Variation and Inheritance

Question 1

What does heterozygous mean?

Answer 1

• if the two alleles for a particular gene are different

Question 2

What type of allele is polydactyly caused by?

Answer 2

• a dominant allele

Question 3

How are embryos screen for alleles that cause disorders?

Answer 3

• DNA is isolated from the embryo’s cells
• a gene probe is produced that will bind to the allele for a specific disorder
• the probe is also labelled so that it can be detected. it is usually a fluorescent chemical that can be seen when UV light is shone
• the probe is added to a mixture containing the DNA sample from the embryo. if the embryo’s DNA contains the allele for the disorder. the probe will bind to it
• UV light is then shone onto the sample, if it has the disorder, it will be glowing

Question 4

What are the pros of GM crops?

Answer 4

• GM crops can increase the yield of a crop, making more food
• GM crops may help developing nations who lack nutrients. e.g. golden rice
• GM crops are being grown outside of UK with no problems

Question 5

What are the cons of GM crops?

Answer 5

• it will affect the number of weeds and flowers, and so the population of insects. reduces farmland biodiversity
• they may not be safe, or people may develop allergies
• transplanted genes may get out into the natural environment, e.g. herbicide resistance gene may create a superweed

Question 6

What shape is DNA and what is the structure?

Answer 6

• shape of a double helix
• two strands are held together by chemicals called bases
• the order of bases decides the order of amino acids in a protein

Question 7

What are the pros of cloning?

Answer 7

• ideal offspring
• lead to a greater understanding of the development of embryo, ageing and age-related disorders
• help preserve endangered species

Question 8

Why do organisms of the same species have differences?

Answer 8

• genetic variation
• environmental variation
• both

Question 9

What is asexual reproduction?

Answer 9

• no fusion of gametes and only one individual is needed as the parent.
• there is no mixing of genetic information and so no genetic variation in the offspring.
• these genetically identical individuals are known as clones

Question 10

What is a dominant allele?

Answer 10

• an allele that controls the development of a characteristic when it is present on only one of the chromosomes

Question 11

How can plants be cloned?

Answer 11

• by tissue culture: a few plant cells are put in a growth medium with hormones and they grow into new plants, clones of the parent plant
• these plants can be made very quickly, in very little space and be grown all year

Question 12

How many pairs of chromosomes are there in every human body cell?

Answer 12

• 23 pairs

Question 13

What are the arguments for embryonic screening?

Answer 13

• it will help to stop people suffering
• treating disorders cost the Government and taxpayers a lot of money
• there are laws to stop it going too far. parents can’t even choose the sex of their baby

Question 14

What is a recessive allele?

Answer 14

• an allele that controls the development of a characteristic one if the dominant allele is not present

Question 15

What are the arguments against embryonic screening?

Answer 15

• it implies that people with genetic problems are undesirable, leading to prejudice
• in the future, maybe everyone will want to screen embryos for a desirable baby
• screening is expensive
• for embryos in the womb, it could lead to termination
• screening is not 100% accurate
• taking cells from embryos in the womb increase the chance of a miscarriage

Question 16

What is DNA?

Answer 16

• stands for deoxyribonucleic acid
• contains coded information
• found in the nucleus of animal and plant cells in really long molecules called chromosomes

Question 17

How can you use embryo transplants to make animal clones?

Answer 17

• sperm cells taken from a prize bull and egg cells from a prize cow
• the sperm are then used to artificially fertilise an egg cell.
• the embryo that develops is then spit many times before any cells become specialised
• these cloned embryos can then be implanted into lots of other cows where they grow into baby calves, genetically identical

Question 18

What does homozygous mean?

Answer 18

• if an organism has two alleles for a particular gene that are the same

Question 19

What is a gene?

Answer 19

• a gene is a section of DNA

- each gene codes for a particular combination of amino acids which are put together to make a specific protein

Question 20

What are alleles?

Answer 20

• Different forms of the same gene

Question 21

What are the cons of cloning?

Answer 21

• you get a reduced gene pool, meaning there are fewer different alleles in the population. a disease could wipe out everything, as there is no allele giving resistance
• cloned animals might not be as healthy
• humans may be clones in the future, unsuccessful attempts may mean there are severely disable children born

Question 22

What are GM crops?

Answer 22

• genetically modified crops are crop plants that have had their genes modified e.g. to make them resistant to viruses, insect attacks or herbicides

Question 23

What is adult cell cloning?

Answer 23

• taking an unfertilised egg cell and removing its genetic material (the nucleus)
• a complete set of chromosomes from an adult body cell (e.g. skin cell) is inserted into the empty egg cell
• the egg cell is then stimulated by an electric shock, making it divide like a normal embryo
• when the embryo is a ball of cells, it is implanted into an adult female, to grow into a genetically identical copy of an original adult body cell

Question 24

What is Down’s Syndrome caused by?

Answer 24

• inheritance of an extra chromosome

- 47 instead of 46

Question 25

What is genetic engineering?

Answer 25

• a useful gene is cut from one organism’s chromosome using enzymes
• this gene is inserted into a vector, usually a virus or a bacterial plasmid
• the vector is then used to insert the gene into a different organism, or into the chromosome of the different organism. the DNA is used to make a protein

Question 26

What type of sickle cell anaemia is polydactyly caused by?

Answer 26

• a recessive allele

- less likely to get malaria if you carry the sickle-cell allele (heterozygous Aa)

Question 27

What type of allele is cystic fibrosis caused by?

Answer 27

• a recessive allele

Question 28

What is sexual reproduction?

Answer 28

• the joining (fusion) of male and female gametes. the mixture of the genetic information from two parents leads to variety in the offspring