Introduction to neurogenetics: L21

Question 1

1. what are the building blocks of genetic code?

2. how many building blocks constitutes the genetic code for a particular amino acid

Answer 1

1. nucleotides or bases

2. a sequence of 3 bases

Question 2

4 different bases in DNA

Answer 2

adenine (A), cytosine (C), guanine (G) and thymine (T)

Question 3

amino acids are

Answer 3

the building blocks of proteins

Question 4

1. how many bases in the whole human genome

2. how many genes that code for proteins

Answer 4

1. 3 billion

2. 20-25 thousand

Question 5

1. the DNA helix is … which carry

2. each bases has a partner on the other strand (2)

Answer 5

1. double stranded, two strands carry redundant information
2. (1) cytosine with guanine (C-G)
   (2) Adenine with Thymine (A-T)

Question 6

1. DNA is bundled in 2. the human karyotype comprises how many chromosomes

Answer 6

1. chromosomes
2. 46:
   22 pairs of autosomal (1-22)
   2 sex chromosomes

Question 7

1. The function of a protein is determined by (2)

2. an amino acid is represented by a sequence of three bases called

Answer 7

1. its structure & the sequence of amino acids

2. a codon

Question 8

1. a change to just a single base can …, which

2. but each amino acid has

Answer 8

1. change the amino acid, which can change the structure and function of the protein
2. multiple possible codons e.g. GCT, GCC, GCA & GCG all = alanine

Question 9

1. a single nucleotide polymorphism (SNP) is
2. the two (can be more) alleles of a SNP are
3. the major & minor =

Answer 9

1. a position on the genome at which the base (nucleotide) differs between individuals
2. the alternative bases
3. most common & less common allele

Question 10

1. an individuals genotype at a SNP is determined by

Answer 10

1. the two alleles on the two copies of the chromosome

Question 11

1. an individuals phenotype is (examples)

Answer 11

1. the presence, absence or value of a trait of interest:
   - psychological diagnosis (binary)
   - parenting style (categorical)
   - IQ (quantitative)

Question 12

Genetic variants

1. single-nucleotide
2. insertion-deletion
3. block substitution
4. inversion
5. copy number

Answer 12

1. 1 different base
2. bases added/missing
3. multiple bases substituted
4. bases replaced with reversed sequence from other strand
5. sequence of bases repeated one or more times

-> refer to images for more details (desktop)

Question 13

1. mutation %

2. polymorphism &

Answer 13

1. rare (<1% of alleles in the population)

2. common ( ≥ 1% of alleles in the population)

Question 14

1. (mammals) genetic females
2. (mammals) genetic males
3. to avoid excess dosage of x chromosome proteins in female, one copy…
   = this process is

Answer 14

1. XX
2. XY
3. of the x chromosome in each cell is silenced or inactivated
   = random in each cell

Question 15

1. when there are 2 x chromosomes in one cell (2)

2. TSIX is the what partner of XIST

Answer 15

1. (1) the XIST gene produces an RNA transcript that coats one chromosome = inactivated as a barr body
   (2) the TSIX gene on the other chromosome produces an RNA transcript that suppresses the transcription of XIST
2. antisense = both encoded by the same stretch of DNA but transcribed in opposite directions

Question 16

Heritability

1. phenotypic variance equation
2. heritability equation

Answer 16

1. P = G + E + (G x E) + 2covGE

P = phenotypic variance
G = variance from genes
E = variance from environment
G x E = variance from environment interactions
2covGE = covariance between genes and environment

2. h2 = G
   ___
   P
   (heritability squared)

Question 17

1. heritability is
2. it is a local measurement
3. it depends on

Answer 17

1. the proportion of the phenotypic variance due to genetic causes
2. valid for a specific population at a specific time
3. the amount of genetic and environmental variation present in the population

Question 18

heritability for the following disorders:

1. depressive
2. anxiety
3. alcohol
4. eating
5. ocd
6. bipolar
7. schizo
8. adhd
9. autism

Answer 18

1. .40
2. .40-.50
3. .50-.60
4. .55-60
5. .60-.70
6. .60-.85
7. .70-.85
8. .60-.90
9. .90

Question 19

1. how is heritability measured

2. these study designs all exploit

Answer 19

1. before molecular genetics, genetic epidemiology was used

2. the fact that related individuals share a predictable amount of genetic material

Question 20

1. twin studies, concordance rates

2. higher concordance in MZ pairs than in DZ pairs suggests

Answer 20

1. monozygotic (MZ) twins inherit identical genetic material, dizygotic (DZ) share half of their genetic inheritance
2. a genetic component (if equally similar environmentally)

Question 21

1. 2 models of inheritance

Answer 21

1. dominant = requires mutation on one copy of the chromosome

recessive= requires mutation on both copies

Question 22

1. 2 modes of inheritance
2. modes can be inferred from
3. chart key

Answer 22

1. autosomal = autosomal traits carried on the autosomal chromosomes 1-12

x-linked = carried on the x chromosome

2. pedigree chart (parents at the top, offspring at the bottom)
3. black circle = affected female
   white circle = unaffected female
   black square = affected male
   white square = unaffected male
   cross through = deceased