DNA & inheritance Flashcards
What is a gene
section of DNA that contains a specific sequence of bases which code for a specific protein
- length of DNA determines single characteristic of an organism
- unit of inheritance
Mutation
sudden change in DNA of an organism
Gene mutation
change in structure of a gene
Chromosome mutation
change in number / structure of chromosome
Sickle cell anaemia
gene that codes haemoglobin undergoes mutation to produce abnormal haemoglobin
- less soluble
- tends to stick together
- distort RBC ; sickle-shaped ( half moon )
- cannot transport oxygen
- may block small capillaries ; larger diameter
- destruction of sickle cells causes severe form of anemia
Albinism
body can no longer produce melanin pigment
- white hair
- very light-coloured skin
- pink eyes
Down’s Syndrome
- 24 chromosomes instead of 23 in ovum
- child will have 47 chromosomes instead of 46
- slow physical & mental development
- broad flat face
- shorter life span
- extra chromosome in 21st group ; 3 instead of 2
Mutagens
agents increasing mutation rate
- change structure of gene ; altering the way it works
Examples of mutagens
- chemicals : mustard gas & tar from cigarette smoke
- high energy radiation : X-rays & UV light
Significance of mutations
main source of genetic variation ; new alleles of genes produced
Other causes of variation
- meiosis
- random mating between organisms
- random fertilisation of gametes