Complex Traits Flashcards
Relationship between alleles at one locus
Can lead to non-mendelian genetics patterns
Mendle
Discovered how alleles at one gene can be dominant or recessive
Did Aa X Aa – go t phenotypic ratio in offspring were predictable
3:1 Phenotypic ratio
3:1 F2 phenotypic ratio in Monohybrid cross
Pattern of inheritance = Mendelian Inheritance –> extends to corsses with heterozygosity at 2 loci
F2 phenotypic ratio in Dihybrid cross AaBb X AaBb
Get phenotypic ratio 9:3:3:1
Non-mendelian inheritance
When phenotypic ratios deviate from 3:1
Non-Mendeian inheritnace at one locus (At one gene)
- Incomplete dominance
- Co-dominance
- maternal Effects + Cytoplasmic Inheritance
- Sex Influence + Sex-linked
- Lethal Alleles
- Conditional Allele
Complex (Quanatative traits)
Demonstrate continuous phenotypic variation + do not behave according to Mendelian Genetics
Mendelian Inheritance
Monohybrid (Aa X Aa)
GR – 1:2:1
PR – 3 Dom: 1 recessive
Incomplete dominance
Relationship between 2 alleles were Aa is intermediate between either homozygote
Example:
P = Purple
p = White
PP = Purple
pp = white
Pp = Violat – mid between purple and white
Pp X Pp – PR –> 1 Purple: 2 Violate: 1 White = deviation from 3:1 = Non-mendelian inheritance
Degree of Dominace (h)
Describes the degree to which the phenotype of the heterozygote resembles the phenotype of a homozygous parent
Range from 0 - 1
Meaning/finding Degree of dominance
You need to define one homozygous phenotype as h = 1
Ex. Flowers
Red – H = 1
White – h = 0
h= 0.5 – midpoint pink
h > 0.5 – Darker pink
h < 0.5 – lighter pink
***need to define one of the homozygotes as h = 1
Answer: C – Incomplete dominance where h = 0.7
Black – h = 1 (given in question)
White – h = 0
Dark grey = closer to black = h >0.5 –> h = 0.7
Expressivity
When phenotypes vary between individuals with a particular genotype
- There is a wide range of phenotypes for a single genotype
High expresivity = there is a BIG range of phenotypes
Expressivity example – Polydactalism
A = dominant to a
AA or Aa = extra digits
aa = normal # of digits
Aa genotypes – have some with just extra small nub and some with many more fingers = wide range of phenotypes but individuals all have the same genotype
- There is a wide range of phenotypes for a single genotype
A = have polydactalism
aa = normal
A = extra digits
Degrees of polydactalism can vary
Autosomal Dominant with incomplete penetrance
Extect II - 1 to show the traut because offspring is affected but they don’t
Expressivity + Incomplete dominance
Expressivity (range of phenotypes) can sometimes explain incomplete penetrance – if you have high expresivity = have very wide range of phenotypes –> if have wide range then you can have a very low end phenotype – since it is very low end it might not be detected but then can have offspring with detected trait
- High expresivity is one way to explain incomplete penetrance
Penetrance
The proportion of individuals with a particular genotype that also express the associated trait
Incomplete penetrance
When some individuals with a particular genotype express the trait while others do not
Calculating penetrance example
Here 90% – because 9 out of 10 individuals with the genotype have the trait
To solve:
Need to find the genotypes of individuals – look at who NEEDS to have the genotype then look at how many out of those actually have the trait
with trait/ # with genotype
Co-dominance
relationship where Aa includes phenotypes of AA and aa
***Example – Red + White –> Red and white spots
Example – Blood types
AA –> Type A – Have A antigen on RBC surface
BB –> Type B – Have B antigen on RBC surface
AB – Type AB (CO-DOMINANT) –> produce BOTH A and B antoigen (Have both AA and BB phenotype NOT a intermediate one)
AB X AB –> Get 1 AA:2AB :1BB Phenotypeic ratio –> Non-mendelian ratio
Blood type adding in i allele
KNOW – AB is co-dominant BUT both are dominant to i
i = no antigen – ii = type O
Type A = AA or Ai
Type B = BB or Bi
Have multiple allles in gene = can make it harder to predict outcome of cross = interupts mendelian inheritance pattern
Having multiple alleles per gene + mendelain inheritance
Have multiple alleles in gene = can make it harder to predict outcome of cross = interupts mendelian inheritance pattern
Example –
Type A = AA or Ai
Type B = BB or Bi
Without knowing the genotypes (AA or Ai) = don’t know outcome of the cross
Allele context
Allelic relations = need context –> Allele is only dominant to another allele BUT if comparing to another allele that might change
Blood transfusions
Type A = doesn’t have B antigen = sees B as a foreign = have immune response producing anti-B antigen = essential that the person with Type A doesn’t get blood with B allele
- Can’t get B or AB
- Can only get A or O
Type B = recognizes A as foreign
- Requires B or O
Type AB = have A and B = no immune response to Type A, Type B ot Type O
- Can accept blood from all blood types –> Universal accpetor
Type O = No Antigen = reocgnizes A and B as foreign
