Download Ch 9 Phenotypes and Genotypes

Lifespan: Chapter Two Handout
From the PowerPoint Presentation:
Genetic Abnormalities
Name
Down Syndrome
Description
Extra/altered 21st
chromosome
Effect
Retardation,
physical
abnormalities
Klinefelter
syndrome
Fragile X
syndrome
Extra X
chromosome (Xxy)
Stretched out X
chromosome
Turner syndrome
X0 in females
Physical
abnormalities
Retardation,
learning
disabilities,
attention
problems
Retardation,
sexual
underdevelopment
Extra height
XYY
Treatment
Surgery, early
intervention,
infant stimulation,
special learning
programs
Hormone therapy
Incidence
1/1,900 at 20 yrs
1/300 at 35 yrs
1/30 at 45 yrs
SpEd, speech &
language therapy
More common in
males than
females
Hormone therapy
1/3000 fem.
None needed
1/1000 males
1/800 males
Phenotypes and Genotypes
One way to calculate the odds that parents with a particular gene in their genotype will pass it on to their
children is to draw a table with the father’s two genes for that genotype on the top and the mother’s two genes
on the left.
Father’s two genes
F1
F2
Mother’s two
genes
M1
M2
The box is filled in very simply. The letters at the top of each column are written into the boxes reading
down and the letters at the side are written into the boxes ready across.
Father’s two genes
F1
F2
Mother’s two
genes
M1
F1M1
F2M1
M2
F1M2
F2M2
As you can see from examining the boxes, a child could inherit any one of four possible combinations
from the parents’ two pairs of genes. The chances of each child inheriting one of these combinations is one in
four, or 25 percent.
Consider how this works in practice. When both parents have two brown –eye genes, all the children
will have brown eyes as well and two brown-eye genes.
Parents’ phenotype (physical manifestation of eye color): brown eyes
Parent’s genotype (genetic inheritance of eye color): Father BB (B being brown) Mother BB.
Using B to represent the gene for brown eyes, fill in the table to show the possible genotypes of the
children.
Father’s two genes
B
B
Mother’s two
genes
B
B
What is the children’s phenotype (what color eyes will all possible children of this union
have)?_______________________
What genotype will all the children of this union be with respect to eye
color?______________________________
The same pattern holds true if both parents have two blue-eye genes. Here we use b to represent the
blue-eye gene.
Parents’ phenotype: blue eyes. Parents’ genotype: Father =bb Mother=bb
Using b to represent the gene for blue eyes, fill in the table to show the children’s genotype.
Father’s two genes
b
b
Mother’s two
genes
b
b
What is the children’s phenotype?_______________________
What is the children’s genotype?________________________
It gets more complicated if one parent- for example, the father, has two brown-eye genes (BB) and the
other, the mother, has two blue-eye genes (bb). All of the children will inherit one brown-eye gene and one
blue-eye genes. This means that they will all have brown eyes, because the brown-eye genes is DOMINANT
over the blue-eye gene (which is RECESSIVE). Dominant genes are always expressed in your phenotype (if
you have a dominant brown gene your eye color will be brown). Recessive genes are only expressed in the
phenotype if you have both genes recessive (the only way to have blue eyes is to have two recessive blue genes).
In this case, even though the children will all have brown eyes, they will be carriers of the recessive blue-eye
gene. Complete the table for this pair.
Father’s two genes
B
Mother’s two
genes
b
B
Bb
b
What is the children’s phenotype (eye color)?__________________
What is the children’s genotype?___________________________
Now, what if one parent- let’s say the father- has one brown-eye gene and one blue-eye gene (Bb),
while the mother has two brown-eye genes (BB). In this case we first observe children who will all have the
same eye color, but will have potentially different genotypes depending on the luck of the draw.
Father’s two genes
B
b
Mother’s two
genes
B
B
What is the children’s phenotype?___________________________
What are the potential genotypes for children of this union?________________________
In the next table, we observe parents with different eye colors. The father has Brown eyes, but carries a
recessive blue gene, while the mother has blue eyes (since blue is recessive we know she must carry two blue
genes). Fill in the table below.
Father’s two genes
B
b
Mother’s two
genes
b
b
What are the potential phenotypes for eye color?___________________ In this case the children have
a _____________ percent chance of having blue eyes.
What are the potential genotypes for eye color?_____________________
In a final case, let’s consider how two brown-eyed parents can produce blue-eyed children. This is
possible if they both have a recessive blue gene.
Father’s two genes
B
Mother’s two
genes
b
B
b
What are the potential phenotypes (eye colors) of the children?_____________________
What are the potential geneotypes (there are 3) of the children?_____________________
What percent chance do these two brown-eyed parents have of producing a blue-eyed
child?
______________________________
One last question.. If you have two blue-eyed parents (and blue is a recessive gene) and they have a
brown eyed child, what do you know to be true about the situation?
A.
B.
C.
D.
The child’s genotype is BB
The child’s phenotype is blue eyes
The child is not the biological child of these parents
The child’s genotype is Bb
Nature/Nurture Exercise
For each of the following situations decide whether the example represents the nature perspective or nurture
perspective.
1. John Locke, a famous philosopher, believed that we are all like chalkboards. We are born blank and
whatever gets "written on us" occurs after birth.
2. Your neighbor is having much trouble with her teenage daughter. When you talk to her about it, she
explains that her daughter is a "difficult" child. She has always been "difficult"--even as a newborn.
3. A woman in your political science study group feels that all criminals should be kept locked up forever or
killed. She does not feel that the government should spend money on trying to rehabilitate these people.
She claims that criminals are just criminal and rehabilitation is useless.
4. The National Institute on Early Education is a private organization that provides funding for early childhood
and pre-school education initiatives. Obviously they believe these initiatives make a difference in the
development of at-risk children.
5. Several members of the board of directors of an organization have done research with identical twins. In
their research, the correlation between IQ scores of identical twins is much higher than the correlation
between IQ scores of fraternal twins or non-twin siblings.
6. A parent has a teenage child with a psychological disorder. Imagine that this parent believes that
psychological disorders are a result of early experience. He believes that his child's disorder was acquired
through a process of learning early in development.