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;
prophase I
Chromosomes visible due to supercoiling. The replicated chromosomes form closely-linked homologous pairs (called tetrads or bivalents), which have two chromosomes and four total chromatids.
non-sister chromatids may cross over at points called chiasmata and exchange equivalent segments of DNA.
Centrioles, migrate to opposite poles and spindle fibres start to form. The nucleolus and nuclear membrane disintegrate.
what are tetrads/bivalents
closely linked homologous pairs
metaphase I
homologous pairs move together along the metaphase plate, the middle. 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.
first division of meiosis
Diploid (2n) → Haploid (n)
second division of meiosis
Separation of chromatids in haploid cells (n → n)
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.
when does crossing over occur
prophase I
each chromatid is…
a long, single strand of double-helical DNA organised by histone proteins.
what is the point at which each chromatid crosses over called
chiasmata (sing. chiasma)
what does crossing over create
new combinations of alleles not present in either original chromosome, forming more variation
what are the two possible chromosome locations for metaphase I
reduction division
random orientation
reduction division
Daughter cells contain only half of the chromosomes that were present in the parent cell. In this case a parent cell has four chromosomes; the daughter cell has two. The parent cell is diploid. The daughter cells will be haploid, having only one version of each chromosome.
random orientation
When pairs of homologous chromosomes line up at the equator of the cell, the paternal copy, for example, has an equal chance of facing either pole. The orientation of one pair (e.g. maternal facing north) does not impact the orientation of any other pair. Each gamete gets one copy of each chromosome, but a random assortment of the maternally and paternally inherited versions.
why is variation important
it gives a species resilience and flexibility in a changing environment.
how is genetic variation increased in offspring
crossing over in prophase I
random orientation
fusion of gametes from two indiviuals
how does fusion of gametes from two indiviuals increase genetic variation
The fusion of male and female gametes (sperm and egg) from different parents combines alleles from two different sources in the diploid zygote. The sperm may carry alleles that have never before combined with alleles found in the egg. Since the genetic information is coming from two different sources, this creates a much broader range of possibilities. Further, which sperm and egg are involved in fertilisation is random.
what is non disjunction
when sister chromatids fail to separate during anaphase II
example of a condition derving from non disjunction
trisomy 21, or down syndrome
what is a trisomy
having an extra copy of a single chromosome (2n+1)
Amniocentesis:
As 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.
when is a developing human called an embryo
during the first 10 weeks /40
when is a developing human called a fetus
after week 10/40
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
what is the chorion
a membrane that surrounds the fetus and develops into part of the placenta.
risks with cvs
bleeding, infection of miscarriage
risks of amniocentesis
infection, fetal trauma from the needle and miscarriage
law of segregation
To segregate means to divide and separate. The inheritance of each characteristic is controlled by a pair of alleles in an individual. The two alleles are separated during meiosis so that each gamete contains only one allele for each gene. Alleles are passed from one generation to the next as distinct units. (There is an exception for genes found on the sex chromosomes. There is a further exception for mitochondrial DNA, which is inherited only from the mother.)
the law of independent assortment
The allele inherited for one trait does not affect which allele will be inherited for any other trait. A gamete contains one copy of each gene; which copy it receives during meiosis is the result of random orientation of homologous chromosomes during metaphase I. (There is an exception for genes whose loci are close together on the same chromosome. These are called linked genes.)
the law of dominace
In an organism with two different alleles, one allele will determine the trait. The allele that determines the trait is dominant; the unexpressed allele is recessive. (There are exceptions for patterns of inheritance other than dominant–recessive, e.g. co-dominance.)
how are dominant and recessive allels represented
capitals and lowercase letters
heterozygous
different
homozygous
same
what is a zygote
a fertilsied egg
P/F1/F2
A specific breeding test in which two parents homozygous for different forms of a trait (e.g. purple flowers and white flowers) are mated. Their offspring (F1 generation) are heterozygous for that trait and are mated with each other to produce the F2 generation.
