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Chapter 4

ANTA01H3 Chapter Notes - Chapter 4: Ecology, Allele, Transfer Rna


Department
Anthropology
Course Code
ANTA01H3
Professor
Genevieve Dewar
Chapter
4

Page:
of 6
ANTA01 Chapter 4 Key Concepts
Genetics
Past: Darwin knew their was variation but didn't know how – didn't know how traits were passed down
genetics: the study of the mechanism of inheritance, Darwin believed it was a “blending”, a mixing of paretal
substances
offspring exhibited traits that appeared to be 50/50 mixtures of their parent's trait
ex. Pink flowers from a cross of red flowers and white flowers
but cannot be true for humans and sex, can only be male or female(trait)
Mendel - said it wasn't blending but...
particulate: the idea that biological traits are controlled by individual factors, than by a single hereditary agent
through pea plant experiments he showed that an organism traits are passed from gen. to gen.
by individual particles, which he called “factors”
- today called genes: the portion of the DNA molecule that codes for a specific protein
The Genetic Code
gene is a set of chemical instructions for the production of a
protein: the family of molecules that makes cells and carries out cellular functions
functions include, structural, supporting the cells's internal structure, + building membranes
some proteins are enzymes: a protein that controls chemical processes – speeds up the reaction
ex. hemoglobin is a protein that carries oxygen to the cells, a few proteins are hormones
*humans can produce atleast 100,000 different proteins
the genetic code is made up of a sequence of bases (family of chemicals) that are part of a long chain,
DNA: the molecule that carries the genetic code
- the strands of DNA are wrapped around a series of proteins that make up,
chromosomes: a strand of DNA in the nucleus of cells
Four bases are in the code: A, T, C, G – chemical bonds between the bases hold the DNA together
bases only bond like this: A-T, T-A or C-G or G-C pairs
* the pairing allows the DNA molecule to make copies of itself during cell division
- ends are twisting in opposite directions – called a double helix
cell-division – the helix unwinds and now the strand has unpaired bases which complementary bases attach,
this is called replication: the copying of the genetic code during the process of cell division
- so when the cell divides and creates two new daughter cells, they have a complete set of base pairs
a gene is a portion of the DNA molecule that carries a code to make a certain protein
- protein synthesis: the process by which the genetic code puts together proteins in the cell
* only a portion is unwound
- mRNA: the molecule that carries the genetic code out of the nucleus for translation into proteins
* one strand carries the code, the other is structural
– transcribes the gene by matching complementary bases to the ones exposed in the DNA coding strand,
where U replaces T
a sequence of 3 DNA bases is known as a codon: a section of the DNA that codes for a particular amino acid
after the code is transcribed by mRNA , it leaves the nucleus to the ribosome, where it is coded into a protein
- tRNA: RNA that lines up amino acids along mRNA to make proteins
– reads the codons to make an amino acid: the chief component of proteins – there is about 20 proteins
* DNA bases represent the sequence of amino acids, which determine the shape&function of the protein
each species has a characteristic number of chromosome (ex. Humans-46, Chimps-48, Dogs-78)
the offspring inherits one chromosome from each parent +gets half of each parent's genetic material
* the genes come in pairs
genes come with alleles: a variant of genes – each with different codons, it produces the same trait but
produce different expressions – the allele pair is known as genotype: the alleles possessed by an organism
codes for as many proteins, scattered and constantly interpreted
2003, sequenced an entire human genome: the total genetic endowment of an organism, 3.1 billion base
pairs, still trying to study how “DNA” builds an organism – determining what proteins are coded and the
function of nongene DNA
most of the genome is not composed of genes, around 98% doesn't code for proteins
the nongene material is known as noncoding DNA – mark the beginning and end of codon sequences, some
function to regulate gene function and activity level (some are made up of repetitive sequences)
* some DNA may be ancient, from a common ancestor transferred from microbes
RNA's function: converts DNA codes into proteins
- turn on and off some genes, blocking the mRNA from producing certain protein(causing disease
development), , shutting down genes and operating as a defense against harmful DNA and viruses – shaping
the genome( by keeping+discarding genes)
The Inheritance of Characteristics
an organism that has two of the same alleles is: homozygous
* when both parents contributed the same allele of that gene
an organism that has two different alleles in a pair is: heterozygous
*where the genes of the parent carry different codes
alleles are products of mutation: a change in an organism's genetic material
(change an existing allele, one that codes for brown eyes to blue eyes)
phenotype: the chemical or physical results of the genetic code - - “expression of the genotype”
