EXAM 1 QUESTIONS Flashcards
*****Describe the difference between Homologous Chromosomes and Sister Chromatids.
!!!!!???
** HC’s = varientas of the same gene
SC’s = exist in exact copies
A couple of homologous chromosomes is a set of one maternal chromosome and one paternal chromosome that pair up with each other during meiosis.
These copies have the same genes in the same locations, or loci.
Sister Chromatids are identical copies formed by the replication of a single chromosome, with both copies joined together by a common centromere. In other words, a sister chromatid may also be said as ‘one-half’ of the duplicated chromosome.
Sister chromatids are the 2 identical halves of a single replicated eukaryotic chromosome.
They are joined at the centromere and genetically identical because, during interphase, they are produced from the 2 complementary strands of a single duplex DNA molecule.
Sister Chromatids: identical, carry the same versions of all their genes because one was produced as an exact copy of the other;
Homologous Chromosomes: the 2 chromosomes of a homologous pair are chromosomes that were inherited from different parents; may contain different versions of some gene
Sister chromatids are exact copies of each other excluding crossing over, forming during mitosis and meiosis II. Homologous chromosomes contain the same genes from the same loci, however contain different variants of these genes.These pairings occur during meiosis I and zygote formation, with one chromosome from each parent.
Describe the differences between dominance, co-dominance, and incomplete dominance.
In true Dominance, the presence of one allele (A) is dominant in the homozygote (AA) and in the heterozygote (Aa); the other allele is recessive (a) and is only phenotypically expressed when it is homozygously present in the genotype.
Incomplete Dominance is like when a red flower is crossed with a white one to produce pink flowers. Neither allele is fully expressed or completely repressed, so an intermediate phenotype is the result.
Co-Dominance occurs when both alleles are fully expressed at the same time, like as in AB bloodtypes.
**What are 3 typical characteristics of an autosomal recessive trait that are observed in a pedigree analysis?
- The characteristic affects males and females equally.
- Two unaffected parents can have an affected child.
- In families in which the parents are unaffected but the children are affected, 1/4 of the children are affected.
***????
A 3-point cross in Drosphila.
What is the relative gene order, and the map distance between these genes, based on the following results from this 3-point mapping cross:
a B d 404 A b D 395 A B d 210 a b D 195 a B D 15 A b d 19 a b d 154 A B D 139
NCOs (parental, non-crossover groups):
aBd* & AbD*
DCOs (double crossover groups):
aBD~ & Abd~
aBd 404* AbD 395* ABd 210 abD 195 aBD 15~ Abd 19~ abd 154 ABD 139
Compare each DCO with the parental which is most like it. For double crossover aBD, the most similar parental is aBd. (It’s the same in 2 of the genes; the other parental is the same in only one gene.) Comparing these, we see that the only gene that is different is the D/d gene. If we compare the other double crossover to the other parental, we get the same result–only the D/d gene is different. So D must be the gene in the middle.
The actual gene order is B-D-A.
Map distances are measured by recombination frequencies:
a-d= 15+19+195+210/1531 = 29
a-b= 210+195+154+139/1531 =46
b-d= 15+19+154+139/1531 =21
The gene order is therefore a-d-b
b-d: 21
“The occurrence of Partial Expressivity and Incomplete Penetrance demonstrates that gene expression can be influenced by biological or environmental context.”
Explain this statement and give examples to support it.
This means that phenotypic expression can be a result of more than one’s genotype.
For example, a person with the genes to be a tall person can experience stunted growth due to malnutrition. Social isolation can keep a child from developing according to the genotypic potential.
When an individual has partial expressivity, there are varying degrees in which genes for the trait, and another individual could have higher expressivity a trait will be expressed. For example, autism may have full penetrance, but expressed in a smaller degree in one individual based on their inherited because their genes were a modified version of the autistic trait.
Incomplete penetrance could influenced by a number of factors. With huntington’s disease, there is 100% penetrance where all individuals who are affected get the disease. But for other diseases, the penetrance may be smaller, providing less of a chance for affected individuals to get the disease either based on medicine (environment) or allelic frequencies.