P
Parental generation, homozygous.
F1
First filial (offspring) generation – offspring of the parental generation, heterozygous.
F2
Second filial generation – offspring of a cross of the F1 generation.
phenotype
An organism’s observable characteristics or traits, including its morphology and biochemical properties.
genotype
The two alleles present in an organism for a particular gene
Heterozygous: Having two different alleles for a particular gene
Examples: Rr or CRCW
Homozygous: Having two of the same allele for a particular gene
Examples: RR, rr, CRCR, or CWCW
gene
a piece of DNA containing information about a particular trait
allele
a particular version of a gene
dominant allele
An allele that has the same effect on the phenotype whether one or two copies are present. In the heterozygous state, it will mask the presence of the recessive allele.
recessive allele
An allele that only has an effect on the phenotype when two copies are present (in a homozygous state).
co-dominant allele
Alleles that jointly affect the phenotype when present together, creating an intermediate or combined phenotype.
punnet squares/grids
diagrams used to determine the expected ratio of genotypes and phenotypes in the offspring of parents with known genotypes. The simplest use of a Punnett grid is a monohybrid cross, where only one characteristic is investigated. In the example above, the characteristic would be pea colour.
phenotype a blood
|A|A or |Ai
phenotype b blood
|B|B or |Bi
phenotype AB blood
|A|B
phenotype o blood
ii
which blood group contains co dominant alleles
|A|B
what does the i stand for in blood groups
isoagglytinogen
why is o the universal doner
it does not trigger an immune response as the genotype ii does not produce any antigens to stick to the surface of the molecule
autosomal
all chromosomes except the sex chromosomes
definition of sex linkage
the condition in which a particualr gene is located on a sex chromosome
give examples of sex linked gentic didsorders
haemophilia
colour blindness
why can human females be homozygous or heterozygous for sex linked genes, and why males cannot
females have 2 X chromosomes
what is the chi squared test
a form of statistical analysis that determines how likely it is that an observed distribution is due to chance.
symbol for null hypothesis
H little 0
chi squared test definition
a statistical test to better understand communities and whether two populations are associated and dependent upon each other or not.
what is the null hypothesis
the hypothesis that states that there is no association between the two populations being tested in the chi-squared test.
what is a chi squared test used for
to anyalayse categorial data
what is categorical data
data is that which is not linear, but can be separated into categories.
what is the ecological frequency
the number of times a plant species occurs in a given number of quadrats. Frequency is usually expressed as a percentage and is sometimes called a Frequency Index.
how to calucate a chi squared value
sum of the two ((O-E)^2/E)
which value for probability do you use
P = 0.05
if your value is larger than the critical value
it is statistically significant
so you can reject the null hypothesis
accept the alternative and assume it has been caused by something and not chance
if your value is lower than the critical value,
it is not statistically signficant, so you must accept the null hypothesis and that it was caused by chance and not a cause
quadrat
a tool used to measure population distribution in a given area. It is often made in a square shape.
what is the degree of freedom
number of readings (n) -1
Which phase of cell division is photographed in order to make a karyogram?
metaphase of mitosis
Which technique causes fragments of DNA to move in an electric field?
gel electrophoresis
Which enzyme is used to fuse the cDNA into the plasmid of a bacterium during the process of gene transfer?
DNA ligase
uses of dna profiling
paternity testing
proving the innocence of someone in a crime
A student compared diploid chromosome numbers of several species with their genome size. Which of the conclusions about the chromosome number and genome size is true?
