Topic 4 Flashcards

Question 1

Q

Which property of the genetic code allows the transfer of genetic material between species? A. Helical B. Degenerate C. Universal D. Non-overlapping

Answer

A

C. Universal

Question 2

Q

Which techniques of recombinant DNA technology (genetic engineering) require the use of plasmids? I. Gene therapy II. DNA profiling III. Gene transfer by gene cloning A. I and II only B. II and III only C. I and III only D. I, II and III (answer not here)

Answer

A

Answer is III Only, which is not listed

Question 3

Q

Which mating represents a test cross? (T is the dominant allele and t is the recessive allele.)

A. Tt x tt

B. tt x tt

C. TT x Tt

D. Tt x Tt

Answer

A

A. Tt x tt

Question 4

Q

Which response summarises meiosis?

Question 5

Q

Which inheritance traits are shown by ABO blood groups?

I. Sex-linkage

II. Codominance

III. Multiple alleles

A. I and II only B. I and III only C. II and III only D. I, II and III

Answer

A

C. Codominance and Multiple Alleles

Question 6

Q

A father is heterozygous for blood group A while the mother is heterozygous for blood group B. What is the probability of a child being born with the motherís blood group?

A. 0.00 B. 0.25 C. 0.50 D. 0.75

Question 7

Q

What is a clone? A. A group of organisms which could interbreed and produce fertile offspring B. A group of cells descended from two parent cells C. A group of organisms of the same species living together and interbreeding D. A group of organisms with identical genotype

Answer

A

D. A group of organisms with identical genotype

Question 8

Q

The diagram below is a karyotype of a human. Which statement about the karyotype is correct? A. Non-disjunction has occurred and the individual is female. B. Non-disjunction has not occurred and the individual is female. C. Non-disjunction has occurred and the individual is male. D. Non-disjunction has not occurred and the individual is male.

Answer

A

C. Non-disjunction has occurred and the individual is male.

Question 9

Q

What is the locus of a gene? A. The characteristics that a gene determines B. All the alleles of a gene C. The position of a gene on a chromosome D. The site of translation of a gene

Answer

A

C. The position of a gene on a chromosome

Question 10

Q

The pedigree chart below shows the inheritance of blood groups in a family. What blood group(s) could the children have?

A. Type A only

B. Type A or B only

C. Type A or B or AB only

D. Type A or B or AB or O

Answer

A

C. Type A or B or AB only

Question 11

Q

When red shorthorn cattle are crossed with white shorthorn cattle the offspring are roan, a colour that has both red and white hairs. What does this cross illustrate?

A. Co-dominance

B. Multiple alleles

C. Sex linkage

D. Mutation

Answer

A

A. Co-dominance

Question 12

Q

What is the name of the process used to copy and amplify minute quantities of deoxyribonucleic acid?

A. DNA profiling

B. Gel electrophoresis

C. Genetic screening

D. Polymerase chain reaction (PCR)

Answer

A

D. Polymerase chain reaction (PCR)

Question 13

Q

Which enzymes are needed to produce recombinant plasmids that are used in gene transfer?

A. DNA polymerase and ligase

B. DNA polymerase and restriction enzymes

C. Restriction enzymes and ligase

D. Helicase and restriction enzymes

Answer

A

C. Restriction enzymes and ligase

Question 14

Q

Explain the use of two named enzymes in biotechnology.

Answer

A

Examples and application: pectinase; obtained from citrus fruits / tomatoes / apples; used in fruit juice production; breaks down pectin allowing cells to separate; assisting in juice formation; juice formed is clear; high juice yield using enzyme; 2nd enzyme: name; source; use; mode of action; advantage of using enzyme; details of enzyme use; [8 max] Possible second example could be meat tenderising – papain from papaya fruit / bromelain from the pineapple plant, biological washing powders – amylases / proteases / lipases, glucose biosensors – glucose oxidase / peroxidase, cheese making – rennin, high fructose syrups – glucose isomerase, breadmaking – fungal amylases / fungal proteases, DNA profiling – DNA ligase, etc.

Question 15

Q

The following is a DNA gel. The results are from a single probe showing a DNA profile for a man, a woman and their four children.

Which fragment of DNA is the smallest?