Penetrance is the percentage of all individuals that show some degree of expression of the mutant genotype. It’s basically the percentage of people with a genotype that express the expected phenotype. In the case of Huntington’s disease, all with dominant mutant gene get the disease and penetrance is 100%.
Expressivity is the degree to which a character is expressed. In the case of polydactylous persons, extra fingers/toes can be fully functional or there can be merely a small tag of skin. Both of these occurrences are due to the effects of other genes and environmental factors that can alter or completely suppress the effect of a particular gene. There are temperature dependent enzymes, for example.
The attachment point on the chromosome for spindle structures in the _______.
kinetochore
List in order of occurrence the phases of Mitosis.
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
(interphase), Prophase, Pro-metaphase, Metaphase, Anaphase, Telophase.
I-P-P-M-A-T
*****Name one characteristic of X-linkage that is often used to identify X-linked genes in pedigree analysis.
^^Criss-cross pattern of inheritance
Affected mothers have affected sons but not affected daughters.
sons exhibit mutant mother phenotype, The phenotype largely or exclusively affects males
Polydactyly in cats (Hemingway’s cats) causes a Variable number of extra toes in cats. This is an example of ____ .
However, cats with the mutation generally have at least one extra toes differs between cats. This is an example of ____.
- Variable Expressivity
2. Complete Penetrance
A human with XX can have a male phenotype if one of the X chromosomes carries a ____
SRY Gene
Albinism, lack of pigmentation in humans, results from an automsomal recessive gene (a).
Two parents with normal pigmentation have an albino child.
What is the probability that their next 3 children will be albino.
.0156
1/64 (because the probability of having a child with albinism is ¼, and the event that each of 3 successive children have albinism is independent from each other.
Therefore, (¼)(¼)(¼)=1/64
The expected ratio of phenotypes among the progeny of a test cross 1:1:1:1.
Out of 200 total progeny, 48 occur in one of the four phenotypic classes.
Given this information, what must be true?
The value of the [OBSERVED - EXPECTED] for this group is [-2]
What is/are the possible inheritance pattern(s) for the characteristic in PEDIGREE 1?
x marks the spot for disease.
O ---------- []
| Ox ---------------- []
autosomal recessive only:
unaffected parents, Affected Daughter, unaffected son
A rare dominant trait, when exhibited in men, is transmitted to half their sons and to half their daughters.
The gene for this trait is carried:
on an autosome.
Mitosis ends with _____, while meiosis ends with _____.
Mitosis ends with 2 diploid cells.
Meiosis ends with 4 haploid cells.
Ability to roll the tongue is caused by a dominant allele. A woman is a “roller,” but one of her parents is not.
What is the woman’s genotype?
heterozygous
A woman who has blood type A has a daughter who is type O and a son who is type B.
Which of the following is a possible genotype for the son?
IB i
In the tetrahybrid cross
AaBbCcDd x AaBbCcDd,
what proportion of the F2 offspring would be expected to be phenotypically recessive.
1/256
If the pedigree is for an Autosomal Recessive characteristic, which individuals are DEFINITELY heterozygous.
[]------O [x]-----O
| |
[x]--O--[x]\_\_\_\_O-------O
|
[]
No affected women.
I-1, I-2, II-4, II-5, III-1
The stage at which “sister chromatids go to opposite poles” immediately FOLLOWS what stage?
Mitotic Metaphase
Round (R) seed shape is dominant to wrinkled (r) seed shape in pea plants.
If an RR plant is crossed with an rr plant, what is the frequency of phenotypes in the F2 generations.
3 round seeds, 1 wrinkled seed
Crossing over can change the….
Linkage of particular variants of 2 or more different gens on the same chromosome
Typical ratios resulting from Epistatic interactions in dihybrid crosses would be.
9:3:4, 9:7
During interphase of the cell cycle…..
