Download Chapter 3, Section 1 Mendel`s Work

Chapter 3, Section 1 Mendel’s Work
I.
Gregor Mendel was a monk. That means that
he spent his life living with a bunch of other
guys, and spent most of his time serving and
worshiping his god. (Which is why he is shown
wearing a “dress” – actually called a habit.)
 Heredity is the passing of traits from parents
to offspring.
II. Mendel’s Peas
 Peas are easy because they have many traits
that are either on or off (short or tall) and
never in the middle.
 Mendel cross-pollinated plants to control the
breeding
III.
Mendel’s Experiments.
 Started with purebred plants – one that
always produced offspring with the same trait
as the parent. Took many generations.
 Then cross-bred purebred tall plants with
purebred short plants.
 Parents are the “P generation.”
 The offspring are the finial generations. The
first is designated “F1 generation.”
 All offspring in F1 were tall – the short trait
had disappeared.
 However, the F2 generation was a mixture of
tall and short. 3/4 tall and 1/4 short.
IV. Other Traits
 He studied 6 other traits – seed shape, seed
color, seed coat color, pod shape, pod color,
and flower position.
 Results were the same as with tall/short
plants – one trait vanished in F1 and
reappeared in F2.
V. Dominant and Recessive Alleles
 Female parent contributes one factor, male
contributes another. We call those factors
“genes.” The different forms of the genes are
called “alleles.”
 So, the gene for height, has one allele for tall
stems and one allele for short stems.
 A dominant allele always shows up.
 A recessive allele only shows up when there
are two of them present.
 In peas, tall is dominant over short, which is
why there were no short plants in F1.
VI. Understanding Mendel’s Crosses
 Purebred plants had two identical alleles.
 In F1, all plants had one tall allele (from the
tall parent) and one short allele (from the
short parent). Since tall is dominant, they
were all tall.
VII.
Using Symbols in Genetics
 Geneticists pick one letter to represent all
possible alleles for a trait (like T for height).
They use the capital letter to show the
dominant trait and a lowercase letter to show
the recessive version.
VIII. Mendel’s Contribution
 Work was lost until 1900. Now known as
Father of Genetics.
Chapter 3, Section 2, Probability and Genetics
I.
Principles of Probability
 Probability is the likelihood that a certain
event will occur
 Is a likelihood, not a certainty
 Every event is independent – that is, even if
you get 10 heads in a row, the probability of a
heads on the next toss is still 50%.
II. Mendel & Probability
 Mendel was the first to recognize that laws of
probability applied to predicting genetic
results.
III.
Punnett Squares
 Reginald Punnett wrote the first textbook on
genetics.
 His squares are charts that show all possible
combinations of alleles.
 Using Punnett Squares
 Used to determine the probability of a
particular outcome.
 The alleles from one parent are placed on
one side of the box, lined up with the
spaces. The alleles from the other parent
are placed on an adjacent side.
 Each box gets the allele from that row and
the allele from than column.
 Predicting Probabilities
 Count the number of squares, and that is
your bottom number.
 The number of crosses that you want is the
top number.
 So, in overhead 11, have 4 boxes & 3 of them
are tall = 3/4 or 75% probability of a tall
offspring.
IV. Phenotypes and Genotypes
 Phenotype is physical appearance, the visible
traits
 Genotype is the genetic makeup, the allele
combination.
 Plants could all be tall (have same phenotype),
but some could be TT and some Tt (different
genotypes).
 Homozygous means the alleles are the same
– TT or tt. (Same as purebred)
 Heterozygous means alleles are different –
Tt. (Same as hybrid)
V. Codominance
 When neither allele is masked – that is, they
both show up.
 Uses superscript to show that it is a different
pattern -- FB & FW.
 In cows, color is codominant, so the offspring
of white and red cows will have both white and
red hair – called roan.
Chapter 3, Section 3, The Cell and Inheritance
I.
Chromosomes and inheritance
 Walter Sutton compared number of
chromosomes in sex cells with number in other
cells. Found that sex cells had exactly 1/2.
 When the sex cells come together, the
offspring have the same number of
chromosomes as the parents.
 Chromosome theory of inheritance – that
genes are carried from parent to offspring on
chromosomes.
II. Meiosis
 Process by which number of chromosomes is
reduced by half to form sex cells.
 Beginning every chromosome is copied.
 Meiosis I chromosomes pair up, and move to
opposite ends of the cell. Cell splits forming 2
new cells.
 Meiosis II centromeres split and the strands
of the chromosome go to opposite ends of the
cell.
 End of Meiosis cell splits to form 2 sex cells,
each with one-half as many chromosomes.
III.
Meiosis and Punnett Squares
 The squares are just a shorthand way to show
what happens during meiosis.
IV. Chromosomes
 Larger animals do not necessarily have more
chromosomes.
 Are made up of many genes strung together.
Chapter 3, Section 4, The DNA Connection
I.
The genetic code
 Genes make proteins; proteins control most
traits.
 DNA made of four nitrogen bases
 Adenine (A)
 Thymine (T)
 Guanine (G)
 Cytosine (C)
 Each gene has up to a million of these bases.
 The order of the bases is the code
 A group of three bases calls for a distinct
amino acid. The amino acids come together
to make up the protein.
II. Protein Synthesis
 The code on a gene in a chromosome makes a
specific protein.
 Chromosomes stay inside the nucleus of the
cell, but proteins are made out in the
cytoplasm. How is that possible?
 RNA does the work. Messenger RNA carries
the code & transfer RNA brings the amino
acids to the growing protein chain.
 DNA chain opens up, and one side serves as
the template for a strand of messenger
RNA. Bases pair up with that template, just
like when making more DNA (except thymine
is replaced by Uracil (U)).
 Messenger RNA goes out into the cytoplasm,
where it meets up with a ribosome. The
ribosome helps control the process.
 Transfer RNA is only 3 bases long. It
attaches to a specific amino acid and brings
it to the party. It drops its amino acid in
the correct spot on the messenger RNA.
 As the amino acids are put into place, they
bond together, making the growing protein.
 The protein is done (and the ribosome stops
working) when the ribosome reaches a “stop”
code in the messenger RNA.
III.
Mutations
 A mutation is a mistake in a gene. It does not
mean a third eye, or other change.
 Types of mutations
 Point mutation is where one base replaces
the correct base. This might have no
effect, or cause a reduced function, or not
work at all.
 Phase shift mutation is when a base is added
or deleted. This changes the whole protein
from that point on: “abc def ghi” becomes
“abZ cde fgh.”
 Mutations are passed on only if in a sex cell.
Mutations in body cells only affect that
organism.
 Some are harmful, but some are helpful.
Some mutations are neither helpful nor
harmful, they just don’t make any difference.
 Depends on environment. A mutation might
be harmful in one environment, if it makes it
harder to survive, but be neutral or helpful
in another environment.