A. I

B. II

C. III

D. IV

Question 16

Q

What is the initial purpose of sequencing the human genome?

A. To determine the order of genes in a chromosome

B. To determine the number of genes in the nucleus

C. To determine the order of bases in DNA

D. To determine the type of chromosomes in offspring

Answer

A

C. To determine the order of bases in DNA

Question 17

Q

A couple has four children whose blood types are A, B and AB. What is the likely combination of the parents’ genotypes?

A. I^Ai and I^Bi

B. I^Ai and I^BI^B

C. I^Bii and ii

D. I^Ai and ii

Answer

A

A. I^Ai and I^Bi

Question 18

Q

Which information is used when constructing a karyotype?

I. Size of chromosomes

II. Position of the centromere of the chromosome

III. DNA content of the chromosome

A. I only

B. II only

C. I and II only

D. I, II and III

Answer

A

C. I and II only

Question 19

Q

The amount of DNA in a haploid cell of an organism can be represented by X. What would be the quantity of DNA in a cell from the same organism at the start of meiosis?

A. 0.5X

B. X

C. 2X

D. 4X

Question 20

Q

A parent organism of unknown genotype is mated in a test cross. Half of the offspring have the same phenotype as the parent. What can be concluded from this result?

A. The parent is heterozygous for the trait.

B. The trait being inherited is polygenic.

C. The parent is homozygous dominant for the trait.

D. The parent is homozygous recessive for the trait.

Answer

A

A. The parent is heterozygous for the trait.

Question 21

Q

(b) Outline the differences between the behaviour of the chromosomes in mitosis and meiosis. [5]

Answer

A

two divisions in meiosis, only one in mitosis; meiosis results in haploid cells, mitosis in diploid cells; crossing over only occurs in meiosis; no S phase precedes meiosis II; chromosome behaviour in meiosis II and mitosis is similar / chromosome behaviour in meiosis I and mitosis is different; chiasmata only form during meiosis; homologous chromosomes move to the equator in pairs only in meiosis; [5 max] Do not accept number of cells produced - it is a result not a behaviour.

Question 22

Q

What causes Downís syndrome?

A. Non-disjunction in the formation of sex cells

B. Random alignment of chromosomes in the formation of sex cells

C. Gene mutation in the formation of sex cells

D. Crossing over in the formation of sex cells

Answer

A

A. Non-disjunction in the formation of sex cells

Question 23

Q

What is a test cross used for?

A. To determine if two individuals belong to the same species.

B. To identify the presence of dominant alleles.

C. To identify the presence of recessive alleles.

D. To test the viability of offspring.

Answer

A

C. To identify the presence of recessive alleles.

Question 24

Q

Which combination of parents could produce children with all of the different ABO blood types?

A. A x B

B. B x O

C. A x AB

D. A x A

Question 25

Q

What feature in a family pedigree chart would suggest that a trait is sex-linked?

A. Numbers of offspring affected by the condition increased over several generations.

B. Girls only inherit the trait from their mothers.

C. Equal numbers of males and females show the trait.

D. One gender was more commonly affected than the other.

Answer

A

D. One gender was more commonly affected than the other.

Question 26

Q

Which of the following terms best describes the failure of chromosomes to separate during meiosis?

A. Codominance

B. Trisomy

C. Crossing over

D. Non-disjunction

Answer

A

D. Non-disjunction

Question 27

Q

A woman of blood group AB marries a man of blood group A, whose father was blood group O. What is the probability that their child will have blood group B?

A. 0 %

B. 25 %

C. 50 %

D. 100 %

Question 28

Q

In addition to blood typing, which of the methods below could be used to determine paternity?

A. PCR

B. DNA profiling

C. Cloning

D. Karyotyping

Answer

A

B. DNA profiling

Question 29

Q

Which of the following correctly identify the most common end products of mitosis and meiosis?

Answer

A

A. mitosis produces 2 diploid cells while meiosis produces 4 haploid cells

Question 30

Q

What are chromosomes with the same size, banding pattern, centromere location but with different alleles called?

A. Sister chromatids

B. Homologous chromosomes

C. Autosomes

D. Daughter chromosomes

Answer

A

B. Homologous chromosomes

Question 31

Q

Which statement explains Mendel’s law of segregation?

