Mendelian Genetics Flashcards
What is Mendelian genetics
-what are they due to
-most commonly what kind of inheritance
the study of inherited single gene disorders
-due to mutations in specific genes
-most commonly show autosomal inheritance
-and Sex linked inheritance (X) -Y linked gene disorders are rare, very few genes on
the Y chromosome
Main classes of gene mutations
- Deletions->frame of translation altered as one nucleotide is deleted
- Insertions->frame of translation shifted due to added nucleotide
- Point mutations->single nucleotide changed
3 types of consequences of point mutations
Change of single amino acid; causes muted protein
Stop codon occurrence; much shorter protein; muted
Silent mutation; no impact on amino acid
What is a somatic mutation
-passed on to who…
-linked to…
A mutation occurring in non germ cells
Mutation arises in one cell and is passed on only to the daughter cells – cell may die (apoptosis)
– cell may give rise to a tumour
-linked to cancer
What is a germ line mutation
Mutations within germ cells
Following fertilisation, every cell of the gamete formed from an egg/sperm with a mutation will carry the mutation
Offspring of the formed adult will also carry the mutation in every cell
Allele
If a disease (or trait) is controlled by a single gene, each individual
has 2 copies of the gene: the 2 copies are termed alleles
Phenotype
Physical appearance of the animal
Genotype
genetic make up of the animal
Homozygous & heterozygous
both alleles at a locus are the same (AA, aa)
alleles at a locus are different (Aa)
If the gene is expressed in the heterozygous state =
If the gene is expressed only in the homozygous state =
Dominant
Recessive
Amount of protein encoded by X linked genes would… this is potentially…
Differ in sexes- this is potentially detrimental
Animals overcome dosage difference through
Dosage compensation; X- chromosome inactivation (Lyonisation)
What does chromosome inactivation do?
Equalises amounts of protein produced by X-linked genes in 2 sexes
X chromosome inactivation
-random or not?
-ensures…
• Allows for…
-Random
-product levels for genes on the X chromosome are similar in both sexes
-allows for dosage compensation
tortoiseshell coat colour of cats is caused by…
X chromosome inactivation
in tortoiseshell colour cat, orange hairs are due to expression of an X-linked allele A, so X^A
non orange hairs are due to expression of the normal allele B, so
X^B therefore tortoiseshell cats must be heterozygous (female) or homozygous (male)😅?
😂😁😭😍
heterozygous female
sometimes we get male tortoiseshell cats. how is this possible? what is the issue with them?
male has an extra X chromosome
they are infertile
what is a pseudochromosmal region
small regions of X chromosome present on Y chromosome
what do psuedochromosmal regions allow gene to do?
escape X chromosome inactivation
One chromosome is inactivated in every
Female somatic cell
Aneuploidy
animal with a change in chromosome number, X0, XXX, XXY
-Random inactivation of all X chromosomes expect one X chromosome
-
In X chromosome inactivation in aneuploidy, inactivated chromosomes can be detected as…
Barr bodies
XX; one barr body
XXX; 2 barr bodies
XXY; one barr body
(Darkly stained heterochromatin)
Modes of inheritance
Autosomal Recessive-> must inherit 2 mutant alleles- both parents must be carriers
Autosomal Dominant-> individual inheriting one mutant allele is affected
Sex linked: X linked Recessive-> affected males don’t transmit disease to sons- females can be affected if father is affected and mother is a carrier
X linked Dominant-> affected males cannot transmit the disease to male offspring, must inherit Y from male father
Y linked inheritance (rare)
Pedigrees used to establish mode of inheritance;
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What must an individual inherit in autosomal recessive (AR) inheritance?
An individual must inherit two mutant alleles
both parents must be what in autosomal recessive?
Carriers of mutant gene
Examples of autosomal recessive diseases in dogs
Canine genetic disease
-canine Leucocyte Adhesion deficiency
Pyruvate kinase deficiency
Von Willebrands disease
Breeding unknown carriers causes what?
increase in the incidence of genetic diseases within a breed
What helps testing breeder to improve health of litter?
DNA testing- screening for genetic disorders
-extremely accurate and reliable way of determining dogs genotype
What are some key factors of AR inheritance?
• Males and females have the condition with equal frequency
• I in 4 chance of offspring being affected (25%)
• Appears in one generation and not the parents- horizontal pattern
• Parents of affected offspring must be carriers
What is an example of autosomal recessive inheritance in horses?
SCID- Severe Combined Immunodeficiency
Pyruvate kinase deficiency in dogs
Mutation leads to…
Effects
Mutation in pyruvate kinase gene leads to shorten lifespan of red blood leading to severe hemolytic anemia
• Symptoms of PKD usually begin to show between four months to one year; weakness, lack of energy, rapid heart rate, heart murmurs, pale gums, and stunted growth.
• Dogs with PKD commonly die before 4 years of age.
• Heterozygous dogs are usually asymptomatic
• It is therefore useful to test for the presence of the mutation before breeding
What is genetic heterogeneity
single phenotype caused by any one of a multiple number gene mutations
What AR disease displayed genetic heterogeneity?
Pyruvate kinase deficiency in dogs
What is double muscling
inherited through what mode of inheritence
overdevelopment of the musculature of the shoulder, back, rump and hindquarters
seen in various beef breeds; angus, belgian blue, charolais
Inherited in an autosomal recessive mode of inheritence
What are the physical abnormalities associated with double muscled animals?
– Macroglossia (enlarged tongue) which makes it difficult for the calf to nurse.
– Weak bones, often leading to bone damage of the hooks.
– Small feet and cannon bones (nice on the carcass but not for
animal locomotion!).
– Dystocia changes in pelvic dimensions associated with difficult calving require caesarean births
Key factors of autosomal dominant (AD) inheritance
• Males and females have the condition with equal frequency
• Each child of an affected individual has a 50% chance of being affected
• Affected offspring have an affected parent (every generation affected)-vertical pattern
• Unaffected individuals do not have children with the condition
True or false, Affected males can transmit x linked diseases to sons
False they can’t, all sons must inherit Y from the father
Key factors of X linked recessive (XLR) Inheritance
• The disease is never passed from male to male offspring
• Males are much more likely to be affected than females-only need one copy
• All affected males in a family are related through their mothers
• Trait or disease is typically passed from an affected grandfather, through his carrier daughters
When an animal inherits a mutant allele for an autosomal dominant genetic disease but does not express the disease this is known as
[Incomplete penetrance]
Dwarfism in poultry follows which one of the types of mendelian inheritance patterns
X linked recessive
Almost all sex-linked disorders are carried on the X-chromosome. Why are Y-linked disorders so rare?
because the Y-chromosome carries very few genes