DNA content essentially doubles.
What types of phenotypes ratios are likely to occur in crosses when dealing with a single gene pair where all the genotypic combination are equal viability.
1:2:1, 3:1
The fundamental Mendelian process that involves the separation of contrasting genetic elements at the same locus would be called ____
A) Segregation B) Discontinuous variation C) Independent assortment D) Dominance or recessiveness E) Continuous variation
segregation
Why did the F1 offspring of Mendel’s classic pea cross always look like one of the two parental varieties?
One allele was dominant
With incomplete dominance, a likely ratio resulting from a monohybrid cross would be:
1:2:1
If a typical somatic cells has 64 chromosomes, how many chromosomes are expected in each gamete of that organism?
32
What are 3 characteristics of an autosomal dominant trait observed in a pedigree analysis?
- Carriers always express the trait
- affected individuals have affected parent
- males and females affected equally
What is the relative gene order based on the results from this 3-point mapping cross below?
What is the recombination distance between A & B locus?
a B f 404 A b F 395 A B f 13 a b F 17 a B F 150 A b f 191 a b f 154 A B F 139
F-A-b
22.07 map units
How do incomplete penetrance and variable expressivity differ?
Incomplete penetrance is a trait being expressed less than 100% of the time.
Variable expressivity is an expressed trait with variable degrees of severity.
Extensive pedigree analysis on a characteristic shows all the following:
If a woman with an affected father has children with an unaffected man, half of the sons and none of the daughters are affected.
Affected females always have an affected father and an affected maternal grandfather.
The trait is never passed from father to son.
What mode of inheritance is suggested?
X-linked recessive
Extensive pedigree analysis on a characteristic shows all of the following:
The characteristic affects males and females equally.
Two unaffected parents can have an affected child.
In families in which the parents are unaffected but the children are affected, ¼ of the children are affected.
What mode of inheritance is suggested?
Autosomal recessive
Which modes of inheritance are influenced by the sex of individuals.
Select all that apply.
Sex-limited Autosomal dominant X-linked Autosomal recessive Y-linked
Sex-limited, Y-linked, X-linked
List 4 terms used to describe the normal morphologies, with respect to arm ratio, of eukaryotic chromosomes.
metacentric, submetacentric, acrocentric, telocentric
Albinism, lack of pigmentation in humans, results from an autosomal recessive gene (a). Two parents with normal pigmentation have an albino child.
What is the probability that their next child will be an albino girl?
⅛
½ prob that child will be girl, ¼ prob that child will inherit both recessive alleles
In anaphase….
Chromosomes move to opposite poles
In the following tetrahybrid cross AaBbCcDd x AaBbCcDd what proportion of the F2 offspring would be expected to be genotypically AaBbCcDd?
1/16
If a typical somatic cell has 32 chromosomes, how many chromosomes are expected in each gamete of that organism?
16
How do the daughter cells at the end of mitosis and cytokinesis compare with their parent cell when it was in G1 of the cell cycle?
The daughter cells have the same number of chromosomes and the same amount of DNA.
Homologous chromosomes move toward opposite poles of the dividing cell during
Meiosis I
The difference between the homogametic sex and the heterogametic sex is that
The heterogametic sex determines the gender of the offspring
A trihybrid cross is a cross between two individuals who are heterozygous for 3 genes.
For example: AaBbCc x AaBbCc. Assuming these 3 genes are unlinked and assorting independently, what segregation ratio would be observed?
27:9:9:9:3:3:3:1
In a healthy male, how many sperm cells would be expected to be formed from
(a) 400 primary spermatocytes?
(b) 400 secondary spermatocytes?
a. 1600
b. 800
Drosophila melanogaster, the fruit fly, has a 2n chromosome number of 8. Assuming that a somatic G2 nucleus contains about 8.0 picograms of DNA, how many picograms of nuclear DNA would you expect in:
1) mitotic metaphase
2) a primary oocyte (metaphase)
3) a secondary oocyte (metaphase)
4) A first polar body (metaphase)
1) 8
2) 8
3) 4
4) 4
Drosophila melanogaster, the fruit fly, has a 2n chromosome number of 8. Assume that you are microscopically examining the mitotic and meiotic cells of this organism. You note that in the female two chromosomal pairs are metacentric and that two pairs are acrocentric.
