregation
What is the law of segregation?
Two factors for each trait separate during gamete formation and unite at random at fertilization
What was Mendel’s experiments involving more then one phenotype called?
Dihybrid cross
What is Mendel’s second law?
The law of independent assortment
What is the law of independent assortment?
During gamete formation, different pairs of alleles segregate independently of each other
What enzyme causes wrinkled peas?
Starch branching enzyme 1 (Sbe1)
What enzyme causes green phenotype?
Lack of an enzyme that breaks down Chlorophyll called stay green (Sgr)
How are family genetics analysed?
Pedigree analysis
What are 2 features of dominant diseases?
- Affected individuals have affected parent
- Doesn’t skip generations
Give an example of a dominant disease in humans.
Huntington’s disease (progressive death of nerve cells)
What is the inheritence of dominant disease also called?
Vertical transmission
What is the mechanism for huntingtons?
Httex1 gene variant produces abnormally folded proteins
Why do misfolded Httex1 genes cause huntingtons?
Protein accumulates in neurons causing damage over time
What are features of recessive diseases?
Affected indivduals parents not always affected (skips generations)
Seen more in consanguineous matings
Give an example of recessive disease in humans.
Cystic fibrosis
What type of transmission are recessive disease?
Horizontal
What is the most common non-functional varient of CFTR?
delta F508 (deleted amino acid at position 508)
Snapdragons show variance from Mendel’s first law because…
Incomplete dominance: F2 gives 1:2:1 red:pink:white
Lentils giving rise to spotted/dotted phenotype not seen in F1 generation is known as…
Co-dominance
How many genotypes and phenotypes are there for blood groups?
6 and 4
Why are blood groups this way?
More than one allele at a locus
Why do dominance series exist?
There are dominance heirachys
Give an example of a dominance series in mammals.
Agouti locus: Coat colour in mouse, wild type allele produces fur with yellow and black bands
One gene can act on multiple systems or tissues. This is called…
Pleiotrophy
Give an example of pleiotriophy in mice.
One Ay locus produces yellow coat colour,
Two Ay are not born (genotype is lethal)
What is epistasis?
The interaction of genes that are not alleles (e.g. supression of the effect of one such gene by another)
What are two key concepts when considering environment interactions of genes?
Penetrance and expressivity
What is penetrance?
Proportion of a population with a genotype that have the phenotype
What is expressivity?
The degree or intensity with which a particular genotype is expressed in a phenotype
Give an example of expressivity
Siamese cats (same genotype, fur colour different), temperature sensitive gene for melanin
Give an example of penetrance.
Phenylketonuria (PKU)
What is phenylketonuria?
Recessive disease, mutation in phenlyalanine hydroylase, unable to metabolose phenylalanine which becomes toxic
Why is phenlyketonuria an example of penetrance?
Phenotype changes depending on diet
Who first demonstrated polygenetic inheritance?
Karl Pearson (1903), height is correlated in families
