Lifespan: Chapter Two Handout
From the PowerPoint Presentation: Genetic Abnormalities Name Description Effect Treatment Incidence Down Syndrome Extra/altered 21st Retardation, Surgery, early 1/1,900 at 20 yrs chromosome physical intervention, 1/300 at 35 yrs abnormalities infant stimulation, 1/30 at 45 yrs special learning programs Klinefelter Extra X Physical Hormone therapy 1/800 males syndrome chromosome (Xxy) abnormalities Fragile X Stretched out X Retardation, SpEd, speech & More common in syndrome chromosome learning language therapy males than disabilities, females attention problems Turner syndrome X0 in females Retardation, Hormone therapy 1/3000 fem. sexual underdevelopment XYY Extra height None needed 1/1000 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
M1 Mother’s two genes 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
M1 F1M1 F2M1 Mother’s two genes 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
B Mother’s two genes 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
b Mother’s two genes 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 B
b Bb Mother’s two genes 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
B Mother’s two genes 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
b Mother’s two genes 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 b
B Mother’s two genes 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. The child’s genotype is BB B. The child’s phenotype is blue eyes C. The child is not the biological child of these parents D. 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.