Genetics Basics

Question 1

Genetic material from macro to micro:
Somatic cell
Chromosome
Chromatid
Chromatin
DNA

Answer 1

Somatic Cell = 23 pairs of chromosomes
Chromosome = 2 chromatids joined at a centromere
Chromatid = 1 copy of the duplicated chromosome
Chromatin = Double stranded DNA macromolecule wrapped around histone protein
DNA = 4 base pairs on a deoxyribose backbone

Question 2

Name the 4 bases and their complementary base-pairing

Answer 2

Adenosine -Thymine

Cytosine - Guanine

Question 3

Explain the different stages of the cell cycle

Answer 3

G1 = Gap 1 
G1 --> G0 = non dividing cells OR
G1 --> S = synthesis of DNA
S --> G2 = Gap 2
G2 --> Mitosis

Question 4

Explain the difference between mitosis and meiosis

Answer 4

Mitosis = 1 cell with 23 pairs of chromosomes--> 2 identical daughter cells with 23 pairs of chromosomes
Meiosis = 1  cell with 23x2 --> 2 identical daughter cells with 23x2 --> recombination of genetic material --> 4 cells with 23 chromosomes each - NOT GENETICALLY IDENTICAL

Question 5

What do genes code for?

Answer 5

1. Peptides/proteins via mRNA
2. Ribosomal RNA
3. Transfer RNA

rRNA and tRNA are involved in protein synthesis

Question 6

What is the central dogma of DNA expression

Answer 6

Information travels from DNA to RNA to Protein only

Question 7

What an exon? What is an intron?

Answer 7

Exons code for proteins

Introns are found between exons

Question 8

What is the role of regulatory sequences?

Answer 8

Control when, where, and how much gene is expressed. Do not have to be in the coding regions being expressed
Eg: Promotor regions –> expression of DNA
Enhancer regions –> increased expressiom
Silencer regions –> decreased expression

Question 9

What is a codon? How are they read? What do they specify?

Answer 9

mRNA is read in groups of 3 called codons. Each codon specifies the sequence of amino acids along a peptide.

Question 10

What is redundancy of the genetic code?

Answer 10

There are 64 codon combinations coding for 20 amino acids

Question 11

What are the different kinds of single-gene mutations?

Answer 11

Base substitutions = Silent = SAME AMINO ACID, Nonsense = STOP, and missense = DIFFERENT AMINO ACID
Deletions
Insertions

Question 12

What is the problem with insertion and deletions in genetic code?

Answer 12

FRAMESHIFT MUTATIONS
Insertions and deletions can alter the reading frame resulting in a different sequence of of amino acids until a stop codon is eventually formed

Question 13

What is an example of a frameshift mutation?

Answer 13

CFTR deltaF508 in cystic fibrosis

Question 14

Explain the difference between genotype and phenotype

Answer 14

Genotype = genetic constitution of the organism
Phenotype = physical characteristics of the organism

Question 15

What is an allele? What are the different kinds of alleles

Answer 15

Allele = alternate versions of the same gene
Homozygous = 2 copies of the same allele
Compound homozygous = 2 different kinds of mutations –> disease in recessive disease
Heterozygous = 2 different alleles

Question 16

What is the best evidence a gene variant is pathogenic?

Answer 16

Animal models