Genetics and inheritance Flashcards
A breeder crossed a black male cat with a black female cat on a number of occasions. The female cat produced 8 black kittens and 4 white kittens.
Explain the evidence that the allele for white fur is recessive.
(1 mark)
- Parents are heterozygous
- Kittens recieve white allele from parents/ black cat
A cat breeder expects an equal no. of 2 types of kittens. Explain why the actual numbers were different from those expected.
(1 mark)
- Offspring ratios are a probablitly
- Gametes may not be produced in equal numbers
- Random fusion of gametes
- Small sample
Explain what is meant by codominant alleles
(1 mark)
- Both alleles are equally expressed within the phenotype
Explain what is meant by the term phenotype
(2 marks)
- Expression due to genetic constitution
- Due to environment
Males are more likely than female to show a phenotype produced by a recessive allele carried on the X chromosome. Explain why
(2 marks)
- Males only have 1 allele
- Females need 2 recessive alleles
Explain how a substitution mutation leads to the formation of a non-functioning enzyme
(3 marks)
- Change in amino acid sequence
- Change in hydrogen/ ionic/ disulphide bonds alters tertiary structure
- Substrate not compementary/ cannot bind to active site
Describe how alterations to tumour supressor genes can lead to the development of tumours
(3 marks)
- Increased methylation of TSG
- Mutation
- Tumour supressor genes are not transcribed
When the queation asks about “alterations” you must specify the alteration (mutation)
Papaya plants reproduce sexually by means of seeds. Papaya plants grown from seeds are very variable in their yield. Explain why.
(2 marks)
- Independant segregation
- Random fertilisation
Explain the advantage of growing plants from tissue culture rather than from seeds
(1 mark)
- All plants will have desired characteristics
Describe the method used to find the mean no. of capillaries per mm^2 of samples of heart muscle tissue
(4 marks)
- Measure diameter of field of view and calculate area
- Using micrometer slide and eyepiece graticule
- Count no. of capillaries in large no. of fields of view and calculate mean
- Select fields of view randomly
Always mention how to improve validity
Define what is meant by epigenetics
(2 marks)
- Heritable chnages in gene function
- Without changes to base sequence of DNA
Explain how increased methylation could lead to cancer
(3 marks)
- Methyl groups added to a tumour supressor gene
- The transcription of tumour supressor genes is inhibited
- Leading to uncontrolled cell division
Give one way in which benign tumours differ from malignant tumours
(1 marks)
Cells of benign tumours cannot metastasise
(1 mark)
Explain how the methylation of tumour supressor genes can lead to cancer
(3 marks)
- Methylation prevents transcription of gene
- Protein not produced that prevents cell division
- No control of mitosis
Explain how an activated oestogen receptor affects the target cell
(2 marks)
- Receptor/ transcription factor binds to promoter which stimuates RNA polymerase
- Transcribes gene
Describe 2 ways in which both malignant and benign tumours may cause harm to the body
(2 marks)
- May damage organ concerned
- May cause blockages/ obstructions
- May damage/ exert pressure on other organs
(Max 2)
Suggest why people with a family history of no cancer are at a greater risk of cancer than those with no family history of cancer
(1 mark)
- Cancer has genetic component/ may have inherited gene which gives predisposition to cancer
Describe he role of 2 named types of enzymes used to insert DNA fragments into plasmids
(2 marks)
- Restrtictionj endonuclease to cut plasmid/ vector
- DNA ligase to join gene to plasmid/ vector
2 mark question means little detail but it’s imortant to remeber its hydrolysis and condensation
Suggest and explain how delayed insertion of a gene could produce offspring of a transgenic species without the desired characteristic
(2 marks)
- Cell division has occured before the gene is added
- Gametes fo not recieve the gene
What is a DNA probe
(2 marks)
- Short single strand of DNA
- Bases complementary with gene/ DNA
During genetic screening, the DNA is treated to form single strands. Explain why.
(1 mark)
So DNA probe binds
Explain the role of reverse transcriptase in reverse transcriptase PCR
(1 mark)
Produces (c)DNA using (m)RNA
Explain the role of DNA polymerase in PCR
(1 mark)
Joins nucleotides to produce complementary strands of DNA
In recombinant DNA technology, an insect gene is inserted into plant DNA. The plant is able to synthesise the insect protein.
Explain why this is possible.
(3 marks)
- Genetic code is universal/ triplets in DNA always code for the same amino acid
- Insect DNA can be transcribed
- Can be translated
Name the type of enzyme used to produce the cDNA
(1 mark)
Reverse transcriptase
Recombinant gene tech question
Explain the purpose fo attaching a gene that codes for a protein that glows green under florescent light.
(2 marks)
- Acts as a marker gene to show that the gene has been expressed
- Only implant cells that show fluoresence
Suggest one reason why very few live birhs result from embryos implanted to produce transgenic animals
(2 marks)
- Mutation/ DNA may be damaged
- May interfere with gene expression
Explain how electrophoresis seperates fragments of DNA
(2 marks)
- Move towards anode
- Different rates of movement related to charge
Explain why radioactive DNA probes are used to locate specific DNA fragments
(2 marks)
- DNA invisible on gel
- Allows detection
Explain why the DNA of different species shows difference in base sequence
(2 marks)
- Different genes (due to mutations), base sequence determines protein
- Different species have different protein structures
The length of replicated DNA fragments is different for each species. Explain why this is important in identifying the species involved.
(3 marks)
- Electrophoresis separates DNA
- So they can be identified by position on gel
- Smaller/ shortest fragments travel furthest
Describe the polymerase chain reaction
(6 marks)
- Heat DNA
- Breaks H bonds/ seperates strands
- Add primers
- Add nucleotides
- Cool
- (to allow) binding of nucleotides/ primers
- DNA polymerase
- Joins nucleotides together
- Repeat cycle many times