A. Genes segregate independently so that one gamete receives one gene independently of the other gamete receiving the other gene.

B. Homologues randomly align during metaphase.

C. Alleles are inherited together.

D. Alleles separate so that half the gametes receive one allele and the other half of the gametes receive the other allele.

Answer

A

D. Alleles separate so that half the gametes receive one allele and the other half of the gametes receive the other allele.

Question 32

Q

(b) Outline DNA profiling (genetic fingerprinting), including one way in which it has been used. (8)

Answer

A

DNA profiling: [4 max] sample of DNA / blood / saliva / semen is obtained; reference samples of DNA are obtained; PCR used to amplify / produce more copies of the DNA; DNA broken into fragments by restriction enzymes; DNA fragments are separated by gel electrophoresis; DNA separated into a series of bands; bands compared between different DNA samples; if pattern of bands is the same then DNA is (almost certainly) from same source; if some bands are similar then individuals are (almost certainly) related; specific example: [1 max] testing of paternity / forensics / classification / archeology / another specific example;

Question 33

Q

Karyotyping involves arranging the chromosomes of an individual into pairs. Describe one application of this process, including the way in which the chromosomes are obtained. (5)

Answer

A

application of karyotyping: [2 max] find gender / test for Down’s syndrome / other chromosome abnormality; identify sex chromosomes / numbers of chromosome 21 / other chromosomes counted; XX=female and XY=male / third chromosome 21 indicates Down’s syndrome / other chromosome abnormality (e.g. Klinefelter’s syndrome); obtaining chromosomes: [3 max] fetal cells obtained from amniotic fluid/amniocentesis / other named source; white blood cells obtained; cells encouraged to divide ; cells accumulated / blocked in metaphase; prepare slide / chromosomes examined;

Question 34

Q

Outline two examples of the commercial application of enzymes in biotechnology. [6]

Answer

A

the name of the enzyme and the substrate; the name(s) of the product(s); a statement as to why the application is useful commercially; Award [3 max] per example. e.g. pectinase acts on (soluble) pectin; produces smaller, more soluble carbohydrates; used in fruit juice clarification/to increase yield; e.g. endonuclease DNA acts on DNA; produces DNA fragments; used in genetic engineering; e.g. protease acts on (insoluble) proteins; produces amino acids; washing powders – stain removal; [6 max] Accept any other suitable examples.

Question 35

Q

Discuss the potential benefits and possible harmful effects of genetic modification. [7]

Answer

A

named example of desired outcome e.g. herbicide resistance; Award [6 max] if no named example given. Award [5 max] if both possible benefits and possible harmful effects are not addressed. Possible benefits: [4 max] benefits include more specific (less random) breeding than with traditional methods; faster than traditional methods; some characteristics from other species are unlikely in the gene pool / selective breeding cannot produce desired phenotype; increased productivity of food production / less land required for production; less use of chemicals (e.g. pesticides); food production possible in extreme conditions; less expensive drug preparation; e.g. pharmaceuticals in milk; human insulin engineered so no allergic reactions; may cure genetic diseases; Possible harmful effects: [4 max] some gene transfers are regarded as potentially harmful to organism (especially animals); release of genetically engineered organisms in the environment; can spread and compete with the naturally occurring varieties; some of the engineered genes could also cross species barriers; technological solution when less invasive methods may bring similar benefits; reduces genetic variation/biodiversity;

Question 36

Q

If a person inherited an allele with the same base substitution mutation from both parents, what sequences could be altered from normal in the person’s cells.

A. One mRNA base sequence only

B. Two mRNA base sequences only

C. One mRNA base sequence and one polypeptide amino acid sequence only

D. Two mRNA base sequences and two polypeptide amino acid sequences only

Answer

A

C. One mRNA base sequence and one polypeptide amino acid sequence only

Question 37

Q

What is Mendel’s Law of Segregation?

A. Alleles of a gene become separated from each other during gamete formation.

B. The number of chromosomes in a cell is halved during meiosis.

C. Male and female gametes are kept apart at the time of fertilization.

D. F1 and F2 plants must be grown separately during crossing experiments.

Answer

A

A. Alleles of a gene become separated from each other during gamete formation.

Question 38

Q

Hemophilia is caused by an X-linked recessive allele. In the pedigree shown below which two individuals in the pedigree must be carriers of hemophilia?

