Inheritance Flashcards
What are the features of autosomal recessive inheritance?
Expressed rarely, as you need to have two recessive alleles
Usually skips generations
Affects both males and females in equal number, as its not sex linked
Requires the affected individual to be homozygous recessive in order to express
A heterozygous individual is classified as a carrier
Can result from two unaffected parents who are carriers
What are the features of autosomal dominant inheritance?
Affects both males and females in equal number, as its not sex linked
Means anybody affected will have an affected parent, as they must have revived a dominant alleles from them
If the parent do not show a disorder no further generation will have the disorder either
Results in non-affected individuals being homozougoue recessive
Anybody affected is either double dominant or heterozygous
What are the features of sex-linked recessive disorders?
Affects more males than females, males only have one X so there’s a greater chance that it will affect them
Not passed on from an affected male to son, as the male would have given his Y chromosome
Needs an individual to be homozygous if they are female
Will be expressed in a male who has one copy of the defective allele
Will not be expressed in a female or male who is normal homozygous
Will not be expressed in heterozygous females
Means that usually the mother of an affected male is unaffected herself
Means that all daughters with affected father will either be affected or be carriers
Means that the daughters who are affected must have a father which is affected and a mother who is at least a carrier
What do squares represent in pedigree charts?
Males
What do circles represent in pedigree charts?
Females
Name the six mechanisms of non-mendelian inheritance
Sporadic cases
Incomplete penetrance
Genomic imprinting
Anticipation
Mitochondrial Inheritance
Multigenic Inheritance
How do sporadic cases result in non-mendelian inheritance?
They result in recurrent de novo mutations
How does incomplete penetrance results in non-mendelian inheritance?
This modifies genes and is an environmental trigger
What is genomic imprinting?
When only one of the two copies inherited from your parents are active. Which copy is active depends on the parent of origin. In other words, gene expression is parent-of-origin dependent.
How does inheriting two maternal genomes effect an embryo? What are these zygotes called?
Poor membrane and placenta development
Abnormal mass of embryonic tissues, which may develop into ovarian teratomas
Gynogenotes
How does inheriting two paternal genomes effect an embryo? What are these zygotes called?
Normal membrane and placenta development but will be abnormal
Mass of placental structures and a mole forming in the mother
Adrogenotes
How does genomic imprinting result in non-mendelian inherticane?
If a mother is a carrier of an autosomal recessive disorder, they can still pass on the disorder to their offspring if they pass on two mutated copies of the chromosome.
What is anticipation?
A triplet expansion of DNA. This trinucleotide repeat is a sequence of three DNA nucleotides that is repeated a number of times in a row.
How does anticipation result in non-mendelian inheritance?
DNA segments with an abnormal number of these repeats are unstable and prone to errors during cell division. The number of repeats can change as the gene is passed from parent to child.
What is mitochondrial inheritance?
Individual inherits a trait which is encoded in the mitochondrial genome
Individuals with a mitochondrial disease may be male or female but they are all inherited maternally. This is because mitochondrial DNA is only passed from mother to offspring. This means no male with the disease can transmit it to his children
What is mitochondrial DNA? How does it compare to normal DNA?
Each mitochondrion is made up of DNA and is referred to as mtDNA.
Much smaller
Chromosomes are round shaped
Chromosomes are not diploid but polyploidy - thousands of copies of mitochondrial genes
What are homoplasmy cells?
Cells that contain identical mtDNA
What are heteroplasty cells?
Cells that contain a mixture of two populations of mtDNA, mutant and wild type
How does mitochondrial disease vary within families? How?
Heteroplasmy
This is because heteroplasmy means that an individual who has a mitochondrial disease that only affects on mitochondrion in each of its cells can produce offspring how can have multiple affected mitochondrion. This can continue throughout several generations, where the number of affected mitochondria continue to increase. The more affected mitochondria, the more affected the individual is by the disease.
How do mtDNA mutations occur?
Lack of DNA repair system
Lack of protective proteins
Inner mitochondrial membrane producing oxygen free radicals during oxidative phosphorylation
What is polygenic inheritance?
Occurs when one characteristic is controlled by two or more genes. Often genes are large in quantity but small in effect, with each of the genes having an equal influence and each of the alleles having an additive effect on the phenotype outcome
What is fitness?
The relative ability of organisms to survive long enough to pass on their genes
What affects fitness?
Alleles - if deleterious, can decrease fitness but if advantageous, can increase fitness. If selective pressure change, the importance of different alleles may change
Social ability - increase their ability to defend themselves, find food and find a sequel partner
What diseases are commonly due de novo recessive mutations?
Sickle cell disease
Thalassaemia
