✨Module 6: Patterns of inheritance Flashcards
(27 cards)
What is a gene?
Sections of DNA within the genome that contain instructions to code for proteins. Contain individual characteristics like eye colour.
How many chromosomes do humans have?
22 pairs of numbered chromosomes (autosomes) and one pair of sex chromosomes (XX or XY).
Define phenotype.
Observable characteristics of an organism like height.
Define genotype.
The alleles it has.
Difference between continuous and discontinuous variation?
Continuous - no distinct categories, due to genetic and environmental variation, controlled by lots of genes (polygenic), e.g. animal mass, skin colour. Quantitative.
Discontinuous - distinct categoric differences, due to mostly genetic variation, controlled by 1 or 2 genes (monogenic), e.g. blood group. Qualitative.
Homozygous means …
Heterozygous means …
2 allele copies are identical in an individual. AA
2 allele copies are different in an individual. Aa
Dominant means …
Recessive means …
Alleles always expressed in phenotype.
Allele only expressed in phenotype if no dominant allele is present.
What is phenotypic variation?
Difference in phenotypes between organisms of same species. Phenotype = Genotype + Environment
Explain why variation in phenotype due to genetics is inherited but the variation in phenotype due to environmental factors is not.
Genetic variation directly affects the DNA of the gametes but variation in phenotype caused by the environment does not.
What is the gene pool?
Complete range of alleles in a population.
Define species.
Group of similar organisms that can reproduce to give fertile offspring.
Describe how natural selection works.
- Individuals within a population vary because they have different alleles. New alleles are usually generated by mutations in genes.
- Predation, disease and competition create a struggle for survival. Because individuals vary, some are better adapted to the selection pressures than others.
- Individuals that have an allele that increase their chance of survival are more likely to survive, reproduce and pass on the advantageous allele.
- Frequency of the advantageous allele increases from generation to generation.
Without a selection pressure, natural selection won’t take place.
How does natural selection occur in a STABLE environment?
Occurs when environmental conditions stay the same any new characteristic is selected against. This is called stabilising selection and results in low diversity/phenotypes.
How does natural selection occur in a changing environment?
Individuals with phenotypes suited to new conditions survive and pass on genes. This is called directional selection. This produces a gradual change in allele frequencies over generations.
What other 3 factors affect the evolution of a species?
Genetic drift
Genetic bottleneck
Founder effect
What is evolution by genetic drift?
Gradual change in allele frequencies in a small population due to chance, rather than environmental factors. By chance, the allele for one genotype is passed on to the offspring more often than others. So the number of individuals with that allele increases. Overtime, some alleles can be lost or favoured purely by chance.
Evolution by genetic drift has a greater effect on smaller populations. In large populations, genetic drift is less likely to have an effect and natural selection has a bigger role in evolution.
What is the genetic bottleneck?
Where a catastrophic event dramatically reduces the size of population, decreasing the variety of alleles in the gene pool. The surviving individuals end up breeding and reproducing with close relatives, which reduces genetic diversity.
What is the Founder effect?
Where a small number of individuals become isolated, forming a new population with a limited gene pool. This can happen as a result of migration. The individuals that migrate and the alleles they carry is completely up to chance.
Similarities and differences between the Founder effect and bottlenecking.
Sim: initially genetic diversity is lost in both systems, both involve a small number of closely related individuals breeding with each other.
Diff: in bottlenecks individuals are killed, reducing the choice for mates. In founder effect, individuals are ecologically separated.
What is speciation?
The evolutionary process where populations diverge and become distinct species. When two populations of the same species become reproductively isolated from each other, they can eventually become genetically isolated. Because the groups of species don’t reproduce, they don’t interchange genes with each other in the production of offspring. The genetic make up changes so the 2 groups can no longer interbreed so have become separate species.
Difference between allopatric and sympatric speciation?
Allopatric - speciation resulting from physical barrier like a river. No genetic exchange.
Sympatric - speciation in the same area resulting from a non-physical barrier like a mutation that no longer allows 2 organisms to produce fertile offspring.
What is artificial selection?
Humans choose particular organisms to breed together to produce a desired characteristic/phenotype in the offspring. This is selective breeding. They need to repeat the selective breeding process over many generations.
E.g. plant seeds that produce larger fruit and veg, cows with higher milk yield are selectively bred.
Ethical issues to artificial selection.
=> Anatomical changes in animals e.g. respiratory issues in brachycephalic dogs.
=> Higher susceptibility to disease in both plants and animals.
What are some characteristics selected for in dairy cows?
=> High milk yield.
=> Calm temperament.
=> Resistance to mastitis and other diseases.
