Essay
Why offspring produced by the same parents are different in appearance
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Why offspring produced by the same parents are different in appearance full essay. 1341 words, mark = 20/25
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Why offspring produced by the same parents are different in appearance.Offspring produced by the same parents are different in appearance due to multiple factors,
including meiosis, gene mutation, Mendelian Inheritance, Polygenetic Inheritance, and the
environment. These can affect the alleles, which are variations of genes, and therefore the
phenotype, which are the physical characteristics of an organism. Therefore, these factors can
change the appearance of the offspring so they look different to the parents and their siblings.
One reason that offspring produced by the same parents are different in appearance is meiosis.
During this process, one cell divides twice to produce four genetically different haploid cells -
gametes. As each of these daughter cells are genetically different, each contains a different
combination of genetic information which is different to either set of chromosomes in the diploid
cells. This, combined with any random mutations, results in modified DNA, and new proteins
and phenotypes. Also, during meiosis, variation is increased through independent segregation.
This means that the chromosomes arrange themselves randomly, ensuring that none of the
daughter cells have the same DNA. Furthermore, crossing over occurs during meiosis. In this
process, homologous chromosomes twist around each other, creating a large amount of tension
that results in breaks in the chromatids. Corresponding fragments of the chromatids may then
be swapped, so genetic material is exchanged, creating new genetic combinations and
increasing the variation in the gametes produced. Because of these processes, the chances of
two offspring from the same parents having the same genetic combinations is highly unlikely, so
they are therefore unable to have exactly the same proteins and phenotypes. This then means
that they look different to each other, despite having the same parents.
Another reason for offspring produced by the same parents being different in appearance is due
to gene mutations. A gene is a section of DNA on a chromosome that codes for one or more
polypeptides. The base sequence of the gene determines the primary structure (amino acid
sequence) of proteins, which in turn determines phenotypes. A mutation is a change in the DNA
of an organism, either in the base pair sequence or the quantity of DNA. If this mutation is a
germline mutation, for example occurring during meiosis, it is passed on to the offspring. Base
sequence mutations can produce new alleles of genes, which affects how the offspring look, as
these genes code for things such as physical traits. Gene mutations can occur through base
substitutions, base deletions, base insertions, or they can be chromosomal. In some cases,
these mutations have no overall change. For example, if a base sequence of TCAGGC had a
substitution mutation to TCAGGT there would be no overall change, as both triplets GGC and
GGT code for the same amino acid Gly. However, usually they cause a change in the amino
acid sequence, which can then cause advantages (shown through evolution) or disadvantages
to the organism. For example, if the base sequence TCAGGC had a substitute mutation to
TCAGTC, this would change the second amino acid Gly to Val, changing the amino acid
sequence, and therefore the structure of the protein. In gametes, this could cause changes in
the appearance of the offspring as the alleles would be different, and could result in the change
of blue eyes to green. These mutations alter the genetic information stored in gametes, and as a
result of this, offspring have different DNA to their parents and to each other, meaning they are
different in appearance, as different alleles are coded for.
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