A. I-1 and II-1

B. I-4 and II-2

C. II-1 and II-2

D. III-2 and III-3

Answer

A

A. I-1 and II-1

Question 39

Q

A single gene in humans causes blood to be either rhesus positive (dominant allele) or rhesus negative (recessive allele). A woman with rhesus negative blood has already had a child with rhesus positive blood. There could be complications during pregnancy if she has another child with rhesus positive blood. What is the probability of this, if the father is the same, and if his mother is known to have rhesus negative blood?

A. 25 %

B. 50 %

C. 75 %

D. 100 %

Question 40

Q

DNA profiling involves the technique of gel electrophoresis. What is separated by this technique?

A. Plasmids from different bacteria

B. Chromosomes of different types

C. Pieces of DNA of different length

D. Mixtures of DNA and protein

Answer

A

C. Pieces of DNA of different length

Question 41

Q

What features must a group of humans have for them to be described as a clone?

I. Identical genes

II. Identical intelligence

III. Identical behaviour

A. I only

B. I and II only

C. I and III only

D. I, II and III

Answer

A

A. I only

Question 42

Q

What is a sex-linked gene?

A. A gene whose locus is on the X chromosome only.

B. A gene whose locus is on the X or Y chromosomes.

C. A gene whose locus is on the both X and Y chromosomes.

D. A gene whose locus is on the Y chromosome only.

Answer

A

B. A gene whose locus is on the X or Y chromosomes.

Question 43

Q

What happens during the first division of meiosis?

A. Alleles for a gene are separated.

B. Identical haploid cells are formed.

C. Diploid cells showing genetic variation are formed.

D. Alleles for a gene fuse.

Answer

A

A. Alleles for a gene are separated.

Question 44

Q

The pedigree chart below shows the inheritance of a genetic disease in a family. What is the nature of the allele that causes this disease?

A. Dominant and sex linked

B. Dominant and non-sex linked

C. Recessive and sex linked

D. Recessive and non-sex linked

Answer

A

B. Dominant and non-sex linked

Question 45

Q

What permits gel electrophoresis to separate fragments of DNA?

A. Differences in the sizes of DNA fragments only

B. The number of negative charges on the fragments only

C. The net charge (negative or positive) on the fragments only

D. The size and the net charge (positive or negative) on the fragments

Answer

A

D. The size and the net charge (positive or negative) on the fragments

Question 46

Q

Which characteristics are used to identify chromosomes when constructing a karyotype?

I. The length of the chromosome.

II. The position of the centromere on the chromosome.

III. The pattern of bands on the chromosome.

IV. The position of the chromosome on the spindle.

A. I only

B. I and II only

C. I, II and III only

D. I, II, III and IV

Answer

A

C. I, II and III only; The length of the chromosome, The position of the centromere on the chromosome, The pattern of bands on the chromosome.

Question 47

Q

What is always a difference between the alleles of a gene?

A. Their position on the chromosome

B. Their amino acid sequence

C. The number of codons that each contains

D. Their base sequence

Answer

A

D. Their base sequence

Question 48

Q

Which of the following conditions has been treated by gene therapy?

A. Emphysema

B. SCID

C. Coronary heart disease

D. Colon cancer

Question 49

Q

Hypophosphataemia is a disorder involving poor re-absorption of phosphate from glomerular filtrate in humans. It shows a sex-linked dominant pattern of inheritance as illustrated in the following pedigree.

Which row in the table correctly identifies the genotypes of individuals 1 and 2?

Question 50

Q

Individual 2 marries an unaffected male. What is the probability that they will have an affected child?

A. 0 %

B. 25 %

C. 50 %

D. 100 %

Question 51

Q

Why is it possible for a gene from one organism to be introduced and function in a different organism?

