topic three Flashcards
what is the genome
all the genetic info in the body
what is a gene
a short stretch of dna that influences a specific characteristic
locus
the specific position of a gene on a chromosome.
alleles
the various, specific forms of a gene that usually vary from each other by one or a few bases.
gene
a heritable factor that consists of a length of DNA and influences a specific characteristic.
having a pair of each kind of chromosome is called
the diploid state
having one copy of each chromosome is
the haploid state
homozygous
two copies of the same allele
heterozygous
two copies of different alleles
gneotype is
homozygous for red eg
phenotype is
erd petals
What is always different between the alleles of a gene?
Their base sequence.
A particular gene has three alleles across the human population. At maximum, how many different alleles can you, an individual human, have for that gene?
2
no genes in e.coli (bacteria)
4 000
no genes in humasn
20000
no genesin rice
35,000
what is the sense strand
the dna strand that is not transcribed
has the same sequence of bases as the mRNA molecule except for thymine being replaced by uracil.
what is the antisense strand
the antisense strand and is complementary to the mRNA molecule.
how does sickle cell anaemia come about
When the HBB locus is transcribed, the mRNA from Hb A has G A G for the 6th codon, which translates to the amino acid called glutamic acid . The mRNA copied from Hb S has the codon G U G, which codes for the amino acid valine
You should be able to recall that one specific base substitution causes glutamic acid to be substituted by valine as the WHAT NUMBER amino acid in the beta hemoglobin polypeptide.
sixth
precise base sub mutation
(from GAG→ GTG in sense DNA), the change to the base sequence of mRNA transcribed (from GAG→ GUG), and the corresponding change to the sequence of a polypeptide in hemoglobin (from glutamic acid to valine in the sixth position).
what forms hemogolobin
2 beta subunits
2 alpha subunits
how does hemoglobin behae differently under low o2 levels
Under normal conditions, hemoglobin formed using either Hb A or Hb S is equally good at carrying and transporting oxygen. However, in specific situations like low oxygen levels in cells, they behave differently. The glutamic acid in Hb A interacts well with water, keeping hemoglobin molecules dissolved within red blood cells. In contrast, the valine in Hb S is hydrophobic, causing the beta subunits to come together and form long fibers. This leads to two problems: the ability to carry oxygen is significantly reduced, and the long fibers distort the cell membrane, resulting in the characteristic “sickle” shape of red blood cells.
problems of sickle cell
They can get stuck and clog blood vessels anywhere in the body, causing intense pain as blood supply fails. If this happens in the brain, the person could have a stroke. Sickled cells must be broken down and eliminated from the body, which strains the liver and causes a shortage of functioning red blood cells (anemia). New red blood cells must be made in the bone marrow to replace the cells lost, and the extra work can damage bone structure.
Sickle cell anemia occurs when a person is homozygous for what
Hb S
all of their hemoglobin contains the alternate beta subunit.
When a person’s alleles are Hb A Hb A , their hemoglobin will never
polymerise and their erythrocytes will never sickle.
waht happens with HbA and HbS
cells will only sickle when infected by plasmodium falciparum
why is it advantageous to have one HbS allele
Because the body eliminates sickled red blood cells, the malarial infection is eliminated along with them.
waht does hemoglobin do with logn fibres
Hemoglobin proteins polymerise into long fibres. There are hundreds of millions of hemoglobin molecules in each red blood cell. `
what is the ident column in genome databases
gives the percentage of identical nucleotides.
why is prokaryotic dna called naked dna
not organised around associated histone proteins
shape of prokaryotic dna
circualr dna double heliz molecule
plasmids can be easily what between bacteria
exchanged, providing a mechanism by which antibiotic resistance spreads
what do homologous chromosomes do
carry the same set of genes in the same locations
what are autosomes
not sex hormones
Which of the following statements about homologous chromosomes is correct?
A particular gene will be found at the same locus on homologous chromosomes.
, Correct answer
Your answer
They are two identical copies of a parent chromosome which are attached to one another at the centromere.
They are chromosomes that have identical genes and alleles.
They always produce identical phenotypes.
A particular gene will be found at the same locus on homologous chromosomes.
genome sizes in order
e. coli
drosophilia melanogaster
homo sapiens
paris japonica
what chromosomes does an egg cell have
22 autosomes and one copy of the x chromosome
wat chromosomes does a sperm have
22 autosomes and one X or Y
whcih chromosomes are which gender
XX female
XY male
each chromosome in a homologus pair is referred to as a
homologue
what is a tetrad
two homologues
what is the best mitotic phase for viewing
metaphase
how are homologus chromosomes aligned in karyotyping
by length, location of the centromere and by bands of colour differences (striations) induced using dyes.
non disjunction
failure of a pair of homologous chromosomes or sister chromatids to seperate
trisomy 21
down syndrome
Two important uses of karyograms are:
To deduce the sex of an individual.
To diagnose for chromosomal abnormalities such as Down syndrome in humans
what is autoradiography
a technique that uses X-ray film to visualise the two-dimensional distribution of a radioactively labelled substance. The image formed through autoradiography is called an autoradiograph.
how did cairns first produce images of DNA molecules using autoradioagraphy
He produced thymidine (the nucleotide containing thymine) labelled with radioactive hydrogen ( 3 H).
