If a hybrid is identical to one parent for the trait under consideration, the allele carried by the parent is deemed _______ to the allele carried by the parent whose trait is not expressed in the hybrid.
dominant
A mating between a pure-breeding white line and a pure-breeding blue line produce F1 hybrids that are white, what does this mean about the relationship between the white line and the blue line? What if he F1 hybrids turned out to be blue?
If the hybrids are white, the white allele of the gene for color is dominant to the blue allele
If the hybrids are blue, the blue allele is dominant to the white one
Mendel relied on complete dominance in sorting out his ratios and laws, but it is not the only kind of dominance he observed. What are the two other types?
Incomplete dominance & Codominance
Incomplete dominance presents F1 hybrids that resemble _______ pure-breeding parent
neither
A cross between pure late-blooming and pure early-blooming pea plants results in an F1 generation that blooms in between the two extremes. This is an example of?
incomplete dominance
Incomplete dominance
The hybrid does not resemble either pure-breeding parent
F1 hybrids that differ from both parents often express a phenotype that is ________ between those of the pure-breeding parents. Meaning?
intermediate
with incomplete dominance, neither parental allele is dominant or recessive to the other; both contribute to the F1 phenotype
A cross between pure-breeding red-flowered snapdragon parents and pure-breeding white yields hybrids with pink blossoms. If allowed to self-pollinate, the F1 pink-blooming plants produce F2 progeny bearing which flowers? In what ratio?
red, pink and white flowers
1:2:1 ratio
The self-pollinated snap dragons genotypic ratio is similar to that of an ordinary ______ ______ (__) self-cross. What is new?
single-gene F1 self-cross (monohybrid)
What is new is the heterozygotes don't look like either homozygote, so the phenotypic ratios are an exact reflection of the genotypic ratios
The simplest biochemical explanation for the incomplete dominance witnessed in the snap dragons (5-story):
Each allele of the gene under analysis specifies an alternative form of a protein molecule with an enzymatic role in red pigment production.
The "white" allele does not give rise to a functional enzyme, but the "red" allele does.
Thus in our snapdragons, the two red alleles per cell produce a double dose of a red-producing enzyme, which generates enough pigment to make the flowers look fully red
In the heterozygote, one copy of the red allele per cell results in only enough pigment to make the flowers look pink
In the homozygote for the white allele, where there is no functional enzyme and thus no red pigment, the flower appears white
A cross between spotted lentils and pure breeding dotted lentils produces _________ that are both spotted and dotted. These F1 hybrids illustrate a second significant departure from complete dominance, _________
heterozygotes
codominance
codominance
offspring look like both parents, which means (in the case of the lentils) neither the the spotted nor the dotted allele is dominant or recessive to the other. both traits show up equally in the heterozygote's phenotype
Self pollination of the spotted/dotted F1 generation creates F2 progeny in what ratio? Meaning?
1 spotted : 2 spotted/dotted : 1 dotted (1:2:1)
The ratio among these F2 progeny establishes that the spotted and dotted traits are determined by alternative alleles of a single gene.
Why do the phenotypic and genotypic ratios of our lentils coincide?
because the heterozygotes can be distinguished from both homozygotes
In humans, some of the complex membrane-anchored molecules that distinguish different types of red blood cells exhibit _________. State the example
codominance
For example, one gene (I), with alternative alleles IA and IB, control the presence of a sugar polymer that protrudes from the red blood cell membrane
Each of the alternative alleles, for blood type, encodes a slightly different form of an ______ that causes production of a slightly different form of the _____ _____
enzyme
complex sugar
In _______ individuals the red blood cells carry both IA- determined and the IB- determined sugars on their surface, whereas the cells of the ________ individuals display the products of either IA or IB alone
heterozygous
homozygous
What tends to happen when both alleles produce a functional gene product?
They are usually codominant for phenotypes analyzed at the molecular levels
Determination of dominance relationships depends on the phenotype that appears in the F1 generation. What happens with F1 generations in complete dominance, incomplete dominance and codominance? What are their ratios in the F2 generations?
With complete dominance, F1 progeny look like one of the true-breeding parents. Complete dominance results in a 3:1 ratio of phenotypes in the F2
With incomplete dominance, the phenotypes of both pure-breeding lines show up simultaneously in the F1 hybrid. Both incomplete dominance and codominance yield 1:2:1 F2 ratios
The dominance relations of a gene's alleles do not affect the alleles' ________. Whether two alternative alleles of a single gene show complete dominance, incomplete dominance, or codominance depends on the kinds of _______ determined by the alleles and the biochemical function of those _______ in the cell
transmission
proteins
proteins
How do phenotypic dominance relations affect the segregation of the alleles during gamete formation? Explain
They don't.