- All other types can accept Type O = universal donor
- Can only get type O
Affect of Recessive Lethal Alleles
Lead to death when homozygous –> Lethal Alleles can lead to missing or reduced #s of genotypes
In monohybrid cross with recessive lethal alleles = have fewer offspring overall
Example Recessive lethal – Agouti in mice
Y = yellow – dominant to y
y = No yellow
Yy = Yellow
yy = no yellow
YY = death
Yy X Yy
GR – 1 YY: 2 Yy: 1 yy
PR – 2:1 – 2 yellow: 1 non-yellow because YY will never develop
Findoing probability in recessive lethal
+ Example
Can take out the one that dies = change the probability of all others
Ff X Ff
1 FF – dead
2 Ff – short
2 ff – tall
Because 1 FF is dead = only 3 pffspring – 1/3 is tall
F = dominat for achodrolasia BUT recessive for lethal (becaise need 1 F for short BUT need two F for dead)
***Doesn’t matter which you assign F or f – gives same results
F = dominant for acondroplasia – only need 1 copy (one copy in Ff = have achsdrolplasia)
F = recssive for lethal because need two copies (FF = dead)
Why ressive lethal if the allele is also dominant
Y = lethal
Y = dominant to y for agouti – because Yy is yellow (heterozygout has phenotype of Y)
BUT
Y = recessive for lethality because need 2 of them – only die if YY
Yy = alive –> y is dominant for lethality
Yy = alive and yy = alive BUT YY is dead = y is dominat for lethality because Yy is like yy
Recessive lethal phenotypic ratio in monohybird
2:1
Recessive Lethal Example 2 – Tail in cats
S = truncated tails and is dominat to s
SS = leads to spindal development probelms and is embryonic lethal
Organelle inheritance
Organelles contain mtDNA or cpDNA that can influence a trait
- Unpredictable organelle inheritance may lead to differences in trait expression
In mitosis – different quanityoes of organelle is ingerited = mtDNA and cpDNA is not inherited according to mendelian ratios = not predictable
What passes on cytoplasmic componenets
IN mammals egg cells (female gametes) pass on all cytoplasmic components – mtDNA is inherited through mothers
Paternal mtDNA is activley elimanted in zygote
Affect of organelle inheritance
Unpredictable organelle inheritance may lead to differences in trait expression
Characteristics of cytoplasmically inherited traits
- Present in Males and Females
- Usually inherited from one parent – usually the maternal parent
- Reciprical crosses give different results
- Exhibit extemsive phenotypic varaition even within a single family
Can there be paternal inheritance of mtDNA
Called Paternal leakage – sometimes –> rare exception NOT general rule
- 17 examples of paternal mtDNA in children
Possibilities for how – defects in the ability to eliminate paternal mtDNA
Maternal affects Genes
Found genes that encode regulatory RNAs that are passed to the offspring in the cytoplasm of the egg
RULE: Mother’s genotype detemrines the offspring’s phenotype
Maternal effects
Moms envirnment to offspring –> envirnment can alter gene expression in offspring that givs rise to phenotype that are reuslt of the materal envirnment
Different envirnment can alter phenotypic ratios in offspring
BUT the mosther’s genotype detemrines the offsrpings phenotype
Sex limits vs. Sex influences traits
BOTH – caused by genes on autosomes = both males and females can transmitt the trait but the trait is only expressed on one sex
- Can be on sex chromosmes (then it will also be sex linked and sex-influenced/sex limited) OR can be on autosomes
Sex limit = trait is ONLY expressed in one sex
Sex influence = trait is mostly expressed on one sex
Can be caused by genes on autsomes – sometimes they are also sex-linked
- Sex linked if they are on sex chromsomes
Example Sex limited – Precocious puberty
P = Early puberty – dominant mutations in autosomal gene encoding hormone receptor can lead to early puberty in boys –> lead to early puberty in boys only
p = normal puberty
Mutation in AUTOSOME – both males and females can pass down but only have trait in males
pp (normal female) X Pp (Early puberty male)
- Gives Normal female, Normal Female, Early male, andnormal male (SEE IN IMAGE)
- Get gametes with pX from mom, and PX PY, pX, pY from dad (because get P on auatsome and get sex chromsomes)
OR
pp (normal male) X Pp (Normal female)
- Daughters and half sons have normal pubey, Half sons have early puberty
Shows both males and femals can pass down trait but only males show the trait
NOT sex linked because when do reciprical cross = we get the same ratios (get 2 normal females, one early male, and one normal male) –> because same ratios = NOT sex linked traits = both can transmit the trait but only males present the trait
Example of sex influenced – male pattern baldness
Mutations in an AUTOSOMAL locus on chr. 21 can lead to hair loss in men, and to a lesser degree women. sex influenced (but not sex-linked)
Sex influneced because can see trait in women but not sex linked because on autosome
Males:
HH = have hair
Hh = have balding
hh = bald
Females (have the same alleles BUT do not see hair loss to full degree):
