Chapter 4 Flashcards
What are alleles and where are they located? What can they help explain?
Alleles are different forms of a gene due to having a different DNA sequence. They are located on specific locus on a given chromosome. They can help explain the variation in genetic traits
Why can we get two different or similar alleles for one chromosome?
This is because we inherit two copies for each chromosome, one from the mother and one from the father. These copies could have different versions of a gene or the same version, making it possible to have two alleles per chromosome.
Explain the law of uniformity of hybrids and provide an example
On a chromosome, the dominant allele produces an enzyme that expressive a specific trait, while a recessive allele does not produce an enzyme and therefore its phenotype is not expressed. This law states than in a heterozygous organism, the dominant allele will determine the appearance of an organism since it is the only one that will be expressed. If two parents were homozygous recessive and homozygous dominant for the gene that determines the shape of the ear lobe and the recessive allele means attached ear lobe and the dominant allele means free ear lobe, all the children would have free ear lobes.
What is an easy way to remember the fact that recessive alleles traits are not expressed
No enzyme= No phenotype
Explain the law of segregation
This law states that alleles on a chromosome for a particular trait separate from one another during meiosis for each haploid gamete to end up with one copy of the allele. This way, both the mom’s and the dad’s gametes have one copy of each chromosome to form a diploid organism that will have two copies of each allele/chromosome.
Explain the law of independent assortment
This law states that the alleles of two or more different genes are inherited independently of one another. So just because you inherit the Y allele does not mean that you will also have the R allele. A gamete could end up having a Y allele and r allele or have a Y allele and an R allele.
What is the difference between the law of segregation and the law of independent assortment?
The law of independent assortment explains how two traits associated with two different genes are inherited while the law of segregation looks at only one gene/trait.
Explain the law of independent assortment
This law states that the alleles of two or more different genes are inherited independently of one another. So just because you inherit the Y allele does not mean that you will also have the R allele. A gamete could end up having a Y allele and r allele or have a Y allele and an R allele.
What does dependent assortment mean?
It means that genes are linked and are therefore inherited together
What happened when natural selection and genetics were reconciled?
Neodarwasnism or modern synthesis was formed and this field mainly helped us understand the genetic basis for evolutionary changes and how continuous variation is transmitted from generation to generation through Mendel’s laws
How does incomplete dominance work?
Incomplete dominance occurs in a heterozygous individual when the recessive allele that normally does not produce any enzyme, produces enzymes but in a very small quantity. Therefore, a small portion of this allele’s phenotype will show up and the final phenotype will be a combination of both the dominant and the recessive alleles.
How does incomplete dominance work and provide an example?
Incomplete dominance occurs in a heterozygous individual when the recessive allele that normally does not produce any enzyme, produces enzymes but in a very small quantity. Therefore, a small portion of this allele’s phenotype will show up and the final phenotype will be a combination of both the dominant and the recessive alleles. An example of this is seen in horses and the alleles associated with the trait for fur color. The dominant allele leads to a brown phenotype and a recessive allele leads to a white phenotype, while a combination of the two in a heterozygote leads to a mix of the two colors, so a cream color
Explain how codominance works and provide an example
This occurs when two alleles for a trait are dominant and are therefore are both going to be expressed in the phenotype. An example of this is seen in chickens. The white color is produced due to a two dominant alleles and the same for the black color. What happens when both chickens are crossed is that you end up with a checkered chicken that has traces of both the black and white color since both alleles were dominant and will therefore both appear in the phenotype
Explain how epistasis works and provide an example
This occurs when the expression of a gene hides or blocks the expression of another gene.
Explain how pleiotropy works and provide an example
This occurs when a gene is expressed and affects many traits at once. An example of this is the Manx cat. These cats are characterized by the short or even lack of tails. The reason behind this is the Manx gene. In homozygous individuals, when this gene is expressed, it affects the development of the vertebral column. This goes on to affect the development of other organs, leading to the death of the organism while still at the embryonic stage.
