BIO Chapter 9 Q's

result in hybrid plants **The offspring of the crossing of different varieties are referred to as hybrids.

recessive to

0 homozygous black (BB): 1 heterozygote (black) (Bb): 1 homozygous orange (bb) **The heterozygous black-eyed MendAlien has the genotype Bb. The orange-eyed MendAlien has the genotype bb. The result of this cross is two Bb offspring and two bb offspring. This 2:2 ratio reduces to 1:1.

1 black : 1 orange **The heterozygous black-eyed MendAlien has the genotype Bb. The orange-eyed MendAlien has the genotype bb. The result of this cross is two Bb offspring and two bb offspring. This means that two of the offspring have black eyes and two of the offspring have orange eyes. This 2:2 ratio then reduces to 1:1.

bb ** The result of this cross indicates that the flat headtop allele is dominant to the wild-type headtop. Thus, the only way to express a wild-type headtop is to be homozygous recessive.

BB ** Since all of the offspring have flat headtops, it is reasonable to conclude that the allele for flat headtop is dominant to the wild-type headtop allele.

Are all Bb ** This cross indicates that the flat headtop allele is dominant to the wild-type headtop allele, so all offspring are indeed Bb.

1. A? x aa ** A testcross is used to determine whether an individual expressing the dominant phenotype is homozygous dominant or heterozygous.

Mendel's law of segregation only ** Mendel's law of segregation is based on gametes getting only one copy of each allele of each gene.

the second filial generation, or the "grandchildren" of the original mating pair **F2 is shorthand for second filial generation, or the "grandchildren" of the original mating pair

Perform a cross between two true-breeding individuals and observe the trait or traits expressed by the F1 individuals. **The F1 plants are hybrids that contain both forms of the gene, so the trait the F1 plants display is the dominant trait.

EEGgcc **Individuals with one or two dominant alleles of a gene are indistinguishable, so EE and Ee have the same phenotype, as do GG and Gg.

a breeding experiment in which the parental varieties differ in only one character.

An organism with two different alleles for a single trait is said to be homozygous for that trait.

NnllddMM

is caused by a recessive allele **The most common lethal genetic disease in the United States is cystic fibrosis, which is recessively inherited. The parents in this case would be heterozygotes, or carriers for the disease.

In the ratio 1:1 homozygotes to heterozygotes ** In a cross between two heterozygotes (Aa), the next generation will be in the ratio 1:1 homozygotes (AA, aa) to heterozygotes (2 Aa).

The same locus on homologous

an alternative version of a gene **A diploid organism has two alleles for each autosomal gene. The two alleles are found at comparable locations on homologous chromosomes. The alleles may be identical or slightly different, but they affect the same genetic character.

independent assortment of alleles of one gene relative to the alleles of any other gene **Independent assortment of alleles of one gene relative to the alleles of any other gene

9:3:3:1

four ... one **DdEe individuals can produce the following gametes: DE, De, dE,de. A ddee plant can produce only de gametes.

Either one of her parents or both of her parents were heterozygous for the trait. **From the information provided, it is not possible to discern which of these is correct for sure. If one of Mary's siblings did develop the disorder, you could determine that both of the parents were heterozygous.

heterozygous for the trait and able

Lethal dominant alleles are harmful whether they are carried in homozygous or heterozygous form, so there is always strong selection against these alleles. **The ability of lethal recessive alleles to "hide" from selection in heterozygotes accounts for their prevalence relative to dominant alleles, which are always visible to selection.

not affected at all by the disease.

1/4 **This is the probability of giving birth to an HH homozygote, the only genotype conferring normal cholesterol levels.

cannot strictly account for the patterns of inheritance of many traits.

hypercholesterolemia

.5 **About half the offspring would be expected to inherit the IA allele and be phenotypically A.

codominance

50% **The woman must be ii. The husband is A, but must be a carrier of the i allele, as his father was B. (The father did not give him a B allele, or the husband would be AB, so he must have given him a recessive i allele.) The cross ii × IA i yields a 50% probability that the child will be ii, or type O.

the pleiotropic effects of the sickle-cell allele ** Sickle-cell disease is pleiotrophic; that is, the gene influences many symptoms.

XX

one X chromosome and one Y chromosome

one

is called a sex-linked gene.

100% **Because daughters receive one of their X chromosomes from their father, and this chromosome contains the dominant allele, all daughters will be affected.

XCXc **Because this is an X-linked recessive condition, she must possess at least one allele for color blindness to have an affected son. Because she has normal color vision, she must also have one normal allele.

50% of sons and 50% of daughters Correct.s Because sons obtain their single X chromosome from their mother, they have a 50% chance of inheriting the homolog that carries the hemophilia allele. And because daughters inherit their father's only X chromosome and one of the two X chromosomes of their mother, in this cross they have a 50% chance of being homozygous for the hemophilia allele.

men need to inherit only one copy of the recessive allele for the condition to be fully expressed.