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• July 20, 1822 - January 6, 1884
• Known as the “Father of Modern
Genetics”
• Austrian monk and scientist that
worked with pea plants to discover
law of inheritance.
• saw that characteristics are passed
from parent to offspring
• work not recognized by scientists
until the early 20th century
• Mendel used pea plants because they
reproduce sexually and contain sex cells
called gametes. Gametes of peas are in
the same flower and fertilize, unite
male and female gametes, through
pollination. (Self-pollinating)
• Mendel was careful with research.
Studied only ONE train at a time and
used cross pollination (took male
gametes from one flower and united
them with female gametes of a different
flower).
• heredity = the passing on of characteristics
from parents to offspring
• traits = characteristics that are inherited
• Genetics = branch of biology that studies
heredity
• gene = the functional unit of heredity (also
called a locus) ; passed from parent to
offspring
•
Organisms have two factors that control
each trait.
1. Characteristics determined by factors
passed down from parents to offspring
-
Genes passed down and located on
chromosomes
- Called alleles, different forms of a gene
- Located on different parts of
chromosomes
2. Principle of Dominance
* States that some alleles will be dominant and some
will be recessive
- dominant = observed trait (shown as uppercase
letter) ex. Tall = T
- Recessive = trait that is masked or disappears (shown
as lowercase letter) ex. Short = t
• only shown when dominant allele not present
* Two different organisms can
look alike but have different
gene combinations
• phenotypes = the way an
organism looks and behaves; the
physical appearance
• genotype = the genetic
combination of the organism
Phenotype = brown hair
Genotype = BB or Bb
Homozygous = same alleles for a trait (purebreed)
Ex. TT, tt, BB, bb, AA, aa
Heterozygous = different alleles for a trait
Ex. Tt, Bb, Aa
* Heterozygous individuals can also be called
hybrids, offspring of parents that have different
forms of a trait
1. Law of Segregation
* States that during
gamete formation, each
allelic pair will
segregate (separate)
from each other leaving
each gamete with one
allele for each gene or
trait.
2. Law of Independent
Assortment
* States that genes for
different traits can
segregate independently
during gamete formation
and pair at random.
Rules for combining probabilities
1. Probability that one event out of a set of mutually
exclusive events will occur is the sum of their
probabilities. (Mutually exclusive events cannot occur
together.) (Look for the word “or”.)
Ex.
What is the probability of rolling a 3 or a 6 on a
6-sided dice?
p = 1/6 + 1/6 = 2/6 or 1/3
2. Probability that both of two independent events
will occur is the product of the independent
probabilities of the single events. (Independent
events do not affect each other.)(Look for the word
“and”.)
Ex.
What is the probability that I roll a 1 and a 3
when rolling two 6-sided dice?
p = 1/6 x 1/6 = 1/36