What stage is represented in the drawing above?
Primary oocyte (metaphase)
A recessive allele in tigers causes the white tiger. If 2 normally pigmented tigers are mated and produce a white offspring, what percentage of their remaining offspring would be expected to have normal pigmentation?
75%
Which of the following parental genotypes will produce only heterozygous F1 offspring?
AA x aa
When crossing an organism that is homozygous recessive for a single trait with a heterozygote, what is the chance of producing an offspring with the homozygous recessive phenotype?
50%
If they live long enough, the penetrance of individuals carrying the Huntington’s Disease allele will be what?
100%
Assume that a black guinea pig crossed with an albino guinea pig produced 5 black offspring. When the albino was crossed with a second black one, 4 black and 3 albino offspring were produced.
What genetic explanation would apply to these data?
Albino = recessive, black = dominant
Name the single individual whose work in the mid-1800s contributed to our understanding of the particulate nature of inheritance as well as the basic genetic transmission patterns.
With what organism did this person work?
Gregor Mendel, pisum sativum
The Chi-square test involves a statistical comparison between measured (observed) and predicted (expected) values.
One generally determines degrees of freedom as ….
one less than the number of classes/entities being compared
If the characteristic followed in the pedigree is x-linked recessive allele, what is III-1’s genotype?
hemizygous for a dominant allele
A couple has one girl and is expecting a second child. What is the probability that this child will be a boy?
½
After several years and several births, a couple now has 4 daughters and is expecting a 5th.
What is the probability that this child will be a boy?
½
After several years and several births, a couple now has 4 daughters and wants 2 more children.
What is the likelihood that the next two children will also be girls?
¼
_________ refers to the splitting of the cytoplasm, separating one cell into two.
Cytokinesis
Where on the chromatid are the microtubules attached? A) Centriole B) Centromere C) Kinetochore D) Telomere
Kinetochore
Codominant alleles are expressed in individuals that are….. A) Penetrant B) Homozygous C) Polymorphic D) Heterozygous E) Mutually exclusive
Heterozygous
A condition in which one gene pair masks the expression of a nonallelic gene pair is called
epistasis
In the following tetrahybrid cross AaBbCcDd x AaBbCcDd, what proportion of the F2 offspring would be expected to be phenotypically ABCD?
81/256
Hemizygosity would most likely be associated with which of the following?
A) Dihybrid crosses B) Incomplete dominance C) Trihybrid crosses D) Sex-linked inheritance E) Sex-limited inheritance
Sex-LINKED inheritance
The ant carries all its genetic information in a single pair of chromosomes. In other words, 2n=2.
(Males are haploid with one chromosome.)
For the purposes of this question, assume that a G1 somatic cell nucleus in a female any contains 2 picograms of DNA.
How much DNA would be expected in Metaphase I cell of a female?
A) 16 B) 32 C) Not enough info to answer D) 4 E) 8
4
Polydactyly man with 6 fingers and 6 toes marries a woman with a normal number of digits.
Extra digits is dominant.
The couple has a son with normal hands and feet, but the couple’s 2nd child has extra digits.
Probability next child will have polydactyly…
A) 1/8
B) 1/32
C) 7/16
D) ¾
E) ½
1/2
A group of cells is assayed for DNA content after mitosis and found to have an average of 8 picograms of DNA per nucleus.
How many pictograms would be found at the end of G2 and the end of metaphase?
A) 8; 8
B) 16;16
C) 16; 8
D) 8;16
E) 12;16
16;16
A situation where there are more than two alternative forms of a given gene would be called \_\_\_\_\_ A) Multiple alleles B) Incomplete dominance C) Codominance D) Alternation of generations E) Hemizygosity
Multiple alleles
Describe the differences between meiosis I & meiosis II
Crossing over occurs in meiosis I and not meiosis II.
