Patterns of Inheritance Flashcards
For genetic diagrams?
pick a letter that looks diff as lowercase and uppercase and only put gametes in genetic diagram
pure bred?
homozygous
format of genetic diagram?
- phenotype
- genotype
- gametes
a hetero cross produces?
9:3:3:1 ratio
CF?
- gene that codes for a membrane carrier protein that allows Cl- into cells but not out
- Cl- attracted to Na+, makes cell salty so dec WP
- water moves in by osmosis
- affects lungs - mucus becomes too thick, goes down through lungs, narrows airways
- mucus takes bacteria into lungs
if someone is a carrier, their phenotype is?
normal
genetic diagrams generate?
theoretical data - just tell u the probability
F1 =
first generation
Co-dominance?
• not all genes are dominant and recessive
• both alleles have an effect
e.g. C^R C^W
must write gene and then allele in superscript
When there are more than 2 alleles for a gene?
- pick a letter for the gene and show the alleles as superscripts
- e.g. blood groups
blood groups?
- A, B, AB, O
- all determined by a single gene which has 3 alleles
- I^A I^B I^O
- A and B are codominant
- O is recessive to A and B
O has?
no surface antigens
What happens if you receive the wrong type of blood?
- most severe reactions: intraventricular haemolysis - the donor’s erythrocytes are destroyed by the recipients AB while they are in blood vessels
- Hb leaked into plasma and excreted in urine turning urine dark brown
- Bilirubin, a metabolite of hb usually secreted into bile by liver accumulates in blood causing jaundice
- reaction is so severe that it can cause shock, kidney failure or death
Universal donor?
BG O, blood cells have no antigens on outside
Universal recipient ?
AB - can receive blood from O, B, A
Sex linkage denotion?
• have to use X and Y and have the alleles are superscript and include sex in phenotype
how many chromosomes are autosomes?
22 pairs
how many pairs of sex chromosomes?
1 pair - XY in boys, XX in girls
each gene has ? gene loci?
2 - one on each chromosome
homologous region of chromosome?
2 alleles per gene
non - homologous region?
•Y chromosome is short so genes found on the X only have one allele
E.g. of sex linked disorder?
- red-green colour blindness
- gene locus is found on the non-homologous region of the X chromosome
- normal allele R = dominant
- deficient allele r = recessive
- so males only need 1 recessive allele, women need 2
when gene loci is on the non-hm bit of chromosome?
Y has no allele so no superscript
sex linked?
any genes only passed on through X chromosome
other example of sex linked inheritance?
haemophilia, normal is dominan, hameo = recessive
dihybrid inheritance?
• inheritance of 2 genes at once, on different chromosomes
parents are dipoloid so
have 2 alleles for each gene
DI: add up ratio to get
size of Punnett square
Chi squared?
- compare observed data with expected data to see whether there’s a sig. difference
- if there’s a big difference = big no.
- small difference = small no.
- always a bit of difference due to chance
Chi squared shows?
if the no.s are close enough or if something else is going on
if there is no sig diff between O and E value?
data proves DI inheritance
DF =
number of categories -1
if X2 is smaller than CV?
• no sig diff so cannot reject NH
Chi squared conclusion?
- say whether test result was > or < than CV at p =0.05
- is there a statistically significant difference
- is the probability that the difference is due to chance less than 5%
- reject/ accept null hypothesis
unlinked =
separate chromosomes
If X2 is Greater than CV
- difference is significant
* so probability that the correlation is due to chance is less than 5%
if X2 is smaller than CV
- not significant
* probability that diff due to chance is less than 5%
As X2 increases,
prob that diff due to chance dec
big probability that diff occurred by chance =
accept hypothesis
What is epistasis?
where more than 1 gene affects the same characteristic - 2 genes affect the same phenotype
e.g. petal colour
can use X2 on anything that has?
observed or expected
autosome =
chromsome other than sex chromosome
epistasis impacts?
the ratio
Autosomal linkage?
- if a phenotypic ratio is not as expected, could be bc genes are linked - don’t et 9:3:3:1 ratio
- not the same as epistasis
- linkage = 2 genes are located on the same chromosome
why is there no independent assortment with autosomal linkage?
- genes on the same chromosome
- unless the genes are separated by chiasmata, both genes would be inherited together
- if chiasma forms, there’s the possibility of other gametes forming
- recombinant gametes are less likely to form than non-recombinant gametes
what are recombinant offspring?
different combinations of either of the 2 parents allele - chiasma formed between the genes
autosomal linkage: the closer the genes are
- the less likely it is that recombinants will form bc the lower the chance of chiasma forming
- the ratio depends on how close the 2 gene loci are - closer= fewer recombinant offspring
- further apart = more recombinant offspring
recombinant frequency?
how much crossing over has occurred
= no. of recombinant offspring/ total no. of offspring
recomb freq values?
