6.2 Patterns of Inheritance and Variation Flashcards
What is chlorosis ?
When leaves look pale or yellow because cells are not producing the normal amount of chlorophyll.
What causes chlorosis ?
Lack of light
Mineral deficiencies
Virus infections
What is a genotype ?
Alleles expressed on the gene.
What is a phenotype ?
Alleles that are expressed as a characteristic.
What is a dominant allele ?
Version of gene that is always expressed if present.
What is a recessive allele ?
Only expressed if it is homozygous recessive.
What is homozygous alleles ?
2 identical alleles for a characteristic.
What is heterozygous alleles ?
2 different alleles for a characteristic.
What is continuous variation ?
Characteristic that has a value within a range Eg., height, weight
What is discontinuous variation ?
Characteristic that only appears in specific values.
What is monogenic inheritance ?
Inheritance of a single gene is shown.
What is codominance ?
when 2 different alleles occur for a gene.
What are sex linked genes ?
Characteristics are determined by genes on the sex chromosomes.
What is dihybrid inheritance ?
Used to show the inheritance of 2 genes and this is known as dihybrid inheritance.
What is the ratio for dihybrid crosses ?
9:3:3:1
Why do ratios differ significantly from those expected ?
Due to linkage meaning genes are located on the same chromosome.
What is autosomal linkage ?
When genes that are linked are found on one of the other pairs of chromosomes.
How are linked genes inherited ?
Inherited as one unit, there is no independent assortment during meiosis unless alleles are separated by chiasmata.
What are recombinant offspring ?
Offspring that have different combination of alleles than either parent.
What is the recombination frequency ?
Measure of the amount of crossing over that has happened in meiosis.
How to work out recombinant frequency ?
Number of recombinant offspring / total number of offspring.
What does recombinant frequency of 50% state ?
Indicates that there is no linkage and the genes are on separate chromosomes. Less than 50% indicates there is gene linkage and independent assortment is hindered.
What is Chi squared ?
Statistical test that measures the size of difference between results you observe and those expected.
Does observed value have to be greater than or less than to be significant ?
Equal to or greater than to be significant so small probability it is down to chance.
How to work out degrees of freedom ?
n-1
(n= number of catagories)
What is dominant epistasis ?
Occurs if a dominant allele results in a gene having an effect on another gene.
What is epistasis ?
Interaction of genes at different loci. Gene regulation is a form of this, with regulatory genes controlling activity of structural genes.
Example of epistasis in Labradors ?
B - black
b - brown
But this is only case if it has dominant gene for fur, F.
What is evolution ?
Change in inherited characteristics of a group of organisms over time. Occurs due to changes in frequency of different alleles within a population.
Factors affecting evolution ?
Mutation, sexual selection, gene flow, genetic drift and natural selection.
What is population genetics ?
Investigates how allele frequencies within populations change over time.
What factors affect size of populations ?
Density-dependent factors such as competition and predation.
Density-independent factors such as climate change, natural disasters, seasonal change and human activities.
What is the founder effect ?
Extreme example of genetic drift. Establishment of new colonies by a few isolated individuals.
What is stabilising selection ?
Norms are selected for and extremes are selected against. Therefore, results in a reduction in frequency of alleles at extremes and increase in frequency of average alleles.
What is directional selection ?
Occurs when there is change in the environment and the normal phenotype is no longer the most advantageous.
What is disruptive selection ?
Extremes are selected for and the norm is selected against.
What is speciation ?
Formation of a new species through process of evolution.
What leads to speciation ?
Members of population are isolated, alleles undergo random mutations and accumulation of mutations lead to large changes in phenotype.
What is allopatric speciation ?
Happens when some members in a population are separated from rest of group by a physical barrier. Eg, finches on Galapagos islands.
What is sympatric speciation ?
Occurs within population that share the same habitat. Less frequent and more common in plants. Occurs when members of different species interbreed and form fertile offspring.
What are reproductive barriers ?
Prezygotic barriers prevent fertilisation but postzygotic barriers are produced as a result of hybridisation.
What are polymorphic populations ?
They display more than one distinct phenotype for most characteristics.
What is artificial selection ?
Same as natural selection but changes in environment leading to survival of fittest due to selective breeding of farmers.
Problems caused by inbreeding ?
Limits gene pool, causes genetic disorders and results in offspring more likely to be homozygous recessive.
What are gene banks ?
Store biological samples that are usually frozen.
