lecture 5 Flashcards
MECHANISM OF GENETIC CHANGE
Gene flow: transfer of genetic variation from one population
to another
Genetic Drift: change in the relative frequency of an allele in a population due to random sampling and chance
Genetic bottleneck: when population size is reduced for at
least one generation (may quickly reduce genetic variation)
Founder effects: a new colony is started by a few members
of the original population (reduced genetic variation & non- random sample of genes)
look at slides if confused
EXAMPLE – AMISH – ELLIS-VAN CREVELD SYNDROME
Founder Effect: Ellis-van Creveld
Syndrome
Polydactyly
Congenital heart defects
Natal teeth
Fingernail dysplasia
Short-limb dwarfism
Short ribs
Cleft palate
REPRODUCTIVE
ISOLATION
Separation of species or populations so they cannot interbreed and produce fertile offspring
REPRODUCTIVE ISOLATION
Cuts off human-associated populations from wild populations
Restricts gene flow and reduces genetic diversity
‘Inbreeding’ may facilitate domestication process
Imprinting/socialisation may reduce
hybridisations with wild populations
ex: dogs and wolfs
m&m example
- we choose a specifci M&M, they reprodeuce until they are the only ones
WHAT
CONCEPTS ARE
ILLUSTRATED BY
THIS EXERCISE?
(Unintentional) selection
Founder Effect
Genetic drift
Genetic Bottleneck - pressure for one generation
Reproductive Isolation - only a few m&M stays and can be reproduced the others are not as present
Identifying wild progenitor populations
Stochastic (chance/random) nature of selection process
THE DOMESTICATION
SYNDROME
D omestication is a sustained multigenerational, mutualistic relationship in which one organism
assumes a significant degree of influence over the reproduction and care of another organism in order to secure a more predictable supply of a resource of interest, and through which the partner organism gains advantage over individuals that remain outside this relationship, thereby benefitting and often increasing the fitness of both the domesticator
and the target domesticate.
Niche Construction Theory: Humans alter the natural environment
Process of domestication fundamentally involves a new set of ‘selective’ pressures resulting from human intervention and adaptation to the ‘human niche’
DOMESTICATION
SYNDROME IN
CEREALS &
ANNUALS
ex: MAIZE, WHEAT, RICE, MILLET,
BUCKWHEAT, QUINOA, MUSTARD SEEDS, PEAS, BEANS, SOYBEAN, COWPEA, ETC
PLANTS IN THE NATURAL ENVIRONMENT
Traits favoured by Natural Selection:
Staggered germination
Staggered seed maturation
Rapid seed dispersal after maturation
Multiple smaller seeds
Thick protective seed coat
Strategies in response to predation and variability of nature
PLANTS IN THE HUMAN ENVIRONMENT
—–
Traits favoured under Artificial Selection:
Simultaneous germination
Simultaneous seeds maturation
Compaction of seeds in terminal stalks
Increase in seed size
Reduction in seed coat thickness
‘Adaptive syndrome of Domestication’ produced by ‘unconscious’ selection
LOSS OF SEED DISPERSAL
Wild types are ‘dehiscent’ (seeds disperse at maturity)
Domesticated types are** ‘non-dehiscent’**
-tied to human plans for haversting
Non-shattering seed heads: Tough rachis mutation
Rachis can only be broken by threshing
Jagged break at the base of the spikelet
No smooth ‘abscission scar’
Plant become fully dependent on humans
result
LOSS OF SEED DISPERSAL
they depend of humans to take their seads away
LOSS OF SEED DISPERSAL
Loss of hairs, hooks and awns
Relaxed selection?
Human selection to simplify postharvest crop cleaning?
INCREASE IN SEED SIZE & NUMBER
Conscious or unconscious selection
20-60% increase in thickness or breadth
May appear much later than other traits
Thought to favour seeding success
A result of deeper burial during cultivation?
Increased number of seeds
More seeds present on terminal ‘packets’
PLANT ARCHITECTURE
Apical dominance: taller, more erect, plants with fewer side branches - less area - more preference to be able to plant more
More plants to fit into each unit of cultivated soil
TIMING OF REPRODUCTION
Simultaneous germination & flowering
Loss of sensitivity to day length and
temperature environmental cues
Decreased seed coat thickness
Legumes: dormancy free-mutation
Shift from winter to summer cycles
Synchronous ripening
Selection for consistent maturation
time
all this causes them to be dependent on humans
WILD & DOMESTIC SUNFLOWER
- Loss of grain dispersal
- Increased seed size & number of seeds
- Apical dominance
- Synchronous ripening - able to harvest at the same time
DOMESTICATION SYNDROME IN VEGETATIVE CROPS
PLANT REPRODUCTION
Many plants have two modes of
reproduction:
Sexual reproduction from
fertilised seed – pollination
(gene flow, recombination)
Asexual reproduction or
clonal growth through
regeneration from plant
structures (clones of the parent
plant).- break up the vegetable plan it and it will grown
VEGETATIVE CROPS
bananas and plantains, manioc, potato, sweet potato,
yams, taro, sugarcane, arrowroot, ginger, turmeric,
strawberries, raspberries, etc.
MODE OF REPRODUCTION
Vegetative reproduction becomes
dominant form (non-sexual)
Loose ability for sexual reproduction
Greater yam
YIELD OF EDIBLE PORTION
Increased fruit or tuber size
- bigger edible portion
Increase in stem-size (sugar cane)
Decrease in seed size (or seed
suppression)
-Banana: reduction of seeds, increased starch,
-Breadfruit: two varieties – seedless (edible pulp) and seeded (edible seeds)
EASE OF
HARVESTING
Fused, multiple or aggregate syncarps – berries, bananas,
Bunching - figs
TIMING OF REPRODUCTION
Typically predominate in tropical areas
Less seasonal, enable cultivation at different times of the year
Broadening of the harvest window