A. All organisms are made of cells.

B. All organisms have nuclei.

C. The genetic code is universal.

D. All organisms have ribosomes.

Answer

A

C. The genetic code is universal.

Question 52

Q

Outline the ethical issues of cloning humans. [6]

Answer

A

clones are genetically identical individuals / cell lines / tissues; risks to society: cloning mammals is expensive/allocation of resources; cloning could lead to copying selected individuals / equity concerns; could lead to uncontrolled / unethical eugenics; risks to individuals: many cloned animals die soon after birth / die from complications / premature aging of clones; cloned humans could experience identity crises/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 being unnatural/against their religion; cloning occurs naturally when identical twins form; benefits: cloning humans may help to provide tissues/organs for transplantation; research in cellular mechanisms/developmental biology/possible medical breakthroughs;

Question 53

Q

Outline how the process of meiosis can lead to Down’s Syndrome. [4]

Answer

A

Accept any of the points below if clearly drawn and correctly labelled in a diagram. in metaphase homologues in centre of cell / spindles attached; homologues are separating; one pair doesn’t separate/ non-disjunction; in telophase cells divide into two; cells have either one more/one less chromosome; can occur in second division of meiosis; sister chromatids fail to separate; fertilization with one gamete / sperm / egg carrying extra chromosome; Down’s syndrome is trisomy of chromosome 21;

Question 54

Q

Discuss the advantages and disadvantages of genetic screening for chromosomal and genetic disorders. (8)

Answer

A

genetic screening is testing for the presence or absence of gene/chromosome; screening for chromosomes can involve karyotyping; genetic screening is controversial; advantages: [4 max] parents can choose to avoid having children with disorder; parents can prepare for a child with a disorder; parents can use IVF to select embryos that are normal; can use gene therapy to correct the problem; treatment can start to prevent symptoms; fewer children with the disorder are born; disadvantages: [4 max] frequency of abortion can increase; parents can select embryos for sex of the child; can have harmful side effects such as depression if you know you will develop a disorder later; can create a genetic underclass; health insurance / treatment can be denied if there is genetic predisposition;

Question 55

Q

Describe the technique for the transfer of the insulin gene using E. coli. [6]

Answer

A

mRNA is extracted; DNA copy of RNA is made using reverse transcriptase; plasmids are cut open with endonucleases (at specific sequences); insulin gene and plasmid are mixed together; addition of “sticky ends” to the DNA copy (so that it will combine with the cut plasmid); DNA ligase will seal the plasmid; recombinant plasmid is inserted into E. coli; E. coli is cultured; E. coli begins to make insulin;

Question 56

Q

What are the components of a eukaryotic chromosome?

A. One DNA molecule and one large protein

B. Many DNA molecules and many proteins

C. One DNA molecule and many proteins

D. Many DNA molecules and one large protein

Answer

A

C. One DNA molecule and many proteins

Question 57

Q

What is a karyotype?

A. Maternal and paternal autosomes arranged in pairs.

B. Chromosomes arranged in pairs according to the number of their genes.

C. Chromosomes arranged in pairs according to their size and shape.

D. Chromosomes arranged in pairs according to their size.

Answer

A

C. Chromosomes arranged in pairs according to their size and shape.

Question 58

Q

What is the cause of sickle cell anemia?

A. Errors in the translation of mRNA

B. A base substitution mutation in DNA

C. A transcription error that replaces A with U

D. A mutation that leads to glutamic acid instead of valine

Answer

A

B. A base substitution mutation in DNA

Question 59

Q

What is the relationship between Mendel’s law of segregation and meiosis?

A. Only one of a pair of alleles appears in a gamete.

B. The separation of “paternal” and “maternal” chromosomes shows no pattern.

C. Gametes contain all dominant or all recessive alleles.

D. Variation only results from two divisions.

Answer

A

A. Only one of a pair of alleles appears in a gamete.

Question 60

Q

What are the possible applications of DNA profiling?

I. Solving paternity suits

II. Aiding certain criminal investigations

III. Identifying people who died last century

A. I only

B. I and II only

C. II and III only

D. I, II and III

Answer

A

D. I, II and III

Question 61

Q

What is gene therapy?