Daughter cells of meiosis I are diploid, and the daughter cells of meiosis II are haploid.
When chromosomes separate during Anaphase of meiosis I, they are in sister chromatin form.
In Anaphase of meiosis II, the sister chromatids separate.
Crossing over (genetic recombination) occurs in
Meiosis I prophase
If the phenotype followed in Pedigree 3 is autosomal recessive, then the genotype of I-1 is….
(refer to diagram a few pages down, not sure which one)
heterozygous
Could the characteristics followed in the pedigree be caused by an X-linked recessive allele?
(Pedigree showing all males affected I-3, II-1, II-3)
[]------O [x]-----O
| |
[x]--O--[x]\_\_\_\_O-------O
|
[]
Yes, all individuals fit the X-linked recessive inheritance pattern.
Match the following term:
Intermediate Phenotype
Incomplete dominance
Match the following term:
Phenotypic ratio of 9:3:3:1
dihybrid cross
Match the following term:
One genotype can be responsible for multiple distinct phenotypes
pleiotropy
*Think Plenty of Phenotypes = Pleitropy
Match the following term:
Both phenotypes are expressed
Co-dominance
Match the following term:
Masks another genes phenotypes
Epistasis
A woman who has blood type A has a daughter who is type O and a son who is type B.
Which of the following is a possible genotype for the son?
I^Bi
A diploid somatic cell from a rat has a total of 42 chromosomes (2n=42). As in human sex chromosomes determine sex: XX in females and XY in males.
What is the total number of chromosomes in a polar body cell from a rat?
21
A diploid somatic cell from a rat has a total of 42 chromosomes (2n=42).
As in humans, sex chromosomes determine sex: XX in females and XY in males.
What is the total number of chromosomes present in the cell during metaphase I of meiosis?
42
What are 2 differences and 2 similarities between mitosis and meiosis?
Differences:
Mitosis has a single cycle.
Meiosis has two cycles (Meiosis I, Meiosis II).
Mitosis segregates the chromosomes into 2 daughter chromatids.
This produces diploid (2n) from a haploid (n).
Meiosis II brings chromosomes together to form functional gametes.
This produces haploid from diploid.
Similarities:
Both involve anaphase, metaphase, prophase and telophase
Both are essential in the replication of chromosomal DNA and have precise stages that are needed in order to make this happen.
Any kind of problem can lead to a mutation during mitosis or meiosis.
Two and three factor testcrosses can both be used to ________ and __________ .
b, d
Map gene loci,
Determine genotype
Purple flower color and yellow seed color are dominant traits. An individual with purple flowers and yellow seeds is crossed to an individual with purple flowers and green seeds.
The offspring of these two parents were as follows:
Purple flowers, yellow seeds: 57
Purple flowers, green seeds: 62
White flowers, yellow seeds: 18
White flowers, green seeds: 20
What is the phenotype of the parent with green seeds?
Ppyy
PpYY
PPYy
PPyy
Ppyy
Purple flower color and yellow seed color are dominant traits. An individual with purple flowers and yellow seeds is crossed to an individual with purple flowers and green seeds.
The offspring of these two parents were as follows:
Purple flowers, yellow seeds: 57
Purple flowers, green seeds: 62
White flowers, yellow seeds: 18
White flowers, green seeds: 20
What is the phenotype of the parent with white flower and yellow seeds?
ppYY & ppYy both possible
ppyy only
PPYy & Ppyy both possible
ppYy only
ppYy only
Human eye color is controlled by two genes on chromosomes 15, and one gene on chromosome 9. Each has many alleles within the human population. How many alleles of each gene can be found in a human gamete?
8 of each 1 of each 2 of each 3 of each One cannot tell because of possible crossing over
1 of each
The DNA of a eukaryotic chromosome is
one long double helix
Which is the smallest unit containing the entire human genome?
