Human bio: genetics + pedigrees Flashcards
what is genetics (4)
study of genes/ genomes and their variation
how is DNA packaged so tightly
it is wrapped around histone proteins
mitotic chromosome
nucleosome definition
each particular histone with DNA wrapped around it
minor and major grooves in DNA helicial structure diagram
what are the purines (4)
A and G
what are the pyrimidines
T and C (bases for purine/pyrimidine pairs)
what are genes known as (4)
transcriptional units
what is the exome
all of the exons in a genome
what is the transcriptome (4) (4)
RNA copies of the active protein-coding genes
what is the proteome (4)
the cell’s repertoire of proteins
what is the DNA in between genes called (4) (4)
intergenic DNA
what do all your genes do
- expression, replication, and maintenance of the genome
- signal transduction
- various other activities
- general biochemical functions of the cell
what does RNA polymerase do specifically (4) (4)
RNA polymerase (enzyme obviously) forms a complex with DNA and other proteins to initiation transcription - typically upstream of first exon (start codon)
a single gene can give rise to more than one transcript - results in different forms of a protein
what are housekeeping genes
genes that are regulatory genes that are needed in all cells
what does non-coding DNA do
regulatory elements
non-coding RNA
other sequences including from viruses (HERVs)
epigenetics
DNA packaging via histone modificaiton can influence the can accessibility of DNA binding proteins sites and in turn expression
methylation of CpG islands in promotor regions can affect expression
why is gene regulation good ? (4) (4) (possibly important)
can regulation can be critical for homeostasis, development and in disease, can be responsive to the environment
what are post-transcriptional control microRNAs
~22 bp long
can originate from precursor RNA
do not code for amino acids
bind to complementary region on mRNA
can block transcription of RNA transcript (and leads to degradation of mRNA)
explain chemical tag DNA modifications
chemical modifications (called tags) to DNA and histones can alter the way DNA is accessible/packaged (responsive to environment)
KEEP IN MIND!!! that these modifications do NOT alter the DNA sequence, they’re reversible and can be inherited
what can epigenetics help us to (4) determine (4)
cell lineages and differentiation
explain the redundancy of the universal genetic code
an amino acid may have one for codon that codes for it
learn tRNA structure lol (be able to annotate a diagram)
explain the transcription modification of information (4)
chromatin remodelling
alternative splicing
microRNAs block protein synthesis
explain the translation modification of information (4)
protein folding
polypeptides shortened
sugars added
polypeptides aggregate
two types of G0 phases
quiescent G0
terminally differentiated G0
what are cancer cells essentially
cells with cell senescence (where cells enter irreversible cell growth arrest)
Explain the G1/S checkpoint
its a restriction point, is it environmentally favourable?
explain the G2/M checkpoint
is all DNA replicated? is environmentally favourable?
metaphase to anaphase transition
are all chromosomes attached to spindle?
checkpoint during S phase
there is a DNA damage checkpoint towards the end of the S phase of the cell cycle
telomere shortening
results in an altered structure that initiates signals for cell senescence
3’ to 5’ endonuclease activity
DNA polymerase can reverse its direction if it detects an incorrect nucleotide has been placed
what can frameshift mutation do
frameshift in coding sequences can create early stop (truncated) and/or polypeptide
translocations
Fragment of a chromosome is moved
(translocated) from one chromosome
to another
The balance of genes is still normal
but transcription of genes can be
altered sometimes due to changes in
gene regulatory elements
types of DNA variation (4)
point mutations (single nucleotide polymorphisms)
simple indel (incl repeats)
copy number variation (CNV) (gene copy duplication)
chromosome inversion/translocation
chromosome number
mutations can (4)
cause changes to protein structure and function and are random
DNA polymerase (4)
has a high fidelity rate but can make rare errors (mutations)
meiosis start with
2n (diploid) but finishes with 1n (haploid)
reductional division of meiosis (important!)
segregation of homologs during meiosis I
equatorial division (important!)
segregation of chromatids during meiosis II
what are the products of meiosis (4)
four different haploid gametes - half received allele A and the other half received allele a
spermatogenesis
spermatogonium (diploid)
primary spermatocyte
1st meiotic division: secondary spermatocyte (haploid)
2nd meiotic division: spermatids (haploid)
spermatid maturation into sperm cells (haploid) in epidymis (nourised by sertoli cells)
oogenesis
production of gametes in females
oogonia
develop into primary oocytes by division + development
primary oocytes rest in prophase I
From puberty Follicle stimulating Hormone (FSH) stimulates one Oocyte a month to
complete meiosis I
Result: 2 cells: Secondary Oocyte and 1st polar body
Secondary Oocyte develops to metaphase II, rests in this state till after ovulation
Only if fertilized completion of Meiosis I (casts off second polar body)
genetic imprinting
for most genes, expression of maternal and paternal form is typical but for some genes only one copy is expressed (genetic imprinting)
non-dysjunctioning during meiosis can
result in differences in chromosome numbers
trisomic and monosomic meaning
trisomic = 3 pairs
monosomic = 1 pair
what does karyotype enable
enables visualisation of gross changes in chromosome number and structure
Triploidy (69,XXX or 69,XYY)
1-3% of all conceptions; almost never born live and do not
survive long
ANEUPLOIDY (AUTOSOMES)
Nullisomy (lacking a pair of
homologs)
lethal at pre-implantation stage
ANEUPLOIDY (AUTOSOMES)
Monosomy (one chromosome
missing)
lethal during embryonic development
ANEUPLOIDY (AUTOSOMES)
Trisomy (one extra
chromosome)
usually lethal during embryonic or fetal# stages, but individuals
with trisomy 13 (Patau syndrome) and trisomy 18 (Edwards
syndrome) may survive to term; those with trisomy 21
(Down syndrome) may survive beyond age 40
ANEUPLOIDY (SEX CHROMOSOMES)
Additional sex chromosomes
individuals with 47,XXX, 47,XXY, or 47,XYY all experience relatively minor problems and a normal lifespan
ANEUPLOIDY (SEX CHROMOSOMES)
Lacking a sex chromosome
although 45,Y is never viable, in 45, (Turner syndrome), about 99% of cases abort spontaneously; survivors are of normal intelligence but are infertile and show minor physical diagnostic characteristics
In humans, the embryonic period spans fertilization through to the end of the eighth week of
development. Fetal development then begins and lasts until birth.
turner syndrome
karyotype of only 45 X, 1:2000 females, only viable monosomy (missing one chromosome) in humans, genetically female, short stature, and normal intelligence, no sexual maturation during puberty and are sterile, often congenital deformities
origin of disjunction may be I or II in either parent
euploidy
diploidy (2n)
(two sets of each homolog)
haploidy (1n)
(one set of each homolog)
polyploidy = more than two chromosome sets)
triploidy (3n)
(three chromosome sets)
tetraploidy (4n)
(four chromosome sets)
aneuploidy
monosomy (2n -1)
(one chromosome missing)
trisomy (2n +1)
(one extra chromosome)
important genetic principles
- genes have multiple effects
pleiotropy - effect of a gene varies between individuals
variable expression - the effect of the gene depends upon the environment
genotype-environment interaction - several different genes can have the same effect
genetic heterogeneity
