Inheritance Patterns Flashcards
Shape of males in pedigree drawing
Square
Shape of females in pedigree drawing
Circle
In a pedigree drawing, what do partners have between them?
Partners have a line between them
In a pedigree drawing, what do siblings have above them
Siblings have a line above them
In a pedigree drawing, who are shaded?
People who are affected are shaded
In a pedigree drawing, who have dots inside?
Carriers have dots inside
In a pedigree drawing, what do double lines mean?
Are a consanguineous couple(Same blood)
What does SB on a pedigree drawing mean?
Still born baby
What does the diamond symbol in a pedigree drawing represent?
Means unknown sex
What do small triangle symbols in a pedigree drawing represent?
Spontaneous abortion
What does a triangle with a line going through it represent?
Represents therapeutic abortion
What represents identical twins, non-identical twins?
Identical twins have diagonal lines and a line between them Non identical twins have only diagonal lines
What does a diamond with the letter P inside represent?
Represents someone who is pregnant of a child with an unknown sex
What symbol represents no offspring?
In what form are autosomal dominant inheritance?
Clearly in heterozygous form
How many generations are affected by autosomal dominant inheritance?
Multiple generations are affected by autosomal dominant inheritance
What will most individuals with autosomal dominant inheritance have?
Most will have an affected parent
What is the risk to offspring for autosomal dominant inheritance?
50% risk to offspring
Characteristics of autosomal dominant inheritance
-Most individuals have an affected parent -Males and females are equally likely to inherit -An affected individuals siblings/children whom aren’t affected, do not carry the mutation and cannot pass it on to their offspring
FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What is penetrance and incomplete penetrance?
Penetrance is the percentage of individuals who carry the mutation and develop symptoms of the disorder -Many dominant disorders show age dependent penetrance Incomplete penetrance is when you have the genotype, but not phenotypically expressed
FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What is variable expressivity?
Variation in several symptoms of disorders between individuals with the same mutation
FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What varies between autosomal dominant disorders?
De novo mutation rate varies considerably between autosomal disorder conditions
FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What is somatic mosaicism?
- Mutn arising at early stage in embryogenesis
- Present in only some tissues/cells (e.g can just be in neuronal cells or skin cells resulting in a difference in the way the disease is presented)
FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What is germ line mosaicism?
It is when new mutations arise during oogenesis or spermatogenesis -Mutation present in variable proportion of gametes and can be transmitted to offspring
FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What is anticipation?
Worsening of disease severity in successive generations -Characteristically occurs in triplet repeat disorders
In what form is autosomal recessive inheritance?
Clearly in homozygous form
Who aren’t affected by autosomal recessive inheritance?
Carriers aren’t affected
What sexes are affected by autosomal recessive inheritance?
Both sexes affected
How many generations are affected by autosomal recessive inheritance?
Usually one generation affected
What may be a factor of autosomal recessive inheritance?
May be consanguinity
What are compound heterozygotes?
-2 mutations in the same gene however these mutations are different
What is a homozygote?
-2 mutations in the same gene however these mutations are identical
What are the features of autosomal recessive inheritance?
-Trait often found in clusters of siblings -All offspring of affected person are obligate carriers
Chromosomes in men and women
Men-XY Women-XX
What are the affects on BOTH genders of X-linked inheritance?(Recessive)
- Women are carriers and are unaffected
- No male to male transmission
- Men will give their Y chromosome to their son
What are the affects on BOTH genders of X-linked inheritance?(Dominant)
-Women are affected -Males are more severely affected
What type of genes are never passed from father to son?
X-linked genes never passed from father to son
In X-linked recessive inheritance, who are the obligate carriers?
All daughters of affected males are obligate carriers
In X-linked recessive inheritance, what do children of carrier females have a chance of inheriting mutant alleles?
Children of carrier females have a 50% chance of inheriting mutant alleles
What is skewed X-inactivation in X-linked recessive inheritance?
-
Skewed X-inactivation: normally most genes on one of a woman’s X-chromosomes are inactivated
- generally random but ~10% of women have uneven or skewed X-inactivation.
- Healthy X chromosome is switched off, resulting in the expression of more unhealthy X chromosomes in cells which can lead to manifesting carriers.
-
Manifesting carriers: manifest (showing), heterozygous carrier however healthy X chromosome has been switched off resulting in the symptoms shown.
- e.g. cardiomyopathy in Duchenne Muscular Dystrophy (mothers of unhealthy boys may be manifesting carrier
Who are manifesting carriers?
manifest (showing), heterozygous carrier however healthy X chromosome has been switched off resulting in the symptoms shown.
e.g. cardiomyopathy in Duchenne Muscular Dystrophy (mothers of unhealthy boys may be manifesting carrier
Y linked inheritance
Always and only passed through fathers to sons
- What is a mutation?
- What is a pathogenic mutation?
- Where can mutations be found?
Mutation = Change in genetic material
Pathogenic Mutation = results in the alteration of the function of the gene product and can cause a disease phenotype
Mutations can be found in coding DNA, Non-Coding DNA(promoters and introns)
What do a pathogenic mutation result in?
Results in an alteration of the function of the gene product and can cause disease
What is a silent mutation?
A base change has no change in the amino acid
What is a nonsense mutation?
- Introduction of a stop codon resulting in a truncated protein.
- Can cause removal of functional parts of protein.
- However, mRNA strand can sometimes be degraded via nonsense mediated decay
What is the difference between in-frame and frameshift mutations?
- In frame = protein product machinery can continue to read the DNA sequence after the mutation. May result in sections with protein missing however the overall function remains
- Frameshift = insertion or deletions of bases of DNA, disrupts the reading frame so the wrong amino acid is put in place, entire sequence following the mutation will be disrupted or read incorrectly
In-frame (multiple of three) or frameshift (not multiple of three)
What is pleiotropy?
Specific mutation that is affecting multiple systems e.gmosaicism, expressivity, penetrance
(one gene will code and control the phenotype or expression of several different and unrelated traits)
Pleiotropy is most often a bad thing, as many diseases are due to a gene controlling so many traits at once. For example, phenylketonuria is a disease caused by pleiotropy.
What does Hemizygous mean?
Hemizygous: Having only a single copy of a gene instead of the customary two copies.
All men are HEMIZYGOUS for anything on the X chromosome