A. Removing non-functioning genes

B. Replacing defective alleles in some cells

C. Replacing defective chromosomes in all cells

D. Inhibiting the expression of chrosomes that cause some disorders

Answer

A

B. Replacing defective alleles in some cells

Question 62

Q

Outline the process of meiosis. [6]

Answer

A

two cell divisions / reduction-division / diploid to haploid / meiosis I and meiosis II; produce four (haploid) cells; for production of sex cells/gametes/spores; daughter cells are different from parent cells; homologous chromosomes / two chromatids pair up; line-up on equator; (spindle fibres) pull homologous chromosomes to opposite poles; two haploid cells are formed; second division/like mitosis, separates chromatids to opposite poles; [6 max] Accept any of the above points if clearly explained in a labelled diagram

Question 63

Q

Which of the following represents a test cross to determine if phenotype T is homozygous or heterozygous? (note: allele T is dominant to allele t.)

A. Phenotype T crossed with another phenotype T

B. Phenotype T crossed with a phenotype T which is homozygous

C. Phenotype T crossed with a phenotype T which is heterozygous

D. Phenotype T crossed with phenotype t

Answer

A

D. Phenotype T crossed with phenotype t

Question 64

Q

Which of the following blood group phenotypes always has a homozygous genotype?

A. A

B. B

C. AB

D. O

Answer 54

A

B. Its nucleus is replaced by the nucleus of the differentiated cell.

Answer 55

A

C. Gel electrophoresis

Answer 56

A

B. To determine the nucleotide sequence of all human chromosomes

Answer 57

A

gene/sequence of nucleotides that controls a (specific) characteristic/trait; gene can be inherited; gene mutation is change in a gene; change of base sequence; examples of gene mutation such as substitution;

Answer 58

A

name of organism that was genetically modified; source of the DNA / gene used to modify organism; effect of the gene / characteristic coded for by the gene; benefit/reason for wanting the recipient to be given this characteristic; detail about benefit; another benefit; detail about another benefit; possible harmful effect; detail of possible harmful effect; another possible harmful effect; detail of another possible harmful effect; reference to gene transfer between species being a natural process (with viral vectors); uncertainty about long-term effect; [8 max] e.g. wheat / maize / other crop plant; Salmonella typhimurium; resistance to glyphosate / roundup herbicide; allows use of herbicide on growing crop; higher yield due to less weed competition; weeds that are very similar to the crop plants can be controlled; gene for glyphosate resistance might be transmitted to weeds; uncontrollable superweeds might be produced; foreign DNA in the crop plant might cause allergies in humans; fewer weeds for wildlife that feed on them; N.B.: Examiners may want to check reliable resources to verify details of

Answer 59

A

D. A point where homologous chromosomes remain in contact during meiosis.

Answer 60

A

A. S, P, Q, R

Answer 61

A

C. SsYy and ssyy

Answer 62

A

A. Genes carried on the same chromosome

Answer 63

A

B. 4 cells each with 6 chromosomes

Answer 64

A

B. Child 2

Answer 65

A

C. 1:1:1:1, in which 50 % are tall, 50 % dwarf, 50 % pink and 50 % white

Answer 66

A

D. The number of Ab gametes will be greater than the number of ab gametes.

Answer 67

A

C. Polynucleotides

Answer 68

A

D. When non-linked genes show independent assortment and when linked genes show crossing over

Answer 69

A

A. X^HX^h, X^HX^H, X^HY, X^hY

Answer 70

A

C. I^Ai and I^Bi

Answer 71

A

D. Aabb, aaBb

Answer 72

A

C. The independent separation of alleles of different genes

Answer 73

A

homologous chromosomes form tetrads / bivalents/pairs / undergo synapsis; crossing over; during prophase I; exchange of DNA/genes/alleles between (non-sister) chromatids / chromosomes; description / diagram of chiasma; new combinations of maternal and paternal genes / alleles / DNA; bivalents/homologous chromosomes orient/align themselves on equator randomly; during metaphase I; orientation of one homologous pair of chromosomes is independent of others; homologous chromosomes separate/move to opposite poles; independent assortment(of unlinked genes); leads to n 23 2 / 2 possible gametes (without crossing over); additional variation when chromatids separate in second division;

Answer 74

A

Arguments against cloning [3 max]: reduces the value / dignity of the individual / causes psychological problems; high miscarriage rates / cloned individuals are likely to have developmental disorders/health problems / cloned individuals may show premature aging; costly process and money could be better spent on other types of healthcare; cloning may be done for inappropriate motives/replace lost loved one/perfect race etc.; Arguments for cloning [3 max]: identical twins are formed by cloning so it is a natural process; cloned embryos can be tested for genetic disease / genetic screening; increased chance of children for infertile couples; cloning research may lead to spin-offs for other research areas such as cancer/transplant research/regeneration research;

