Download Concept 2: Living things inherit TRAITS in PATTERNS* We can

Concept 2: Living things inherit
TRAITS in PATTERNS…
We can PREDICT Traits!
Review:
Observe the
Family Below
and list some
observable
TRAITS
What traits
seem to have
been passed
down?
Traits Review
• Some traits are inherited
▫ Similar to the traits your parents have
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Eye color
Hair color
Height
Number of arms
• Some traits are acquired
▫ These traits your develop over your lifetime
 Athletic ability
 Reading and writing
 Language
Review: Traits are coded by GENES
• Genes are made out of DNA
• Genes are located on your chromosomes
▫ You (human) contain 23 pairs of chromosomes
(homologs).
• Individuals inherit genes from their parents
• Half of your genetic material is from your mom
and half is from your dad.
▫ Crossing over during meiosis leads to genetic
variation.
Traits are Controlled by Interactions
of Genes
• Each homolog (pair of chromosomes) contains sites
where genes are located.
• The gene will be present on both of the chromosome
pairs, however the form of the gene may be different
• Different forms of the same gene are called alleles
The Father of Genetics
• Gregor Mendel performed the first major
experiments investigating heredity (how genes are
passed on)
• University trained in Mathematics and Science
• Experimented between 1856-1863
• Investigated inheritance among pea plants in his
monastery’s garden
Mendel’s Experiment
• Observed eight different traits of pea plants:
•Plant height
•Seed shape
•Pod shape
•Flower postion
•Pod postion
•Seed color
•Flower color
•Pod color
• Using one trait at a time, Mendel crossed two
plants who were opposite forms of the same trait
• Example: Trait – plant height
▫ Tall plant vs. a dwarf plant
Mendel’s Conclusions
• Each plant must have two “factors” for each
possible trait, one factor from each parent
• Some forms of a trait can be masked
• Traits able to be masked can only be seen if both
the plant’s factors are for that form of the trait
• Mendel’s “factors” are now known as genes and
alleles
Genetic Terms
• Phenotype describes the physical characteristic
that is displayed by your genes; observable (eye
color, hair color)
• Genotype describes the actual genes that you
have on your DNA; not always obvious
(increased risk of Breast Cancer)
Two Forms of Every Gene
• Mendel found that your have two copies of each
allele (one from your dad and one from your mom).
• Alleles can be Dominant or Recessive
▫ Dominant Allele
 Always expressed as a capitol letter (T)
 Physically expressed, regardless of the other allele it is
paired with (Tt or TT)
▫ Recessive Allele
 Physically expressed only when paired with another
recessive allele (tt)
 Always expressed in a lowercase letter (t)
Take Away Messages
• The interactions of the alleles determines the
phenotype of a certain trait.
• Mendel found that there are two factors that come
together when determining traits (one gene from
your mom and one from your dad).
• Alleles can either be recessive or dominant.
▫ In order for a recessive trait to be observed, there must
be TWO copies of that recessive allele.
▫ In order for a dominant trait to be observed, there
must be ONE dominant allele present.