Genetics Assignment: Concepts in Genetics and Evolutionary Biology

This document provides a comprehensive solution to a genetics assignment, addressing key concepts in evolutionary biology and Mendelian genetics. It begins with an explanation of Darwin's postulates and how they explain evolution by natural selection, followed by a discussion of conceptual difficulties that challenged Darwin's theory. The assignment then delves into Gregor Mendel's significant contributions to understanding inheritance, including his laws of segregation, independent assortment, and dominance. The concept of heterozygote advantage is explained, with a focus on the malaria case study and the role of sickle cell trait in providing resistance. The assignment concludes with an exploration of evolutionary theory on aging, examining the decline of fitness with age and its impact on physical decline and disease. The document also includes a demonstration of calculating offspring genotypes using a Punnett square and references relevant literature.

Running head: GENETICS
Genetics
Name of the student:
Name of the University:
Author’s note

1GENETICS
Darwin postulates:
Darwin postulates were as follows:
 All individuals in a population have unique variations
 Some of these variations are transferred to the offspring
 Favorable variations are those that reproduce the most and have greater chance of
survival (Richards, 2016).
The above theory explains evolution by natural selection by showing that organisms which
are able to adapt to the environment and survive and reproduce are able create new organisms.
Due to the process of natural selection, those with favorable traits have greater probability to
reproduce and create new offspring with the same trait. However, the Darwin’s theory of natural
selection was threatened by the following three conceptual difficulties:
1. Many typical features of different species hindered their survival instead of helping them
to survive. This relates to the impact of non-fitness on natural selection
2. The second problem was regarding the lack of clarity regarding the mechanism of
inheritance. He failed to explained the mechanism by which the adaptive variations were
transferred to the offspring
3. The third problem was the issue of altruism as the theory revealed as many organism do
not have behave in their self-interest to survive (Donnelly et al. 2016).
Gregor Mendel’s work:
The work of Gregor Mendel is significant as he gave answer to the mechanism of
inheritance which was not answered by Darwin. One major gap in the Darwin’s theory of natural
selection was the lack of explanation regarding the mechanism of inheritance. Mendel explained

2GENETICS
the mechanism of natural selection through his experiment on pea plants which he followed till
eight generations. His experiment gave rise to three laws inheritance. The first law was the law
of segregation which states that every genes come in pair and one units from each gene is
inherited from each parents. The second law was the law of independent assortment which gave
the idea that inheritance of one gene is different from the other gene. The third law was the law
of dominance which states that dominant alleles will always be expressed first and recessive
allele will always be masked by the dominant alleles (Birchler 2015).
Heterozygous advantage:
Heterozygote advantage is a situation in which heterozygous allele have high fitness level
compared to the homozygous dominant or homozygous recessive alleles. In other words,
heterozygote advantage is referred to as the situation in which carriers of the disease or those
with heterozygous allele are likely to survive better than those without the disease allele.
Deleterious recessive trait cannot be eliminated out of the population. This is understood
from the malaria case study which shows the human resistance to malaria. In the regions were
malaria dominates for more than 50 years, the sickle cell trait in the region of these genes has
played a role in protecting its carrier from Malaria. Sickle cell anemia is an autosomal recessive
disease or a disease of the homozygotes (SS). People with either heterozygous hemoglobin A
with hemoglobin S (HbAS) or homozygous with hemoglobin S (HbSS) shows symptoms of
sickle cell anemia. However, for those with homozygous recessive S, severe symptoms are seen.
However, it protects the carrier from malaria. The explanation for this is that sickle cell trait
evolves because of its protection trait. In addition, according to Mendel law, those with
heterozygous trait survive better than those with homozygous trait (Luzzatto 2012).

3GENETICS
Evolutionary theory on ageing:
Ageing is associated with physical decline because ageing is a product of natural
selection. This is because all the force of natural selection decline with age. The theory of natural
selection is designed to promote survival and reproductive success for an individual. However,
ageing could not be prevented because of the process of evolution due to the decline of fitness at
old age. The more fit genes survive according to evolutionary concept. Hence, the decline in the
force of selection with age is a reason behind physical decline and sickness at old age. In
addition, alleles with negative effects accumulate in successive generation and are retained by
selection. This finally results in functional decline and dominance of disease in old age (Vijg and
Kennedy 2016).
Calculation of genotype of offspring using Punnett square:
Punnett square is a graphical representation of analyzing combination of genotypes of
parents and identifying the combination of genotypes for offspring. It helps to predict the
frequency of all of the genotypes among offspring’s after each reproduction cycle.

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References:
Birchler, J.A., 2015. Mendel, mechanism, models, marketing, and more. Cell, 163(1), pp.9-11.
Donnelly, D.F., Namdar, B., Vitale, J.M., Lai, K. and Linn, M.C., 2016. Enhancing student
explanations of evolution: Comparing elaborating and competing theory prompts. Journal of
Research in Science Teaching, 53(9), pp.1341-1363.
Luzzatto, L., 2012. Sickle cell anaemia and malaria. Mediterranean journal of hematology and
infectious diseases, 4(1).
Richards, R.J., 2016. Darwin’s theory of natural selection and its moral purpose. Debates in
Nineteenth-Century European Philosophy: Essential Readings and Contemporary Responses,
pp.211-225.
Vijg, J. and Kennedy, B.K., 2016. The essence of aging. Gerontology, 62(4), pp.381-385.