Extensions to Mendel's Law

In some gene interactions, the four Mendelian genotypic classes produce fewer than four observable phenotypes. Why?

In the case of the Labrador coat colors, the dominant B allele of the first gene determines black, while the recessive bb homozygote is chocolate brown. With the second gene, the dominant E allele has no visible effect on black or chocolate coat color. What happens when there is a double dose of the recessive allele (ee)?

Epistasis

The allele doing the masking (e allele of the E gene) is ________ to the gene that is being masked (the _______ gene).

In our Labrador coat example, where homozygosity for a recessive e allele of the second gene is required to hide the effects of another gene, the masking phenomenon is called ________ ________. Why?
The recessive ee homozygous genotype is considered _______ to any allelic combo at the first gene

What is the result of crossing pure-breading BB EE labs and one type of pure-breeding yellow retriever (bb ee) labs. Determine the coat color of the F1 generation and the possible coat colors of the F2 generation as well as the expected ratio (use a Punnett Square)

In the dihybrid cross of the Labradors, why are there only three phenotypic classes?

The telltale ratio of recessive epistasis in the F2 generation is:

Why can't you tell simply by looking, if the genotype of a yellow Labrador will be B- (black) or bb (chocolate) at the B locus

Explain why, in rare instances, two parents who appear to have blood type O, and thus would be predicted to be genotype ii, produce a child who is either blood type A (genotype I^Ai) or blood type B (genotype I^Bi)

The Bombay phenotype actually arises from __________ for a mutant recessive allele (hh) of a second gene that ______ the effects of any ABO alleles that might be present

In construction of the red blood cell, surface molecules that determine blood type, type A individuals make an ______ that adds polysaccharide A onto a sugar polymer known as ________; type B individuals make an altered form of the ______ that adds polysaccharide B onto the sugar polymer _______. Type O individuals make ________ _______.

With regard to their substance H, what is the result of type O individuals making neither A-adding nor B-adding enzyme?

All people of A, B, or O phenotype carry at least one _______ _____-_____ H allele for the second gene and thus produce some _______.

In the rare Bombay phenotype individuals with genotype hh for the second gene, they do not make ________ at all, so even if they make an ________ that would add A or B to this polysaccharide base, they have ________ to add it onto. The result is that they appear to be type ___

Due to circumstances resulting in Bombay phenotype individuals appearing to be type O, __________ for the recessive h allele of the H-substance gene ______ the effects of the ABO gene, making the hh genotype _______ to any combo of I^A, I^B, and i alleles

A person who carries I^A, I^B, or both I^A and I^B but is also an hh homozygote for the H-substance gene may appear to be type O, but he or she will be able to pass along an ___ or ___ allele in sperm or egg.

The offspring receiving, let's say an I^A allele for the ABO gene and a recessive h allele for the H-substance gene from its father plus an i allele and a dominant H allele from its mother would have blood type ___ (genotype ___, ___) even though neither of the parents is phenotype A or AB

Many different types of biochemical pathways may produce any specific F2 phenotypic ratio. The ratio may suggest or limit possibilities, but it cannot by itself provide enough information to allow you to infer the ______ ______. Does this go both ways?

Epistasis can also be caused by a _______ ______

In summer squash, two genes influence the color of the fruit. With one gene, the dominant allele (A-) determines yellow, while homozygotes for the recessive allele (aa) are green. A second gene's dominant allele (B-) produces white, while bb fruit may be either yellow or green depending on the ________ of the first gene.

In the interaction between these two genes, the presence of B _____ the effects of either A- or aa, producing white fruit, and B- is thus _______ to any genotype of the A gene. The recessive b allele has _____ effect on fruit color determined by gene A

Epistasis in which the dominant allele of one gene hides the effects of another gene

In a cross between white F1 dihybrids (Aa Bb), the F2 phenotypic ratio is:

T or F:  Based on knowledge of similar phenomena in other plants (like the summer squash), a likely biochemical pathway underlying the 12:3:1 genotypic ratio is shown
True False

White leghorns have a doubly dominant AA BB genotype for feather color; white wyandottes are homozygous recessive for both genes (aa bb). A cross between these two pure-breeding white strains produces an all white dihybrid (Aa Bb) F1 generation, but birds with color appear in the F2 generation. What is the ratio?

