Pedigrees Flashcards
What is the value of a pedigree
- Social connection –> Shows connecteness
- Follow alleles through meiosis (Genetic pedigree)
How to label individuals in a pedigree
Row number – give each row (each generation) a Roman numeral
Individual Number – Give each indivual in the row a number (INCLUDE ALL INDIVUALS IN THE ROW NOT JUST CHILDREN)
- Cpount Left to right and assign each indiviual a number
Affected or not affected
Filled in = Affected
Not filled in = not affected
Labeling Individuals in pedigree example
Sex in a Pedigree
Square = Male
Circle = Female
Proband
The individual with an arrow pointing at them in the pedigree – this is the individual that you got the information from
- Person who initiates pedigree – gives information
Value of the proband
Because when making a pedigree = you are showing who you got the information from which is important because the infomration can get clouded as you move farther from the proband
***The information closer to the proband is more relaible
***Useful for clincials because it provides a condifence interval – individual is more liley to be accurate with immediate family
- if damily member is more distant you might be less confident in health information
What does // indicate in a pedigree?
Severed relationship
What does /\ indicated in a pedigree
Fraternal twins
Fraternal twins = siblings that were born at the same time
Practice – In the following pedigree assign the genotypes to everyone and indicate individuals that would be affected or carries
When filling this out:
1. Assume that anyone coming in as a spouse does not have the rare allele (is homozygous for the non-rare allele)
- Assume that spouses are all aa because it is a rtare allele = peope coming in are not carriers and do not have the trait
- When you have different pheontypes from teh cross = assume that they are evenly distributed between boys and grils
Example – if have Aa and aa in the offpring – assume we have 4 kids (2 boys and 2 girls) – assume one boy and one girl is Aa and one boy and one girl is aa
- need to be one boy and one girl (even between both boys and grils) - Since this is a dominent trait and only need one allle – assume that the affected are heeterozygous (unless need to be homozygous from punnet square) – assume that they are heterozygous because rare allele
Safe assumtions in pedigree
- Assume that people entering are not carries (assume that non-blood relatives are not carriers)
- IF you know the mode of inheritance and you know that in order for the pedigree to work then they MUST be a carrier then you can assume that they are a carroer
- Assume that is dominent trait and don’t know if the person is homozygous or heterozygous then they are heterozygous
- For dominent traits – the first person in teh pedigree to show the trait is most likley heterozygous
What does this symbol mean (what does it mean if something is partially filled in)
Means that the individual is a carreier
Practice – In the following pedigree assign the genotypes to everyone and indicate individuals that would be affected or carries
We can assume that the spouses coming in are AA because a is rare
Remeber – that when have two genotypes – there needs to be an equala mount of boys and girls with that genotype
- If two genotypes –> have 4 kids (2 boys and 2 girls) and 1 boy and one girl is one genotype and one boy and one girl is the other genotype
Practice – In the following pedigree assign the genotypes to everyone and indicate individuals that would be affected or carries
Trends of passing X chromsome (general)
Males pass the X to all daughters and NO sons
Females = pass X to both daughters and sones (if have two diferent alleles on their X chromsomes thebn 1/2 the kids will get one of the tyoes of X and half the kids get the other type of X)
- AND – the passing of one type of X (half of them are boys and half are girls) AND the otehr half of kids that get the other X (Half of them are boys and half are girls)
Trends of passing X chromsome (general)
Males pass the X to all daughters and NO sons
Females = pass X to both daughters and sones (if have two diferent alleles on their X chromsomes thebn 1/2 the kids will get one of the tyoes of X and half the kids get the other type of X)
- AND – the passing of one type of X (half of them are boys and half are girls) AND the otehr half of kids that get the other X (Half of them are boys and half are girls)
Practice – In the following pedigree assign the genotypes to everyone and indicate individuals that would be affected or carries
Practice – In the following pedigree assign the genotypes to everyone and indicate individuals that would be affected or carries
***NOTE – the affected should be the male in the first generation
Practice – In the following pedigree assign the genotypes to everyone and indicate individuals that would be affected or carries
NOTES:
- Affected males don’t pass down the trait to kids
- Affected females pass down the trait to ALL kids
Where do you get mtDNA from?
