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35 Cards in this Set
- Front
- Back
Explain how meiosis can result in genetic variety in gametes. (8)
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meiosis provides opportunities for new combination of genes;
crossing over in prophase I; due to chiasmata formation; segments of (non-sister) chromatids are exchanged between homologous chromosomes; chromosome mutations could occur; leading to the formation of new combination of alleles (on chromosomes of gametes) / the formation of new linkage groups; the random orientation of homologous chromosomes/bivalents in metaphase I; gives independent assortment of (maternal and paternal) chromosomes in anaphase; as homologous chromosomes migrate to opposite poles randomly; 223 possible gametes; non-disjunction could occur leading to diploid gametes/trisomy; random orientation in metaphase II; gives the independent assortment of chromatids in anaphase II |
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Outline how the chi-square test can be used in analyzing monohybrid crosses. (6)
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Chi squared test is used to determine whether a difference between expected and observed results is due to chance;
tests the significance of data; data must consist of discrete / discontinuous variables; between observed (O) and expected result (E); the hypothesis to be tested (the null hypothesis) is that there are no significant differences between them; (Chi-squared) = Σ x (O E)^2 / E ; example given e.g. values for O and E in cross between tall and dwarf; establish degree of freedom; statistical tables used to identify probability; critical value of 5 %; |
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Describe the inheritance of human skin colour. (5)
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characteristic caused by the combined effect of more than one gene;
example of polygenic inheritance; linked to human melanin production; skin colour shows continuous variation; phenotypes do not follow simple Mendelian ratios of dominance and recessiveness; the more loci/alleles concerned, the greater the number of phenotypic classes; giving different shades of skin colour; the environment also affects gene expression of skin colour / sunlight/UV light stimulate melanin production; the more recessive alleles there are, the lighter the skin colour; |
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Describe the relationship between genes, polypeptides and enzymes. (4)
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a. gene is a sequence of DNA bases;
b. DNA/gene codes for a specific sequence of amino acids/polypeptide; c. enzymes are proteins/composed of polypetides; d. sequence of amino acids determines tertiary structure/folding/shape of active site; e. change in the gene/mutation will affect the active site/function of an enzyme; f. enzymes are involved in replication/transcription of genes; g. enzymes are involved in synthesis of polypeptides; |
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Distinguish between the sense and antisense strands of DNA during transcription. (1)
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only the antisense strand is transcribed / the antisense strand is transcribed to mRNA and the sense strand is not transcribed/has the same base sequence as mRNA (with uracil instead of thymine)
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Compare the DNA found in prokaryotic cells (PC) and eukaryotic cells (EC). (2)
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PC = circular EC = linear
PC=in cytoplasm EC=enclosed in the nuclear membrane PC=naked EC=associated with proteins/histones PC=plasmids EC=no plasmids both prokaryotic and eukaryotic DNA consist of a double helix of (deoxy)nucleotides / phosphate, deoxyribose and base/ATC and G; |
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Outline the various stages of the cell cycle. (4)
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G1 the cell grows/duplication of organelles;
S is synthesis stage when DNA is synthesized/replicated; G2 the chromosomes begin condensing/preparation for cell division; G1 , S and G2 make up interphase; during mitosis nuclear division occurs/all four stages listed; during cytokinesis cytoplasm/cell divides/daughter cells formed; |
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Explain how an error in meiosis can lead to Down syndrome. (8)
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non-disjunction;
chromosomes/chromatids do not separate / go to same pole; non-separation of (homologous) chromosomes during anaphase I; due to incorrect spindle attachment; non-separation of chromatids during anaphase II; due to centromeres not dividing; occurs during gamete/sperm/egg formation; less common in sperm than egg formation / function of parents' age; Down syndrome due to extra chromosome 21; sperm/egg/gamete receives two chromosomes of same type; zygote/offspring with three chromosomes of same type / trisomy / total 47 chromosomes; |
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List two examples of how human life depends on mitosis.
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growth/production of (extra) body cells;
first stage of spermato/oo/gametogenesis / forming oogonia/spermatogonia; embryo development; wound healing / (tissue) repair / hair growth / replacement of skin cells; clonal selection / division of lymphocytes (for antibody production); |
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Describe the importance of stem cells in differentiation. (3)
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stem cells are undifferentiated cells;
embryo cells are stem cells; stem cells can differentiate in many/all ways / are pluripotent/totipotent; differentiation involves expressing some genes but not others; stem cells can be used to repair/replace tissues/heal wounds; |
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Outline the bonding between DNA nucleotides. (2)
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hydrogen bonds between nucleotides on opposite strands/complementary bases/adenine and thymine and cytosine and guanine;
covalent bonds between nucleotides within strands/between sugar/deoxyribose and phosphate; |
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Explain why carriers of sex-linked (X-linked) genes must be heterozygous. (2)
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carrier has (one copy of) a recessive allele;
must also have a dominant allele to prevent having the condition/disease; [2] or cannot be homozygous dominant or they would not carry the recessive allele; cannot be homozygous recessive or they would have the condition/disease; |
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State two general types of enzymes used in gene transfer.
