HUMAN HEREDITY
Vocab
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Allele
Codominance
Dihybrid cross
Dominant
F1 generation
F2 generation
Genetic disorder
Genetics
Genotype
Heredity
Heterozygous
Homozygous
•Incomplete dominance
•Law of Independent Assortment
•Law of Segregation
•Monohybrid cross
•Multiple Alleles
•Mutation
•Pedigree
•P generation
•Phenotype
•Probability
•Recessive
•Sex linked trait
Mendel and Heredity
R. GILBERT
Why are you the way you are?
What’s different about these
people?
• Have people ever said you look similar to
your mom or dad?
• Do you look exactly like either of your
parents?
• Why do you think this happens?
Genetics is the study of how
traits are inherited.
Gregor Mendel
• Considered the “Father of
genetics”
• Austrian monk who studied
the plants in his garden;
specifically the pea plant
• The first to use the
mathematics of probability
to explain heredity
Heredity
The passing of traits from the
parent to the offspring
Genetics
The study of heredity
Genes and alleles
• Genes on chromosomes control the
traits that show up in an organism
– Genes control traits like
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Eye color
Skin color
Dimples
Hair type
Many more…
• Alleles are different forms of a trait that
a gene may have.
– The gene for controlling dimples has two
alleles:
Dimples
No dimples
– The gene for controlling hair color has
many alleles:
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Blonde
Black
Red
Brown
Many, many others
Mendel’s
contribution
• Hybrids – offspring that receive different
genetic information for a trait from each
parent…YOU ARE A HYBRID!
• Dominant alleles – covers up or dominates
the other trait (written as a capital letter)
• Recessive alleles – the trait that seems to
disappear (written as a lower case letter)
Traits
• For each trait, an individual has two
factors: one from mom and one from
dad
– If the factors have the same information
the individual is homozygous
• Two dominant alleles or two recessive alleles
– If the factors have different information the
individual is heterozygous
• One dominant and one recessive allele
Parent
Parent
Dimples (d)
No Dimples (D)
(Recessive)
(Dominant)
Offspring
(Dd)
No dimples
Laws of Heredity
• Law of
Segregation –
members of
each pair of
alleles
separate when
gametes are
formed
(meiosis)
Laws of Heredity
• Law of
Independent
Assortment –
pairs of alleles
separate
independently
of one another
during gamete
formation
Genotype- the genetic makeup of an
organism (examples: TT, Tt, tt)
• Homozygous- an organism with two
alleles for one trait that are the
same (TT)
• Heterozygous- an organism with two
alleles for one trait that are
different (Tt)
Phenotype- what an organism looks like
because of its genotype
Probability helps you predict the chance
that something will happen.
• Punnet Squares
– Help you predict
what an offspring
will look like
• Upper case lettersstand for dominant
alleles
• Lower case lettersstand for recessive
alleles
Monohybrid Cross
A cross that
provides data
about one pair
of contrasting
traits
Dihybrid Cross
A cross that involves two pairs of contrasting
traits
Incomplete Dominance
• An individual displays a trait that is
intermediate between two parents
– Example: red flower x white flower =
pink flower
Codominance
• Two dominant
alleles are
expressed at
the same time
– Example: red
coat horse x
white coat
horse = red
and white
coat horse
Multiple Alleles
• Traits that
have genes
with more than
two alleles
– Example:
human blood
types have
three alleles –
A, B, O
Pedigrees
• Family history of traits recorded over
generations
• Used to study human heredity and identify
which relatives exhibit a trait