ch3: i love how it's canon that laszlo fucked his clone

Question 1

outline the consequences of base substitution mutation (2)

Answer 1

insertion of an incorrect nucleotide in the DNA strand
sickle-cell anemia
antisense strand of DNA: CTC → CAC
sense strand of DNA: GAG → GTG
mRNA/transcription: GAG → GUG
amino acid/translation: glutamic acid → valine

Question 2

explain the causes and consequences of sickle-cell anemia (8)

Answer 2

gene mutation of haemoglobin by base substitution
antisense strand of DNA: CTC → CAC
sense strand of DNA: GAG → GTG
mRNA/transcription: GAG → GUG
amino acid/translation: glutamic acid → valine

in homozygotes: HbSHbS
RBC become sickle-shaped
↓ oxygen carried → oxygen stress
RBC will burst + block blood vessels → circulatory problems can cause organ failure
in heterozygous: HbAHbS → malaria resistance

Question 3

explain the consequences of altering a DNA base in the genome of an organism (8)

Answer 3

altering a base in DNA = point mutation
only has an effect if base is in a gene
when mRNA is produced by transcription one mRNA base is different
one codon in mRNA is different
one amino acid is different in the polypeptide produced by translation of mRNA
degenerate: some base changes do not change the amino acid coded for
structure of polypeptide may be altered: usually does not function as well
sickle cell anemia shit above

Question 4

define the term “gene” and “gene mutation” (2)

Answer 4

gene = sequence of nucleotides that controls a specific characteristic
can be inherited

gene mutation = change in the base sequence of a gene
e.g. base substitution

Question 5

why do mutations occurring in gametes have much greater effects on organisms than those occurring in body cells? (2)

Answer 5

mutations are inheritable → affect individuals of further generations
all body cells of further generations will have the mutation

Question 6

explain the construction and use of karyotyping in human genetics (8)

Answer 6

karyotype = no. & image of chromosomes in a cell

construction
cells in metaphase collected from chorionic villus/by amniocentesis
burst cells and spread chromosomes to take a photo
arranged in pairs according to size/structure/position of centromere/banding pattern

uses:
identify sex
male: XY
female: XX
identify non-disjunction
e.g. Down syndrome due to trisomy of chromosome 21
prenatal diagnosis of chromosome abnormalities → whether to abort the fetus or not + prep for consequences of abnormality in offspring

Question 7

discuss the role of genes and chromosomes in determining individual and shared character features of the members of a species (7)

Answer 7

genes:
genes are inherited from parents
mutation causes genetic differences
genes can have multiple alleles that give different characters
alleles are different forms of a gene
e.g. eye colour alleles
dominant alleles determine trait even if recessive allele is present
both alleles influence the characteristic with codominance
certain genes expressed in all members of a species
not all genes are expressed in an individual

chromosomes:
same locus of genes
same number of chromosomes in a species
some individuals have an extra chromosome
e.g. Down syndrome
polyploidy divides a species/creates a new species
sex chromosomes determine the sex of an individual
meiosis give new combinations of chromosomes/genes

Question 8

describe the Hershey and Chase experiment (3)

Answer 8

radioactive isotopes used to label bacteriophages
proteins labelled with radioactive sulphur
DNA labelled with radioactive phosphorous

phage infects bacterium
only viral DNA enters bacterium
parts of phage remaining outside bacterial cell are removed
bacteria contain the radioactive DNA

Question 9

explain how an error in meiosis can lead to Down’s syndrome (4)

Answer 9

trisomy of chromosome 21
non-disjunction during anaphase I/II in meiosis
I
metaphase: homologous chromosomes in equator
anaphase: separate → 1 pair doesn’t separate
telophase: cells divide into 2 → cells have either one more/less chromosome
II: sister chromatids fail to separate
fertilisation with 1 gamete carrying an extra chromosome

Question 10

explain how reduction division results in genetic variety (8)

Answer 10

occurs during meiosis
cell undergoes meiosis I
homologous chromosomes pair up in equator
each chromosome in homologous pair came from maternal/paternal parent
randomly oriented to either side of cell
homologous chromosomes separate → cytokinesis
2 cells from 1st division undergo meiosis II: chromosomes separate again

1 cell → 4 cells
diploid number 2n → haploid number n
haploid cell contains only 1 chromosome from each original homologous pair
mixture of maternal & paternal chromosomes in any haploid cell is different
bc random orientation during meiosis → basis for 1st variety

Question 11

outline the process of meiosis (6)