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restriction enzymes/endonucleases
ligases reverse transcriptase |
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Outline the structure of a ribosome. (4)
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small subunit and large subunit;
mRNA binding site on small subunit; three tRNA binding sites / A, P and E tRNA binding sites; protein and RNA composition (in both subunits); |
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Outline the formation of chiasmata during crossing over. (5)
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crossing over/chiasmata formed during prophase I of meiosis;
pairing of homologous chromosomes/synapsis; chromatids break (at same point); (do not accept chromatids overlap), non-sister chromatids join up/swap/exchange alleles/parts; X-shaped structure formed / chiasmata are X-shaped structures; chiasma formed at position where crossing over occurred; chiasmata become visible when homologous chromosomes unpair; chiasma holds homologous chromosomes together (until anaphase); |
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Outline the structure of nucleosomes. (2)
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(eight) histone (proteins);
DNA wrapped around histones/nucleosome; further histone holding these together; |
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Define the term polygenic inheritance.
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character/affected/influenced/defined/determined/ controlled by two or more genes
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Explain, using a named example, how polygenic inheritance gives rise to continuous variation. (4)
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human skin colour can vary from pale to very dark / amount of melanin varies;
skin colour/melanin controlled by (alleles from) at least three/several genes; no alleles are dominant / alleles are co-dominant / incomplete dominance; many different possible combinations of alleles; skin colour controlled by cumulative effect/combination of genes/alleles; |
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Describe the inheritance of colour blindness in humans. (3)
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sex linked condition;
carried on an X chromosome / absent from Y chromosome; if present in male causes colour blindness; (allele is) recessive so heterozygous females are not colour blind; homozygous females are colour blind; |
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Explain prokaryotic DNA replication. (8)
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DNA replication is semi-conservative / each strand of DNA acts as template;
(DNA) helicase separates two strands/forms a replication fork; new strand built / nucleotides added in a 5' to 3' direction; (deoxy)nucleoside triphosphates hydrolysed to provide energy for nucleotide formation/base pairing; on one strand DNA polymerase III builds continuous strand; on other strand short chains of DNA/Okazaki fragments are formed; each short chain starts with RNA primer; added by RNA primase; then remainder of chain of DNA built by DNA polymerase III; DNA polymerase I removes RNA primer and replaces it by DNA; DNA ligase joins DNA fragments together forming complete strand; replication only occurs at a single replication fork; |
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Outline a basic technique for gene transfer involving plasmids. (6)
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gene transfer takes a gene from one species/organism and inserts it into another;
plasmid – small loops of DNA in bacteria; remove plasmid from bacteria; restriction enzyme/endonuclease cuts/cleaves (at target sequence) in plasmid; sticky ends left/made/added at ends of cut plasmid; isolate mRNA of specific gene; DNA copies made with reverse transcriptase / cut donor DNA with the same restriction enzyme; DNA ligase joins the DNA (to sticky ends) of open plasmid; (results in) recombinant plasmid; uptake/insert plasmid to (host) cell; clone cells; |
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Explain how sexual reproduction promotes variation in a species. (8)
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meiosis results in four haploid cells/gametes;
random assortment of chromosomes; in metaphase I; gives rise to variety of haploid gametes; 2n possible gametes where n is the haploid number; crossover may occur between homologous chromosomes; in prophase I; causes new combinations of genetic material/alleles; non-disjunction causes changes in chromosome numbers; infinite variety in gametes; random process of fertilization; random process of mating; new combinations even with same parents; mutation can occur in prophase I e.g. deletion / inversion / translocation; |
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Compare the structure and composition of DNA with RNA. (4)
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both are polymers of nucleotides / both nucleic acids;
sugar is deoxyribose in DNA and ribose in RNA; DNA is double stranded and RNA is single stranded; DNA has a (double) helix; DNA has thymine while RNA has uracil; both contain four nitrogenous bases / A, G, C, T for DNA and A, G, C, U for RNA; |
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Describe the characteristics of stem cells that make them potentially useful in medicine (5)
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a. (stem cells) have/retain the capacity to divide;
b. can be used to produce cell cultures/large number of identical cells; c. can be used to repair/replace damaged/lost cells/tissue; d. (stem cells) are undifferentiated / have not yet differentiated/specialized; e. can differentiate/specialize in different ways / are pluripotent/totipotent; f. can be used to form a variety of different tissues / form organs; g. used in medical research; h. used in treatment of (named) disease; |
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Explain the use of karyotyping in human genetics. (8)
