Chapter 54. Genetic Inheritance
Learning Objectives
Understand how the genetic traits of parents are passed to their biological children.
Describe the connection between dominant-recessive traits and genotype-phenotype differences.
Review
Review
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1. Every important human trait is shaped by the interaction of heredity (“nature”) and environment (“nurture”). The hereditary influences are passed from parents to their child through the specific set of genes contained in the father’s sperm cell and the mother’s ovum.
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2. Each individual gene is a segment of DNA (deoxyribonucleic acid) that can synthesize a specific protein. The total package of genes a child receives—called the genome—contains a complete set of instructions for assembling the human body, as well as for wiring the brain in ways that will make some behaviors more likely than others. These instructions are carried in the 23 pairs of chromosomes found in every human cell (except the sperm cell and the ovum, which have 23 single chromosomes each).
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3. Many genes come in several different versions called alleles. The particular set of alleles a child receives (one from each parent) is called the genotype. Sometimes one allele is dominant over the other recessive allele, and the child’s phenotype (the expressed traits) will not reflect the presence of the recessive allele.
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4. Let’s consider the genetic disease called sickle-cell anemia, one of the rare traits that is controlled by a single gene pair. If we use an uppercase “S” to refer to the dominant “healthy” allele and a lowercase “s” to refer to the recessive allele, this illustration shows the possible combinations of alleles from the mother and father making up the child’s genotype. Only if the child receives the recessive allele from both parents will the child’s phenotype show the disease.
Practice 1: Principles of Genetic Inheritance
Practice 1: Principles of Genetic Inheritance
Each of the large letters represents one of the possible alleles at this gene location. Roll over each letter to view the dominant-recessive pattern of that allele.
To review the principles of genetic inheritance, we will consider human blood types within the ABO blood group system: another rare example of an important trait controlled by a single gene pair. This gene comes in three versions, or alleles, named A, B, and O. Some of the alleles display the familiar dominant or recessive outcomes when paired, but one particular pair displays an unusual pattern called codominance.
A is dominant to O but codominant with B.
B is dominant to O but codominant with A.
O is recessive to both A and B.
Practice 2: Predicting Phenotypes
Practice 2: Predicting Phenotypes
Roll over each genotype combination to view the associated phenotype.
Given the dominant-recessive pattern of alleles for blood groups, what phenotypes (blood type) can you predict from the genotypes: the various combinations of alleles?
| Letter pairs represent the genotype of the child | Father’s contribution | |||
| A | B | O | ||
| Mother’s contribution | A | AA |
AB |
AO |
| B | AB |
BB |
BO |
|
| O | AO |
BO |
OO |
|
Genotype: AA ➔ Phenotype: Type A blood
Genotype: AB ➔ Phenotype: Type AB blood
Genotype: AO ➔ Phenotype: Type A blood
Genotype: AB ➔ Phenotype: Type AB blood
Genotype: BB ➔ Phenotype: Type B blood
Genotype: BO ➔ Phenotype: Type B blood
Genotype: AO ➔ Phenotype: Type A blood
Genotype: BO ➔ Phenotype: Type B blood
Genotype: OO ➔ Phenotype: Type O blood
Quiz 1
Quiz 1
Match the terms to their descriptions by dragging each colored circle to the appropriate gray circle. When all the circles have been placed, select the CHECK ANSWER button.
Quiz 2
Quiz 2
Given the genotypes and phenotypes of the parents, match each child to the correct genetic outcome by dragging each genotype and phenotype to its proper location next to one of the children. When all the genotype and phenotype labels have been placed, select the CHECK ANSWER button.
Conclusion