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Topic: Genetics
Aim: What is genetics?
Do Now: Complete the chart.
DNA
Number of Strands
Sugar
Nitrogen Bases
Where it’s found in the
cell
RNA
Topic: Genetics
Aim: What is genetics?
Do Now:
•What is a
trait?
•What is
GENETICS?
•What is
heredity?
• a physical
characteristic of an
organism
• hair color, eye color,
height, skin color…
• The study of heredity
• The passing on of
traits from parent to
offspring
Topic: Genetics
Aim: What is genetics?
Do Now: What are the three
different types of RNA? How does each
relate to protein synthesis?
What is the chromosome theory of
inheritance?
• Genes are carried from
parents to offspring on
chromosomes
Topic: Genetics
Aim: How are dominant and
recessive genes different?
Do Now: What is a trait? Provide three
traits that you express.
•Who is Gregor • Father of Genetics
Mendel?
• Studied how traits
are passed on from
one generation to the
next
• Used PEA PLANTS
and cross-pollinated
them
• Traits studied:
height, seed color,
seed shape
•What
are
genes?
• Units of heredity that control
a trait
• Found on chromosomes
• There are 2 genes (ALLELES)
for every trait (1 comes from
each parent)
• Alleles: different forms of a
gene
• Example: T = tall gene
T
sperm
+
T 
TT
egg
zygote
A Gene
ALLELE
Gene from dad
ALLELE
Gene from mom
Homologous chromosomes
•Dominant • “stronger” gene/trait
• Capital letter
gene
•
•Recessive
gene
Example: T = tall pea plant
• “weaker” gene/trait
• lower case
• Example: t = short pea plant
Recessive “weaker”
Dominant “stronger”
Possible Gene Combinations
• Gene
combinations
• TT
• Tall
T +
T
 TT
• Pure or homozygous dominant
• tt
• Short
t
+
t
 tt
• Pure or homozygous recessive
• Tt
• Tall
T
+
t

• Hybrid or heterozygous
• *ALWAYS SHOWS
DOMINANT TRAIT*
Tt
Topic: Genetics
Aim: What are genotypes and
phenotypes?
Do Now: 1. Who is the father of
genetics? What did he study to explain
his theories of heredity?
2. Explain the difference
between dominant and
recessive genes.
•Phenotype • Physical appearance
• Tall, short, blue eyes,
brown hair
•Genotype
Phenotype (red)
Genotype (RR)
• Genetic Makeup
• Homozygous/pure dominant
(TT)
• Homozygous/pure recessive
(tt)
• Hybrid/ Heterozygous
(Tt)
• Example:
• G = green seeds
• g = yellow
seeds
• Give 3 possible
gene combos
with
phenotypes and
genotypes.
• GG, gg, Gg
• GG
• Phenotype = green
• Genotype = homozygous dominant
or pure dominant
• gg
• Phenotype = yellow
• Genotype = homozygous recessive
or pure recessive
• Gg
• Phenotype = green
• Genotype = hybrid or
heterozygous
• LAWS OF
GENETICS
• Law of
• Some alleles are
Dominance dominant, and some are
recessive
• Dominant genes hide
recessive genes when
both are inherited by an
organisms (hybrid)
• Law of
Segregation
• During meiosis, every sex
cell gets 1 gene from each
pair of chromosomes
• Alleles are separated
during gamete formation
• Law of
Independent
Assortment
• Each pair of genes for a trait are
inherited independently of gene pairs
of other traits
• Example: The height of a pea plant
and the color of its seeds have no
impact on each other.
• (On the chromosomes, the genes for
height are separate from the genes for
seed color)
Topic: Genetics
Aim: How can we predict
genotypes and phenotypes?
Do Now: Explain the difference
between dominant and recessive genes.
What are Punnett Squares?
• Special charts that show possible gene
combinations between 2 organisms
• Shows four possible offspring
What are Punnett Squares?
•
Example:
T = tall t = short
TT x tt (tall x short)
1.
2.
3.
4.
Draw Punnett Square
Set up
Fill in boxes
Describe offspring
T
T
t
Tt
Tt
t
Tt
Tt
How can we describe the offspring?
• Give phenotype and
genotype
T
T
t
Tt
Tt
t
Tt
Tt
• 4 Tt
• Phenotype: 4/4 or 100% Tall
• Genotype: 4/4 or 100% Heterozygous
(hybrid)
Topic: Genetics
Aim: How do we use Punnett Squares to
predict genotypes/phenotypes?
Do Now: Use the information you
learned in class to complete the
worksheet.
Topic: Genetics
Aim: How can we use Punnett
Squares to predict traits?
Do Now: Let T = tall, t = short. Cross a
pure dominant tall pea plant with a pure
recessive short pea plant. What is the
probability of having a homozygous recessive
offspring?
Topic: Genetics
Aim: How can you create a
Halloween monster?
Do Now: A man who is heterozygous for
brown hair marries a woman who is hybrid for
brown hair. If blonde hair is a recessive
trait, what is the probability of having an
offspring with blonde hair. Also, give the
phenotypes and genotypes of all possible
offspring.
Topic: Genetics
Aim: What is incomplete
dominance?
Do Now: Cross a pea plant that is pure
dominant for seed shape with another pea
plant that is homozygous recessive for seed
shape. Describe the offspring.
S – spherical
s – dented
• Incomplete
Dominance
(codominance)
• When certain genes are neither
dominant or recessive
• Get a blending or mixing of
traits
• Example: four o’clock flowers
• RR
x
WW
 RW
red
white
pink
Principles of Genetics
• Traits are passed on from one generation
to the next.
• Traits are controlled by genes.
• Organisms inherit genes in pairs (2 alleles
for every trait – 1 from mom, 1 from dad).
• Some genes are dominant, some are
recessive.
• Dominant genes hide recessive genes when
both are inherited by an organism.
• Some genes are neither dominant nor
recessive (incomplete dominance)
Topic: Genetics
Aim: How can we create superhero
babies?
Do Now: Why are males more likely than
females to express a sex-linked trait?
Quiz
•
•
B – black b – white
Two parents, one homozygous recessive
the other heterozygous black, have
offspring.
1. What is the probability that an offspring
will be white?
2. What is the probability that an offspring
will be pure recessive?