State the biochemical explanation for dominant epistasis in the generation of chicken feather color. You may use the Fig 3.18b on pg 62 to help (4-story)

In maize, two genes, A and B, control leaf development. Normal broad leaves develop as long as the plant has either a dominant A allele or a dominant B allele (A- B-, A -bb, or aa B-). However, the leaves of plants that have neither dominant allele (aa bb) are skinny. Why?

Why is the F2 phenotypic ratio signifying redundant gene action 15:1

The proteins (A and B) encoded by the dominant alleles function in _______, ________ pathways that recruit _______ cells to become part of the leaf

Often, redundant genes specify nearly identical proteins that perform the same function. Why does the organism have two genes that do the same thing?

It takes a dominant wild-type allele at each of ___ genes (that can possibly cause deafness) to produce normal hearing. Thus, deafness is a __________ trait (define)

It is not always possible to determine which of many different genes has mutated in a person who expresses a hetergeneous mutant phenotype. For example deafness, in which we usually cannot tell whether a particular deaf man or woman carry mutations at the same gene. What is one way to find out?

Define complementation (1), and how does it affect mutation (2)?

complementation test

If offsring receiving two recessive mutant alleles, one from each parent, express the mutant phenotype, ____________ does not occur. This is because the two mutation are _________ altering the same gene. Thus, the occurrence of complementation reveals genetic _________

Use 5 points to summarize how several variations on the theme of multifactorial traits can be identified

All the points mentioned on identifying multifactorial traits result in the merging of two or more of Mendel's four genotypic classes into one phenotypic class except?

For any type of gene interaction, the alleles of one or both genes may exhibit incomplete dominance or codominance, and these possibilities increase the potential for phenotypic ________. What does this picture depict? 

According to the picture, allele A is _______ _______ to allele a and allele B is ________ _______ to allele b. For each gene, two alleles generate ______ phenotypes and the F2 progeny will have _____ phenotypes

How do geneticists know whether a particular trait is caused by the alleles of one gene or by two genes interacting in one of a number of possible combinations?

Penetrance

T or F: Retinoblastoma can affect one or both eyes
True False

Penetrance can be ________, as in the traits that Mendel studied or ________, as in retinoblastoma

Expressivity

Expressivity can be ________, as in retinoblastoma, or _______ as in pea color

3 factors that affect penetrance and expressivity

Describe the four possible scenarios with penetrance and expressivity

Not all genes that influence the appearance of a trait contribute ______ to the phenotype. Major genes have a large influence, while _______ genes have a more subtle secondary effect.

Modifier genes alter the ________ produced by the alleles of other genes. There is no formal distinction between major and modifier genes, instead, there is a _______ between the two, and the cutoff is _______

_________ is one element of the environment that can have a visible effect on phenotype. (example)

Siamese cats are ________ for one of the multiple alleles of a gene that encodes an _______ that catalyzes the production of the dark pigment known as _______.

The form of the enzyme generated by the variant  "Siamese" allele does not function at the cat's ______ ______ _____ temperature. It becomes active only at the ______ temperatures found in the cat's _______, where it promotes the production of melanin, which darkens the animal's ears, nose, paws and tail.

The enzyme generated by the variant "Siamese" allele is thus ________ sensitive

Under normal environmental conditions in temperate climates, the Siamese phenotype doesn't vary much in _________ from one cat to another, but one can imagine the expression of a very different phenotype (with no _____ extremities) in equatorial deserts, where the ambient temperature is at or _____ normal body temp.

Temperature can also affect _________. In one type of experimentally bred fruit fly, some individuals develop and mulltiply normally at temps between 18C and 29C; but if the thermometer climbs beyond that cutoff for a short time, they become ________ ________; and if the temp remains high for more than a few hours, they _____

Whether a carrier of the retinoblastoma mutation develops the phenotype, and whether the cancer affects one or both eyes, depend on additional ______ events that occur ______.

To produce retinoblastoma, these events must alter the ______ ______ of the gene in specific body cells. This can be caused by routine exposure to _____ ____

Chance events provide the second "hit" (explain) necessary to turn a normal retinal cell into a cancerous one.

By contributing to incomplete penetrance and variable expressivity, modifier genes, the environment, and chance give rise to phenotypic _______.

What is the difference between the probability of epistasis or recessive lethality and the probability of penetrance and the level of expressivity

Discontinuous trait

Continuous trait

The main difference in populations exhibiting discontinuous trait and those exhibiting continuous traits