Chapter 20: Genetics and Human Inheritance Flashcards
What is the ratio of genotypes and phenotypes in the offspring resulting from a cross between a homozygous dominant individual and a homozygous recessive one?
All the offspring will be heterozygous for the trait. Their phenotypes will be the dominant phenotype.
What is a pedigree? What can a family pedigree reveal about the inheritance of a trait?
A pedigree is a diagram showing all the known phenotypes for a particular trait of individuals in an extended family. It can be helpful in determining whether a person who has the dominant phenotype is homozygous or heterozygous. This information can be useful in determining whether a person is a carrier for a harmful recessive trait.
Explain what is meant by codominance by using an example.
Codominance is the condition in which the effects of both alleles are separately expressed in a heterozygote. The human blood type AB is codominant because both the A and the B allele are expressed.
Differentiate multiple alleles from polygenic inheritance.
Multiple alleles occur when there are more than two different alleles for a trait. Human blood types (ABO) are an example of multiple alleles. Polygenic inheritance occurs when more than one gene controls the trait. The effects of polygenic inheritance are a range of phenotypes depending on the number of dominant or recessive alleles inherited. Human height is an example of polygenic inheritance.
What are linked genes? Why are they usually inherited together? What can cause such genes to become unlinked?
linked genes are genes located on the same chromosome. Independent assortment does not apply to linked genes. Crossing over can “unlink” the genes.
Explain why the pattern of inheritance for recessive X-linked genes is different from the pattern for recessive autosomal alleles.
The pattern of inheritance for recessive X-linked genes in males is different from the pattern for recessive autosomal alleles in females because males inherit only one X chromosome. When a male inherits a recessive allele on the X chromosome, the allele is expressed without the other recessive allele present. In contrast, recessive autosomal alleles are not expressed unless they are homozygous.
What two procedures are used for prenatal genetic testing?
Chorionic villi sampling and amniocentesis are two forms of prenatal genetic testing. In amniocentesis, a small amount of amniotic fluid is removed for genetic testing of living fetal cells in the fluid. Chorionic villi sampling involves removal of a small piece of a chorionic villus to be genetically tested. The villi have the same genetic makeup as the fetlus.
Which of the following crosses could produce offspring with the recessive phenotype?
a. AA x aa
b. Aa x Aa
c. AA x Aa
d. AA x AA
answer: B
All of the following crosses have 50% probability of producing heterozygous offspring except:
a. AA x aa
b. Aa x Aa
c. AA x Aa
d. Aa x aa
answer: A
Which of the following is an example of a phenotype?
a. a man with hemophilia
b. a female carrier for cystic fibrosis
c. XY
d. a heterozygote
answer: A
Huntington’s disease is caused by a dominant allele. If a mother has Huntington’s disease but the father does not carry the dominant allel, what is the probability that the first child will be normal?
a. 0%
b. 25%
c. 50%
d 100%
answer: C
In the previous example, what is the probability that the second child will be normal?
a. 0%
b. 25%
c. 50%
d. 100%
answer: C
How many different gametes could a person with the genotype Aabbcc form?
2
How many different games could a person with the genotype AaBbCc form?
16
Cystic fibrosis is caused by a recessive allele, c. What is the probability that two people who are carriers for cystic fibrosis will have a child who is also a carrier?
50%