- 50% = not linked
- less than 50% = some gene linkage
- very low = genes are very close together
recomb freq tells u
how far apart the 2 gene loci are
how is recom freq found out?
crossing hetero indiv for the 2 linked genes with a ‘double recessive’ - test cross
chromosome mapping?
- finding the relative positions of linked gene loci on chromosome
- can tell the order of genes of a chromosome
max % of recombinants =?
49% - of 50 then not linked
Hardy Weinburg principle?
- if we know how many people in a population have a phenotype that is caused by a homo r genotype, when we can use it to estimate how many are hetero/ homo dom
- to calc how many ppl have the allele
what is assumed w the HWP?
• Allele and genotype freq in a pop remain constant from generation to generation
5 conditions that need to be met in order for the HWP to be met?
- no mutations so that new alleles don’t enter pop
- no gene flow can occur (no immigration/ emigration from pop)
- random mating must occur (individuals must pair by chance)
- pop must be large so no genetic drift can cause allele freq to change
- no selection so certain alleles are not selected for/ against
in reality (HWP)
- theoretical situation
- always disturbing influences in nature
- so these conditions are never met by a pop
p =
freq of dominant allele
q =
Freq of recessive allele
continuous variation?
• a continuous range of values between extremes
discontinuous variation?
a few clear cut categories e.g. blood group
polygenic inheritance is?
- characteristics that show continuous variation often have an environmental component but some show CV can be purely genetic
- this is polygenic inheritance
Polygenic inheritance bckgrnd?
- many characteristics determined by combined effects of many genes, often w multiple alleles
- shows continuous normal distribution
- bell shaped curve is distinctive of a characteristic that exhibits cont. variation
Factors affecting evolution of a species?
• factors that can change the freq of alleles in a gene pool and thfr cause evolution to happen
- selection
- genetic drift
- genetic bottleneck
- the founder effect
gene pool?
All of the alleles of all of the genes present in a population of interbreeding organisms
evolution =
a change in the characteristics of a population over successive generations
3 types of selection?
- stabilising selection
- directional selection
- disruptive selection
stabilising selection?
- the forms at the 2 extremes of CV are at a selective disadvantage
- selected against
- flatter graphs
directional selection?
- one of the extreme forms is at a selective advantage - 1 allele is selected for
- graphs shifts to the right
disruptive selection?
- extreme phenotypes selected for and intermediate phenotype is selected against
- rare
genetic drift?
- changes in the allele freq of a population (the gene pool)
- as a result of a chance
- much more sig in small isolated population
- smaller population = more chance of allele going extinct quicker
What is speciation?
- formation a new species
* can be allopatric or sympatric
species =
a group of organisms that can breed to produce fertile offspring with similar morphology, physiology and biochemistry
morphology =
form and structure
physiology =
function and activity
in order for a new species to form,
- some of the individuals must become morphologically and/ or physiologically different
- no longer be able to interbreed w members of the original species to produce fertile offspring -> reproductively incompatible
how can speciation occur?
- if a pop is split (isolated) for a long time, when they are reintroduced, they can no longer interbreed
- so, are now 2 diff species
allopatric speciation?
- geographical
- diff appear due to selection pressures/ genetic drift
- population has become geographically sep, so gene flow between 2 groups stops so indiv are physically sep
- bc the 2 groups have diff envir, diff selection pressures act on pop so diff physical adaptations - evolution
what is sympatric speciation?
• Sympatric speciation is speciation that occurs when two groups of the same species live in the same geographic location, but they evolve differently until they can no longer interbreed and are considered different species
sympatric speciation?
- changes in some traits keeps species reproductively isolated, so gene flow between the 2 groups stops
- e.g. colourful flap of skin under lizard’s thorats
- colour changes bc of light
- over many gens, lizards body changes to adapt to envir
why does sympatric speciation occur?
bc of prezygotic and post zygotic isolating mechanisms
prezygotic =
anything that prevents mating and fertilisation
types of prezygotic isolation?
- ecological
- behavioural
- temporal
- mechanical
- gametic
Prezygotic: ecological?
- groups may occur diff ecological niches - their role in a habitat may be different
- e.g. 2 crickets - 1 prefers to live on sandy soil and the other on natural soil at the edge of rainforests - which contributes to reproductive isolation
Prezygotic: behavioural?
- during selection of a possible mate, indiv may reject each other bc they don’t have same courtship behaviour
- e.g. diff in songs sung by males of 2 grass hopper species - females attached to song of own species
Prezygotic: temporal?