One human somatic cell
The ant, Myrmecia pilosula, is found in Australia and is named bulldog because of its aggressive behavior. It is particularly interesting because it carries all its genetic information in a single pair of chromosomes. In other words, 2n=2. (Males are haploid and have just one chromosome.)
Which of the following figures would most likely represent a correct configuration of chromosomes in a Metaphase I cell of a female?
A.
(the illustration shows 2 chromosomes lined up one on the left, one on the right)
l.l l.l
l l l l
Often, a mutation in a gene results in a reduction or loss of the product of that gene. The term given for this type of mutation is:
Loss-of-function mutation
Assume that a dihybrid cross is made in which the genes’ loci are autosomal, independently assorting, and incompletely dominant.
How many different phenotypes are expected in the offsprings?
9
Assume that an organism has a diploid chromosome number of six. Two chromosomal pairs are telocentric, and the other pair is metacentric. Assume that the sex chromosomes are morphologically identical. The drawing above could represent which stage(s)? Check all that apply.
secondary oocyte (metaphase)
secondary spermatocyte (metaphase)
first polar body (metaphase)
primary oocyte (metaphase)
If the picture shows 2 columns of chromosomes (6 pairs total), diploid (2n), it is primary oocyte.
If it is one column (3 pairs total), haploid (n), it is secondary (spermatocyte and oocyte) and first polar body.
In the G0 stage of the cell cycle, which of the following is true:
stem cells are produced the cell exits the cell cycle RNA replicates DNA content doubles the nuclear membrane disappears
the cell exits the cell cycle.
When Thomas Hunt Morgan crossed his red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies.
Remarkably, all the white-eyed flies were male. What was the explanation for this result?
The gene involved is on the X chromosome
Genes come in different versions called…
alleles loci genotypes chromosomes genomes
alleles
During the cell cycle, chromosomal replication occurs in…
prophase
interphase
telophase
metaphase
interphase
An allele is…
one of the bases in DNA
an alternate form of a gene
another term for epistasis
present only in males and is responsible for sex determination
found in mitochondria but not in nuclei
an alternate form of a gene
Assume that a cross is made between AaBb and aabb plants and that the offspring fall into approximately equal numbers of the following groups: AaBb, Aabb, aaBb, aabb.
These results are consistent with the following circumstance:
independent assortment incomplete dominance alteration of generations codominance hemizygosity
independent assortment
If a pair of homologous chromosomes fails to separate during anaphase of meiosis I, what will be the chromosome number of the four resulting gametes with respect to the normal haploid number?
n+1, n+1, n-1, n-1
If an organism is diploid and a certain gene found in the organism has 18 known alleles (variants), then any given organism of that species can/must have which of the following?
at most, 2 alleles for that gene
Extensive pedigree analysis on a characteristic shows all of the following:
only males are affected
affected fathers always pass the trait to sons
What does this pedigree indicate?
This is a Y-linked gene
An organism has a haploid number of 6. How many possible assortments of chromosomes are possible based on the Independent Assortment of the chromosomes?
64
In order to determine if mutations from different organisms that exhibit the same phenotype are allelic, which test would you perform?
testcross
epistasis test
complementation test
biochemical test
complementation test
A form of a gene that has slightly different sequence than other forms of the same gene but encodes the same type of an RNA or protein, is called a(n)
allele
Cytokinesis is
the formation of two cells at the end of mitosis in both plants and animals
What conditions are likely to apply if the progeny from the cross AaBb X AaBb appear in the 9:3:3:1 ratio?
no gene interaction
independent assortment
complete dominance
Normal diploid somatic (body) cells of the mosquito, Culex pipiens, contain 6 chromosomes.
The “m” superscript indicates that the homolog is maternally derived, while the “p” indicates a paternally derived homolog.
Assume that in the genus Culex, the sex chromosomes are morphologically identical.
In the drawing above, what stage is represented?
If one column, mitotic metaphase,
if 2 columns, metaphase of meiosis I.