The size of the genome cannot be deduced from the number of chromosomes.
what is chorionic villus sampling
sampling cells from the placenta. the chorion is part of the placenta and is fetal in origin
during which phase of meiosis does crossing over occur in
prophase I
function of gel electrophoresis
using an electrical current to move molecules through a semisolid medium. the molecules, dna, rna or protein, are seperated by their size and charge
gel electrophoresis def
Gel electrophoresis is a technique used to separate proteins or fragments of DNA according to size.
which end will dna or rna molecules move to in an electric field and why
towards the positive electrode because of their negative electric charge
why is normal dna not suitable for gel electrophoresis
too long (milions of base pairs)
how can dna be changed to become appropriate for gel electrophoresis
digested with special enzymes called restriction endonucleases
what do restriction endonucleuases do
digest dna by cutting the backbone of the dna double helix at highly specific sequences, producing shorter dna segments and distinctive fragment patterns. used to produce dna profiles unique to each indiviual
how does gel electrophoresis work
Samples with fragments of DNA are loaded into small depressions, called wells, on one end of the gel (a jelly-like polymer), as seen in Figure 2. The gel is submerged in a buffer solution, and an electric current is run through the gel. The DNA samples must begin near the negative pole, so that they can spread out as they are drawn toward the positive pole. The consistency of the gel allows separation of the DNA fragments by size. The gel is made of long polymers, often the polysaccharide agarose, that bind together in an interwoven mesh or sieve. The DNA must travel through the spaces between the polymers. Smaller pieces can slip through the spaces more easily, allowing them to travel further along the gel in a given amount of time. By using higher concentrations of polymer, the average size of the pore can be reduced, and smaller pieces of DNA can be separated. Usually, one or more of the wells is filled with a ‘DNA ladder’, which contains DNA fragments with a range of known lengths. By using the DNA ladder, the length of sample fragments can be determined.
when can gel electrophoreisis be used
whenever the source of dna needs to be identified. e.g. which strain of bacteria or which parent
what does pcr do
repeatedly copy fragments of dna
stages of pcr
denaturation
annealing
extension
denaturation in pcr
temp is increased to 98C to seperate dna strands by breaking hydrogen bonds
annealing in pcr
temp is decreased to 60C to allow primers to base pair to complementary dna templates
extension in pcr
heat resistant taq-polymerase replicates dna to build a new dna strand
what does the reaction chamber of pcr contain
many free nucleoside triphosphates, primers that allow replication to occur from the desired point
why is taq polymerase used instead of dna polymerase
it does not denature
what is dna profiling
a technique that examines variable portions of dna to create a profile or fingerprint that is unique to the indiviual.
dna profiles come from
our parents. they are EXACTLY the same number and length of dna fragments, since a persons dna sequence is the same in all cells.
transgenic organims are
gentically modified organisms
what is the universal genetic code
all genetic code is essentially the same between species because lall living things share a common ancestor
process of gene transfer in bacteria
isolate desired gene using restriction endonucleases
isolate an appropriate plasmid
cut the plasmid with the same restriction endonuclease. this will open the loop of the plasmid. (sticky or blunt ends). add a series of guanine nucleotides to the 5’ end and a series of cytosine endonucleases to the 5’ ends. this complementary sequcnes will allow them to stick together
mix many copies of the target gene and cut plamsid 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 permenantly sealing the gene into the plasmid loop.
transfer the plasmid with the target dna (recombinant plasmid) back into the bacteria
grow colonies to produce a eukaryotic protein
benefits of GMO crops
Introduction of new positive traits to the crop
Economic advantages
Environmental advantages
Ecosystem damage
risks of GMO crops
Increasing monoculture
Corporate control over food supply
Human health concerns
How does being a carrier of sca give malaria immunity
Cells usually only sickle if infected with plasmodium falciparum. Because the body eliminates sickled red blood cells, the malarial infection is eliminated along with them. Having two alleles leads to sca so you must only have one.
In sca:
Hemoglobin proteins polymérisé into long fibres. There are hundreds of millions of hemoglobin molecules in each RBC.
Rbcs take a sickle shape when stretched out by the hemoglobin fibres inside.
Genotypes for sickle cell anemia
HbA HbA - homozygous for normal hemoglobin, no sickling, no protection from malaria
HbA HbS - heterozygous, carriers of the sickle cell trait, protection from malaria
HbS HbS homozygous for altered hemoglobin, sca, no protection from malaria