Answer 75

A

B. Human skin colour

Answer 76

A

B. They have the same phenotypes.

Answer 77

A

A Polygenic inheritance

Answer 78

A

gene is a heritable factor / unit of inheritance; gene is composed of DNA; gene controls a specific characteristic / codes for a polypeptide/protein; allele is a form of a gene; alleles of a gene occupy the same gene locus/same position on chromosome; alleles differ (from each other) by one / a small number of base(s) / base pair(s);

Answer 79

A

multiple alleles means a gene has three or more alleles / more than two alleles; ABO blood groups / other named example of multiple alleles; ABO gene has three alleles / equivalent for other example; I^AI ^B and i shown (at some point in the answer) / equivalent for other example; Accept other notation for alleles if clear. any two of these alleles are present in an individual; homozygous and heterozygous genotype with phenotypes (shown somewhere); all six genotypes with phenotypes given (shown somewhere); example / diagram of a cross involving all three alleles;

Answer 80

A

linked genes occur on the same chromosome / chromatid; genes (tend to be) inherited together / not separated/do not segregate independently; non-Mendelian ratio / not 9:3:3:1 / 1:1:1:1; real example of two linked genes; Award [1] for each of the following examples of a cross between two linked genes. key for alleles involved in the example of a cross; homozygous parental genotypes and phenotypes shown; genotype and phenotype shown / double heterozygote genotype and phenotype; F1 possible genotypes and phenotypes shown; F2 recombinants identified; recombinants due to crossing over; in prophase I of meiosis; diagram / explanation of mutual exchange of parts of chromatids during crossing over;

Answer 81

A

A. If a particular gene is present or not.

Answer 82

A

D. I, II and III

Answer 83

A

pair of genes on same chromosome; do not follow expected ratio in cross between heterozygous parents; more offspring with parental characteristics; genes tend to be inherited together; P genotype shown; P phenotype stated; gametes; F genotype; 1 F phenotype; 1 gametes; F genotype; 2 F phenotype; 2 e.g. L= long wings l= short wings R= red eyes r= white eyes P L L R R l l r r ; long wing red eyes x short wings white eyes; Gametes L R l r ; F 1 L l R r ; 100 % long wings, red eyes; Gametes L R and l r ; F 2 L l R r L L R R l l r r ; 75 % long wings, red eyes 25 % short wings white eyes; [8 max] Award [6 max] if the example of the genes is not correct but the rest of the outline is carried through correctly. i.e. the example of genes chosen are not linked but the rest of the outline is correct. Linkage notation is expected for points in the markscheme where it is shown.

Answer 84

A

example of co-dominance; multiple alleles/3 alleles; (phenotype) 0 has (genotype) ii; A can be AA A II Ii or ; B can be BB B II Ii or ; AB is A B I I ; (P are) A A ii I I × ; (gametes) i and A I ; ( F genotype) 1 A I i ; ( F phenotype) blood group A; 1 [5 max] Accept other notations if used consistently and if phenotype and genotype are clearly distinguished.

Answer 85

A

gene carried on sex chromosome / X chromosome / Y chromosome; inheritance different in males than in females; males have only one X chromosome therefore, only one copy of the gene; mutation on Y chromosome can only be inherited by males; women can be carriers if only one X chromosome affected; example of sex linked characteristics (e.g. hemophilia / colour blindness); example of cross involving linkage;

Answer 86

A

D. Homologous chromosomes

Answer 87

A

A. Test-cross

Answer 88

A

B. Trisomy 21

Answer 89

A

B. The seven different pairs of alleles behaved as if they were on different chromosomes.

Answer 90

A

more than one gene controls/affects one characteristic; Reject more than 2 alleles can cause continuous variation / many different possible phenotypes; e.g. skin colour / other valid example; allele of each gene promotes melanin production or not / other valid example; e.g. grain colour in wheat / other valid example; allele of each gene promotes pigment production or not / other valid example; [5 max] If first or second example is incorrect do not accept third or subsequent examples.

