Introduction to Neurogenetics

Question 1

True or False: Genetic material is large in size.

Answer 1

False. Genetic material is extremely small.

Question 2

What are the words used to describe the building blocks of genetic code?

Answer 2

Nucleotides or bases.

Question 3

How many bases can be present in DNA? List them.

Answer 3

There are 4 different bases in DNA: adenine (A), cytosine (C), guanine (G) and thymine (T).

Question 4

What are amino acids referred to as?

Answer 4

The building blocks of protein.

Question 5

How many bases are required to constitute the genetic code for a given amino acid? Can the be attributed to randomness?

Answer 5

A SPECIFIC sequence of THREE bases constitutes the genetic code for a particular amino acid.

Question 6

Quantify the number of bases contained within the complete set of genes or genetic material present in the human being (human genome).

Answer 6

3 billion bases exist in the human genome, with 20-25,000 genes that code for proteins.

Question 7

What is the composition of DNA described as?

Answer 7

The DNA helix is described as double-stranded, with the 2 strands carrying redundant information.

Question 8

What does DNA stand for?

Answer 8

Deoxyribonucleic Acid.

Question 9

Each of the 4 bases has a partner on the opposing strand. Which base pairs with which?

Answer 9

CYTOSINE pairs with GUANINE (C-G).

ADENINE pairs with THYMINE (A-T).

Question 10

How is DNA bundled?

Answer 10

In what is referred to as “Chromosomes” (thread-like structures located inside the nucleus of animal and plant cells).

Question 11

What is meant by the human ‘Karyotype’?

Answer 11

The number and visual appearance of the chromosomes in the cell nuclei of an organism or species.

Question 12

The human ‘Karyotype’ comprises how many chromosomes? Describe (briefly) their composition.

Answer 12

The human ‘Karyotype’ comprises 46 chromosomes, 22 pairs of which are ‘autosomal’ chromosomes (44 total) and 2 of which are sex chromosomes (XX or XY).

Question 13

How is the function of a protein determined?

Answer 13

By its structure.

Question 14

How is the structure of a protein determined?

Answer 14

By its sequence of amino acids.

Question 15

How is an amino acid represented?

Answer 15

By a sequence of 3 bases called a CODON.

Question 16

A change to just a single base can change the amino acid. Is this always the case?

Answer 16

Not always, because each amino acid has multiple possible codons.

For example, the codons GCT, GCC, GCA and GCG all represent Alanine.

Question 17

Does changing the amino acid alter the structure and function of the protein?

Answer 17

Changing the amino acid can definitely change the

structure and function of the protein.

Question 18

What does SNP stand for when investigating genetic variants? Define it.

Answer 18

SNP stands for single-nucleotide polymorphism, and it is a position on the genome at which the base (or nucleotide) (4) may differ between individuals.

Question 19

When observing a SNP, what are the alternative bases?

Answer 19

The two (or more) alleles (a variant form of the gene) of a SNP are the alternative bases.

Question 20

How is an individual’s genotype at a SNP determined?

Answer 20

An individual’s genotype at a SNP is determined
by the two alleles on the two copies of the
chromosome. This may be slightly different for genetic males.

Question 21

What is a phenotype?

Answer 21

An individual’s phenotype is the presence, absence or
value of a trait of interest. In other words, the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

Question 22

Define the insertion-deletion variant.

Answer 22

When bases have been added or are missing.

Question 23

Define the block-substitution variant.

Answer 23

When multiple bases are substituted.

Question 24

Define the inversion variant.

Answer 24

When bases are replaced with a reversed sequence from another strand.

Question 25

Define the copy-number variant.

Answer 25

When the sequence of bases is repeated one or more times.

Question 26

When discussing genetic variants, how common is mutation?

Answer 26

Mutation is rare. It is present in <1% of alleles in the population.

Question 27

When discussing genetic variants, how common is polymorphism?

Answer 27

Polymorphism is common. It is present in >1% of alleles in the population.

Question 28

Fill in the blank: Genetic females have __ chromosomes and males have __ chromosomes.

Answer 28

XX, XY.

Question 29

How is excess dosage of the X-chromosome protein in females avoided?

Answer 29

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, this process is random in each cell.

Question 30

What occurs when there are 2 X-chromosomes in one cell?

Answer 30

When there are two X-chromosomes in one cell:

1 • XIST gene produces an RNA transcript that coats one
chromosome, which is inactivated as a Barr body.

2 • TSIX gene on the other chromosome produces an RNA transcript that suppresses transcription of XIST.

3 • TSIX is the antisense partner of XIST.

4 • Both are encoded by the same stretch of DNA, but are transcribed in
opposite directions.

Question 31

When discussing classical genetics, define heritability.

Answer 31

Heritability is the proportion of the phenotypic variance due to genetic causes. It is a local measurement, valid for a specific population at a specific time. Dependant on the amount of genetic and environmental variation present in the population.

Question 32

Fill in the blanks: Phenotypic variance is a summation of ____ and ____.

It is furthermore affected by _____ and added to by _____.

Answer 32

Phenotypic variance is a summation of VARIANCE FROM GENES and VARIANCE FROM ENVIRONMENT.

It is furthermore affected by VARIANCE FROM GENE-ENVIRONMENT INTERACTIONS and added to by COVARIANCE BETWEEN GENES AND ENVIRONMENT.

In other words:
P= G+E+GxE+2covGE

Question 33

Fill in the blanks: Heritability is a result of investigating ____ over ____.

Answer 33

Heritability is a result of investigating VARIANCE FROM GENES over PHENOTYPIC VARIANCE.

(p. 54 of pdf for scale)

Question 34

What are the 2 modes of inheritance?

Answer 34

Dominant and Recessive.

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 35

What may Psychological Disorders have?

Answer 35

A percentage of heritability.

Question 36

How is heritability measured?

Answer 36

Prior to molecular genetics, genetic epidemiology was used. Study designs in genetic epidemiology exploit the fact that related individuals share a predictable amount of genetic material.

Question 37

What do twin studies look at?

Answer 37

Concordance rates. Monozygotic (MZ) twins inherit identical genetic material while dizygotic (DZ) twins share about half of their genetic influences. Higher concordance in MZ than DZ suggests a genetic component.

Question 38

What are the other 2 modes of inheritance?

Answer 38

Autosomal and X-Linked.

AUTOSOMAL traits are carried on the autosomal chromosomes, and X-LINKED traits are carried on the X chromosome.

Question 39

What is used to infer modes of inheritance?

Answer 39

A pedigree chart.

Question 40

What are dominant traits unable to do?

Answer 40

Cannot skip generation and two unaffected parents cannot have affected offspring.

Question 41

What are recessive traits unable to do?

Answer 41

Cannot have two affected parents cannot have unaffected offspring.

Question 42

True or False: Autosomal are equally common in both sexes according to the pedigree chart.

Answer 42

True.

Question 43

Can X-Linked traits transfer father-to-son?

Answer 43

No.