Inheritance Flashcards
Content • The Passage of Information from Parent to Offspring • The Nature of Genes and Alleles, and their Role in Determining the Phenotype • Monohybrid Crosses • Variation • Natural and Artificial Selection
explain the terms dominant, recessive, codominant, phenotype and genotype
- dominant allele: expresses itself & gives the same phenotypes in both the homozygous & heterozygous conditions
- recessive allele: does not express itself in the heterozygous condition, express only in homozygous condition
- co-dominance: results when the 2 alleles controlling a trait both express themselves in the organism
- phenotype: refers to expressed trait in an organism, for eg, the outwards appearance of an organism
- genotype: is the genetic make-up (airs of alleles) of an organism, that is, the combination of genes in an organism
explain why observed ratios often differ from expected ratios
- small sample size
- ratio figures are based on chance & probabilities
key headings for genetic diagrams
- phenotypes of parents
- genotypes of parents
- gametes
- offspring genotypes
- offspring phenotypes
explain co-dominance with examples
- co-dominance occurs when 2 alleles controlling a specific trait are both expressed in an organism
- in blood grouping, the allele for blood type A is co-dminant to the allele for blood type B
- if a homozygous individual for blood type A has an offsrpng with a homozygous individual with blood type B, the offspring will have both the A and B alleles resulting in AB blood type
- so the offspring will have both antigens A & B and no antiboodies for blood type A or B
explain mutiple alleles
~ is a term used for a gene that exist in more than 2 alleles
eg, occurence of blood group
- IA & IB are dominant over IO
define mutation & describe the examples
mutation: sudden, random change in the structure of gene or in chromosme number, eg:
Sickle-cell anaemia:
- where the gene mutation results in the change in the structure of the gene (a change in sequence of bases or nucelotides in DNA)
- mutated gene produces haemoglobin S(HbS), a change in 3D shape of haemoglobin
- HbS molecules clump tgt, making cell sickle-shaped
- when oxygen conc in blood decreases, RBCs become sickle-shaped which interfers with the oxygen-carrying capacity of the RBCs and makes them fragile
down’s syndrome:
- normally, zygotes with extra chromosomes would fail to develop
- offspring of 2 normal parents might get an extra copy of chromosome 21, they have 47 chromosomes
- the older the mother, the higher the chances that copies of chromosome 21 will not separate during gamete formation
factors increasing rate of mutation
mutagenic agents/mutagens
- ultraviolet light, and alpha, beta & gamma radiations
- chemicals present in certain concentrations such as tar & formaldehyde(in cigarette smoke), lysergic acid diethylamide(LSD)
describe the difference between continuous and discontinuous variation and give examples of each
- DV: deals with a few clear-cut phenotypes, CV: deals with a range of phenotypes
- DV: controlled by 1 or a few genes, CV: controlled by many genes
- DV: genes do not show additive effect, CV: genes show additive effect
- DV: relative unaffected by environmental condition, CV: greatly affected by environmental conditions
variation & competition
- In natural selecttion, nature select those varieties that are more competitive, more resistant to diseases & better adapted to changes in env, to survive & reproduce their kind
- the other varities that are susceptible to diseases or environmental changes may die
- mutation provides new genes or alleles (variations) for natural selection to operate on
- hence, variation and competition lead to differential survival of, and reproduction by, those organisms best fitted to the environment
examples of environmental factors that act as forces of natural selection
- food shortage
- diseases
- predation
explain the role of natural selection as a possible mechanism for evolution
- more beneficial quaitites may accumulate in a species over the years
- the new breed of organisms may be better adapted to their new env
- hence, evolution happened
examples of artificial selection - selective breeding
- breeding of soya bean plants: breeders want seeds that have high oil content - analyse seeds & select plants that produce seeds with high oil content
- cows that produce plenty of milk & good meat are selected & used as female parents for the next generation - breeders mate cows with desirable traits with a bull that has known required traits so that they are more likely to obtain the desirable gene combi
artificial vs natural selection
NS: selection occurs when natural environmental conditions change
while
AS: humans select the varieties of organism that suit their needs
NS: varieties produced by mutations
while
AS: varieties are produced by selective breeding