N02 Heredity Flashcards
Sources of ancient hereditary ideas
- Hippocrates - pangenesis (hereditary particles passed to children from sex organs)
- Aristotle: potentiality + form = actuality
- Bible - experiences of the mother during pregnancy will affect the offspring
Joseph Merrick
- believed to be case of maternal impression
- mothers experience with elephants caused her soon to appear the way he did
- elephant man
Hybridizations of different animals
- thought that weird hybridizations of different animals would yield offspring that are intermediate in appearance
(ex. camels + leapords = giraffes)
Where does the concept of genetic purity come from
essentialism
-no geneticists talk about genetic purity
Ancient debate on inheritance
-is inheritance the transmission of pre existing form (preformationism) or is it the ability to create form (epigenetics)
Blending inheritance
- hybrid of the parents
- red and white flowers create pink offspring
Augustinian order in Brno
community of scholars that Mendel joined after he ran out of money in uni
When did Mendel perform his pea experiments and what did it require
late 1850 to early 1860’s.
- required immense amounts of data
- published in 1866
What were Mendel’s setbacks
- didn’t receive a lot of recognition
- tried and failed to replicate his experiment with other plants
- selection for position at the monastery where he wasn’t able to pursue his work following his short scientific career
What did Mendel observe in his hybridizations of pea lines with different traits
segregation of traits
what is segregation of traits
uniform parents could give differing progeny (opposite of hybridization)
-2 purple parents can produce white offspring
Had segregation of traits been observed before and what was different about Mendel
yes, but Mendel actually counted the progeny and tried to derive an abstract model to explain how the numbers work
Mendel’s explanation for the segregation of traits
- particulate inheritance
- hereditary factors are distinct indivisible entities (not continuous)
- traits of parents to not mush together (discrete and upheld through generations)
- differed from blending and pangenesis model
What did Mendel observe but not name?
- independent assortment
- whether one trait was inherited independently of another trait
Who did Mendel’s work interest once published
Karl Nageli
What did Nageli suggest
-suggested that Mendel repeat his work with a different plant
What plant did Nageli suggest?
Was this a good suggestion? Why?
Hawkweed
-terrible suggestion, this plant is not sexual. Get flowers but no sexual function. Mendel’s results were not repeated.
What did Nageli study?
- worked on cell theory
- saw that cells only come from preexisting cells
Other models of inheritance of the late 19th century
- Darwin’s pangenesis with gemmules
- Germplasm theory
- The biometrical approach
Difference between Darwin’s pangenesis and Mendel’s model
-gemmules, was a particulate model (like Mendel). But Darwin’s gemmules changed over an individual’s life (natural selection) unlike Mendel’s particles
Who is credited with Germplasm theory
-August Weismann
What did August Weismann distinguish between
2 kinds of cells in genetics:
- Germplasm
- Somatoplasm
(germplasm: sex cells responsible for generational continuity, somatoplasm: rest of cells in our body, not passed to offspring)
Similarites between Mendel’s and Weismann’s inheritance theory
-both involved particles rather than fluids
Where did Weismann think these hereditary particles were found?
- on chromosomes
- a guess, just knew that they separated and knew nucleus was home to genetic variation
What did a germ cell contain (according to Weismann)
- hundreds of complete sets of hereditary particles passed on from previous generations
- thought that having many genomes could explain the reappearance of traits that had not been seen in a long time
What is the biometrical approach to science
-application of statistics to biological problems
Who created biometrics
Sir Francis Galten (Charle’s Darwins cousin)
Speculations of Galten
- first to recognize individuality of fingerprints
- wanted to know how prayer worked
Major different between Galten and Mendel
-mendel studied discrete (discontinuous) variation, Galton more interested in quantitative (continuous) variation
What did Galten think the key to studying hereditary and evolution was
- continuous variation
- practical problems of genetics (how to increase milk production for cows)
Galton’s Law of Ancestral Heredity
you receive 1/2 of hereditary information from each parent, 1/4 from each grandparent
Why didn’t Galton’s thinking stand up to the pattern of inheritance proposed by Mendel?
because two of the four grandparents are not accounted for
What is Galton also considered the founder of?
