Ch 11- Introduction to Genetics

BIG IDEA: How does biological info.
pass from one generation to another?
Genetics is the science of heredity, or how
traits are passed through each generation.
Gregor Mendel is considered the father of
• Austrian monk
• Worked with pea plants
Why might someone choose to work with pea
plants to study genetics?
Fertilization occurs when the male and the
female sex cells join together to form a new
Traits are genetic characteristics (ex: hair
color, eye color, height, etc.)
-To prevent plants from self-pollinating he cut
the male parts from the flower and dusted
pollen from them onto the desired flowers.
(Cross pollination)
Mendel’s Principles of Inheritance:
1. The factors that pass from one
generation to the next are called
- The different forms of each gene
are alleles
2. Some alleles are dominant and
some are recessive
- Dominant traits mask recessive
traits and are seen if 1 of the 2
alleles present are dominant
3. Allele pairs separate or segregate
during gamete formation, and randomly
unite at fertilization.
- A trait may not show up in an individual
but can still be passed on to the next
Generations in crossing
P generation= Parental generation, each being
true-breeding (SS or ss)
F1= 1st generation cross. Cross between 2 truebreeding organisms
F2=2nd generation cross. Cross between two F1
offspring. The generation where recessive alleles
may re-appear
During gamete formation, the alleles for
each gene segregate from each other, so
that each gamete carries only 1 allele for
each gene
See if link works??
Probability is the likelihood that a
particular event will occur.
- The principles of probability can be used
to predict the outcomes of genetic
Homozygous organisms have 2 identical
alleles (Ex: TT/tt)
Heterozygous organisms have 2 different
alleles (Ex:Tt)
Probabilities predict averages/ratios:
F1 produce all tall plants, or 4:0, or 100%
F2 produce mostly tall plants, or 3:1, or
Phenotype: physical traits
Genotype: genetic makeup
Example: Tt=genotype, tall=phenotype
Punnett squares are used to
predict the genotype and
phenotype combination in genetic
How to for 1 factor and 2
factor crosses: pg. 316
To test if certain traits were linked to each other
Mendel performed a “Dihybrid” cross, involving 2
-F1- rryy x RRYY, all offspring were heterozygous for
each trait
-F2 generation produced approximately 9:3:3:1
He found out that seed shape and color are not
Independent assortment states that genes for
different traits can segregate independently.
A summary of Mendel’s Principles:
-Genes are passed from parents to
-2 or more alleles exist for each trait,
they may be dominant or recessive
-Genes segregate from each other when
forming offspring
-Alleles for diff. genes usually sort
There are some exceptions to Mendel’s principles
Some alleles are neither dominant or recessive
-Incomplete dominance shows the heterozygous
phenotype to be an intermediate between the 2
dominant parental phenotypes
Codominance produces offspring that show
both dominant phenotypes at the same time
Ex: Roan cow
Many genes exist in several different forms
and are therefore said to have multiple
Polygenic traits are the traits that are
produced by the interaction of several genes.
-Ex: height, skin color
Environmental conditions can affect
gene expression and influence
genetically determined traits.
Examples: different temperatures,
diets, toxins
How many sets of genes are found in most adult
All offspring receive 1 chromosome from each
parent, forming homologous pairs.
Diploid (2n)=2 sets
Haploid (1n)=1 set
The diploid cells of most adult organisms
contain 2 complete sets of inherited
chromosomes and 2 complete sets of genes.
Meiosis is the process by which the # of chromosomes
per cell is cut in ½ through the separation of
homologous chromosomes in a diploid cell
Remember: PMAT
Prophase I:
Each replicated chromosome pairs w/ its
corresponding homologous chromosome.
Crossing-over produces new combinations of allleles
Metaphase I: Paired homologous
chromosomes line up across center of
the cell
Anaphase I: Spindle fibers pull each
homologous chromosome pair toward
opposite ends of the cell
Telophase I: Nuclear membrane forms
around each cluster of chromosomes.
Cytokinesis follows, forming 2 new cells
Prophase II: Chromosomes become invisible
Metaphase II, Anaphase II, Telophase II:
Similar to meiosis I, but the result is 4
haploid daughter cells
Fertilized egg= zygote
 Produces
sex cells
 Result= 4 1N cells
 Reduces
number by half
 Produces
 Result=2 2N cells
 No change in
Alleles of different genes tend to be
inherited together from one generation to
the next when those genes are located on
the same chromosome.
Genes that are far apart assort independently, genes
that are linked are on the same chromosome.
Genes that are close together on a chromosome are
NOT likely to cross-over.
The frequency of crossing over between genes can
determine the distances those traits are from each
other on chromosomes. = Gene mapping

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