Mendelian Genetics

Question 1

What is Mendelian genetics
-what are they due to
-most commonly what kind of inheritance

Answer 1

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

Question 2

Main classes of gene mutations

Answer 2

1. Deletions->frame of translation altered as one nucleotide is deleted
2. Insertions->frame of translation shifted due to added nucleotide
3. Point mutations->single nucleotide changed

Question 3

3 types of consequences of point mutations

Answer 3

Change of single amino acid; causes muted protein
Stop codon occurrence; much shorter protein; muted
Silent mutation; no impact on amino acid

Question 4

What is a somatic mutation
-passed on to who…
-linked to…

Answer 4

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

Question 5

What is a germ line mutation

Answer 5

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

Question 6

Allele

Answer 6

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

Question 7

Phenotype

Answer 7

Physical appearance of the animal

Question 8

Genotype

Answer 8

genetic make up of the animal

Question 9

Homozygous & heterozygous

Answer 9

both alleles at a locus are the same (AA, aa)

alleles at a locus are different (Aa)

Question 10

If the gene is expressed in the heterozygous state =
If the gene is expressed only in the homozygous state =

Answer 10

Dominant
Recessive

Question 11

Amount of protein encoded by X linked genes would… this is potentially…

Answer 11

Differ in sexes- this is potentially detrimental

Question 12

Animals overcome dosage difference through

Answer 12

Dosage compensation; X- chromosome inactivation (Lyonisation)

Question 13

What does chromosome inactivation do?

Answer 13

Equalises amounts of protein produced by X-linked genes in 2 sexes

Question 14

X chromosome inactivation
-random or not?
-ensures…
• Allows for…

Answer 14

-Random
-product levels for genes on the X chromosome are similar in both sexes
-allows for dosage compensation

Question 15

tortoiseshell coat colour of cats is caused by…

Answer 15

X chromosome inactivation

Question 16

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)😅?
😂😁😭😍

Answer 16

heterozygous female

Question 17

sometimes we get male tortoiseshell cats. how is this possible? what is the issue with them?

Answer 17

male has an extra X chromosome
they are infertile

Question 18

what is a pseudochromosmal region

Answer 18

small regions of X chromosome present on Y chromosome

Question 19

what do psuedochromosmal regions allow gene to do?

Answer 19

escape X chromosome inactivation

Question 20

One chromosome is inactivated in every

Answer 20

Female somatic cell

Question 21

Aneuploidy

Answer 21

animal with a change in chromosome number, X0, XXX, XXY
-Random inactivation of all X chromosomes expect one X chromosome
-

Question 22

In X chromosome inactivation in aneuploidy, inactivated chromosomes can be detected as…

Answer 22

Barr bodies
XX; one barr body
XXX; 2 barr bodies
XXY; one barr body
(Darkly stained heterochromatin)

Question 23

Modes of inheritance

Answer 23

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)

Question 24

Pedigrees used to establish mode of inheritance;

Answer 24

Page 11 of 38

Question 25

What must an individual inherit in autosomal recessive (AR) inheritance?

Answer 25

An individual must inherit two mutant alleles

Question 26

both parents must be what in autosomal recessive?

Answer 26

Carriers of mutant gene

Question 27

Examples of autosomal recessive diseases in dogs

Answer 27

Canine genetic disease
-canine Leucocyte Adhesion deficiency
Pyruvate kinase deficiency
Von Willebrands disease

Question 28

Breeding unknown carriers causes what?

Answer 28

increase in the incidence of genetic diseases within a breed

Question 29

What helps testing breeder to improve health of litter?

Answer 29

DNA testing- screening for genetic disorders
-extremely accurate and reliable way of determining dogs genotype

Question 30

What are some key factors of AR inheritance?

Answer 30

• 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

Question 31

What is an example of autosomal recessive inheritance in horses?

Answer 31

SCID- Severe Combined Immunodeficiency

Question 32

Pyruvate kinase deficiency in dogs
Mutation leads to…
Effects

Answer 32

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

Question 33

What is genetic heterogeneity

Answer 33

single phenotype caused by any one of a multiple number gene mutations

Question 34

What AR disease displayed genetic heterogeneity?

Answer 34

Pyruvate kinase deficiency in dogs

Question 35

What is double muscling
inherited through what mode of inheritence

Answer 35

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

Question 36

What are the physical abnormalities associated with double muscled animals?

Answer 36

– 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

Question 37

Key factors of autosomal dominant (AD) inheritance

Answer 37

• 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

Question 38

True or false, Affected males can transmit x linked diseases to sons

Answer 38

False they can’t, all sons must inherit Y from the father

Question 39

Key factors of X linked recessive (XLR) Inheritance

Answer 39

• 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

Question 40

When an animal inherits a mutant allele for an autosomal dominant genetic disease but does not express the disease this is known as

Answer 40

[Incomplete penetrance]

Question 41

Dwarfism in poultry follows which one of the types of mendelian inheritance patterns

Answer 41

X linked recessive

Question 42

Almost all sex-linked disorders are carried on the X-chromosome. Why are Y-linked disorders so rare?

Answer 42

because the Y-chromosome carries very few genes