ANTA01H3 Lecture Notes - Lecture 3: Genetic Drift, Gamete, Telomerase Reverse Transcriptase

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27 Apr 2012
Chapter 3 Lecture Notes: Genetics
What is evolution and Natural Selection working on?
We know the mechanism but what are the processes and what is actually changing?
Genetic flow
Genetic drift
Gregor Mendel-Austria 1822-1884
Breeding experiments with pea plants
Traits in offspring are not passed solely by either parent
o traits are passed in small, independent packages from both parents
o we call these packages genes
found what evolution was working on
Mendel, Wallace and Darwin all publishing at the same time, but there may have been a language barrier or else they could
have come up with more theories
Mendel’s breeding program
Cross bred green peas with green peas
Offspring of any generation always had green peas
Cross bred yellow peas with green peas
All offspring plants (f1 generation) bore green peas
Cross bred green offspring plants (f2 generation) had green peas and some had yellow peas
Ration of green to yellow plants in f2 generation was always 3:1
F3 generation
what would the punnet square look life if we crossed:
green YY and Green Yy
each observed trait derives from a package of information (gene) acquired by the individual at conception
For each trait, an individual processes two genes: one from each parent.
o Two matching genes homozygous state: for a give trait, individual receives the same gene form from parents. Green
and Green
o Heterozygous state: Individual receives two different gene forms from parents. Green and Yellow
The whole set of different forms for a give gene are known as alleles
o Mendel’s peas had alternative genes or alleles for greed seeds and for yellow seeds
o Sometimes the yellow allele was expressed (appeared in the plant)
o Sometime the green allele was expressed
Dominant genes: always expressed in the individual who carries them such as green peas.
Recessive genes: overpowered by a dominant gene if one is present, and not expressed such as yellow peas
o Recessive genes are expressed only if they are homozygous (if no dominant gene is present)
o Recessive genes are as likely to be passed to offspring as are dominate geneseven though their presence may be
unknown to the observer
Independent Assortment
During reproduction, each individual crease a gamete (egg or sperm) which consists of half of your genes (meiosis)
o Probability of a gene passing on from your mother/father is 50%
o Dominant genes don’t have any dominance in this process; recessive genes are equally likely
o we can’t predict which genes will be passed on
Example Eye Color
gene color exists in two alleles or states
o B dominant brown
o B recessive blue
Each parent passes on al allele in his/her gamete
Offspring’s genetic makeup contains al allele form each parent
Offspring’s outward appearance (phenotype) reflects the dominance of this gene pair
Brown eyes, BB, Bb, or bB
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Blue eyes only bb
Other examples of Simple traits?
Thumb dominance-left on tome is dominant
Darwin’s tubercle-recessive trait but becoming more dominant
Hair whorl-even
Tongue curling-dominant present
Genotype: all the genes in an individual
The genotype represents our real genetic structure, or DNA
Phenotype: the visible individual
o He expression of genetic dominance +
o Physical changes caused by events in the individual’s life
o Tattoos’, limp all part of phenotype
The phenotype is what we actually see
Genome- The entire range of alleles in a species, the gene pool
Most physical traits represent complex associations of several different genes
o Gene Complex: often include genes on completely different chromosomes
o Some genes can be co-dominant: blend together rather than dominating or submitting (hair color)
o Sometimes the nature of one gene determines the dominance or recessivity of another
Genes and DNA
DNA is a double helix
Genetic code is made up of four different bases
Adenine, Guanine, Thymine, and Cytosine
A-T and C-G only
Group of three bases= codon
Genes are a sequence of codons, like sentences on a DNA string
Genes are organized in DNA and wounds a strings within chromosomes
o Chromosomes are paired
o One comes from each parent
o Matching locations on paired chromosomes are alleles of a single gene
46 chromosomes in all23 from each parent
o 23 paired autosomes and 2 sex chromosomes
Chimps have 24 pairs, humans had 24 but two sets fused together
Sex Chromosomes
X largest chromosome in any mammalian cell, Lots of genetic information
Y smallest chromosome in any mammalian cell, Very little genetic info
Combination of sex chromosomes influence physical sex characteristics of individual
o XX female XY Male
Hemophelia and colour blindness based on sex cells
What causes new Traits?
Change in genes
Changes in chromosomes
New complexes or combinations between genes
Source of Variation? Process of Evolution
Genetic Mutation-direct effect on genes, when RNA is transcribed incorrectly
Genetic Flow
Genetic Drift
Advantageous, deleterious or neutral
Random mechanical errors during DNA synthesis-sickle cell anemia
Chemical pollutants
Cosmic nuclear radiation
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