Chapter 29: Heredity - Check Your Understanding
What term refers to chromosomes other than our sex chromosomes?
Chromosomes other than sex chromosomes are called autosomes.
Is an allele represented by a capital letter presumed to be dominant or recessive?
An allele represented by a capital letter is presumed to be a dominant allele.
Adam is homozygous for the dominant alleles HH, CC, and LL, and heterozygous for Bb and Kk. He is blonde and blue-eyed and has a very hairy chest. Which of these descriptions refers to his phenotype?
Descriptions of his phenotype are blonde, blue-eyed, and hairy chest.
MAKING CONNECTIONS: When a geneticist orders a karyotype, the cells studied are in metaphase. From your knowledge of the cell cycle, state why it is that chromosomes are more easily identified during metaphase than during interphase.
Chromosomes are not visible during interphase. The DNA-containing material is the form of dispersed strands of chromatin. As mitosis begins, the chromatin coils and condenses, becoming visible as chromosomes. Chromosomes continue to condense throughout prophase and are most visible during metaphase.
We said that genetic variability is introduced by independent assortment. Just what is assorting independently?
The alleles on different pairs of homologous chromosomes are segregated independently of each other to different gametes.
How does crossover increase genetic variability?
It causes separations of linked genes on the same chromosome, produced gametes with more varied genomes.
Why are there so few genetic disorders caused by dominant genes?
Dominant genes are expressed. Thus if the gene is lethal, the carrier will probably not live very long or will die during development.
How does incomplete dominance differ from codominance?
In incomplete dominance, the heterozygote has a phenotype intermediate between that of the dominant and recessive alleles [for example, for the sickling gene, the dominant homozygote (SS) has no evidence of sikcling; the heterozygote (Ss) has sickle-cell trait; and the homozygote for the recessive gene (ss) has sickle-cell anemia]. In codominance, both dominant alleles are expressed (as in ABO blood types).
Why does a male always express an X-linked recessive allele?
A male always expresses an X-linked recessive allele because, unlike a female, he does not have a second X chromosome containing homologous alleles to blunt or counteract the effect. The Y chromosome lacks most of the genes carried on the X chromosome.
How can you explain why parents of average height can produce very tall or very short offspring?
Height is an example of a trait conferred by poly gene inheritance in which several genes on different chromosomes contribute to the trait. Such traits show a distribution of phenotypes that yields a bell-shaped curve.
Which of the following factors may alter gene expression? Other genes, measles in a pregnant woman, lack of key nutrients in the diet.
Other genes, measles in a pregnant woman, and lack of dietary nutrients all may alter the gene expression.
What process labels genes as paternal or maternal?
Genomic imprinting labels genes as maternal or paternal.
What is the source of the genes that confer extranuclear inheritance?
Maternal mitochondrial DNA confers extranuclear inheritance.
Which fetal testing procedure depends on analyzing amniotic fluid?
Amniocentesis analyzes chemicals and cells in amniotic fluid.
What non invasive imaging procedure is used to determine some aspects of fetal development?
Ultrasound imaging is used to determine some aspects of fetal development (fetal age for example) and is non invasive.