inheritance and genetic diseases

Question 1

How is genetic variation generated?

Answer 1

• mutation
• diploid cells (random fertilisation)
• homologous recombination between chromosomes during meiosis

Question 2

Describe homologous recombination

Answer 2

• occurs during long prophase of meiosis 1
• 2-3 crossover events per chromosome per meiosis
• highly similar DNA sequence binds to complementary sequence on homologous chromosome

Question 3

How does genetic variation happen during gamete formation?

Answer 3

• independent assortment of chromosomes
• homologous recombination

Question 4

What is non-disjunction?

Answer 4

When a pair of homologous chromosomes fail to seperate during meiosis

Question 5

What are the 3 types of survivable trisomy?

Answer 5

• 21 (down’s syndrome)
• 13 (patau’s syndrome)
• 18 (edwards syndrome)

Question 6

What are autosomal chromosomes?

Answer 6

not sex chromosomes

Question 7

How are genetic diseases passed down through the generatons?

Answer 7

• autosomal dominant
• autosomal recessive
• x-linked

Question 8

Define genotype?

Answer 8

set of genes carried by an individual

Question 9

Define phenotype?

Answer 9

observable characteristic of an organism

Question 10

Define allele?

Answer 10

an alternative form/different version of a gene

Question 11

What percentage of miscarriages are due to chromosomal abnormalities?

Answer 11

around 50%

Question 12

What is Turner’s syndrome?

Answer 12

monosomy of C chromosome

Question 13

What are some other sex chromosome disorders (XXY, XXX, XYY)?

Answer 13

• XXY: Klinefelter
  syndrome (male,
  reduced fertility, lower IQ)
  May go undiagnosed
• XXX: undiagnosed
• XYY: undiagnosed

Question 14

What is CFTR and where is the gene for it located?

Answer 14

• Cystic Fibrosis Transmembrane Conductance Regulator
• chromosome 7

Question 15

What is an example of an autosomal ‘incomplete’ recessive disease?

Answer 15

sickle cell disease

Question 16

Which gene is mutated in sickle cell disease and where is it found?

Answer 16

• HBB gene
• chromosome 11

Question 17

What is an example of an autosomal dominant disease?

Answer 17

Huntington’s disease

Question 18

What gene is mutated in Huntington’s disease and where is it located?

Answer 18

• HTT gene
• chromosome 4

Question 19

Give an example of a X-linked recessive disease?

Answer 19

haemophilia A

Question 20

What is haemophilia A caused by?

Answer 20

• x-linked recessive trait
• deletion/inversion in F8 gene

Question 21

Describe haemophilia A

Answer 21

• blood clots slower
• loss of function, lack of blood clotting factor VIII

Question 22

How common are monogenic disorders?

Answer 22

1 in 200 births