3 genetics Flashcards
gene
a heritable factor that consists of a length of DNA and influences a specific characteristic.
allele
the various, specific forms of a gene that usually vary from each other by one or a few bases.
gene locus
the specific position of a gene on a chromosome.
what is the diploid state
having a pari of each kind of chromosome
what is the haploid state
having one copy of each chromosome
homozygous if
two copies of the same allele
heterozygous if
you have two different alleles
chromosomes
long DNA molecules, which contain many genes.
how are new alleles created
by mutation
causes of mutation
random
radiation
environment
mutagens
what is a base substitution mutation
a mutation that changes one nitrogenous base in a sequence
what is a genome
all the genetic information of an organism.
HUMAN GENOME PROJECT
.
what is sickle cell anemia
a common genetic disease in areas where malaria is endemic.
what causes sickle cell anaemia
one base substitution causes the glutamic acid to be mutated to valine as the sicth amino acid in the beta haemoglobin polypeptide
GAG to GTG in sense DNA
GAG to GUG in the base sequence of mrna
how is hemoglobin formed
by 2 copies of the beta subunit combining with two alpha subunits and four heme groups
what happens to hemoglobin in low oxygen levels
the glutamic acid interacts well with water, keeping all the hemoglobin molecuels dissolved inside the erythocyte. the valine is hydrophobic, allowing the beta subunits to join together. when the hemoglobin polymerises into long fibres it causes two problems, its ability to carry oygen is significatnyl reduced and the long fibres poke into the cell membrane, giving the red blood cell the characteristic curved sickle cell appearane.
problems cauesd by sickle cell
can get stuck and clog blood vessels anywhere in the body, causing intense pain as blood supply fails. if this happens in the brain it could cause a stroke.
what must be done iwth sickle cells
broken down and eliminated from bidy which strains the liver and causes a shortage of functioning red blood cell. new red blood cells must be madei n the bone marrow to replace the cells lost, and the extra work can damage bone structure
what is pleiotropy
when one gene has multiple effects
when does sickle cell anemia occur
when a person is homozygous for Hb S
what if someone has a heterzygous genotype of HbA HbS
the hemoglobin contains some beta subunits with valinea nd some with glutamic acid. the cells will ony sickle when ingected with plasmodium falciparum (parasite causing malaria) as the body destroys the sickled blood cells, it destryous malaria with it.
Hb A Hb A
homozygous for normal hemoglobin, no sickling, no protection from malaria
Hb A Hb S
heterozygous, carriers of the sickle cell trait, protection from malaria
Hb S Hb S
homozygous for altered hemoglobin, sickle cell anemia, no protection from malaria
What can be easily exchanged between bacteria
Plasmids
What is the singular, circular prokaryotic chromosome referred to as and why
Naked because it is not associated with any proteins
What are plasmids
Small circular DNA molecules that are easily exchanged between prokaryotes and may contain several genes
What are eukaryote chromosomes
Linear DNA molecules associated with histone proteins
What do homologous chromosomes carry the same sequence of
Genes but not necessarily the same alleles of these genes
Compare prokaryotes and eukaryotes
Prokaryotes have circular DNA and eukaryotes have linear DNA
plasmids see only present in prokaryotes, not eukaryotes.
Prokaryotes have one chromosome only, eukaryotes have two or more different chromosomes.
Prokaryotes are naked with no associated proteins, but eukaryotes are associated with histone proteins
Diploid nuclei have
Pairs of homologous chromosomes
Haploid nuclei have
One chromosome of each pair of homologous chromosomes
Diploid
Full 46
Haploid
Half 23
What is a homologoue
Each chromosome in a homologous pair
What is a tetrad
A structure consisting of two homologoues
What are autosomes
Chromosomes that do not determine sex
Chromosome no in Homo sapiens
46
what is the best mitotic phase for viewing
metaphase. The chromosomes are fully condensed, making them easier to identify. The chromosomes are spread apart by squashing the cell. This allows images to be captured and analysed, usually by computer.
what is viewing chromosomes under light microcopes and then graphing them called
karotyping
what is a karogram
a photograph or image of the homologous pairs of chromosomes in decreasing length
what does a karyogram show
the chromosomes of an organism in homologous pairs of decreasing length
what can karograms do
detect sex or find missing or extra chromosomes. not able to detect differences in allele or mutations
what is non-disjunction
the failure of a pair of homologous chromosomes or sister chromatids to separate
when is trisomy caused
when one gamete has an extra chromosome
what is autoradiography
Autoradiography is 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.
what did cairns first produce images from
e.coli
how did cairns produce images from e.coli
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.
homologous chromosomes carry the same…
sequence of genes, but not necessarily the same alleles of those genes
the two dna molecules formed by dna replication prior to cell division are considered to be sister chromatids until…
the splitting of the centromere at the start of anaphase
list the order of genome sizes of T2 phage
Escherichia coli , Drosophila melanogaster ,
Homo sapiens and
Paris japonica .
what is genome size
total length of dna in an organism
diploid nuclei have pairs of…
homologous chromosomes
list the diploid chromosome numbers of
Homo sapiens , Pan troglodytes , Canis familiaris , Oryza sativa and Parascaris equorum .
what is a genom
the whole of the genetic information of an organism
what is a gene locus
refers to the specific position of a gene on a chromosome
what is the constant difference between the alleles of a gene
their base sequence
describe the changes when a base substitution mutation occurs
the altered allele codes for an altered polypeptide which is folded into a different enzyme, doing a different role and giving a different effect to the organism
one copy of the sickle cell allele provides
protection from malaria.
2 copies DOES NOT
what do you read on a genome database to find the similarity to humans
indent
prokaryotes do not have dna associated with…
histones/proteins
a particular gene will be found at the same locus on
homologous chromosomes
Paris japonica (woodland plant) has a larger genome than
drosophila melanogaster (fruit flies) and homo sapiens (humans)
what is meiosis
a form of nuclear division that produces four haploid nuclei from one diploid nucleus.
what occurs prior to meiosis
the DNA of the cell is replicated during the S phase of interphase. Thus meiosis begins, as mitosis does, with replicated chromosomes.
what does meiosis involve
two cycles of division, meiosis I and II, which are themselves divided into four phases: prophase, metaphase, anaphase and telophase
what does cytokinesis do
divide the cytoplasm of the parent cell to create two daughter cells
what does meiosis produce
Four haploid nuclei
what is reduction division
Cells begin with two copies of each chromosome and end with only one;