Inheritance Flashcards
Define inheritance
the transmission of genetic information from generation to generation
Define chromosomes
a thread of DNA, made up of a string of genes
Define genes
a length of DNA that is the unit of heredity and codes for a specific protein
Define allele
any of two or more alternative forms of a gene
Define haploid nucleus
a nucleus containing a single set of unpaired chromosomes (e.g. sperm and egg)
Define diploid nucleus
a nucleus containing two sets of chromosomes (e.g. in body cells)
Describe the inheritance of sex in humans (XX
and XY chromosomes)
- Egg: X chromosome
- Men: X or Y chromosome
- XX = girl, XY = boy => 50%
Define mitosis
- 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
Define meiosis
- reduction division in which the chromosome number is halved from diploid to haploid
- gametes are result. results in variation
Define genotype
genetic makeup of an organism in terms of the alleles present (e.g. Tt or GG)
Define phenotype
physical or other features of an organism due to both its genotype and its environment
Define homozygous
having two identical alleles of a particular gene .Two
identical homozygous individuals that breed together will be pure-breeding
Define heterozygous
having two different alleles of a particular gene
Define dominant and recessive
- 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
Define continuous variation
influenced by genes and environment, resulting in a range of phenotypes between two extremes
Define discontinuous variation
caused by genes alone and results in a limited number of distinct phenotypes with no intermediates
Define mutation
- 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
Down syndrome
- Cause: Trisomy 21 (3 copies of chromosomes 21) when there’s a fault in meiosis
Describe sickle cell anaemia, and explain its
incidence in relation to that of malaria
- 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
Outline the effects of ionising radiation and
chemicals on the rate of mutation
Rate is increased. Ultra violet radiation, X-rays and gamma rays are the most damaging
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
- IA and IB are codominance
- IO is recessive to both
- When codominance => both alleles are expresses in the phenotype
Define natural selection
The greater chance of passing on of genes by the best adapted organisms
Importance of natural selection as a possible mechanism for evolution
Competition for resources => only those with advantageous phenotypes are more likely to feed/survive => stay alive => breed and pass on genes => evolution
Describe the development of strains of antibiotic resistant bacteria as an example of natural selection
- Bacteria exposed to an antibiotic most are killed. Some are resistant due to mutation => survive => reproduce and pass on genes for offsprings
Describe the role of artificial selection in the production of varieties of animals and plants
- 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
Define genetic engineering
taking a gene from one species and putting it into another species
Explain why, and outline how, human insulin
genes were put into bacteria using genetic engineering
- 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