Get ALL mtDNA from your mom
***ONLY the mom passes mtDNA to ALL kids
Weird think in mitocondrial pedigrees
HAS incomplete dominence
- Affected mom might have unefefcted kids and unaffecte dmom (that still has the mutation but doesn’t show the phenotype) might have affected kids
Can have an affected mother pas one the trait to one BUT NOT all of the kids (ALL of the kids get the mutated mtDNA but not all will show the phenotype)
Can have an unaffected mother (that has some mutated mtDNA) pass the mutation to kids and have affected offspring (She can have kids that show the phenotye BUT she does not show the phenotye BUT she must have a mutated allele because she has affected offspring)
Autosomal Dominent Trends
- Trait appears equally in males and females
- Trait doesn’t skip generations
- Affected children have an affected parent
- Unaffcted children do not transmitt the disease
Autosomal recessive traits Trends
- Trait appears equally in males and females
- Trait skips generations
- More appear among the progeny of related parents
What does ====== line in pedigree mean?
Means consigous relationship (Example – between first cousins)
X-Linked dominent Trait trends
- Trait does not skip generations
- Affected males pass the trait to all daughters and no sons
- Affected heterozygous females pass the trait to half of the sons and half of the daughters
X-linked Recessive Trait trends
- Affected males proudce carrier daughters
- No sons of affected males are affected
- Males are more likley to be affected than females
- Half of the sons of an unaffected carrier will be affected
Y-link Trait trends
- Traits ONLY appear in males
- All of the sons of affected males will be affected
mtDNA traits Trends
- Affected females pass the trait to ALL children
- Affected males never pass down the trait
Trend in mtDNA traits
Often show incomplete penetrance
Incomplete penetrance
When not every indivduals must be a particular genotype to show the expected phenotype
- Not everyone with teh allele shows the trait
Example – with mtDNA
- Can have an affected mother pas one the trait to one BUT NOT all of the kids (ALL of the kids get the mutated mtDNA but not all will show the phenotype)
- Can have an unaffected mother (that has some mutated mtDNA) pass the mutation to kids and have affected offspring (She can have kids that show the phenotye BUT she does not show the phenotye BUT she must have a mutated allele because she has affected offspring)
Heteroplasmy
The Co-existance of multiple mtDNA variants in a single cell or among cells within an individual
- Different mtDNA can have different sequences
***mtDNA heteroplasmy = common in humans
Amount of mtDNA in a cell
There are many copies of mtDNA in a cell – they don’t all need to be the same sequence
- You can have different type of mtDNA
How is mtDNA inherited
NOT inheridted in mendialian ratios
- Since have random segaration AND you can have different sequances in mtDNA –> you can have some cell that get a lot of the mutated mtDNA and some that do not = thats the reason that a mom without the phenotype can have kids with mutant phenotype OR a mom that does have the phenotype can have kids without the phenotype
Organelle Inheritance
DOES NOT follow mendialian ratios – have random segeragation of mtDNA during meiosis that leads to unequal inheriyance of mtDNA
- There is NO way to predict this – it is just where the mtDNA happens to be when segregating
**Image = shows that sometimes you coudl get more of teh blu mitocondria and sometime syou get more red during mitosis and meiosis – don’t know what varaiant of mtDNA will be in the highest concentration after cell division
When does mitondrial disease arise
If the mtDNA varaint that contains a disease causing alelle reaches a certain tgreshold disease symtoms can arise
- If have a mom that has disease mtNDA they can
pass down enough copies for the child to have the disease through ranodm segration (because of random segregation the children can have more copies) OR through random segregation the child can have few copies
- It can increase when passed down to a point where the individuakl receives enough copies = starts to show the disease
Carries of mtDNA diesease
A granddaught from a grandmother that has mutated mtDNA can have the diease even of her own mom does not have the diesease because her mom still has some copies of the mutant mtDNA but does not have enough for the threholf of disease
Carries of mtDNA diesease
A granddaught from a grandmother that has mutated mtDNA can have the diease even of her own mom does not have the diesease because her mom still has some copies of the mutant mtDNA but does not have enough for the threholf of disease
Pedigree
Genetic representation of a family tree
Relationship line between spouse
Not genetically related but have a relationships
Descent line (shows offspring)
What does a slash through an individual mean in a pedigree
Dead
Birth order in pedigree
The child all the way to the left is the 1st born – goes down from there (Be careful not to count spouses only look at siblings)
Numbering people in pedigree
