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Evolution in population

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1 Evolution in population
by: Courtney okoyeocha

2 Genetics joins evolutionary theory
In the 1900s researcher discovered that changes in the genes and chromosomes create variation. In natural selection, variation is an important part because natural selection acts directly on phenotypes. In a population some organisms have better traits then others giving them a better fitness or chance of survival and reproduction, leaving them and their offspring with the same traits in the population.

3 Populations and gene pools
A population shares a gene pool. It contents all the genes and different alleles for each gene in a population. Allele frequency is the number of times an allele occurs in a gene pool, compared to the total number of alleles in that pool for the same gene. Evolution, in genetic terms, involves a change in the frequency of alleles in a population over time.

4 Source of genetic variation
Three sources of genetic variation are: Mutations- the change in the phenotype may or may not affect fitness. Genetic Recombination in Sexual Reproduction- crossing-over during meiosis increases the number of new genotypes created in each generation. Lateral gene transfer- passing over of genes to another individual that isn’t its offspring, even if their from different species. The number of phenotypes produced for a trait depends on how many genes control the trait.

5 How natural selection works
Natural selection on single-gene traits can lead to changes in allele frequencies resulting in chances in phenotype frequencies. Natural selection on polygenic traits can affect the relative fitness of phenotypes and thereby produce one of three types of selection.

6 Genetic drift In small populations, individuals that carry a particular allele may leave more descendants than others, just by chance. Over time, a series of chance occurrences can cause an allele to become more or less common in a population is called genetic drift. The bottleneck effect is when just by chance there’s a disaster and a change in allele frequency followed a dramatic reduction in the size of a population. A severe bottleneck effect can sharply reduce a population’s genetic diversity. The founder effect is when a species colonize a new habitat and just by chance carry different allele frequencies and therefore creates a new gene pool.

7 Evolution versus genetic equilibrium
Genetic equilibrium is when a population doesn’t evolve. Gene shuffling during sexual reproduction produces many gene combinations by themselves they don’t change allele frequencies. Hardy-Weinberg produced a principle that predicts allele frequencies for populations like Punnett squares predicts for an individual. The hardy-Weinberg principle predicts that nonrandom mating, small population size( immigration or emigration), mutations, or natural selection can disturb genetic equilibrium and cause evolution.

8 Isolating Mechanisms When a population splits and stop interbreeding those gene pools can’t spread to the other. Because they don’t interbreed anymore this is called reproductive isolation. When populations become reproductively isolated, they can evolve into two separate species. Reproductive isolation can develop as behavioral, geographic, and temporal isolation. When there is a new formation of species it is called speciation.

9 Molecular clock Researchers uses a molecular clock that uses mutation rates in DNA to estimate the time that two species have been evolving separately. neutral mutations, that have no effect on phenotypes, tend to accumulate in the DNA of different species at the same rate. Researchers can compare this and determine how many mutations have occurred independently in each group. The more DNA sequences that differs between species, the more time has on since both species shared a common ancestor.

10 Gene Duplication One way new genes evolve is through duplication and then modification of existing genes. During meiosis in the process of crossing-over unequal swapping of DNA can occur. A part of a gene can be duplicated to an entire genome. Gene duplication can produce gene families. Group of related genes that produces similar, yet slightly different proteins. Sometimes, extra copies of a gene undergo mutations that changes its function. The new gene evolves without affecting the original copy and function.

11 Click to
Miller & Levine biology book

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