Cells carry two copies of each gene, and these copies (pair of either similar or dissimilar alleles) segregate during gamete formation
Fertilization then restores two alleles to each cell without reference to whether the alleles are the same or different
Variations in dominance relations thus do not detract from Mendel's law of segregation
Variations in dominance reflect differences in the way gene products control the production of ________, adding a level of complexity to the tasks of interpreting the ______ results of gene transmission and inferring genotype from _______
phenotype
visible
phenotype
T or F: A gene can have more than two alleles
True
If a person with blood type A mates with a person with blood type B, it is possible in some cases for the couple to have a child that is neither A nor B nor AB, but a fourth blood type called O. The reason? (5-story)
The gene for the ABO blood types has three alleles: IA, IB and i
Allele IAgives rise to blood type A by specifying an enzyme that adds sugar A
IBresults in blood type B by specifying an enzyme that adds sugar B
i does not produce a functional sugar-adding enzyme.
Alleles IA and IBare both dominant to i, and blood type O is therefore a result of homozygosity for allele i
All possible ways to achieve phenotype A, B and AB in blood types
A phenotype: from two genotypes, IAIA or IAi
B phenotype: from two genotypes, IBIBor IBi
AB phenotype: from two genotypes, IAIB
Although the ABO blood group gene has ____ alleles, each person carries only ____ of the alternatives. There are thus ____ possible ABO genotypes.
three
two (IAIA, IBIB, IAIB, IAi, IBi, or ii)
six
With regard to ABO blood groups, why does Mendel's law of segregation remain intact? (2)
Each individual carries no more than two alleles for each gene, no matter how many alleles there are in a series
As a result, in a sexually reproducing organism, the integrity of two alleles of a gene separating during gamete formation remains intact
An allele (is or is not?) inherently dominant or recessive; its dominance or recessiveness is always relative to a ______ _____.
is not
second allele
Dominance relations are ______ to a pair of alleles. For example, IAis completely dominant to __, but its codominant with __.
unique
i
IB
What would happen if a blood transfusion left a person with A blood type with some B blood?
A blood type makes anti-B antibodies. These antibodies cause coagulation of cells displaying foreign molecules
Which antibodies do B, AB and O produce?
B type: anti-A antibodies
AB type: neither
O type: anti-A and anti-B antibodies
O type people have historically been known as ______ _____ because their red blood cells carry no ______ molecule that will stimulate and antibody attack in a transfusion recipient
universal donors
surface molecule
People with blood type AB are considered ______ ______, because they make neither _______, which if present, would target the _______ molecules of incoming blood cells
universal recipients
antibodies (anti-A or anti-B)
surface
In a paternity suit, if the mother is type A and her child is type B, what does logic dictate about the genotype of the father?
The IB allele must have come from the father, whose genotype may be IAIB, IBIB or IBi
Lentils offer another example of multiple alleles. A gene for seed coat pattern has _____ alleles. Name them
5
spotted
dotted
clear
two types of marbled
dominance series
alleles are listed in order from most dominant to most recessive
Reciprocal crosses between pairs of pure-breeding lines of all patterns of lentil seed coating have clarified the dominance relationship of all possible pairs of the alleles to reveal a dominance series. What does this look like?
How do the multiple alleles of an allelic series arise?
Chance alterations of the genetic material known as mutations, arise spontaneously in nature.
Once mutations occur in gamete-producing cells, they are faithfully _______. Mutations that have phenotypic consequences can be ______. To what end?
inherited
counted
Such counting reveals that they occur at low frequency.
The frequency of gametes carrying a new mutation in a particular gene varies anywhere from 1 in ___ to 1 in ___. This range exists because different ______ have different _______ rates
10K
1 Million
genes
mutation
_______ make it possible to follow gene transmission. If, for example, a _______ specifies an alteration in an enzyme that normally produces yellow so that it now makes green, the new phenotype (green) will make it possible to recognize the new ______ _______
Mutations
mutation
mutant allele
It takes at least ____ alleles, that is, some form of ________ to see the transmission of a gene
two
variation
Because each organism carries two copies of every gene, you can calculate the number of copies of a gene in a given population by _______ the number of individuals by ____.
multiplying
2
Allele frequency
The percentage of the total number of gene copies accounted for by each allele of the gene
Wild-type alleles
The most common alleles in a population and are often designated by a superscript plus sign (+)
An allele is considered wild-type if it is present in the population at a frequency greater than ____.
