Katy Connole
BIOL 1610
1. Suppose that the allele for brown eyes (B) is dominant to the allele for hazel eyes
(b). If both parents have brown eyes and are heterozygous (Bb), what are the
chances that their first child will have hazel eyes? Brown eyes? What are the
chances that if they have two children, both will have hazel eyes?
If both parents have brown eyes but are heterozygous they can produce three different
combinations of alleles according to Mendel’s principle of segregation. They will
produce either BB, Bb, or bb. Since the child with BB or Bb allele combinations will
have brown eyes there is a 33% chance the child will be bb and have hazel eyes. There is
a 67% chance that their child will be Bb or BB and have brown eyes. If they were to have
two children there is an 11% chance that both of those children will be bb and have hazel
eyes.
2.
How may the degradation of telomeres result in cellular aging?
Important genetic information is retained by protective end caps of the chromosomes,
called telomeres. Telomeres do not contain protein-coding genes and consists of short,
simple non-coding DNA sequences that repeat many times. As a cell divides over and
over a small amount of telomeric DNA fails to replicate each time and the cell will start
to lose essential genetic information. The gradual shortening of telomeres throughout the
life of a cell contributes to the aging and eventual apoptosis (programmed death) of the
cell. Most somatic human cells do not contain the DNA replication enzyme, telomerase.
Telomerase can lengthen telomeric DNA by adding repetitive nucleotide sequences to the
ends of eukaryotic chromosomes. Consequently, normal somatic cells of the human body
lose their ability to divide after a limited number of cell divisions. The presence of
telomerase in a cell elongates the telomeres and enables that cell to divide much longer
than a cell without this enzyme.
3.
What evolutionary role is served by the redundancy of the genetic code?
There are 64 codons that code for only 20 amino acids found in cells. This is very
beneficial from an evolutionary standpoint since this redundancy protects the cell from
mutations, which are changes in the nucleotide sequence of DNA, which might be
detrimental to the cell. The redundancy enables it to still code for the correct amino acid
and helps ensure the proper translation of the genetic code. The overall mutation rate of
DNA is much higher than the frequency of damage to DNA. This is due, partly, to the
redundancy of the genetic code.
4. What part of Darwin's theory was incomplete due to a lack of knowledge at the
time of publication? How does the synthetic theory of evolution explain this?
Darwin’s theory of evolution based on natural selection is based on the premise that
individuals transmit traits to the next generation. Darwin was unable to explain how this
occurs or why individuals vary within a population. Darwin was apparently not familiar
with Mendel’s work on basic patters of inheritance, which was not recognized by the
scientific community until the early part of the 20th century. In the 1930’s and 40’s
biologists combined the principles of Mendelian inheritance with Darwin’s theory of
natural selection. A unified explanation of evolution resulted and is known as the
synthetic theory of evolution. The modern synthesis incorporates our expanding
knowledge in genetics, systematic, paleontology, developmental biology, behavior, and
ecology. It explains Darwin’s observation of variation among offspring in terms of
mutation. Mutations provide genetic variability on which natural selection acts during
evolution.
5. Why is the Hardy-Weinberg principle important, since genetic equilibrium seldom
occurs in nature?
The Hardy-Weinberg principle of genetic equilibrium tells us what to expect when a
sexually reproducing population is not evolving and shows that if a population is large,
the process of inheritance does not by itself cause changes in allele frequencies. It
explains why dominant alleles are not necessarily more common than recessive ones.
While the Hardy-Weinberg principle represents situations that are rarely found in nature
it does provide biologists with a model for understanding the real world and the
mechanisms of evolutionary change in sexually reproducing populations. It lets us use
phenotype frequencies to calculate the expected genotype and allele frequencies and
provides a basis of comparison in succeeding generations of the population. During that
time, if the allele or genotype frequencies deviate from the values predicted by the
Hardy-Weinberg principles, then the population is evolving.
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