Lecture 8: Molecular Genetics

Question 1

What do genetics determine?

Answer 1

Disease susceptibility
How we react to drugs
Our appearance

Question 2

What are the 4 bases of DNA? RNA?

Answer 2

DNA:
Adenine
Guanine
Cytosine
Thymine

RNA:
Adenine
Guanine
Cytosine
Uracil

Question 3

What is mitochondrial DNA inherited from?

Answer 3

Mom AKA MATERNAL

Question 4

How many amino acids are there?

Answer 4

20

Question 5

How many codons are there?

Answer 5

64

Question 6

What are synonyms in codons?

Answer 6

Codons that only differ at the third base (they usually code the same AA or similar AA)

Question 7

What is monogenic? Polygenic?

Answer 7

Single alleles
Multiple alleles

Question 8

What defines a polymorphism?

Answer 8

A specific genetic change that does not have an associated phenotype change.

Question 9

What kind of DNA changes can be inherited?

Answer 9

DNA in gametes only.

Question 10

What is penetrance?

Answer 10

The ability of a gene to express a mutation.

Question 11

What are the common types of mutations? Most common?

Answer 11

Most common is a SNP, or single nucleotide polymorphism.

Nonsense mutation: substitution causing an AA to be changed to a stop codon.

Missense mutation: substitution causing an AA to be changed to a different AA.

Splice site mutation: substitution near the intron-exon boundary, causing a skip in reading.

Silent mutation: substitution resulting in no change in AA

Regulatory polymorphism: substitution causing a change in binding affinity, affecting transcription.

Question 12

What are the three types of RNA?

Answer 12

mRNA (messenger RNA)
rRNA (ribsomal RNA)
tRNA (transfer RNA)

Question 13

When is mRNA formed?

Answer 13

During transcrption.

Question 14

What is the purpose of rRNA?

Answer 14

Makes up the ribosomes that perform translation.

Question 15

What is the purpose of tRNA?

Answer 15

Delivers the amino acid, recognizing and binding it.

Question 16

What is transcription?

Answer 16

Copying DNA to form the complementary strand of RNA.

Question 17

Where does transcription occur?

Answer 17

In the nucleus.

Question 18

What are exons and introns? Why are they significant?

Answer 18

Introns and Exons are segments of RNA/DNA. We skip introns when going from RNA to mRNA, so mRNA is made only of EXONS.

Question 19

Where does translation occur?

Answer 19

Cytoplasm, on the ribosome

Question 20

How many chromosomes does a somatic cell have?

Answer 20

23 pairs

Question 21

How many chromosomes are sex chromosomes?

Answer 21

2 (X and Y)

Question 22

What is the difference between mitosis and meiosis?

Answer 22

Mitosis is for somatic cells, same genetic makeup.
Meiosis is for gametes, half the genetic makeup.

Question 23

What is recombination?

Answer 23

Chromosomes separating and coming back together.

Question 24

What is nondisjunction?

Answer 24

Failure of chromosomes to separate

Question 25

What is aneuploidy?

Answer 25

Unequal amount of chromosomes being passed on

Question 26

When does nondisjunction usually occur?

Answer 26

Oogenesis

Question 27

Who is most at risk for aneuploidy?

Answer 27

30+ (increasing as you get older)
under 16
females

Question 28

If I have disjunction in Meiosis I, how many erroneous gametes will I have?

Answer 28

4 (AKA all of them.)

2 will have one less chromosome
2 will have one more chromosome

Question 29

If I have disjunction in Meisosis II, how many erroneous gametes will I have?

Answer 29

2

1 will have one less chromosome
1 will have one more chromosome

Question 30

What is monosomy and the one exception?

Answer 30

Having one less chromosome in a pair. This usually is incompatible with life.

Exception: Turner syndrome, where you have 45 chromosomes because you only have an X chromosome.

Question 31

What is Turner syndrome? Characteristics?

Answer 31

Lack of a second sex chromosome, so they are genetically X and therefore female.

Involves short stature, wide-set nipples, webbed neck, lack of secondary sex characteristics.

Normal intelligence.

Diagnosed most commonly due to short stature or failure to enter puberty.

Question 32

What is polysomy? Examples?

Answer 32

Presence of more than 2 chromosomes in a set.

Trisomy 21: Down syndrome (most common)
Trisomy 13 & Trisomy 18 (Edward syndrome): Not compatible with life usually.

Trisomy of sex chromosomes:
47 XXX = triple X syndrome
47 XXY = Kleinfelter syndrome

Question 33

What is Trisomy 21 more commonly known as? Characteristics?

Answer 33

Down syndrome, commonly caused by Nondisjunction in meiosis (95%)

Most common chromosomal disorder.

Flattened nasal bridge, epicanthal folds, protruding tongue, simian crease

Often found during prenatal screening.

Question 34

What is XXY syndrome more commonly known as? Characteristics?

Answer 34

Kleinfelter syndrome: caused by disjunction during maternal meiosis most commonly.

Affects 1 in 1000 males.

Enlarged breasts, sparse body hair, small testes, high voice

Infertility & osteoporosis later
Treated via androgens

Question 35

What is mosaicism?

Answer 35

Presence of two or more genetically different sets of cells, caused by early mitosis errors.

AKA certain areas of the body can be genetically different.

Question 36

What is genetic linkage?

Answer 36

Genes in close proximity sort together.

Question 37

What is the main structural abnormality that occurs?

Answer 37

Translocation: large segment of DNA breaks off a chromosome and attaches to a different chromosomes, most often during meiosis.

Causes Familial Down syndrome, which is translocation of chromosome 14 to 21.

Question 38

What are the types of structural abnormalities in chromsomes?

Answer 38

Deletion
Duplication
Inversion
Insertion
Translocation
Ring chromosome
Isochromosome
Derivative chromosome

See slide 51 for visual images

Question 39

What initiates RNA transcription?

Answer 39

RNA polymerase