*trait as a result of the genetic code
these traits may be dominant or recessive, where they actually get expressed depending on the blending of
heterozygous pairs and expression(more complex-Dd) of homozygous pairs(no alternative-DD)
recessive: an allele of a pair that is not expressed
dominant: an allele of a pair that is expressed (can't say it is more better or more common)
during organism's reproduction, cannot pass on both alleles of each pair to its offspring, so organism
produces reproductive cells that are different from the cells that make up the organism – called sex cells
* gametes: the cell of reproduction (ex. sperm or egg) – formed in the process of meiosis
- where the chromosomes are split (the allele pairs), so each gamete has one of each gene
Mendel called this segregation: the breaking up of allele pairs during gamete production – chromosome split
when a sperm from the males parent fertilizes an egg from the female parent – it forms a
zygote:a fertilized egg before cell division [which has pairs of chromosomes(pairs of each gene)]
as a result since both parent's also have different combinations, the combination of each pair of gene will be
different – which causes variation within the same species or of the same parent (offspring)
- each cell has half the normal number of chromosomes
ex. sickle cell anemia – erroneously only with African Americans, result of mutation of gene on chromosome
11, which affects hemoglobin – as a result the amino acid is coded wrong and substituted with another
protein – this is an example of a point mutation: a mutation of a single letter in a codon
* this allele is usually recessive, so a person must be homozygous for this abnormal genotype to get the
disease – heterozygous parents may still carry the allele, but they only have ¼ of chance for producing an off
spring that is homozygous for sickle cell – this process can be shown in a punnett square
heterozygotes may somehow be an intermediate between the homozygote, and show the phenotypes of both
alleles – alleles that exhibit this feature is codominant: the expression of both alleles of a gene pair
ex. People who are recessive for sickle cell, still have 40% chance of producing abnormal hemoglobin +
show some symptoms, not as extreme as homozygous
*phenotype may not be a complete expression of the genotype
phenotypic traits are not coded by a single gene: monogenic, but is coded by many genes: polygenic
the relationship between the genotype and phenotype can be influenced by environmental factors – factors
that are besides the codon to trait – could depend on health, sun exposure emotional state
Mendel helped develop the mechanism of inheritance and the source of variation*
The Genetics of Population – evolution is the change in allele frequency over time
the evidence of evolution is change in the phenotypic features of the organism
the overall genetic make up of the individual does not change – individual's don't evolve, unless isolated
mutations – the unit of evolution is population: a reproductive unit – group within which mates are found
some species are unevenly distributed, who contain subunits of interbreeding individuals – defined by
adaptations and physical characteristics – these groups are called breeding populations: a population with
some degree of genetic isolation from other population of the species, also called demes.
* the demes are like a collective evolution, because populations change independently as they interact with
one another and exchange genetic material
breeding populations are distinguished by identifying how often a certain allele appears in the population,
relative to the other alleles of the same gene, this is called allele frequency.
the process of evolution, is the changes that bring about the allele frequency
frequency is calculated by individual alleles, depending on the number of people who possess that trait
*divided by the number of people in the population
Phenotype Genotype Number
Normal AA 35
Heterozygote AS 100
Sickle Cell SS 10 *Total 145
Number of A Alleles: (35x2)+100=170
Number of S Alleles: (10X2)+100=120 Total number of alleles: 170+120=290
*to calculate the percentage(frequency) of occurrence of each allele: divide each allele by the total # of AIP
A Allele: 170/290 =0.59 S Allele: 120/290=0.41
Therefore, within the population of 145 individuals, the allele for normal hemoglobin occurs 59% of the
time, and the allele for sickle cell occurs 41% of the time – allele frequencies for the population
Hardy-Weinberg equilibrium, is used to determine genotype percentage under no evolutionary change
A + S is substituted with the frequency of A as p, and the frequency of S as q
Possible Products are:
Genotype Product of Frequencies
AA pXp=p2
AS pXq=pq
SA qXp=qp *both AS/SA = 2pq ALL genotypes are accounted as p2+2pq+q2=1
SS qXq=q2100% of all the genotypes
Genotype Expected Frequency Expected Number Observed Number
AA p^2=0.59^2=0.3481 0.3481X145=50 35
AS 2pq=0.59 X 0.41 X 2 0.43838X145=70 100
= 0.43838
SS q^2=0.41^2=0.1681 0.1681X145=24 10
* the observed numbers are not in equilibrium, therefore we can determine that evolution is taking place,
because there are fewer number of “normal” individuals, more heterozygotes and fewer homozygous