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Genetics

Genetics

Test Your Knowledge

Mendelian Genetics Questions

1. How do the genotype and phenotype of an organism relate to each other? (The genotype is the genetic constitution of an organism, the phenotype is the physical manifestation of the genotype).

2. What kinds of gametes does a heterozygous pea plant with yellow seeds produce? Hint: its genotype is Yy. (50% "Y", 50% "y").

3. What are the genotypes of the parents in this Punnett square? (Rr and rr)

4. Can a true-breeding individual make more than one kind of gamete for a given character? (No, they have no genetic variation as they only carry one type of allele)

5. What is the difference between a gene and an allele? (A gene is a section of DNA that forms a functional unit of biological inheritance. An allele is variation of a gene sequence)

Mendelian Genetics Answers

Genetic Linkage Questions

1. When two alleles are genetically linked, what does it mean? (They are on the same chromosome and are likely to be inherited together)

2. If humans have 46 chromosomes in total, how many chromosomes are in eggs or sperm? (23)

3. What is genetic recombination? (The exchange of reciprocal chromosome parts between homologous chromosomes during meiosis).

4. What affects the chances of recombination between two loci on the same chromosome? (The size of the chromosome – there is more chance of recombination in larger chromosomes – and how far apart the loci are on the chromosome)

Genetic Linkage Answers

Modification of Dominance Relationships Questions


1. A lizard with shiny scales crossed to a lizard with dull scales produce baby lizards with both shiny and dull scales. This is an example of:
a. codominance
b. incomplete dominance
c. dominance
d. recessiveness
e. incomplete recessiveness

2. In incomplete dominance, the phenotype of the heterozygote is _______ the phenotype of the parents.
a. Similar to
b. intermediate between
c. identical to
d. unrelated to
e. none of the above

3. A man of what blood type could not father a child of blood type O? (AB, as he can only donate an IA or and IB allele to his offspring. If he was A or B, then he might possibly be heterozygous and hiding the recessive IO allele).

4. The roan coat color in shorthorn cattle is controlled by two alleles that are codominant, CR (red hairs) and CW (white hairs); roan cows are heterozygotes. What color offspring would you expect to see, and in what phenotypic ratio, if you mated two roan cattle? (25% red, 50% roan, 25% white)

Modification of Dominance Relationships Answers

Lethal Alleles Questions

1. Brachyphalangy is a condition in humans that causes shortened fingers in heterozygotes; it is lethal to homozygotes carrying only the faulty allele. If a woman with brachyphalangy marries a normal man, what phenotypic ratio would you expect to see in their children?
a. 3 affected : 1 unaffected
b. 2 affected : 1 unaffected
c. 1 affected : 1 unaffected
d. 1 affected : 2 unaffected
e. All affected

2. What would the phenotypic ratio be if the affected woman had married an affected man instead?
a. 3 affected : 1 unaffected
b. 2 affected : 1 unaffected
c. 1 affected : 1 unaffected
d. 1 affected: 2 unaffected
e. All affected

3. Unlike most other dominant lethal alleles, the Huntington allele has not been lost from the human population. Why? (Because the symptoms for Huntington's disease don't usually occur until after the age of 35, after most sufferers have already had children and unknowingly passed on the faulty allele)

Lethal Alleles Answers

Gene Interactions Questions

1. Two genes interact to determine coat color in Labrador Retrievers. This is an example of:
a. epistasis
b. pleiotropy
c. variable penetrance
d. dominance
e. recessiveness

2. A single gene affects temperature resistance, longevity, and coat color in mice. This is an example of:
a. epistasis
b. pleiotropy
c. variable penetrance
d. dominance
e. recessiveness

3. Not every woman carrying a mutation known to be associated with breast cancer develops the disease. This is an example of:
a. epistasis
b. pleiotropy
c. incomplete penetrance
d. dominance
e. recessiveness

Gene Interactions Answers

Sex Determination and Inheritance of Sex-Linked Traits Questions

1. What are the main differences between autosomes and sex chromosomes? (Sex chromosomes are associated with sex, while autosomes are not. Autosomes come in matching pairs, while sex chromosomes can be totally different, such as X and Y).

2. In what sex determination system are the females diploid whilst the males are haploid? (Haplodiploidy)

3. In humans, a form of color blindness is caused by an X-linked, recessive mutant gene. If parents with normal color vision have a son with color blindness, what can you deduce about the mother's genotype? (She is heterozygous at this locus).

4. If ducks (where sex is determined by the ZW sex determination system) had a sex-linked, similar disorder to hemophilia or color blindness, would male ducks or female ducks be more likely to be affected? (Female ducks, because they are the heterogametic sex).

Sex Determination and Inheritance of Sex-Linked Traits Answers

Quantitative Genetics Questions

1. Name two quantitative and two qualitative traits in humans. (Quantitative: height, weight, skin color, foot length, hand span, hair color. Qualitative: blood group, gender, ear lobes attached or detached, eye color – although there is more than one gene controlling eye color, everyone technically has either brown, blue or green eyes)

2. List two differences between qualitative (Mendelian) traits and quantitative traits? (Qualitative traits are determined by a single gene, quantitative traits by many genes; qualitative traits fall in discrete categories (black or white), quantitative show a continuous, smooth distribution (from white, through progressively darker grays, to black); qualitative traits are not usually affected much by the environment, while quantitative traits are very sensitive to the environment).

3. What are the components of genetic variance? (Additive genetic variance, dominant genetic variance, and epistatic genetic variance).

Quantitative Genetics Answers

Extranuclear Genetics Questions

1. What parts of the cell other the nucleus contain their own DNA? (Mitochondria and chloroplast)

2. Why is mitochondrial DNA inherited only from the mother? (Because the egg contributes most of the cytoplasm to the developing embryo)

3. Is your mtDNA the same as your maternal or your paternal grandmother? (Maternal)

4. After millions of years of its ancestors living inside eukaryotic cells, a mitochondrion attempts to leave and make its own way in the world. Could it survive on its own? (No. Both the mitochondrion and the cell have become mutually dependent on each other for survival, and the mitochondrion's DNA no longer contains all the genes it would need)

Extranuclear Genetics Answers

The Chi-Squared Test Questions

1. The total number of offspring from a monohybrid cross was found to be 600 and the expected phenotypic ratio was 1:2:1. For the purposes of a χ2-test, what would the calculated values of E be?
a. 150 : 300 : 150
b. 100 : 200 : 100
c. 125 : 350 : 125
d. 150: 350: 150
e. 100: 250: 100

2. How many degrees of freedom does the above cross have?
a. 0
b. 1
c. 2
d. 3
e. 4

3. A dihybrid cross was carried out between two heterozygous organisms and 1440 offspring were obtained. If the two genes were believed to be in an epistatic relationship, what phenotypic ratio would you expect to see in the F2?
a. 9:3:3:1
b. 9:3:4
c. 1:1:1:1
d. 1: 2: 1
e. 3: 1

4. Using the information from Q2, what would the largest and smallest calculated E values be for this cross?
a. 810 & 270
b. 810 & 90
c. 90 & 90
d. 270 & 180
e. 270 & 90

5. If the calculated χ2 value is larger than the probability from the χ2 table for the correct degrees of freedom and significance level, do you accept or reject the null hypothesis? (You reject it. The calculated χ2 value must be lower than the value in the χ2 table to be able to accept the null hypothesis)

The Chi-Squared Test Questions


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