Evolution and Genetics - GED Science

Alleles are different forms of the same gene. For example, the gene for flower color in a plant may come in two allele varieties: white or purple. Both alleles code for flower color (the same gene), but represent different types of the genetic expression.

Humans are diploid organisms, meaning that they carry two alleles for each gene, one from each parent. Organisms with two copies of the same allele are considered homozygous, while those with copies of two different alleles are considered heterozygous.

When an organism has only one type of allele for a given gene, it is described as homozygous ("homo-" meaning one). Organisms can be either homozygous dominant, meaning they have two dominant alleles, or homozygous recessive, meaning they have two recessive alleles.

A heterozygote, or hybrid, has two different types of alleles for a given gene. When the dominant allele causes the recessive trait not to be represented in the phenotype, the organism is considered a carrier for the recessive trait.

When a gene is sex-linked, it means that the gene is located on one of the sex chromosomes. These chromosomes are the X and Y chromosomes, with the Y chromosome only being found in males. Sex-linked genes provide the opportunity for the frequency of a phenotype to be seen more often in one gender than the other.

Sex-linked genes can be represented in either sex; if the trait is on the X chromosome, it can be displayed in both males and females but may appear more frequently in males.

Nonsense mutations alter the position of the stop codon in the mRNA strand, which creates a different product. The result is a shorter polypeptide chain that may not be able to function.

Silent mutations do not alter the final protein product. A missense mutation causes an amino acid to be replaced by another, different amino acid. A frameshift mutation changes how the mRNA strand is read by the ribosome, resulting in a dramatically different product.

In the case of the giraffe, chameleon, and rose, the species naturally adapted in order to survive. However, in the case of the dogs, there was intervention by man. Certain species and individuals were crossed to select for the desired genes that result in hypoallergenic fur, allowing the dogs to be kept by owners who would otherwise be allergic. Therefore, the dogs are an example of ARTIFICIAL selection, while the other choices demonstrate NATURAL selection. Natural selection is also referred to as survival of the fittest.

Natural selection is when nature makes certain traits more common due to their inherent advantage in a given environment. When a prairie dog is better hidden based on its fur color, that color will become more common over time as the darker fur colors are eaten away by predators. Humans can also make certain traits more common over time, such as in dogs, but this is an example of artificial selection, not natural.

a heterozygous organism will have one copy of the dominant allele and one copy of the recessive allele for a given gene. The recessive phenotype is the expression of the recessive allele; this will only occur if the offspring as two copies of the recessive allele.

Since two heterozygotes are mating, each one has a 50% chance of contributing their recessive allele to the offspring. Keeping that in mind, the probability of this happening just becomes 50% multiplied by 50%. This gives us a 25% chance that the offspring will display the recessive phenotype.

In other terms, we can look at all the possible combinations for the offspring. Assume that A represents the dominant allele and a represents the recessive allele.

Each parent will have the genotype Aa. The cross will be Aa x Aa. The possible resulting offspring will be AA, Aa, aA, and aa. Only aa will show the recessive phenotype; therefore, there is a one-fourth chance (25%) that the offspring will show the recessive phenotype.

There are only 23 chromosome pairs in human beings, but there are thousands of genes. This means that many genes will be found on the same chromosome. When two genes are found on the same chromosome, they are said to be linked. Genes that are very close to each other on the chromosome are more likely to travel with each other to the same haploid cell during meiosis, and are frequently inherited together.

An example of linked genes are blue eyes and blond hair. These traits are frequently inherited together because they are found in the same region on the same chromosome.

Common ancestors are the branching points in a phylogenetic tree, from which multiple species originate. Chimpanzees and humans share a common ancestor. Through evolution, the genetic changes to this ancestor gave rise to two separate species: chimpanzees and humans. This divide occurred roughly 5 million years ago, according to fossil evidence.

To say that chimpanzees are the most recent common ancestor to humans implies that humans actually evolved from chimpanzees. Similarly, to say that humans are the most recent ancestor to chimpanzees suggests that chimpanzees evolved from humans. Neither of these statements are correct, as both species are actually derived from a shared ancient relative (the most recent common ancestor).

There are three eras that divide geologic time: the Paleozoic era, the Mesozoic era, and the Cenozoic era. The Mesozoic era was the age of the dinosaurs. Following their extinction, the Cenozoic era began and mammals started to dominate the landscape. This gives the Cenozoic era the nickname "the age of the mammals."

