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How were genetics
involved?
(3 – 5 sentence answer)
Heredity
Why do you look like you look?
What made you the way you
are?
All of your genetic information is contained on your
CHROMOSOMES!!
GENES are on your chromosomes!!
DNA is found on your genes!!
Different organisms contain different numbers of
chromosomes!!
Dogs - 78
Cats – 38
Human body cells
46 chromosomes
23 from mom 23 from dad
23 pair of chromosomes
Each pair has a number
from 1-23.
Chromosome 1 from dad/mom
have similar
genetic information.
This is also true for the other
22 pairs.
These chromosome pairs are called
HOMOLOGOUS CHROMOSOMES
Genes that
determine a specific
trait are found in the
same location on
that pair of
chromosomes
Example: the gene
that determines ear
shape is located in
same place on
2 homologous
chromosomes.
Sex Chromosomes
In humans, females
have 2 “X”
chromosomes. So,
each egg contains one
“X” chromosome.
Males have both an
“X” and a “Y”
chromosome. Each
sperm cell contains
either an “X” or a “Y”
chromosome.
Those homologous
chromosomes carry the
genes that make you—YOU!!
Those two make up your
GENOTYPE
Genes passed to offspring.
Genotype determines
Phenotype.
PHENOTYPE
Actual (expression)
Physical appearance.
Dominant and Recessive Alleles
Different forms of same gene
are called
Trait
ALLELES
Alleles will be either:
Dominant = Stronger Trait
Recessive = Weaker Trait
Many traits are controlled
by a single gene.
Hair
Type
Trait Made Trait Made
By
By
Dominant Recessive
Allele
Allele
Curly or Straight
Wavy
Hair
Color
Dark
Light
Earlobe
Free
Attached
Present
Not
Present
Look at the table to the right
for examples of human traits. Dimples
Identifying Genotypes and Phenotypes
Genotype trait is written as
2 letters.
Dominant Allele-Capital Letter
Recessive Allele-Lowercase Letter
The allele that causes free earlobes
is dominant over the allele for
attached earlobes.
So F is used for free earlobe gene.
What do you think is used for
attached earlobe gene?
Lowercase f
Offspring receive 2 copies of
each gene-1 from each parent.
3 possible genotypes
FF, ff, or Ff
The 2 alleles are the exact same-“Homo” ---“the same.”
Homozygous genotypes
Homozygous Dominant-- FF
Homozygous Recessive-- ff
a.k.a--purebred
“Hetero” --- “different.”
Heterozygous genotype
1 dominant allele and
1 recessive allele-- Ff
a.k.a--Hybrid
If an organism inherits a
dominant allele, the
dominant trait is expressed.
Allele for free earlobes –
dominant.
How would you write the
possible genotypes for
free earlobes?
FF and Ff
How would you write the
genotype for attached
earlobes?
ff
Punnett Squares are
used to predict
results of genetic
crosses.
Cross-Mating of 2 parent
organisms
Punnett Squares are used to
calculate probability of
genotypes/phenotypes
in offspring.
Let’s make a Punnett Square with the information below.
Predict outcome of crossing tall pea plant with short pea plant.
First, we must know the genotype of each parent plant.
There are 3 possible genotypes : TT, Tt, and tt
Genotype of pure tall plant : TT <---- It has 2 dominant alleles
Genotype of pure short plant : tt <--- It has 2 recessive alleles.
To make a Punnett Square, 1st separate the parent alleles.
Place 1 pair across top of square, and other pair down the left side.
T
T
t
Tt
tall
Tt
tall
t
Tt
tall
Tt
Genotype –
Genes/letters
Phenotypes –
physical
tall
Dominant Gene always 1st in genotype
Let’s consider a cross between 2 plants with
heterozygous genotypes : Tt (mom) x Tt (dad)
T
t
T
t
TT
Tall
Tt
Tall
Tt
Tall
tt
Short
How many possible genotypes here?
TT, Tt, tt
How many phenotypes?
Tall , Short
Probability
of tall
plants?
3 out of 4,
or 75%.
Probability
of short
plants?
1 out of 4,
or 25%.
We’re done! Let’s answer some questions.
1. 2 different forms of the same gene are called
A. phenotypes. C. dominant traits
B. genotypes. D. alleles
2. An organism’s expressed traits make up its
A. recessive traits C. phenotype
B. genotype
D. alleles
3. A pea plant that is homozygous dominant for seed color
is crossed with a pea plant that is homozygous recessive for
seed color. Since yellow is the dominant color, the letters Y
and y represent the genes for seed color. What cross
represents these 2 plants?
A. Yy x Yy
B. YY x Yy
C. YY x yy
D. Yy x yy
4. Suppose you crossed a pea plant that has round seeds (R)
with a pea plant that has wrinkled seeds (r). If 50 percent of
the offspring have round seeds and 50 percent of the
offspring have wrinkled seeds, what are the genotypes of the
parent plants? Make a Punnett Square to help you
answer the question.
5. You meet a person and notice that she has dimples.
What can you say for sure about the phenotypes of her
parents?
A. At least 1 of her parents has dimples.
B. Both of her parents have dimples.
C. Neither parent has dimples.
D. 1 of her parents does not have dimples