Genetics Unit
Heredity, DNA, and Genetic
Disorders
What is Genetics?
• The study of heredity
What is heredity?
• The handing down of traits from parents
to offspring
What are gametes?
• Reproductive cells that carry genetic
information.
• Male-sperm
• Female-egg
What is fertilization?
• When gametes are combined and a
zygote is formed
What is a zygote?
• A fertilized egg
What are Genes?
• Units for Hereditary information
• Contain the instructions for making
proteins
What are phenotypes and
genotypes?
• Phenotypes- the way an organism looks
and behaves i.e. tall or short
• Genotype- the gene combination an
organism contains
• i.e. TT tall
• i.e. tt short
What are alleles?
• DNA sequences that
codes for a gene
• Each parent donates 1
allele for a trait
• Mom donates T for tall
• Dad donates T for tall
• Child is TT for tall or
homozygous dominant
What is a homozygous trait?
• When the alleles are
the same
• Ex TT or tt
• Capital letters indicate
dominant
• Lowercase letters
indicate recessive
What is heterozygous trait?
• When you have one
of each allele for a
trait
• Ex. Tt
• Mom donates t
• Dad donates T
• Child will be tall
• Heterozygous
dominant
What does dominant mean in
genetics?
• The dominant gene is
the one that wins out
and its instructions
are carried out.
What does recessive mean in
genetics?
• Refers to the gene
that is suppressed by
the dominant gene
when matched in a
heterozygous pair.
• The only time you see
the recessive gene
expressed is in a
homozygous situation
such as tt
Gregor Mendel
• Why is Gregor
Mendel so important?
1st person to succeed
in predicting how
traits would be
transferred from one
generation from the
next
How did Mendel Succeed?
• He picked pea plants
because they
reproduced sexually
• Mendel could
manipulate parents by
cross pollinating
What is cross pollinating?
• When parents from one
generation can be
physically manipulated to
produce particular traits in
the next generation.
• A person opens flower
and and puts pollen from
selected plant directly on
pistal
What is self pollinating?
• Is the natural method
• No interference from
humans
• Pollen is transferred from
wind, water, & animals such
as insects
What experiment did Mendel
Conduct?
• Mendel crossed a
pure line of Tall pea
plants with a pure line
of short peas. This is
the parent generation
(P1)
• TT-tall pea plants
• tt -short pea plants
Punnet Squares
• A chart that shows all
possible gene
combinations
• The cross produces
the f1 generation or
the filial generation
• As you see here, all 4
offspring will produce
tall plants because
they all have the
dominant trait for tall
F1 generation
• All offspring are tall
He allowed the F1 generation to
self pollinate
• The offspring of the F1 generation were
called the F2 generation
F2 Generation
• The F2 generation were both tall and short
• 1 out of 4 offspring were short
What did all this mean?
• 1) a distinct unit of heredity was
responsible for inherited traits
• 2) 2 units (alleles) control any single trait
• 3) in the F1 generation, the tall factor was
dominant (factor that is seen)
• 4) In the F2 generation, the short factor or
(t) produced 1 short plant So short is
recessive (factor not seen)
Mendel’s Laws
• Law of Segregation
– 2 alleles(factors) or
each trait must be
separate when
gametes are formed
– A parent passes at
random only one
allele(factor) for each
trait to each offspring
Law of Independent Assortment
• Genes for different
traits are inherited
independently of each
other