Inheritance

Question 1

Define inheritance

Answer 1

the transmission of genetic information from generation to generation

Question 2

Define chromosomes

Answer 2

a thread of DNA, made up of a string of genes

Question 3

Define genes

Answer 3

a length of DNA that is the unit of heredity and codes for a specific protein

Question 4

Define allele

Answer 4

any of two or more alternative forms of a gene

Question 5

Define haploid nucleus

Answer 5

a nucleus containing a single set of unpaired chromosomes (e.g. sperm and egg)

Question 6

Define diploid nucleus

Answer 6

a nucleus containing two sets of chromosomes (e.g. in body cells)

Question 7

Describe the inheritance of sex in humans (XX

and XY chromosomes)

Answer 7

• Egg: X chromosome
• Men: X or Y chromosome
• XX = girl, XY = boy => 50%

Question 8

Define mitosis

Answer 8

• nuclear division giving rise to genetically identical cells in which the chromosome number is maintained
• roles: growth, repair of damaged tissues, replacement of worn out cells and asexual reproduction

Question 9

Define meiosis

Answer 9

• reduction division in which the chromosome number is halved from diploid to haploid
• gametes are result. results in variation

Question 10

Define genotype

Answer 10

genetic makeup of an organism in terms of the alleles present (e.g. Tt or GG)

Question 11

Define phenotype

Answer 11

physical or other features of an organism due to both its genotype and its environment

Question 12

Define homozygous

Answer 12

having two identical alleles of a particular gene .Two

identical homozygous individuals that breed together will be pure-breeding

Question 13

Define heterozygous

Answer 13

having two different alleles of a particular gene

Question 14

Define dominant and recessive

Answer 14

- an allele that is expressed if it is
present 
- an allele that is only expressed
when there is no dominant allele of the gene
present

Question 15

Define continuous variation

Answer 15

influenced by genes and environment, resulting in a range of phenotypes between two extremes

Question 16

Define discontinuous variation

Answer 16

caused by genes alone and results in a limited number of distinct phenotypes with no intermediates

Question 17

Define mutation

Answer 17

• a change in a gene or chromosome => leads to variation

- cause: damage to DNA or failure in the copying process that occurs before nuclear division

Question 18

Down syndrome

Answer 18

• Cause: Trisomy 21 (3 copies of chromosomes 21) when there’s a fault in meiosis

Question 19

Describe sickle cell anaemia, and explain its

incidence in relation to that of malaria

Answer 19

• An inherited disease
• The gene for haemoglobin exists in 2 forms: HbN and HbS.
• HbSHbS = people who have the disease and experience fatigue and pains in joints
• RBC are misshaped => not as flexible and will block up blood vessels => cannot get oxygen
• Relation to malaria:
  + Protect against malaria
  + Natural selection

Question 20

Outline the effects of ionising radiation and

chemicals on the rate of mutation

Answer 20

Rate is increased. Ultra violet radiation, X-rays and gamma rays are the most damaging

Question 21

Explain codominance by reference to the inheritance of ABO blood groups – phenotypes, A, B, AB and O blood groups and genotypes IA , IB , and IO

Answer 21

• IA and IB are codominance
• IO is recessive to both
• When codominance => both alleles are expresses in the phenotype

Question 22

Define natural selection

Answer 22

The greater chance of passing on of genes by the best adapted organisms

Question 23

Importance of natural selection as a possible mechanism for evolution

Answer 23

Competition for resources => only those with advantageous phenotypes are more likely to feed/survive => stay alive => breed and pass on genes => evolution

Question 24

Describe the development of strains of antibiotic resistant bacteria as an example of natural selection

Answer 24

• Bacteria exposed to an antibiotic most are killed. Some are resistant due to mutation => survive => reproduce and pass on genes for offsprings

Question 25

Describe the role of artificial selection in the production of varieties of animals and plants

Answer 25

• Humans choose a feature of animal/plant to improve
• Animals/plant showing these features are bred to produce the next generation
• Process = selective breeding
  => economy improved

Question 26

Define genetic engineering

Answer 26

taking a gene from one species and putting it into another species

Question 27

Explain why, and outline how, human insulin

genes were put into bacteria using genetic engineering

Answer 27

• Safer to use human insulin because less risk of rejection, more cost-effective, and less risks of diseases from animals
• The gene that codes for production of insulin is identified and remove it from the rest of the DNA using endonuclease enzyme
• Plasmid (a circular piece of DNA) is removed from a bacterium
• The endonuclease opens the plasmid
• The human insulin making gene is put into the plasmid using ligase
• The plasmid is placed back into the bacterium => asexual reproduction