Next, he grew E. coli bacteria in a medium containing the radioactive thymidine. When the E. coli cells replicated their DNA, they used the radioactive thymine, creating radioactive DNA.
He then lysed the cells (ruptured their cell walls and membranes) to release the cell contents, including the intact bacterial DNA, onto slides.
Next, he covered the slides with photographic emulsion and stored them in the dark for two months.
During that period, high energy electrons emitted by the radioactive decay of 3 H within the DNA caused the appearance of dark spots on the photographic emulsion.
The pattern of dark spots indicated the presence of labelled DNA (as shown in Figure 1 ).
The length of the E. coli chromosome could then be measured and was worked out to be about 1 mm, nearly 1 000× longer than the typical E. coli cell.
What creates the dark spots seen on the photographic emulsion in an autoradiograph?
High energy electrons released from the DNA itself
Cairns used autoradiography as a technique to measure the length of:
DNA molecules
what is meiosis
a form of nuclear division that produces four haploid nuclei from one diploid nucleus.
prophase I
Chromosomes become visible due to supercoiling. The replicated chromosomes form closely-linked homologous pairs (called tetrads or bivalents), which have two chromosomes and four total chromatids.
At this stage, non-sister chromatids may cross over at points called chiasmata and exchange equivalent segments of DNA.
Centrioles, if present, migrate to opposite poles and spindle fibres start to form. The nucleolus and nuclear membrane disintegrate.
metaphase I
Homologous pairs move together along the metaphase plate, which lies halfway between the two poles. Maternal and paternal homologues show random orientation towards the poles.
The spindle fibres attach to the centromeres of each chromosome and gently pull to align them along the equatorial metaphase plate.
Spindle fibres connect each centromere to one pole only.
anaphase I
Spindle microtubules shorten, pulling homologous chromosomes apart towards opposite poles. Unlike mitosis, sister chromatids remain connected at the centromere and move to the same pole.
telophase I
The first meiotic division effectively ends when the chromosomes arrive at the poles. Note that each chromosome still consists of a pair of chromatids.
The chromatids partially uncoil and a nuclear membrane then reforms around each nucleus formed.
Although technically not part of meiosis, cytokinesis usually occurs during telophase I. Cytokinesis results in two daughter cells with haploid nuclei from meiosis.
prophase II
Chromosomes condense again. Centrioles, if present, migrate to opposite poles and spindle fibres start to form. The nucleolus and nuclear membrane disintegrate.
metaphase II
The spindle fibres attach to the centromere and connect each centromere to both poles. They exert a gentle pull to align the sister chromatids at the equator.
anaphase II
Centromeres divide and chromatids are moved to opposite poles by spindle fibres.
Once sister chromatids are separated, they are called chromosomes.
telophase II
Chromosomes reach opposite poles and uncoil. This is followed by nuclear envelope formation and cytokinesis.
Meiosis is now complete, resulting in four haploid daughter cells. Note that each of the four cells are genetically distinct.
meiosis I
Reduction division – Cells begin with two copies of each chromosome and end with only one;
Diploid (2n) → Haploid (n)
meiosis II
Separation of chromatids in haploid cells (n → n)
Meiosis results in the formation of haploid gametes. this means the number of chromosomes
halves
when does crossing over occur
prophase I
compare metaphase of mitosis with metaphase I
Amniocentesis
s the fetus develops in the uterus, it is cushioned by amniotic fluid, as seen in Figure 2. Amniocentesis is usually performed between weeks 14 and 20 of pregnancy. A doctor uses ultrasound imagery to guide a syringe needle through the abdomen and uterine wall without piercing the fetus. The needle is then used to withdraw a small amount of amniotic fluid. Fetal cells floating in the fluid are cultured and karyotyped.
Chorionic villus sampling (CVS):
Early in pregnancy there is not enough amniotic fluid to perform amniocentesis safely; however, during weeks 10–13, CVS can be used. As in amniocentesis, ultrasound imaging is used to guide the medical professional during the sampling and avoid harm to the developing embryo or fetus. Fetal cells are sampled by inserting a suctioning tool (often a catheter or syringe) through the vagina or abdomen to reach the fetal cells in the chorion, as seen in Figure 3. The chorion is a membrane that surrounds the fetus and develops into part of the placenta.
PCR
steps of gene transfer
Isolate the desired gene from the original species using restriction endonucleases.
Isolate an appropriate plasmid (a small loop of DNA containing a few genes that is often traded between bacteria).
Cut the plasmid with the same restriction endonuclease that was used to remove the desired gene. This will open the loop of the plasmid, forming a string with two ends.
Mix many copies of the target gene and cut plasmid together to allow their complementary unpaired sequences to join together, thus adding the gene into the plasmid.
Use the enzyme DNA ligase to covalently bond the DNA backbones of the gene and plasmid together, permanently sealing the gene into the plasmid loop.
Transfer the plasmid with the target DNA (called a recombinant plasmid) back into the bacterium.
Grow colonies of the genetically modified bacteria that now produce a eukaryotic protein.
cloning by fragmentation of an embryo