Answer 11

2 cell divisions: meiosis I + II
for production of gametes
chromosome number halved: diploid to haploid → 4 haploid cells
daughter cells different from parent cells

meiosis I
prophase
homologous chromosomes pair up → form a synapsis
crossing over occurs in non-sister chromatids
nuclear envelope breaks down
metaphase: homologous chromosomes line up at the equator of the spindle
attachment of microtubules to centromeres
anaphase: homologous chromosomes separate and move to opposite poles
telophase: chromosomes reach poles and unwind
nuclear envelopes do not reform bc meiosis II

meiosis II
prophase
chromosomes condense and become visible
new spindles form
metaphase: chromosomes line up at the equator of the spindle
anaphase: sister chromatids separate and move to opposite poles
telophase: chromatids reach the poles and unwind

Question 12

describe how the behaviour of chromosomes differ during the processes of mitosis and meiosis and the consequences of it (4)

Answer 12

mitosis = the separation of the chromatids into 2 daughter cells
the chromosome number of the parent cell is maintained in the daughter cells
the daughter cells are genetically identical to the parent cell

meiosis:
prophase I: crossing over occurs between non-sister chromatids
recombination of genetic make-up on different chromosomes
1st meiotic division: homologous chromosomes are separated into 2 daughter cells
the homologous chromosomes are independently assorted when separated
2nd meiotic division: chromatids are separated into 4 daughter cells
results in the production of haploid cells, which are genetically different

Question 13

define chromosome, allele, codominant alleles, recessive allele, locus, sex linkage and genome (6)

Answer 13

chromosome: structure formed by DNA and proteins
allele: one specific form of a gene
codominant alleles: a pair of alleles that both are both expressed in the phenotype when present in a heterozygote
recessive allele: an allele that expresses its characteristic phenotype only when present in homozygous state → aka when the dominant allele is not present
locus: the particular position of a gene on a homologous chromosomes
sex linkage: a gene located on a sex (X/Y) chromosome
genome: the whole of the genetic information of an organism

Question 14

distinguish between autosomes and sex chromosomes in humans (4)

Answer 14

X and Y chromosomes determine sex: females XX and males XY
X chromosome carries more genes than the Y chromosome
22 pairs of autosomes: males and females have same types of autosomes

Question 15

ALL HEMOPHILIA QUESTIONS (8)

Answer 15

hemophilia is due to a recessive allele
sex linked + X-linked: allele is on the X chromosome
Y chromosomes do not have the allele
female: XX → can have both dominant and recessive allele at the same time
male: XY → can only have dominant or recessive allele → only 1 copy so recessive allele is not masked → hemophilia is more common

conditions
males inherit X chromosome from mother → 50% chance if mother is a carrier
carrier is heterozygous for the gene → genotype XHXh
dominant allele masks the recessive allele
females inherit one X chromosome from father and one from mother
hemophilia allele could have been inherited from either parent
can have affected sons/carrier daughters
hemophiliac males have carrier daughters if mother pass on dominant allele but cannot pass the condition on to sons
affected father + carrier mother → affected homozygous recessive daughter → fatal

Question 16

describe the inheritance of ABO blood groups (9)

Answer 16

one gene determines ABO blood groups
genes have different/alternative forms called alleles
there are three alleles (IA, IB and i) for this gene

example of multiple alleles, where 3 alleles can result in 4 phenotypes
IAIA and IAi both give blood group A
IBIB and IBi both give blood group B
IAIB gives blood group AB
ii gives blood group O

alleles that are codominant both affect the phenotype in a heterozygote
IA and IB are codominant
IA and IB are dominant over i

each individual has 2 alleles but only 1 is passed to offspring
example of a cross involving ABO blood groups

Question 17

positive outcomes of the Human Genome Project (3)

Answer 17

mapping: easier to study how genes influence human development
knowledge of the gene position on chromosomes, no. & base sequence of genes
discovery of proteins

ancestry: more information on the origins, evolution and migration of humans
screening: help identify genetic diseases
therapeutic: allows the production of new drugs based on base sequences of genes
international cooperation

Question 18

outline the use of polymerase chain reaction to copy and amplify minute quantities of DNA, including the role of Taq polymerase (2)

Answer 18

strands of DNA fragments split by heat
forms new double-stranded DNA by adding complementary nucleotides to split strands when cooling
Taq DNA polymerase can withstand high temperatures without denaturing
primers bind to targeted DNA sequences at lower temperature
heating and cooling cycle is repeated until enough DNA is obtained
example of PCR application: paternity cases, forensic investigations

Question 19

outline the process of DNA profiling, including ways in which it can be used/to determine paternity (6)

Answer 19

DNA sample obtained from hair/blood/semen
amplified by PCR → cut into fragments by restriction enzymes
gel electrophoresis separates fragments according to size → produces a pattern of bands
patterns of bands from different sources are compared
pattern of bands is unique to the individual
↑ difference in pattern of bands → ↓ closely related the organisms are

used in cases of paternity/criminal investigations:
DNA sample from child, mother and possible father(s) are taken to establish paternity
done for legal reasons/inheritance or for personal reasons/self-esteem issues for children/fathers/parents
analysed for matches between child with mother and possible father
half the child’s bands will match the father

