Module 6.2 - Patterns Of Inheritance Flashcards
Define sex linkage
When a gene is present on one of the sex chromosomes
Define autosomal linkage
When 2 or mor genes on the same chromosome are inherited together
They do not undergo independent assortment (metaphase 1)
Ratios
3:1 for two genes - autosomal linked and no crossing over
Non 9:3:3:1 with 4 phenotypes for 2 genes - autosomal linked with crossing over
Define phenotype
Appearance of a characteristic
Define genotype
Genetic makeup of an organism (influences phenotype)
Continuous variation
No defined categories/distinct groups Range - any value is possible Polygenic (caused by more than one gene) Often caused by environment Quantitative
Discontinuous variation
Defined categories
Monogenic (caused by one gene)
Genes at different loci may interact to influence one characteristic and cause discontinuous variation (epistasis)
No/very little environmental effects cause it
Qualitative
Define deletion
Part of a chromosome is lost
Define inversion
Section of a chromosome breaks off and rotates 180° and then rejoins
Genes still present but may be too far from regulatory genes to be expressed
Define translocation
Section of one chromosome breaks off and attaches to another chromosome
May interfere with regulatory genes
Define duplication
A piece of a chromosome may be duplicated causing over expression of the gene
Define non-disjuntion
One pair of chromosomes or chromatids fail to separate during meiosis generating gametes with an extra chromosome
Conditions for Hardy Weinberg
Large population
Random mating
No selective advantage for any genotype
No gene mutation, migration or genetic drift
What is stabilising selection?
Occurs when organisms’ environment doesn’t change
Favours intermediate phenotypes over extremes
Reduces variation in a population
What is directional selection?
Occurs when environment changes
Favours a new/extreme phenotype
Causes a change in population mean phenotype
Define genetic drift
Random changes in allele frequency in small populations
Why does genetic drift happen in small populations?
Each individual forms a larger proportion of the gene pool and therefore has a greater effect on the gene pool
It is all easier to ‘lose’ a gene from a small gene pool
Describe genetic bottleneck (genetic drift)
An event rapidly reduces the numbers of a population
Some alleles are lost from the population at random
Genetic variation is reduced
Describe the founder effect
Small number of individuals from an original larger population establish a new population
Some alleles are lost from the population at random
Genetic variation reduced
Define speciation
The splitting of a population into 2 isolated populations that over time undergo genetic changes which result in reproductive isolation and therefore the formation of two different species
Geographical isolation
Leads to allopatric speciation
Populations are physically separated
Barrier prevents gene flow between populations
Genetic changes occur in species (caused by genetic drift, mutations or natural selection due to different pressures in different areas)
Populations become so genetically different they can no longer interbreed to produce fertile offspring
Reproductive isolation
Leads to sympatric speciation
Can be caused by: behavioural changes; biological changes; genetic changes
Define artificial selection
Selective breeding of organisms in order to produce desired phenotypes in an organism (often beneficial to humans)
Stages of artificial selection
Male and female with desired characteristic chosen
Male and female interbred
Best offspring selected and interbred
This is repeated over many generations
Why is genetic material maintained in selective breeding?
Selective breeding tends to reduce the gene pool (so if there was a rapid environmental change the organisms would not have the variation to survive)
What are gene banks?
Used to maintain a source of alleles for future breeding
Can counteract the loss in genetic variation, inbreeding and extinction
Can preserve currently unknown useful traits alleles (e.g. medicinal uses)
Can be seed/sperm/egg/embryo banks, rare breed farms, botanic gardens, zoos
Points about inbreeding
As genetic diversity decreases with each generation, individuals become more related (inbred)
Likelihood of unintentionally selecting 2 copies of a harmful recessive allele can increase in a small gene pool
Can lead to increased susceptibility to disease
To avoid this, breeders can ‘outcross’ individuals with their wild types (or individuals from gene banks) to prevent the gene pool becoming too small
Ethical considerations of selective breeding
Often doesn’t take into account animal welfare (inbreeding can increase susceptibility to disease)
Many domesticated animals would not survive if released into the wild (easy prey, wrong fat:muscle ratio to survive in cold)