Ncea Level2 Bio- Variation And Change

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Heredity

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Members of a species typically live in a populations and so share a common gene.

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Genetic Pool/ Gene Pool

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The total amount of genetic material (alleles) of the population of a species.

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Genetic Variation

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These variations are due to slight differences in the genetic variation between individuals within a population.

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Importance of Variation

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Variation helps the survival of a species. If there is a change in food supply or climate, or if a new disease develops, variation increases the likelihood that some members of a species will survive the new conditions. When the survivors reproduce, the population, and therefore the species will continue to exist, and this will lead to natural selection.

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Sexual Reproduction

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Produces a new mix of alleles, because meiosis gives unique gametes and fertilization (fusion of parent gametes) it is random chance which sperm fertilizes the egg.

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Meiosis

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A process where a single cell divides twice to produce four cells containing half the original amount of gametic information. These cells are sex cells.

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Mutation and

Natural Selection

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Involves the environment selecting for/ against certain phenotypes. These "better adapted" phenotypes will have a better chance of survival and produce offsprings carrying the "beneficial" allele. This is how mutations can become more frequent within a population if they are beneficial to the individual.

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Gene Flow

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Any movement of genes from one population to another and is an important source of genetic variation. As individuals immigrate and emigrate between populations they can bring new alleles which can alter the frequency of alleles in a particular gene pool.

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Independent Assortment

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Independent assortment occurs when the homologous pairs line up in random order during Metaphase of Meiosis. It is chance which ends of the cell each chromosomes goes to. Each daughter cell will end up with a random arrangement of chromosomes and alleles.

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Crossing Over

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Alleles that are on the same chromosomes are linked, since they are inherited together. However, linked genes can be separated by crossing over. Occurs during Prophase 1 of meiosis. Parts of the chromosomes of non-sister chromatids can cross over at a point called a chiasmus, followed by breaking and recombining.

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Result of Crossing Over

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As a result of crossing over, linked alleles are separated, so different combinations of alleles form those of the parent can result.

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Law of Segregation

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Segregation refers to the independent separation of alleles on different chromosomes. Alleles occupy the same locus (section) on a chromosome, each diploid cell has up to two different alleles for each gene. The law of segregation involves the alleles into the daughter cells/ gametes during meiosis.

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Mono Hybrid Inheritance

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Mono hybrid inheritance is the inheritance of one characteristic controlled by one gene which can have two or more different alleles at the same locus on a homologous pair of chromosomes.

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Complete Dominance

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Occurs when the information on the allele is always expressed in the phenotype when the allele is present in the genotype. The presence of a dominant allele masks the presence of the recessive allele. A recessive allele is only expressed in the phenotype when only recessive alleles are present.

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Pure Breeder

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When both alleles in the genotype are the same, the individual is called homozygous for that trait and is said to be pure breeder, because it can pass on only one type of allele to it's offspring.

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Hybrid Inheritance

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When both alleles are different, the individual is heterozygous for that trait and is not pure breeder, and it is a hybrid because it can pass on either type of alleles to it's offspring.

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Test Cross

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Test cross is used to determine the genotype of an individual (whether homozygous or heterozygous). In a test cross the individual being tested is crosses with an individual that has recessive phenotype and hence the recessive trait.

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Incomplete Dominance

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Incomplete dominance inheritance occur when neither alleles dominates the other. When both are present in the genotype (heterozygous) they both contribute to produce a phenotype that is the blend of genetic information. Therefore three different phenotypes may occur.

White (rr) ✖Red (RR) =Pink (Rr)

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Co-dominance

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Co-dominance inheritance occurs when both alleles are equally dominant- when both alleles are present in the heterozygous genotype they are both expressed in the phenotype. Therefore three different phenotypes can occur. In co-dominance, the alleles for the gene are both capital letters to indicate that they are both dominant alleles.

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Multiple alleles

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Multiple alleles occur within genes that have more than two different alleles though an individual will have only two of the alleles in its genotype. Inheritance of human blood groups shows multiple alleles, complete dominance and co-dominance. Three different alleles exist for what is known as the ABO blood groupings.

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Lethal Alleles

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A lethal allele occurs when a mutation occurs in an allele that produces a non-functional version an essential protein. If an individual inherits a lethal combination of mutated alleles it will die before or shortly after birth.

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Dihybrid Inheritance

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Dihybrid inheritance is the inheritance of two genes controlling two different features. The gene may have two or more different alleles. The allele may be on the same (homologous) chromosomes so are linked, or they may be on different (homologous) chromosome, so are not linked.

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Sex Linked Traits

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Sex linked traits are characteristics that are inherited from genes found on the sex chromosomes. Females=xx Males=xy

Almost all sex-linked traits are found on the x chromosome. Y chromosome contains very few genes and is mainly involved in sex determination.

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Natural Selection

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Natural Selection involves environment selecting for/ against certain phenotype. These 'better adapted' phenotypes survive and leave more offspring carrying the 'better allele'.

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Types of Natural Selection

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Stabilising Selection- Selection in favor of the average

Directional Selections- Selection in favor of the extreme

Distruptive Selection- Both extreme are favored resulting in two distinct new species

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Genetic Drift

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Involves the loss, decrease, or increase of an allele in a small population by chance done.

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The Founder Effect

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If only a few individuals move into a new area, they may only have a few of the available genes from the gene pool of that species. Isolated islands have shown rapid evolution because of this. The new 'founder' population will have the potential to be different so evolution will occur faster due to different gene pools.

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Bottleneck Effect

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Disasters can reduce a population to a few survivors. Deaths are often random so the survivors are not representative of the original gene pool. Some alleles will be above normal number, and some will be lost altogether. Bottleneck effect reduces genetic variability in the population.

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Migration

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Immigration- individuals entering a population (population increasing genetic diversity).

Emmigration- individuals leaving a population (potential decreasing genetic diversity)