A population will not experience evolution if all of the following requirements are met:

1. Very large population numbers.

2. No new mutations entering the population.

3. No new organisms entering the population and changing the gene pool.

4. All mating is random.

5. No natural selection.

These tenets are the foundation of Hardy-Weinberg equilibrium. If mating is no longer random, evolution will take place in the population. Similarly, if mutations occur, new organisms enter the population, the population size is small, and natural selection is in effect, then evolution will be enhanced.

There are a variety of mutations that can affect how a protein product is made in the body. Of the options listed, a silent mutation is the only type that does not change the final protein product. In a silent mutation, the DNA sequence is changed, but the amino acid product remains the same. Because there is no change in functionality, a silent mutation cannot harm the organism.

All of the other types of mutations listed will change what the final protein looks like, and can affect the organism in a negative way.

Alleles are different forms of the same gene. For example, the gene for flower color in a plant may come in two allele varieties: white or purple. Both alleles code for flower color (the same gene), but represent different types of the genetic expression.

Humans are diploid organisms, meaning that they carry two alleles for each gene, one from each parent. Organisms with two copies of the same allele are considered homozygous, while those with copies of two different alleles are considered heterozygous.

When an organism has only one type of allele for a given gene, it is described as homozygous ("homo-" meaning one). Organisms can be either homozygous dominant, meaning they have two dominant alleles, or homozygous recessive, meaning they have two recessive alleles.

A heterozygote, or hybrid, has two different types of alleles for a given gene. When the dominant allele causes the recessive trait not to be represented in the phenotype, the organism is considered a carrier for the recessive trait.

When a gene is sex-linked, it means that the gene is located on one of the sex chromosomes. These chromosomes are the X and Y chromosomes, with the Y chromosome only being found in males. Sex-linked genes provide the opportunity for the frequency of a phenotype to be seen more often in one gender than the other.

Sex-linked genes can be represented in either sex; if the trait is on the X chromosome, it can be displayed in both males and females but may appear more frequently in males.

Nonsense mutations alter the position of the stop codon in the mRNA strand, which creates a different product. The result is a shorter polypeptide chain that may not be able to function.

Silent mutations do not alter the final protein product. A missense mutation causes an amino acid to be replaced by another, different amino acid. A frameshift mutation changes how the mRNA strand is read by the ribosome, resulting in a dramatically different product.

In the case of the giraffe, chameleon, and rose, the species naturally adapted in order to survive. However, in the case of the dogs, there was intervention by man. Certain species and individuals were crossed to select for the desired genes that result in hypoallergenic fur, allowing the dogs to be kept by owners who would otherwise be allergic. Therefore, the dogs are an example of ARTIFICIAL selection, while the other choices demonstrate NATURAL selection. Natural selection is also referred to as survival of the fittest.

Natural selection is when nature makes certain traits more common due to their inherent advantage in a given environment. When a prairie dog is better hidden based on its fur color, that color will become more common over time as the darker fur colors are eaten away by predators. Humans can also make certain traits more common over time, such as in dogs, but this is an example of artificial selection, not natural.

a heterozygous organism will have one copy of the dominant allele and one copy of the recessive allele for a given gene. The recessive phenotype is the expression of the recessive allele; this will only occur if the offspring as two copies of the recessive allele.

Since two heterozygotes are mating, each one has a 50% chance of contributing their recessive allele to the offspring. Keeping that in mind, the probability of this happening just becomes 50% multiplied by 50%. This gives us a 25% chance that the offspring will display the recessive phenotype.

In other terms, we can look at all the possible combinations for the offspring. Assume that A represents the dominant allele and a represents the recessive allele.

Each parent will have the genotype Aa. The cross will be Aa x Aa. The possible resulting offspring will be AA, Aa, aA, and aa. Only aa will show the recessive phenotype; therefore, there is a one-fourth chance (25%) that the offspring will show the recessive phenotype.

There are only 23 chromosome pairs in human beings, but there are thousands of genes. This means that many genes will be found on the same chromosome. When two genes are found on the same chromosome, they are said to be linked. Genes that are very close to each other on the chromosome are more likely to travel with each other to the same haploid cell during meiosis, and are frequently inherited together.

An example of linked genes are blue eyes and blond hair. These traits are frequently inherited together because they are found in the same region on the same chromosome.