Introduction To Genetics

Question 1

What makes up a DNA nucleotide

Answer 1

A phosphate, sugar(deoxyribose) and a base (adenine, thymine, cytosine and guanine)

Question 2

Which bases pair with each other

Answer 2

Adenine always pairs with thymine (joined by two hydrogen bonds)
Cytosine always pairs with guanine (joined by 3 hydrogen bonds)

Question 3

Define anti-parallel

Answer 3

Each DNA strand goes in a 5’ to 3’ direction in opposite directions

Question 4

What charge does a DNA molecule have

Answer 4

Negative charge on the phosphate group means DNA is negatively charged

Question 5

How is the polymer of DNA formed

Answer 5

The 5’ phosphate group joins to Carbon 3 removing an OH group from carbon 3 and a H from the phosphate group

Question 6

How is DNA packaged

Answer 6

It is packaged in a structure known as a double helix. The sugar-phosphate backbone twist and turn naturally to form the double helix structure.
Double helix also contains a major and minor groove

Question 7

What is the width and length of a DNA molecule

Answer 7

Width: 2nm
Length (vertically): 3.4nm

Question 8

How many base pairs are there in the human genome?

Answer 8

2,000,000,000

Question 9

How long is the DNA in one cell

Answer 9

2m

Question 10

How big is a nucleus?

Answer 10

5-10 micrometers

Question 11

Describe the structure of a nucleosone

Answer 11

Each nucleosome is made up of 8 histone proteins that then have DNA wrapped around them about 1.65 times (approximately 210 base pairs).
This gives a structure known as “beads on string”.
Each nucleosome is about 11nm in length

Question 12

How do we get from a nucleosome to a chromatid

Answer 12

Nucleosomes themselves then roll up and fold again to form a 30nm fibre. The 30nm fibre then form loops to form a 300nm loop. These loops are then compressed and folded to form 250nm wide fibre. Ultimately, these fibres then get coiled and tightened further to form a chromatid

Question 13

What are the main components of the nucleus

Answer 13

Nuclear Envelope
Euchromatin (light)
Heterochromatin (dark)
Nucleolus

Question 14

Define euchromatin (light)

Answer 14

Loosely packed chromatin
DNA more accessible
More gene activity (gene transcription)

Question 15

Define heterochromatin (dark)

Answer 15

Chromatin tightly packed
DNA less accessible
Less gene activity

Question 16

Define karyotype

Answer 16

Karyotype is an individual’s complete set of chromosomes (or can refer to the output from assessing the chromosomes)

Question 17

How do we prepare a karyotype

Answer 17

Prepare by using a DNA stain (usually Giemsa) on a cell arrested in metaphase (usually white blood cells)

Question 18

What are the stripes on the karyotype called

Answer 18

G-banding

Question 19

What does a darker G-band mean

Answer 19

Dark bands take up lots of dye, tightly packed DNA, high A and T content, gene poor region

Question 20

What does a lighter G-band mean

Answer 20

Contains G and C content, lightly packed and have more genes than dark G-bands

Question 21

Define Mendelian trait

Answer 21

A mendelian trait is one that is controlled by a single locus in an inheritance pattern

Question 22

What are the 2 definitions of a gene

Answer 22

A gene is a unit of inheritance which is transferred from a parent to offspring that determines a characteristics of the offspring.
In science, a gene also means a distinct nucleotide sequence from which some function or activity can be identified (may or may not encode for a protein)

Question 23

What are Mendel’s 3 laws

Answer 23

Law of segregation
Law of independent assortment
Law of dominance

Question 24

Define law of segregation

Answer 24

During gamete formation, the allele from each gene will segregate from each other so that the gamete carries only one allele for each gene

Question 25

Define law of independent assortment

Answer 25

Genes for different traits can segregate independently during the formation of gametes

Question 26

Define law of dominance

Answer 26

Some alleles are dominant, others recessive. An organism with at least one dominant allele will display the effect of the dominant allele

Question 27

Define X-linked disorders

Answer 27

X-linked disorders refer to conditions where the mutant gene is on the X chromosome but not found on the Y chromosome. There are dominant and recessive variants

Question 28

Define co-dominance

Answer 28

For some traits, multiple alleles can be present and some of these can be equally dominant i.e. both present in the phenotype