Question 20

describe the steps taken in the processing of a small sample of DNA found at a crime scene (6)

Answer 20

DNA samples are taken from crime scene, suspects and victims
DNA is stable → can be processed long after the crime
amplified by PCR → cut into fragments by restriction enzymes
gel electrophoresis involves placing sample between electrodes → separates fragments according to size
create DNA profiles → comparison is made between the patterns → criminals/victims can be identified

Question 21

outline a basic technique for gene transfer (6)

Answer 21

plasmid used for gene transfer
a small circle of DNA
e.g. E. coli

mRNA is extracted
DNA copy of mRNA is made using reverse transcriptase
restriction endonucleases cut a small fragment of DNA from an organism
same restriction enzymes used to cut DNA of plasmid
sticky ends are the same in both cases

gene + plasmid mixed tgt → fragment of DNA is inserted into the plasmid
spliced together by ligase → recombinant DNA
recombinants can be inserted into host cell and cloned
e.g. E. coli is cultured → begins to make insulin

Question 22

state advantages of producing insulin by using recombinant DNA technology in plasmids of bacteria over extracting insulin from animals (3)

Answer 22

contains fewer impurities
can be produced in a larger quantity in a shorter time
lower production cost
can avoid allergic problem

Question 23

discuss the potential benefits and possible harmful effects of one example of genetic modification in a named organism (8)

Answer 23

genetic modification = when the DNA of an organism is artificially changed by the addition/removal of a gene → alters some phenotypes of the organism
e.g. Bt gene transferred from bacterium to maize
universal genetic code allows genes to be transferred between species
google docs

Question 24

explain benefits and risks of using genetically modified crops for the environment and also for human health (8)

Answer 24

environment:
benefits:
pest-resistant crops can be made → ↓ pesticides needed
less fuel burned in management of crops
longer shelf-life for crops → less spoilage
shorter growing time
allows crops to be grown where they would not grow naturally

risks:
non-target insects may be killed as well
genes transferred to crop plants to make them herbicide resistant could spread to wild plants making superweeds
GMOs reduces biodiversity

health:
benefits:
nutritional value of food improved by increasing nutrient content
crops could be produced to contain edible vaccines to provide natural disease resistance

risks:
proteins from transferred genes could be toxic or cause allergic reactions
antibiotic resistance genes used as markers during gene transfer could spread to bacteria
transferred genes could cause unexpected problems

Question 25

discuss the ethical arguments for and against the cloning of humans (4)

Answer 25

clones are genetically identical individuals

risks to society:
expensive
lead to uncontrolled eugenics

risks to individuals:
many cloned animals die from premature aging of clones
cloned humans could experience problems in psychological development
reduction of human dignity
cloned tissues will still possess genetic diseases
risk for unknown consequences is too great

belief systems:
artificial cloning in humans is opposed by some as it is against their religion
cloning occurs naturally when identical twins form

benefits:
cloning humans may help to provide organs for transplantation
possible medical breakthroughs

Question 26

outline natural methods of cloning in some eukaryotes (3)

Answer 26

clones = genetically identical organisms
asexual reproduction in plants (e.g. tubers)
common in invertebrates (e.g. budding in hydra)
budding in yeast/fungi
identical twins are clones because they originate from the same cell

Question 27

outline a technique for cloning using differentiated animal cells (5)

Answer 27

differentiated cells taken from donor animal → diploid nucleus removed
ova removed from donor animal → haploid nucleus removed
diploid nucleus inserted into ovum
embryo implanted in uterus of surrogate mother
normal pregnancy and birth is completed
offspring is a clone of the donor mother of the diploid nucleus

Question 28

find the probability of [phenotype]

Answer 28

let F be the allele of (dominant characteristic) and f be the allele of (recessive)
blood groups: Let IA/B be the allele that produces antigen A/B, giving type A/B blood + Let i be the recessive allele producing neither antigen A nor antigen B, giving type O blood

genotype of parents
punnett's grid (rmb to write the phenotype of each genotype in each smol box)
genotypic ratio
phenotypic ratio
probability is [...]

Question 29

sex linkage

Answer 29

XX: female
XY: male
sex linked: gene responsible for disease is on either X or Y sex chromosome in human
a mother only transmits X sex chromosome to offspring. A father segregates with X or Y sex chromosome to an offspring
a dominant allele will always express its phenotype in both a a male and a female individual.
a recessive allele will also express its phenotype in a male individual but it requires homozygosity for expressing the controlled phenotype in a female participant

Y-linked: it is expected that all male progeny of an affected father will be affected individuals
however…

X-linked and recessive
it is expected that all affected female inherited the disease-causing alleles from father and mother
OR
it is expected that an affected female produces affected male progeny

X-linked and dominant
it is expected the affected son must inherit his disease-causing allele from his mother which is an affected individual too
OR
it is expected the female progeny of an affected father will be affected