heritability

mendel's laws

1. law of dominance

2. law of segregation

3. law of independent assortment

law of dominance

Some alleles are dominant and some are recessive

law of independent assortment

the law that states that genes separate independently of one another in meiosis

Law of Segregation

first law of heredity stating that pairs of alleles for a trait separate when gametes are formed

complete dominance

a relationship in which one allele is completely dominant over another

co dominance

both alleles are expressed

partial dominance

both alleles blend, can create intermediate phenotypes

a gene can have any

number of alleles

dominance hierarchy of alleles

In cases where genes have more than two alleles, 1 phenotype will be most dominant, 1 moderately dominant, and 1 will be the least dominant (the recessive).

dominance in human blood groups

A> O

B>O

A + B codominant

O is recessive

how is resistance to a disease that strongly affects the flea inherited?

epistasis

epistasis

interaction between genes/ loci for example one gene may supress another

epistasis in water fleas

A masks B, animals with A susceptible regardless of B

A in water fleas

suppresses B, complete dominant resistance allele vs parasite

a in water fleas

recessive susceptible to allele C1

B in water fleas

complete dominant resistance allele vs parasite strain C19

b in water fleas

recessive susceptible allele C19

AaBb water fleas cannot exist in the lab

they do exist in the wild- evidence of another allele

C locus in water fleas

provides resistance to both parasites, A and B do not matter

epistasis of three genes in water fleas

C > A > B

epistasis in fur of mice

cannot express fur colour if pigment allele not present, pigment gene suppresses the effect of the fur colour gene

linkage

traits on the same chromosome, when inheritance occurs they are together

recombination

crossing over of chromosomes during meiosis

distance between loci determines

# of recombinants

close genes less likely to

recombine as genes on opposite ends of the chromosome

recombination rate is

species and condition dependent, eg cats vs opossum have different rates,

conditions like desication, starvation and infection effect it also

resistance in daphnia depends on

three linked loci that epistatic interact. each locus has 2 alleles with resistance completely dominant over susceptibility

T haplotype in mice

recombination can separate poison and antidote

inversions

reverse the direction of parts of chromosomes, suppress recombinants

inversions occur when

there was a failure to align chromosome regions

formed recombinants can have

unbalanced gametes

mouse T haplotype has ___ inversions

4

Quantitative genetics

many genes underly continuously varying phenotypes

many traits are coded for by

many loci, each is independently inherited which results in continuous distribution

examples of quantitative genetics

- Height

- Crop yield

- Weight gain in animals

- Fat content of meat

- IQ

- Learning Ability

- Blood Pressure

- etc.

Bdelloid rotifer

up to 10% of all genes from other species, during desiccation membrane becomes leaky and chromosomes break on drying out, upon rehydration genome is reassembled

Bdelloid rotifer genome

in a tetraploid state, four homolog sets of chromosomes

horizontal gene transfer

transformation, transduction, conjugation

Meloidogyne incognita

parasitic nematode that borrowed cell wall degrading enzymes from a bacteria

Tetranychus urticae

spider mite acquired carotenoid synthesis genes from a fungus

transformation

uptake of DNA from environment. needs cell to be competent, a state which is induced under stress but is costly

transduction

DNA introduced into host cell by virus, rare event where virus particle incapsulates part of bacterial chromosome, upon insertion into host can recombine with host chromosome

conjugation

bacterial sex

donor cell passes DNA and often plasmid through direct contact, requires bridge formation (pilus)

phenotypic plasticity

the ability of an organism to change its phenotype in response to changes in the environment.

phenotypic plasticity allows for

survival under changing conditions, allows for evolution when environmental variation is predictable

snails, sun fish and plasticity

predator fish= larger, stronger snail shells- selection for stronger shells

herbivore fish= large shells until snails realise they are safe= selection for smaller shells

arms race

natural selection, sun fish and snails

• favours plasticity in areas where a predatory sunfish is frequent

• will disadvantage snails that grow slower in presence of herbivorous sun fish where predators are absent

epigenetics

the study of environmental influences on gene expression that occur without a DNA change

C. elegens and epigenetics

modified with fluorescent gene which is only expressed at warm temps

worms warmed from 20-25 then cooled back to 25 so gene is expressed. offspring expressed for seven generations

C elegens warmed for 5 generations

offspring expressed gene for 14 generations

Zhang et al 2018

compared variation of lines that differed in DNA methylation patterns with near identical DNA sequences

some traits epigenetic variance was equal to natural pops

epigenetics can create

phenotypic variation

epigenetics may be important for

adaptation when genetic variation is limited, can move pops closer to a fitness peak

epigenetics will enable

survival in new environments, similar to plasticity, allows time for adaptative mutations to occur

Lamarck says…

inheritance of acquired characteristics- not entirely wrong with study of epigenetics

rate of spontaneous gains and losses of methylates sites (epimutation rate)…

is higher than DNA mutation rate

Epimutation rate is higher than

DNA mutation rate