Intro to neurogenetics

Question 1

What is the building blocks of the genetic code

Answer 1

Nucleotide or bases

Question 2

What are the four bases in DNA

Answer 2

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

Question 3

What are the building blocks of proteins

Answer 3

Amino acids

Question 4

What constitutes the genetic code for a particular amino acid?

Answer 4

A specific sequence of three bases, called codon

Question 5

What is the structure of a DNA helix

Answer 5

Double-stranded

Question 6

What is about the two strands in a DNA helix

Answer 6

Each base has a partner on the other strand Cytosine pairs with Guanine (C–G) Adenine pairs with Thymine (A–T)

Question 7

Where is DNA bundled in

Answer 7

Chromosomes

Question 8

How many chromosomes the human karyotype comprises

Answer 8

46 chromosomes 22 pairs of autosomal chromosomes (1–22) Two sex chromosomes (XX or XY)

Question 9

What determines the function of a protein

Answer 9

its structure

Question 10

What determines the structure of a protein

Answer 10

its sequence of amino acids

Question 11

Can a change to just a single base of a codon change the amino acid?

Answer 11

can but not necessary as each amino acid has multiple possible codons; for example, the codons GCT, GCC, GCA and GCG all represent Alanine

Question 12

What is a SNP

Answer 12

Single-nucleotide polymorphism

A position on the genome at which the base (nucleotide) differs between individuals

e.g., some of us have a T (the major, most common) while some have G (the minor, less common)

Question 13

What determines an individual’s genotype at a SNP

Answer 13

the two alleles on the two copies of the chromosome

Question 14

What are the types of genetic varients?

Answer 14

Single-nucleotide variants

Structural variants:

• Insertion–deletion variant - Bases added or missing
• Block-substitution variant - Multiple bases substituted
• Inversion variant - Bases replaced with reversed sequence from other strand
• Copy-number variant - Sequence of bases repeated one or more times

Question 15

What is the random X-chromosome inactivation

Answer 15

To avoid excess dosage of X-chromosome proteins in females, one copy of the X chromosome in each cell is silenced or inactivated. In many mammals (including humans), this process is random in each cell, and occurs earlier in the development

Question 16

What will happen where there are two X-chromosome in one cell

Answer 16

The XIST gene produces an RNA transcript that coats one chromosome, which is inactivated as a Barr body The TSIX gene on the other chromosome produces an RNA transcript that suppresses transcription of XIST TSIX is the antisense partner of XIST, both are encoded by the same stretch of DNA, but are transcribed in opposite directions

Question 17

What is RNA transcript in X-chromosome inactivation

Answer 17

An RNA transcript is an intermediate step in the process of converting a gene encoded in DNA to a protein

Question 18

What is the formula for classical genetics heritability

Answer 18

• P (phenotypic variance) = G (variance from genes) + E (variance from environment)
• P = G + E + G*E (variance from gene-environment interactions)
• P = G + E + G*E + 2covGE (covariance between genes and environment)

H(heritability)² = G/P:

• It is a local measurement, valid for a specific population at a specific time
• It depends on the amount of genetic and environmental variation present in the population

Question 19

How can we measure heritability?

Answer 19

Before the advent of molecular genetics, we used genetic epidemiology

Study designs in genetic epidemiology all exploit the fact that related individuals share a predictable amount of genetic material

For example, in twin studies, we look at concordance rates

Question 20

Dominant vs recessive

Answer 20

Dominant traits require mutation on one copy of the chromosome for expression of the phenotype Recessive traits require mutation on both copies (or only copy) of the chromosome

Question 21

Autosomal vs X-linked

Answer 21

Autosomal traits are carried on the autosomal chromosomes (1–22) X-linked traits are carried on the X chromosome

Question 22

In a pedigree chart, what represents female and male

Answer 22

female is circle male is square

Question 23

Which mode of inheritance says equally common in both sexes

Answer 23

autosomal dominant autosomal recessive

Question 24

Which mode of inheritance says cannot transfer father to son

Answer 24

X-linked dominant X-linked recessive

Question 25

Which mode of inheritance says cannot skip generations

Answer 25

autosomal dominant X-linked dominant

Question 26

Which mode of inheritance says two unaffected parents cannot have affected offspring

Answer 26

autosomal dominant X-linked dominant

Question 27

Which mode of inheritance says two affected parents cannot have unaffected offspring

Answer 27

autosomal recessive X-linked recessive

Question 28

Which mode of inheritance says daughter of affected father must be affected

Answer 28

X-linked dominant

Question 29

Which mode of inheritance says father of affected daughter must be affected

Answer 29

X-linked recessive

Question 30

Which mode of inheritance is more common in males

Answer 30

X-linked recessive

Question 31

Which mode of inheritance

Answer 31

recessive

Trait cannot be dominant as unaffected parents have affected offspring

Question 32

Which mode of inheritance?

Answer 32

autosomal recessive

Trait cannot be X-linked recessive as an unaffected father has an affected daughter

Question 33

Which mode of inheritance?

Answer 33

dominant

Trait cannot be recessive as affected parents have unaffected offspring

Question 34

Which mode of inheritance?

Answer 34

autosomal dominant

Trait cannot be X-linked dominant because affected father has an unaffected daughter

Question 35

Which mode of inheritance?

Answer 35

Probable X-linked dominant inheritance

Sex linkage cannot be confirmed (only disconfirmed) from pedigree charts

Autosomal traits could generate the same pedigrees

Unaffected father with affected daughter rules out X-linked recessive inheritance

Question 36

Which mode of inheritance?

Answer 36

Probable X-linked dominant inheritance

Affected father with all daughters and no sons affected suggests X-linked dominance

Question 37

Which mode of inheritance?

Answer 37

Probable X-linked recessive inheritance

Unaffected father with affected offspring rules out dominant inheritance

Question 38

Which mode of inheritance?

Answer 38

Probable X-linked recessive inheritance

Unaffected parents with all sons and no daughters affected suggests X-linked recessive inheritance

Question 39

Which mode of inheritance best explains this pedigree?

Answer 39

Autosomal: Father-to-son transmission

Dominant (most likely)*: No skipping over five generations

Question 40

Which mode of inheritance best explains this pedigree?

Answer 40

Recessive: Unaffected parents with affected offspring

X-linked (most likely): Only males affected in large pedigree