Eugenics
What is Eugenics
The science of improving the human race heritably by selective reproduction
- Alberta persued this from 1928-1972
- tried to sterilize low IQ on individuals
Hugo de Vries
-performed breeding experiments with poppies and got same observations as Mendel
Hugo de Vries results
- Traits must be studies as separate hereditary units (didn’t accept blending)
- Dominance and recessiveness (Mendel’s term)
- Reappearance of the recessive trait in the F2 generation
- 3:1 ratio in the F2 generation
- some of the F2’s bred true while others segregated
What did de Vries conclude the hereditary units were
concluded that hereditary units were intracellular pangenes, prob on the chromosomes
Did de Vries repeat his experiment on other plants
Yes, by 1900 de Vries observed the same segregation behaviour in 15 plant species
Did de Vries discover Mendel’s paper
- Yes
- did not mention Mendel in his own paper
- de Vries was not given credit with the discovery
Carl Correns
- student of Karl Nageli
- studied paired traits in peas and in Maize
- forced de Vries to mention Mendel in a later paper
What term did Correns coin
‘Mendel’s Laws’
Erik Von Tschermak
bread peas (yellow/green, round/wrinkled) same pairs of traits Mendel studied. -derived same 3:1 ratio
William Bateson
- large defender of Mendel
- wrote “Mendel’s Principles of Heredity: a Defense”
Who coined the term ‘genetics’
Bateson, 1906
Who coined the term ‘gene’
Wilhelm Johannsen (Danish Bottanist)
Who was Thomas Hunt Morgan
-critic of Mendel, lots of objections
What were Thomas Hunt Morgan’s objections to Mendelism?
- Mendel’s Laws could not be demonstrated in all organisms, particularly animals
- Dominant/recessive relationship could not explain the 1:1 sex ratio
- Often progeny are intermediate in their appearance, Mendel couldn’t explain this
- No physical basis for Mendel’s hereditary determinants had yet been found
What questions whether preformationism is really true?
- Mendel’s work suggest that offspring are miniature versions of their parents from very early development
- does this suggest preformation?
Walter Sutton
observed that chromosomes in meiosis behave the same was that Mendel’s hereditary determinants do
Assumptions about genes in relation to chromosomes
- must be more genes than chromosomes
- if genes are on the same chromosome some genes should segregate together and wind up in the same sex cell
-problem: something Mendel and Mendelists never observed
What did William Bateson discover in 1906?
- co-segregation of genes in plant breeding experiments (2 or more genes on the same chromosome close together end up in same daughter cell)
- resisted the chromosome theory but that’s what he was seeing
Who’s lab was most productive genetics lab of the 20th century?
-Thomas Hunt Morgan
Workers of Thomas Hunt Morgan’s lab?
- Herman Muller (discovered that x-ray’s cause mutations)
2 other students….
What did Thomas Hunt Morgan put at the centre of genetics?
fruit flies
What made fruit flies ideal to study genetics
- quick genetic rates and easy to observe
- can easily knock them out and breed
Thompson Hunt Morgan’s lab achievements
- Sex linkage
- Genetic Maps
- Genetic information is one dimensional
- Creation of mutants is a way to discover new genes
- Chromosomal aberrations to mutant phenotypes (extra and missing chromosomes)
- Anticipated population genetics as a was of relating Mendelian genetics to evolutionary theory
How did Thompson Hunt Morgan achieve sex linkage
- saw that white eyed trait seemed to be inherited with the sex chromosome
- noted that white eyed gene seemed to follow a certain chromosome (Y)
- ** proved that genes were on chromosomes
Who achieved genetic maps and how
Alfred Sturtevant
- knew genes could be assigned to places on chromosomes relative to each other
- through breeding can create a genetic map
- additive nature
- ** suggested one dimension of genes
Explain Thompson Hunt Morgan’s lab achievement of creation of mutants to discover new genes
- need to have allele alternatives to have mendelian genetics
- Can’t define a gene if you have all the same alleles
- increase in mutation rates = increase in variation
