Transcript Mendelian Genetics

Introduction to Genetics
The study of heredity: how genetic factors are
passed down from one generation to the next
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His experiments with
pea plants laid the
foundations of the
science of genetics
Male part: produces pollen
Female part: where fertilized egg
will become a seed
Mendel cross-pollinated
a purple plant with a white plant
He found all the
offspring produced
purple flowers.
What happened to the
white flower trait?
P generation: Parental generation; always
True-breeding, or “pure-bred”
F1 generation: First Filial Generation;
offspring of P gen, always hybrids
PP
pp
x
Pp
Pp
PP
Pp
Pp
pp
Mendel made the F2 generation by
crossing plants from F1 together. He found
3 purple flowers for every 1 white flower.
Mendel found the same pattern with
many other pea plant traits.
Mendel’s Law of Segregation
explains how genes are passed to
the next generation.
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
Alleles are segregated into separate egg
cells and sperm cells. Each reproductive
cell will pass on ONE of the alleles.
New pairs of genes are created for the
next generation during fertilization
Because of sexual reproduction, you
are a product of your mom’s genes and
your dad’s genes
Each chromosome contains thousands of
genes. Each gene is the DNA code for
making a specific protein. The proteins give
you your trait.
The alternate forms of genes
are called alleles.
You always get two alleles for a trait.
The combination of alleles for a
specific trait are called the genotype.
This is represented by two letters.
P
p
If both alleles are the same, then they
are homozygous. If they are different,
they are called heterozygous.
http://www.abpischools.org.uk/page/modules/genome/dna2.cfm
Sometimes, one allele
is expressed as a trait
and the other isn’t.
The dominant allele is
expressed and the
recessive allele is not.
The observable trait is called the
phenotype. The phenotype is a
result of the genotype.
P p
If you know your genotype for a specific
trait, you can predict the traits of your
offspring! Use a Punnett Square.
P
p
Offspring
Genotypes
p
P
How to Solve a genetics
problem
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Read the problem
Take notes:
 _____=Gray body
 _____=black body
Box the parent descriptions:
 Heterozygous gray body
 Black body
Determine the genotypes of the parents (_, _)
Fill in the Punnett square and solve
G
g
g
Heterozygous X black
Gray (Gg)
(gg)
g
Genotype probabilities: Gg=50%, gg=50%
Phenotype probabilities: gray bodies=50%,
black bodies=50%
Situation: A client wants to buy pure bred
black puppies from your dog. This means
your dog must be pure black to make pure
bred puppies.
How can you tell if
your black lab is
BB or Bb?
Conduct a test cross and breed it with a
brown lab (homozygous recessive) to find
out and examine the traits of the puppies.
These puppies are not for sale,
but give you important information
about your dog.
Practice Makes Perfect
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Now practice using the terminology and
Punnett Squares to determine possible
traits