Heredity Heredity is the passing of traits from one generation to another, or inheritance.

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HeredityHeredity is the passing of traits
from one generation to another, or inheritance.
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Inherited Traits vs. Environmental Factors

• Inherited Traits are those that are passed from
  parent to offspring
• Environmental Factors can also have an effect on
  how you look
• Diet
• Exercise
• Smoking/Drinking
• Sun exposure

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Why do I look like my parents?!You look like
your parents because genetic information (DNA) is
passed from parent to offspring during sexual
reproduction.Each sex cell (egg or sperm) of the
parent organism (plant or animal) contains
one-half of the genetic material needed to create
a new organism.
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Who do you look like?Draw a picture of yourself
and then label all of the traits that you
inherited from someone in your family (write the
family members name beside that trait)For
example, if your hair is red and your mothers
hair is red, write her name beside your hair.
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What are Chromosomes?A structure found in the
nucleus of a cell that contains the genetic
information (DNA).Remember, these are those
things you were drawing that doubled and split in
Mitosis and Meiosis. Humans have 46 in every cell
except sex cells, which have 23.
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What Is a Gene?

• A gene is a segment of DNA found on a chromosome
  that determines the inheritance of a particular
  trait.
• Genes are what make one individual look different
  from another

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Principles of Heredity

• Each trait is governed by two factors now
  called genes.
• 2. Genes are found in alternative forms called
  alleles.
• 3. Some alleles are dominant and mask alleles
  that are recessive.

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Dominant TraitsDominant Trait- a trait that
will always be expressed in the phenotype.These
alleles are represented by a capital letter.Ex.
Having a widows peak is dominant to not having a
widows peak.
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Recessive Trait
Recessive Trait- a trait that will only be
expressed in the phenotype if two recessive
alleles are present. In the presence of a
dominate trait, the recessive trait will not be
expressed. These alleles are represented by
lowercase letters. Ex. Hitchhikers thumb is
recessive to straight thumb.
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Seven Traits used by Mendel in Genetic Studies
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Genotype and Phenotype
Genotype alleles carried by an individual
ex. RR, Rr, rr Phenotype physical
characteristic or appearance of an individual
ex. Round, wrinkled
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Principles of Heredity
Homozygous Dominant
Homozygous Recessive
Heterozygous
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Homozygous parents can only pass one form of an
allele to their offspring.
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Heterozygous parents can pass either of two
forms of an allele to their offspring.
R
r
R
r
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Principles of Heredity

• Mendel was a scientist studying peas as a way to
  explore genetics.
• He needed to explain
• Why one trait seemed to disappear in the first
  generation.
• 2. Why the same trait reappeared in the second
  generation in one-fourth of the offspring.

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Mendels Principle of Genetic Segregation

• In the formation of gametes, the members of a
  pair of alleles separate (or segregate) cleanly
  from each other so that only one member is
  included in each gamete.
• Each gamete has an equal probability of
  containing either member of the allele pair.

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Genetic Segregation
Parentals RR x rr
F1 x F1 Rr x Rr
R R r r
R r R r
½ R ½ r
r r
¼ RR
¼ Rr
R R
½ R ½ r
Rr
Rr
¼ Rr
¼ rr
Rr
Rr
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Genetic Segregation
Genotypic Ratio ¼ RR ½ Rr ¼ rr Phenotypic
Ratio ¾ Round ¼ Wrinkled
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Mendels Principle of Independent Assortment

• When gametes are formed, the alleles of one gene
  segregate independently of the alleles of another
  gene producing equal proportions of all possible
  gamete types.

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Using Probability in Genetic Analysis
1. Probability (P) of an event (E) occurring
P(E) Number of ways that event E can occur
Total number of possible outcomes
Eg. P(Rr) from cross Rr x Rr 2 ways to get
Rr genotype 4 possible outcomes
P(Rr) 2/4 1/2
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Sex Determination
Female Male XX x XY
½ X ½ X
¼ XX
¼ XX
½ X ½ Y
¼ XY
¼ XY
Phenotypic Ratio of Offspring ½ Female ½ Male
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Colorblindness
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Pedigree for Colorblindness, an X-linked
Recessive Trait
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