Genes and inheritance

Question 1

Lavender foal syndrome

Answer 1

lethal inherited disease

autosomal recessive mode of inheritance

Question 2

Which breed have a higher frequency of developing lavender foal syndrome

Answer 2

Arabians

Question 3

LFS allele frequency in USA and Europe

Answer 3

USA
-Egyptian arabans- 10.3%
-non-egyptian Arabians- 1.8%
Europe
-Throughbreds: 0%
-Standardbreds: 0%
-Arabians: 3.2%

Question 4

Signs of Lavender foal syndrome

Answer 4

neurological- prevents standing and nursing

• opisthotonus (head and neck arched dorsally)
• tetanic like seizures
• paddling leg movements
• nystagmus
• hyperesthetic and exaggerated flexor reflexes

Question 5

Diagnostics for LFS

Answer 5

DNA test

• pulled hair, whole blood EDTA or cheek swab
• PCR based RFLP

Question 6

LFS is due to a problem with?

Answer 6

Myosin V- copped myosin Va tail

Question 7

LFS mutation

Answer 7

• chromosome 1
• MYO5A gene, exon 30
• single base deletion of cytosine at 4459 base pair
• frameshift that resulted in a premature stop codon
• substituted AA Arg with Alanine leading to truncation of almost half the protein tail

Question 8

How do we know if the family is normal?

Answer 8

Clinical history
Pedigree
Diagnostic testing

Question 9

Clinical history

Answer 9

• family members affected- accuracy of diagnosis
• how close to the patient?
• family and breed disopostions?
• environmental influence?
• similar disease in other species?

Question 10

Why genetic counselling?

Answer 10

• Help clients understand medical facts (diagnosis, prognosis, and possible therapy/management)
• help client’s understand hereditary contributions, risk of transmission and risk mitigation

Question 11

Genotype

Answer 11

genetic constitution

• chromosomes
  - autosomes- species dependent, named after size with 1 being the longest
• genes- part of chromosome coding for specific polypeptide or nucleic acid molecule and are located at specific sites called LOCI
• alleles- alternative forms of a gene

Question 12

Phenotype

Answer 12

-observable traits
-combination of genotype and environment
P=GxE

Question 13

Germ cells

Answer 13

reproductive cells: oocytes and spermatocytes

Question 14

Somatic cells

Answer 14

soma=body

cells of the body except germ cells

Question 15

Interphase

Answer 15

cytokinesis
G1- cellular contents, excluding the chromosomes, are duplicated
S- each of the 46 chromosomes is duplicated by the cell
G2- the cell double checks the duplicated chromosomes for error, making any needed repairs

Question 16

Most cells are in _____ phase

Answer 16

G0-not dividing doing tissue function

Question 17

Chemotherapy drugs

Answer 17

work at various stages to stop an overactive cell cycle

1. inhibitors of cell growth
2. inhibitors of DNA duplication
3. inhibitors of cell division

Question 18

meiosis

Answer 18

chromosomes are not inherited unchanged

homologous chromatids exchange genetic material

Question 19

Linakge

Answer 19

the probability of loci being passed on together
-physical distance between two loci on the same chromosome is directly related to the probability of them getting separated at crossing over r

Question 20

Meiosis I

Answer 20

gene exchange and chromosome doubling

Question 21

Meiosis II

Answer 21

sister chromatid separation into haploid cells

Question 22

Female meiosis arrested in ______ until fertilization

Answer 22

metaphase II

Question 23

Modes of inheritance

Answer 23

1. monogenic/mendelian traits
2. polygenic/complex inheritance/mutlifactorial traits
3. mitochondrial inheritance

Question 24

Monogenic inheritance

Answer 24

• single locus
• one or more alleles
• 2 distinct patterns of inheritance (dominant when 1 copy enough, recessive when 2 copies needed)

Question 25

Mendel’s first law

Answer 25

law of segregation

• alleles from same loci separate into separate germ cells
• homologous chromosome separation in Meisosis I and sister chromatid separation in meiosis II

Question 26

Mendel’s second law

Answer 26

law of independent assortment

-phenotype segregation ratio of 9:3:3:1

Question 27

Autosomal dominant traits

Answer 27

every affected individual has an affected biological parent
no skipping generations
males and females same risk
recurrence risk of each offspring of an affected parent is 50%
normal siblings of the affected individual do not transmit the trait to their offspring

Question 28

Autosomal recessive traits

Answer 28

most affected individuals will have normal parents
all offspring of affected parents will be affected
the parents may be related
may skip generations
males and females have same risk of being affected

Question 29

X-linked dominant traits

Answer 29

• males and females are affected
• all daughters of an affected male and a normal female are affected
• all sons of an affected male and a normal female are normal
• mating of affected females and normal males produce 50% of affected offspring, regardless of sex
• males more frequently and severely affected than females

Question 30

X-linked recessive traits

Answer 30

• may skip generations
• all offspring of two affected parents are affected
• more common in males than females
• affected females breed to normal males produced 100% affected males and 100% carrier females