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Definition and construction of karyotypes:
a. karyotype is the number and type / image of chromosomes in a cell; b. cells collected from chorionic villus / by amniocentesis; c. requires cells in metaphase / stimulate cells to divide and reach metaphase; d. burst cells and spread chromosomes / photo taken of chromosomes; e. chromosomes are arranged in pairs; f. according to size/structure/position of centromere/banding pattern; Uses for karyotypes: g. karyotypes used to identify sex/gender; h. male is XY and female XX; i. used to identify chromosome mutations/abnormal numbers/non-disjunction; j. Down syndrome due to extra chromosome 21 / other trisomy/aneuploidy example; k. used for pre-natal diagnosis of chromosome abnormalities; l. may lead to a decision to abort the fetus; m. prepare for consequences of abnormality in offspring; |
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Explain the processes that result in genetic variation in the sperm produced by an adult male. (5)
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meiosis;
independent assortment/random orientation of bivalents/pairs of chromosomes/homologous chromosomes; in metaphase I; 223/2n possible combinations (where n is the haploid number of chromosomes); crossing over / recombination of linked genes; during prophase I; can occur anywhere along a chromosome; random orientation of chromatids (in metaphase II); (gene) mutations may occur; |
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features of a homologous chromosome
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paired/formed a bivalent / tetrad / there is
crossing over between the chromosomes / they have the same genes (in the same sequence) / they are the same size and shape |
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what are recombinants of linked genes
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combinations of genes not found in parents
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Translation occurs in living cells. Explain how translation is carried out, from the initiation stage onwards. (9)
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translation involves initiation, elongation/translocation and termination;
mRNA binds to the small sub-unit of the ribosome; ribosome slides along mRNA to the start codon; anticodon of tRNA pairs with codon on mRNA: complementary base pairing (between codon and anticodon); (anticodon of) tRNA with methionine pairs with start codon / AUG is the start codon; second tRNA pairs with next codon; peptide bond forms between amino acids; ribosome moves along the mRNA by one codon; movement in 5 to 3 direction; tRNA that has lost its amino acid detaches; another tRNA pairs with the next codon/moves into A site; tRNA activating enzymes; link amino acids to specific tRNA; stop codon (eventually) reached; |
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Explain the methods and aims of DNA profiling. (8)
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DNA sample obtained;
from hair/blood/semen/human tissue; DNA amplified / quantities of DNA increased by PCR/polymerase chain reaction; satellite DNA/highly repetitive sequences are used/amplified; DNA cut into fragments; using restriction enzymes/restriction endonucleases; gel electrophoresis is used to separate DNA fragments; using electric field / fragments separated by size; number of repeats varies between individuals / pattern of bands is unique to the individual/unlikely to be shared; forensic use / crime scene investigation; example of forensic use e.g. DNA obtained from the crime scene/victim compared to DNA of suspect / other example of forensic use; paternity testing use e.g. DNA obtained from parents in paternity cases; biological father if one half of all bands in the child are found in the father; genetic screening; presence of particular bands correlates with probability of certain phenotype / allele; |
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Distinguish between RNA and DNA. (3)
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DNA is double-stranded while RNA is single-stranded;
DNA contains deoxyribose while RNA contains ribose; the base thymine found in DNA is replaced by uracil in RNA; one form of DNA (double helix) but several forms of RNA (tRNA, mRNA and rRNA); |
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Outline the consequences of a base substitution mutation. (2)
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changes triplet code/codon;
different amino acid (may be) coded for/inserted; (may) change protein/polypeptide/primary structure/sequence of amino acids / may code for a different protein; may cause sickle cell anemia/other correctly named disease / form stop codon; |
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Mendel crossed tall, round-seeded plants with short, wrinkled-seeded plants.
All F1 produced were tall, round-seeded plants. When F1 plants were crossed with other F1 plants, the F2 generation produced many more than 1/16 short, wrinkled-seeded plants. Deduce, with reasons, the inheritance of these genes. |
dihybrid cross would give 9:3: 3:1 ratio in this F2 if genes not linked;
(give credit for punnett grid showing this) therefore the genes are linked; more homozygous recessive offspring / 3:1 ratio expected if linked; |
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Explain why the process used during protein synthesis in cells is called translation. (2)
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codon/triplet of bases to amino acid;
nucleic acid / base sequence / (m)RNA to polypeptide / protein / amino acid sequence; genetic code has to be translated; |
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Explain briefly how termination of translation occurs. (2)
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stop/terminator / nonsense codon (is reached);
polypeptide is released; mRNA detaches from ribosome; subunits of ribosome separate; |