- indivs may be fertile at diff times of the year
* e.g. some frog species reproduce earlier in the year than others
Prezygotic: mechanical?
- diff species may have diff sex organs which aren’t compatible
- e.g. male reprod organs of related species of damselfly have distinctive shapes
- each enables male to mate only w own species
Prezygotic: gametic?
- sperm must reach ovum for fertilisation
- chemicals that the sperm and ovum use to attract each other may vary from species to species
- so gametes won’t recognise each other, no fertilisation
- e.g. coral species release eggs and sperm into water
if a hybrid has an odd number of chromosomes?
cannot produce gametes - chromosomes have diff pairing up
post zygotic isolating mechanisms?
- gamete incompatibility - digestive enzymes of sperm don’t work on egg
- zygote inviability
- hybrid sterility
Post zygotic isolating mechanisms?
- prevent a hybrid zygote from developing into a viable, fertile adult
- hybrid inviability
- hybrid infertility
why do some plant species reproduce to produce plants that cannot interbreed with the parent species?
• diff chromosome number
hybrid inviability?
sometimes hybrid dies prematurely :(
hybrid infertility?
even if an offspring is produced from the mating of diff species, infertile as diff chromosome number - why mules are sterile
Population bottleneck?
- size of population decreases dramatically
- OP has a large GD
- bottneck event means only few remain
- bc new pop is the offspring of the few remaining individuals, less GD
Founder effect?
- few ppl start their own colony
- non-rep sample of alleles
- dec GD in new population
gene =
specific length of DNA coding for a protein
allele =
one form of a particular gene
locus =
position of gene on chromosome
phenotype =
observable characteristic, caused by genotype
genotype =
alleles of a gene/ genes possessed by an organism
dominant =
causes phenotype if genotype is hetero or homozygous
recessive=
causes phenotype only when homozygous
heterozygous =
genotype has 2 diff alleles for a particular gene
homozygous =
alleles for a particular gene are the same
homozygous =
alleles for a particular gene are the same
codominant =
both alleles contribute to the phenotype when genotype is heterozygous
AS is the same as
SB, they both speed evolution up
natural selection?
- selection pressures cause survival of fittest & more likely to reproduce
- variation within a population
- selection pressures act on a population
AS:
- SP controlled by humans, not natural
- ‘fitness’ determined by humans based on what are the desirable characteristics
- parents selected for these characteristics
cows?
- Friesan - milk production
- Highland - hardiness
- Jersey - maturity speed and quality of milk
General principles of SB?
- select cow w desirable characteristic
- select bulls that have produced high quality progeny - bc milk yield is sex limited
- artificial insemination to cross
- carefully monitor for desirable characteristics
Modern AS techniques are?
- automated milking &feeding
- progeny testing
- artificial insemination
- sexed semen
- genomics
- IVF and embryo splitting
Modern AS techniques: milking
automated milking and feeding machinery which tracks each cow’s yield precisely
Modern AS techniques: progeny testing?
accurate and detailed
Modern AS techniques: artifical
insemination and online semen purchase
Modern AS techniques: sexed semen
sperm cells w only X chromosome
Modern AS techniques: genomics?
selecting parents based on genetic markers rather than phenotype
Modern AS techniques: IVF and
embryo splitting - cloning
how to ensure pollen gets to right plants w no genetic contamination?
- removing anthers b4 they mature, produce pollen and self pollinate
- transfer pollen by hand
- keeping plants isolated after pollination, by bagging flowers
Problems associated w AS can be:
physical, due to linked genes or interbreeding
physical problems associated w AS?
- can cause sig. health problems
- e.g. selecting high milk ield Holstein Freisans causes mastitis
- flattened fce of bulldog causes issues w breathing
linked genes?
- if the gene locus of a DC is v close to gene locus of another characteristics, then these alleles will often be inherited together
- e.g. in Dalmatians, gene for pots is close to gene for ear canal -> leads to deafness
interbreeding?
• increases channce of rare homo recessive allele combinations which can cause problems like birth and development defects
solutions to problems assoc w AS?
- can be min. by:
- maintaining resource of genetic material for in SB
- to include ‘wild type’
- avoid crossing closely related individuals
this can be done thu?
- conservation of wild type organisms in situ or ex situ- e.g. millennial seed bank, conservation parks
- constant movement of male parents to prevent em breeding w daughters
- genetic monitoring, progeny testing and record keeping to avoid inbreeding
ethical considerations of AS? +
+ organisms selected based on DS, so offspring better suited to envir and more liekly to survive
+ same effect as NS but selection pressure caused by humans, =ethical bc would happen anyway
ethical considerations of AS? -
- harmful - can cause health problems
- reduced GV -> pop less robust
- genes may be linked so undesirable characteristics can be inherited too