Each genertion = roman numberal
Each person in line is a number (left = 1) – includes everyone (Children and spouses)
How do you indicate a severed relationship
Put dashes through the relationship line
What do roman numeral indicate in pedigree
Indicate generation – everyone in that line is the same genertaion
Considered “generation line” – put everyone in the same generation in the same line
Pedigrees are…
Social construction and genetic representation
How do you show identical twins
How do you show fratermal twins
Twins = born at the same time = lines going down start at the same point
- No line in the middle
How do you show adopted kid
With a dotted line (rather than a solid decent line)
***Putting social context on pdeigree but indicates no genertic information was passed down
Showing a father who was a sperm donor but has no relationship with daughter
Line goes to the mother but the duaghter only comes off of mother is not connected to the father
What does a partially filled individual mean
The person is a carrier
What does a diamond indicate
Individual does not fall neatly under male/female
- Could be trans or intersex or might not know gender yet
Consigous relationship
Shown by double lines – is incest
- Might share the same mother
***Frowned upon in humans
Pedigree (helpful reminders/symbols)
Use of pedigrees
Can help genetocists understand how traits are inherited between genertions
Example Sutosomad recessive disorders
- Sinckle cell – RBC diseae
- Cystic fibrcous – chloride chanel defect
- PKU – Phenylzalanine metabolism defect
- Tay Sachs – Lipid metabolism disorder
**Each are on a single gene – need 2 copies of recessive allele to show phenotype
Fill out genotypes
I – ned to be Aa because both need an a to give II3
II3 = aa because affected
II3 and II4 – need Aa to give a to IV2
III1 – if heterozyguous need to get a from mom bvecayse II1 is AA BUT II2 is not affected so she has to be Aa
***Can determine partial genotype – III1 is not affacted so is A_ and we know needs an A but we don’t knwo if mom gave A or a
***Assume that anyone coming in is AA because rare trait – safe to assume that non-relatives coming in are not carriers –> they are AA
Example Autosomal Dominenant disorders
1 – Achyndroplasia – skelatal disorder causing dwrafism
2 – Huntingtons – nerodegenerative disease
3. Marfan syndrome – Connected tissue disorder
Fill out genotypes
For dominenet – since it is rare you can assume that am affected individual that has unknown genotype is heterozygous (unlikeley that both parents could give them allele) – like I2
Example Sex linked traits
- Red green color blindness
- Duchene muscular distrophy
- hemophelia – blook clotting disorder
***Traits on sex chromsomes
Fill out the genotypes
II4 – can assume XX because it is rare and she is not related = can assume she is not a carrier
II2 – has an affected son but she is not affected = needs to be a carrier
IV2/3 – Need to be Xr because the dad is XrY and he gives them one X chromsome
Look at page 8 of notes
X-linked dominant Disease
Very rare – they are often are lethal before birth in males = only seen in females
- Aicardi syndrome (brain defect)
- Incontinetia Pigement – skin lesions
- X-linked Rickets – Bone lesions
Fill out genotypes
Notes:
- Parents that are not carriers don’t have trait = no affected kids
- Unaffected parents have unaffected kids
III7 – is not affected = got not affected X from mom
Y-linked disorders
Overall – easy to follow because the trait only affects individuals with Y chromsomes = only affects males
- Traits appear only in males
- Every generation – all males receive the trait causing alleles
Examples:
1. Certain alleles of the SRY gene (sex determination)
2. Certain alleles of SOX2 (male pattern baldness)
Mitocondria (overall)
Mitocondria = make structural network in cell that produces energy – mitocondria are the powerhouse of the cell
Most organisms inheritance of mtDNA
Usually it is uniparental – only get it from one parent
***In mammals inheritance of mtDNA = materall –> egg has all mtDNA
mtDNA trend
because mtDNA = tramistted through egg – THEN if you have affected female = passes the trait to ALL kids
- Affected females pass affected mtDNA tp all kids but affected males do not pass down mtDNA to offspring = affected males do not have affected kids
What leads to incomplete penetrance in mtDNA
Unequal division
Why is mtDNA inheritnace not straight foward
Because offspring can receive different amounts of the different types of mtDNA that are present
- Might have enough of mutant to show phenotype or might not have enough to shwo phenotype
Example of a typical mtDNA inheritance
Have a daughter that passes mtDNA to son and daughter who weren’t affected but her grandchildren are affected
- Kids can be affected but the mom is not affected
***mtDNa shows incomplete penetrance were not every individual that has the mutant mtDNA has the trait
Example mtDNA disease
- Mitocondrial myopathy muscle loss
- Lebers heriditary optic nueropathy – loss of eyesight
- Leighs syndrome – encepalopathy
- MERF syndroome – epilepsy
- mtDNA depletion syndrome