Answer 91

A

Mitosis Meiosis one cell division two divisions / reduction division; chromosome number does not change (do not award mark for diploid cells produced as mitosis can occur in haploid cells) converts diploid to haploid cells; products genetically identical products genetically diverse; separation of sister chromatids in anaphase separation of homologous chromosomes in anaphase I and sister chromatids in anaphase II; no crossing over crossing over in prophase I; no formation of tetrads / no synapsis formation of tetrads / synapsis; produce cells for growth / tissue repairs / asexual reproduction produce sexual cells / gametes for sexual reproduction; two cells produced four cells produced; daughter cells with both copies of chromosomes/random assortment does not occur; random assortment of maternal / paternal chromosomes (provides genetic diversity); replication of DNA in interphase replication in interphase I; four phases: prophase, metaphase, anaphase, telophase same four phases twice;

Answer 92

A

B. Some genes on the X chromosome are absent from the Y chromosome.

Answer 93

A

A. I and II only

Answer 94

A

B. Random chromosome assortment

Answer 95

A

C. The inheritance may be polygenic.

Answer 96

A

(law of segregation) states that for a pair of alleles, each gamete receives only one of the alleles; meiosis has two divisions; cells go from diploid to haploid; (law of independent assortment) states that the segregation of alleles of one gene is independent of the segregation of the alleles of another gene; alleles of a gene are carried on homologous chromosomes; homologues line-up at metaphase I; homologues of one chromosome line-up independently of homologues of other chromosomes at metaphase I; homologues separate at anaphase I ; homologues of different chromosomes separate randomly at anaphase I ; haploid cells have a random assortment of homologues; only unlinked genes (or genes that are far apart on the chromosome) assort independently;

Answer 97

A

genetic screening: testing an individual for the presence/absence of a gene; advantages: [4 max] individuals can see if they are carriers of a gene before they have children; fewer children with genetic disease; lower long-term health costs; frequency of harmful alleles reduced; allows early diagnosis of disease; treatment can start for disease; prepare parents emotionally/financially for affected children; plant/animal breeders can screen plants/animals for desired traits; disadvantages: [4 max] risk of false negative/false positive; increase in abortion; against religious beliefs; cost to administer; can discriminate against people / selection of genetic traits; deny health insurance; if diagnosed with genetic disease can lead to emotional problems;

Answer 98

A

use reverse transcriptase on mature mRNA to make DNA; cut plasmid with restriction enzymes; sticky ends added to donor DNA; place plasmid and DNA together; use DNA ligase to splice them together; place plasmids within E. Coli; test uptake with antibiotics; culture E. Coli with recombinant plasmids;

Answer 99

A

B. Karyotyping

Answer 100

A

A. When A antigens and B antigens are present on red blood cells.

Answer 101

A

D. TS, ts

Answer 102

A

advantages: [5 max] genetic screening is the testing of an individual for the presence/absence of a particular gene/allele; fewer children born with abnormalities / named genetic disorders; parents can prepare for special needs of the child when it is born / early diagnosis leads to more effective treatment; may help parents decide for an abortion; positive step in evolution of human species as deleterious alleles become less common; advanced notice allows more informed life choices; confirmation of animal pedigrees; disadvantages: [5 max] may increase rates of abortion; some tests give probability of disease rather than certainty; false positives / false negatives; advanced notice may create psychological issues; may be abused by employers/insurance companies / privacy issues / immigration disputes; ethical issues associated with gender/“ideal” phenotype/eugenics; [7 max] Award [5 max] if only advantages or disadvantages are discussed.

Answer 103

A

D. Two chromosomes with the same set of genes, in the same sequence, sometimes with different alleles

Answer 104

A

D. 1 × normal wings, normal body : 1 × normal wings, ebony body : 1 × vestigal wings, normal body : 1 × vestigal wings, ebony body

Answer 105

A

B. Genes carried on the same chromosome

Answer 106

A

A. I and II only

Answer 107

A

A. 4 cells, each with 8 chromosomes

Answer 108

A

C. The male is heterozygous.

Answer 109

A

D. The life expectancy of children produced by cloning might be lower than normal.

Answer 110

A

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; [6 max] Award credit for any of the above points in clearly drawn and correctly labelled diagram.

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