1%
Mutant Allele
A rare allele in the same population
Monomorphic
A gene with only one common, wild-type allele
Polymorphic (state an example)
Genes that have more than one common allele
Ex: ABO blood type system, all three alleles IA, IB and i are relatively common
Although all three of the ABO blood type system alleles can be considered wild-types, geneticists usually refer to the high-frequency alleles of a polymorphic gene as ______ _______
common variants
Pleiotropy
The phenomenon of a single gene determining a number of distinct and seemingly unrelated characterisitcs
Each gene determines a specific _____ and each one can have a cascade of effects on an organism, which can give rise to _______.
protein
pleiotropy
Mendel assumed that all genotypes are equally viable. Explain
All genotypes have the same likelihood of survival.
If all genotypes weren't viable and, say, a large percentage of homozygotes for a particular allele died before germination or birth, you would not be able to count them after birth. What would be the result?
This would alter the 1:2:1 genotypic ratios and the 3:1 phenotypic ratios predicted for the F2 generation
Recessive lethal allele
An allele that prevents the birth or negatively affects the survival of a homozygote resulting in death of the homozygote.
*two of the same allele (homozygous) that inevitably lead to the death of an organism
Recessive lethal mutations usually do not show a _______ _______ phenotype for some other trait. Lethal mutations can arise in many different genes, and as a result, most animals, including humans, _______ some recessive lethal mutations.
visibly dominant phenotype
carry
Lethal mutations usually remain ______ except in rare cases of homozygosity, often caused by __________ _______. If a mutation produces an allele that prevents production of a crucial molecule, homozygous individuals will not make any of the vital molecule and will not ______.
silent
consanguineous matings
survive
In cases of lethal mutations, heterozygotes have _____ copy(copies) of the deleterious mutation and one ______ _____ allele, can produce 50% of the ______ ______ amount of the normal molecule; this is usually ________ to sustain normal cellular processes such that life continues
one
wild-type allele
wild-type
sufficient
3.2] Although some traits are indeed determined by allelic variations of a single gene, the vast majority of common traits in all organisms are ________ (define)
multifactorial: arising from the action of two or more genes, or from interactions between genes and the environment
In genetics, the term environment has an unusually broad meaning:
Encompasses all aspects of the outside world an organism comes into contact with like temperature, diet and exercise as well as the uterine environment before birth
Two genes can interact in several ways to determine a _____ ______. State 3 examples
single trait
chicken feathers
dog's fur
seed coat
For simplicity, we sometimes refer to a gene name using the symbol for the _______ _____. In addition, we refer to the protein product of allele A as _______, and when appropriate, that of allele a as _______
dominant allele
protein A (no italics)
protein a (no italics)
Example of Novel phenotypes resulting from gene interactions
Genotypic class
A grouping defined by a set of related genotypes that will produce a particular phenotype.
The term genotypic class is most useful in describing progeny of _______ or _______ crosses involving complete dominance; for example, in a cross between Aa Bb individuals, the genotypic classes are:
dihybrid or multihybrid
the genotypic classes are: A-B-, A-bb, aa B-, and aa bb
Why do the four F2 genotypic classes produce fewer than four observable phenotypes in some two-gene interaction?
That is because some of the phenotypes include two or more genotypic classes.
A cross between two lines of pure-breeding white-flowered sweet peas is unexpectedly producing all purple F1 progeny. After self pollination, the novel hybrids produced a ratio of 9 purple : 7 white in the F2 generation. Explain
Two genes work in tandem to produce purple sweet-pea flowers, and a dominant allele of each gene must be present to produce that color
Complementary gene action
Genes working in tandem to produce a particular trait
Why is only the A-B- genotypic class, which produces active forms of both required enzymes, able to generate colored flowers?
Because it takes two enzymes catalyzing two separate biochemical reactions to change a colorless precursor into a colorful pigment
The other three genotypic classes (A- bb, aa B-, and aa bb) become grouped together with respect to phenotype. Why?
Thats because the do not specify functional forms of one or the other requisite enzyme and thus give rise to no color, which is the same as white
Explain the 9:7 ratio in the diagram
The 7 encompasses the ratio 3:3:1 of the 9:3:3:1 ratio of two genes in action. The 9:7 ratio is a phenotypic signature of the type of complementary gene interaction in which the dominant alleles of two genes acting together (A- B-) produce color or some trait while the other three don't
