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
