Patterns Of Inheritance Flashcards
Define phenotype
The observable characteristics of an organism
How can meiosis bring about genetic Variation ?
- Random arrangement of chromosomes during lining up
- Crossing over of chromatids before the first division
How does random fertilisation bring about genetic variation ?
Gametes are haploid, meaning they only contain half of a persons DNA. As this is determined by meiosis, every gamete contains different DNA. Therefore the same two individuals can produce genetically different offspring
Define mono genetic inheritance
Where one phenotypic characteristic is controlled by a single gene
Define dihybrid inheritance
Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at same time
What is meant by sex-linkage ?
Where an allele is located on one of the sex Chromosomes, meaning its expression depends on the sex of the individual
What is meant by multiple alleles ?
A gene with more than two alleles
What is meant by codominant alleles ?
Two dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the characteristics appearing together
What is meant by autosomal linkage ?
Where two or more genes are located on the same (non-sex) chromosome. In this case, only one homologous pair is needed for all four alleles to be present. For genes that aren’t linked, two homologous pairs are needed
What is meant by epistasis ?
Where two non-linked genes interact, with one gene either masking or suppressing the other gene
What is the chi-squared test ?
A statistical test to find out whether the difference between observed and expected data is due to chance or a real effect. Can be used to compare expected phenotypic ratios with observed ratios
How is the chi-squared test performed ?
The formula results in a number, which is then compared to a critical value (for the corresponding degrees of freedom) . If the number is greater than or equal to the critical value, we conclude there is no significant difference and the results occurred due to chance
How can the number of genes coding for a characteristic influence variation ?
- Discontinuous Variations = Characteristic determined by one gene, influenced by only genetics
- Continuous variation = Characteristics determined by more than one gene, influenced by both environment and genetics
What is stabilising selection ?
Occurs when environmental conditions stay the same. Individuals closest to the mean are favoured, and any new characteristics are selected against. Resulting in low genetic diversity
What is directional selection ?
Occurs when environmental conditions change. Individuals with phenotype suited to the new conditions will survive and pass on their genes. Over many generations majority of the population have this characteristic
What is genetic drift ?
A change is the populations allele frequencies that occur due to chance rather than selective pressures.
What is meant by a genetic bottleneck ?
Where a catastrophic event dramatically reduces the size of a population, thereby decreasing the variety of alleles in the gene pool and causing large changes in allele frequencies, e.g Natural disaster
What is meant by the founder effect ?
When a small number of individuals become isolated, forming a new population with a limited gene pool, with allele frequencies not reflective of the original population
What is the Hardy-Weinberg principle ?
Allows us to estimate the frequency of alleles in a population, as well as if allele frequency is changing over time
Explain the Hardy-Weinberg equation for calculating allele frequency
The frequencies of each allele for a characteristic must add up to 1.0. The equation is: p+q=1
Where p= Frequency of dominant allele and
q= frequency of recessive allele
Explain the Hardy-Weinberg equation for calculating genotype frequency
The frequencies of each genotype for a characteristic must add up to 1.0. The equation is therefore; p^2+2pq+q^2=1
Where p^2= Frequency f homozygous dominant
2pq= frequency of heterozygous, and q^2= frequency o homozygous recessive
Define speciation
Where a population is split and isolated, there are different selective pressures on the two groups. If the genetic makeup changes to the extent the two groups can no longer interbreed, they have become separate species
What is meant by allopatric speciation ?
Speciation resulting from a physical barrier e.g. river, mountain range. The environments occupied by two groups are different, and therefore different alleles are favoured.
What is sympatric speciation ?
Speciation resulting from a non-physical barrier e.g. a mutation that no longer allows two organisms to produce fertile offspring. Any changes in anatomy or behaviour may also prevent breeding
