Deck 2: C: Genetic Bases of Child Development

Question 1

Explain what is meant by a reaction range and give an example of how a reaction range might work.

Answer 1

A good answer will include the following key points:
Reaction range: The same genotype can produce a range of phenotypes, in reaction to the environment where development takes place.
For example, individuals with the genotype for phenylketonuria (PKU) lack an enzyme that breaks down the amino acid, phenylalanine, which is found in many foods that children regularly eat. If phenylalanine is ingested, it will accumulate in the child's body, damage the nervous system and lead to delayed mental development. If, though, the child is placed on a diet that limits phenyl- alanine, the disease does not emerge and the nervous system develops normally.

Question 2

You and a friend were talking about the role of heredity and environment and your friend said, "Heredity is destiny. When someone inherits genes for bad diseases there is nothing about the environment that can change the negative effects." What can you tell your friend about the interaction of heredity and environment in cases such as those involving individuals with phenylketonuria?

Answer 2

A good answer will be similar to the following:
You can tell your friend that heredity is not destiny. One can inherit a particular genotype but that genotype can interact with a particular environment to change the phenotype. In the case of phenylketonuria (PKU), an individual may inherit the gene for PKU. Typically, the individual lacks an enzyme that breaks down phenylalanine. Phenylalanine is found in many foods such as meats and dairy products. When the phenylalanine is not broken down it builds up and produces toxins that damage the nervous system, which leads to mental retardation. However, if the environment is changed so that the amount of phenylalanine in a child's diet is reduced, then the damage to the nervous system does not occur and normal intelligence occurs. In other words, the same genotype for PKU can interact with two different environments (either a regular diet or a low-phenylalanine diet) to lead to two very different outcomes (either normal intelligence or mental retardation). So, even in the case of a negative, inherited disorder the environment can still play an important role in shaping the environment.

Question 3

Why are African Canadians more likely to inherit sickle-cell disease?

Answer 3

African Canadians are more likely to inherit sickle-cell disease because the sickle cell has a benefit: Individuals with this allele are more resistant to malaria. Therefore, in parts of the world (such as Africa) where malaria is found you are also more likely to find individuals carrying this trait. Having two alleles for sickle-cell disease has devastating consequences to the carrier. However, having only one sickle cell allele results in a person who is more resistant to malaria and yet suffers from the disorder only when put under extreme conditions (in instances of low oxygen). Therefore, having sickle-cell trait is quite adaptive in Africa. However, it has no adaptive value in Canada and accordingly we are seeing fewer and fewer individuals with sickle-cell trait in successive generations of African Canadians.

Question 4

Explain basic concepts of single gene inheritance using the terms alleles, chromosomes, homozygous, heterozygous, dominant, recessive.

Question 5

Name and briefly describe some common disorders associated with recessive alleles.

Question 6

Explain how (a) twin studies and (b) adoption studies are used to determine the influence of heredity on a trait and discuss a potential flaw of each type of study.

Question 7

Name and describe (a) a disorder caused by an abnormal number of autosomal chromosomes, and (b) a disorder caused by an abnormal number of sex chromosomes.

Question 8

Your friends Shania and Ricky are expecting a baby. Both Shania and Ricky are farsighted and have cheek dimples. Shania and Ricky have said that they hope that their baby won't need to wear glasses or have cheek dimples because they both hate their glasses and dimples. What can you tell them about genetic inheritance and the likelihood that they will get their wish?

Question 9

Explain the general properties of the paths from genes to behaviour.

Question 10

Describe phenylketonuria. What is it, its causes, its symptoms, and treatment?

Question 11

The other day I heard someone say "There is no such thing as twins who are brother/sisters (mix-sex twins)." What would you have said if you had been there?