HH = normal
hh = have thinning of hair BUT not bald in same way that males will be
***Inherited on autosomes = not sex linked
Sex linked male pattern baldness
Varaints on gene on X chromosome leads to hair loss in men but not wome (Sex linked because on X chrosmomes AND sex limited because only in men)
Xh = hair loss in men
xH = no hair loss (full hair)
xhxH or xHxH = full hairs
Sex linked – on sex chromosome vs. Sex infulenced is on autosomes
Conditional alleles
Influence mendelian ratios –> Allels that ONLY show phenotype in certain envirnments
- Only present their phenotype under certain envirnmments
- Conditional on envirnment
Ex. Siemmese cats – temperature sensitive alleles
cs = non-functional at high temperatures but functional at low temp
CS = WT – can produce melasis = get full color
CS is dominant to cs
cs at low temp expressed = can produce pigment but at high temp not expressed = cannot produce pigment –> expression is dependent on envirnment
Siemesse cats = cscs –> can make tyrosnine to get pigment at low temperature but not at high –> when they are born they are born all white because at high tempeture in the womb = no tryosinase = no pigemnt –> as they grow their expremities cool but their body stays warm = extremeisties get opigment because of cooling and body stays white because warm (warm areas stay white)
This is conditional allele because expression of the allele depends on the envirnmen
cs = Temperature sensative allele
- The extremities = get cold = have color
- The core stays warm = no color
- ALL cells have the alelle but its not expressed in all
- When first born = all white because wamr in the womb = no color
Conditional alleles can be
Lethal –> means that they are lethal only under certain conditions = have conditional lethal allele
Example conditional lethal allele – favism
X-linked recessive mutation –> mutation prevents G6P dehydrogenase
- Mutation in Glu-6-P dehydrogenase = reduced glutathione = RBCs are not protected against oxydants = cells undergo hemylysis = can lead to death
- Leads to low glutathione, an antioxidant that protects red blood cells
- Hemolysis can occur if oxidant loads are too high
Trigger for increase in oxidants = fava beans + antimalarial drugs + some antibiotics + henna
Most people homozygous for mutation are fine BUT only have health issues if oxidants level increases = conditional lethality
Allele frequencey for favism varaint
Offers protection against malaria
- Individuals that have favism allele = protected against malaria
- Increase in malarua alleles = increase in allele frequncey of favism vraints
May explain why some cultures use chickpeas instead of fava beans
Given X-inactivation – why do Turner (XO) or Klinfelder (XXY) syndromes exist
At certain times during embryonic development both X chromsomes are needed
- finally a cell with select 1 at random for X chromsome inactivation
ALSO sometimes there is expresion of certain genes from teh condensed X chromosome
Common mechanism in XY females
Androgen insensitivity syndrome
Low response to testostrone
Overproducing testosterone
XX with congential Adrenal Hyperplasia – genetic variants can cause an overproduction of testosterone
XX individuals with CAh can be:
1. Typicaly female
2. Typical male
3. Cmbined male and female charachteristics
XX males
XX can develope as males if SRY targets are activated errenously – if have recombination between X and Y chrosmoems that adds SRY to X chromsome
- Recombination doesn’t normally happen between X and Y chrosmomes but sometimes mistakes happen
Sex chromomomes across biology
Not always X and Y
Ex. Lots of repriles and bird and some invertabrates
Female = ZW (heteroganetic –> can make gamated with Z or W chromsomes)
Male = ZZ (homogametic –> can only make one type of gamete)
Still have sex chrosmomes but not called X and Y called Z and W
Ex. 2 – Some Invertabrates
Female = XX
Male = XO (1 X only)
Extreme sex chromsomes
Some species take sex chromosomes to the extreme
Ex. Platapus
Female = XX, XX, XX, XX, XX
Male = XY, XY, XY, XY, XY
Have 5 sets of sex chromosomes
Sex + Ploidy
Some rely on ploidy rather than specific sex chromsomes
Ex. Bees
Males = Haploid – basically unfertalized gamete becomes male
Females = diploid
Haploids = develope as malel Diploid develop as female
Genic Mating System
A single gene determines mating types in some
organisms – the allele of that gene determines Sex
- No sex chromsomes
Ex. Yeast
- Has two mating types – A and Alpha –> mate to form diploid –> controled by a single gene
- The gene = flanked by silent copies of both mating types –> chnages alleles at mating type locus = daughter cells can change mating type
Mating types in yeast:
Saccharomyces cerevisiae: 2 mating types
Tetrahymena thermophila: 7 mating types –> have pheranomes + pheramone receptors that allow this to happen
Cryptococcus neoformans: 2 mating types but
~20 different mating receptors
How are there multiple mating types in yeast
Have pheranomes + pheramone receptors that allow this to happen