Introduction To Genetics Flashcards
What makes up a DNA nucleotide
A phosphate, sugar(deoxyribose) and a base (adenine, thymine, cytosine and guanine)
Which bases pair with each other
Adenine always pairs with thymine (joined by two hydrogen bonds)
Cytosine always pairs with guanine (joined by 3 hydrogen bonds)
Define anti-parallel
Each DNA strand goes in a 5’ to 3’ direction in opposite directions
What charge does a DNA molecule have
Negative charge on the phosphate group means DNA is negatively charged
How is the polymer of DNA formed
The 5’ phosphate group joins to Carbon 3 removing an OH group from carbon 3 and a H from the phosphate group
How is DNA packaged
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
What is the width and length of a DNA molecule
Width: 2nm
Length (vertically): 3.4nm
How many base pairs are there in the human genome?
2,000,000,000
How long is the DNA in one cell
2m
How big is a nucleus?
5-10 micrometers
Describe the structure of a nucleosone
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
How do we get from a nucleosome to a chromatid
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
What are the main components of the nucleus
Nuclear Envelope
Euchromatin (light)
Heterochromatin (dark)
Nucleolus
Define euchromatin (light)
Loosely packed chromatin
DNA more accessible
More gene activity (gene transcription)
Define heterochromatin (dark)
Chromatin tightly packed
DNA less accessible
Less gene activity
Define karyotype
Karyotype is an individual’s complete set of chromosomes (or can refer to the output from assessing the chromosomes)
How do we prepare a karyotype
Prepare by using a DNA stain (usually Giemsa) on a cell arrested in metaphase (usually white blood cells)
What are the stripes on the karyotype called
G-banding
What does a darker G-band mean
Dark bands take up lots of dye, tightly packed DNA, high A and T content, gene poor region
What does a lighter G-band mean
Contains G and C content, lightly packed and have more genes than dark G-bands
Define Mendelian trait
A mendelian trait is one that is controlled by a single locus in an inheritance pattern
What are the 2 definitions of a gene
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)
What are Mendel’s 3 laws
Law of segregation
Law of independent assortment
Law of dominance
Define law of segregation
During gamete formation, the allele from each gene will segregate from each other so that the gamete carries only one allele for each gene
Define law of independent assortment
Genes for different traits can segregate independently during the formation of gametes
Define law of dominance
Some alleles are dominant, others recessive. An organism with at least one dominant allele will display the effect of the dominant allele
Define X-linked disorders
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
Define co-dominance
For some traits, multiple alleles can be present and some of these can be equally dominant i.e. both present in the phenotype
