Module 4 Flashcards
MATCH THE TERM WITH THE DEFINITION
XY sex determination
X/A ratio
Epistasis
Hemizygous
Dosage compensation
Sex-limited
Overdominance
Temperature-dependent sex determination
Barr body
Complete dominance
Definitions
A. Only one copy of a gene present (e.g., X-linked genes in males).
B. Heterozygote has an advantage over both homozygotes.
C. One X chromosome in females is inactivated.
D. Gene at one locus masks expression of another gene.
E. Phenotype is entirely determined by one dominant allele.
F. Sex determined by temperature during development.
G. Genes expressed only in one sex (e.g., milk production in cows).
H. X chromosome to autosome ratio determines sex (e.g., fruit flies).
I. Process balancing gene expression between sexes.
J. Sex determined by presence of XY or XX chromosomes.
1 → J
2 → H
3 → D
4 → A
5 → I
6 → G
7 → B
8 → F
9 → C
10 → E
MATCH THE TERM WITH THE DEFINITION
Codominance
Penetrance
Pleiotropy
Allelic series
ZW sex determination
Epigenetic inheritance
Xist
Sex-influenced
Incomplete dominance
Sex-linked
Definitions
K. Both alleles fully expressed (e.g., AB blood type).
L. Long non-coding RNA silences one X chromosome.
M. Multiple alleles exist with a ranking of dominance.
N. Expression depends on sex (e.g., baldness dominant in males).
O. Some individuals with a genotype don’t show expected phenotype.
P. Trait is carried on a sex chromosome (X or Y).
Q. One gene affects multiple traits (e.g., Marfan syndrome).
R. Female is heterogametic (ZW), male is homogametic (ZZ).
S. Gene expression modified by environment, not DNA changes.
T. Heterozygote shows a blend of both homozygous traits.
11 → K
12 → O
13 → Q
14 → M
15 → R
16 → S
17 → L
18 → N
19 → T
20 → P
What is epistasis?
When one gene affects or masks the expression of another gene.
Example: Labrador coat color.
pleiotropy
When a single gene influences multiple, unrelated traits.
Example: Sickle cell anemia affects oxygen transport, resistance to malaria, and blood cell shape.
How do epistasis and pleiotropy differ?
Key Difference: Epistasis is about gene interactions; pleiotropy is about one gene affecting multiple traits.
Why might two identical twin Siamese cats have different fur patterns?
hint: same DNA, different fur! Cooler areas activate melanin, making paws, ears, and tails darker.
Temperature-sensitive gene expression (a form of gene-environment interaction).
Explanation: The tyrosinase gene controls melanin but is inactive in warm areas and active in cooler areas, causing darker fur on extremities.
Phenotypic Expression: Temperature-dependent pigmentation.
At the molecular level, how is an individual with type AB blood an example of codominance?
Both A and B alleles are expressed equally, producing both A and B antigens on red blood cells.
If the wild-type allele for plant height in sweet peas is partially dominant over a recessive allele, what phenotype would result from a TT x tt cross?
🔹 TT = Tall, tt = Short
🔹 Tt (F1 generation) = Intermediate height (between tall and short) due to incomplete dominance.
🔹 Incomplete dominance results in a blended phenotype rather than one allele fully masking the other.
For the sickle cell gene (hb), individuals homozygous dominant (hbShbS) are susceptible to malaria, while individuals homozygous recessive (hbshbs) generally suffer from sickle-shaped red blood cells and associated complications. What is the condition of heterozygous (hbShbs) individuals, and how is this an example of overdominance?
Heterozygotes (hbShbs): No sickle cell disease + Malaria resistance.
This is overdominance (heterozygote advantage), where the heterozygote is healthier than either homozygote.
Two white-flowered pea plants are crossed, and all of the offspring are purple-flowered. Diagram how this surprising result could occur based on the concept of complementation.
Two different genes involved (e.g., C and P genes).
White parents had mutations at different genes → their offspring inherited at least one functional allele at both loci, producing purple flowers.
How can an individual Drosophila carrying a Y chromosome be a female phenotypically?
🔹 Sex in Drosophila is determined by the X-to-autosome (X/A) ratio, not just the presence of a Y chromosome.
🔹 If X/A ratio = 1.0 (e.g., XXY), the fly develops as a female, even with a Y chromosome.
🔹 Y chromosome carries genes for fertility, but not for determining sex.
Q10: What is a methyl group? How can this molecule affect inheritance patterns?
🔹 Methyl Group: A chemical group (-CH₃) that attaches to DNA.
🔹 Effect on Inheritance: Can turn genes on or off without changing the DNA sequence (epigenetics).
Plays a role in genomic imprinting, where only one parental allele is expressed.
Can be influenced by environment (e.g., diet, stress).
How can an individual Drosophila carrying a Y chromosome be a female phenotypically?
Sex in flies is determined by the X-to-autosome ratio, not the presence of Y.
XXY = Female in Drosophila.
Why might fathers who started smoking before age 11 be more likely to have overweight sons?
🔹 Possible epigenetic inheritance: Early smoking exposure could lead to DNA methylation changes in sperm, affecting metabolism-related genes in offspring.
🔹 Not direct Mendelian inheritance, but environmental effects on gene expression passed across generations.
How does co-dominance differ from incomplete dominance? Give an example of both.
Codominance: Both alleles are fully expressed (e.g., AB blood type).
Incomplete dominance: Blended phenotype (e.g., red × white flowers = pink).
Q14: Give four examples of environmental influence on phenotype (one human example).
🔹 Siamese cat fur color – Temperature-sensitive gene causes darker fur in cooler body regions.
🔹 Hydrangea flower color – Changes with soil pH (acidic = blue, alkaline = pink).
🔹 Beetle horn size – Depends on nutrition availability.
🔹 Human height – Influenced by diet and childhood nutrition.
A husband and wife both carry a deleterious mutation in one allele of their BRCA1 gene. They produce six daughters. One daughter died shortly after birth. One daughter developed breast cancer in her 20s. One daughter developed breast cancer in her 30s. The remaining daughters passed from natural causes after the age of 60. Hypothesize at least two mechanisms to explain this family pedigree.
Variable expressivity: BRCA1 mutations affect individuals differently.
Other genetic/environmental factors: Different mutations or lifestyle choices may influence cancer risk.
What are the possible phenotypes when crossing albino X full color, albino X chinchilla, and albino X Himalayan rabbits?
🔹 Albino (cc) X Full Color (CC or Cc) → All full color (Cc) if dominant.
🔹 Albino (cc) X Chinchilla (cchcch or cchc) → All chinchilla (if cch is dominant over c).
🔹 Albino (cc) X Himalayan (chch or chc) → All Himalayan (if ch is dominant over c).
🔹 Key Concept: Multiple alleles exist in a dominance hierarchy (C > cch > ch > c)
How might a male’s testosterone deficiency affect his odds of balding later in life?
🔹 Male pattern baldness is a sex-influenced trait.
🔹 DHT (dihydrotestosterone) triggers baldness in genetically susceptible males.
🔹 If testosterone levels are low, less DHT is produced, reducing the likelihood of baldness.
Define Hemizygous + Example
Hemizygous: Only one copy of a gene is present.
Example: Males (XY) are hemizygous for X-linked traits.
An extensive family pedigree shows that certain members of a family develop a severe reaction after eating fava beans, involving anemia and jaundice. It is almost exclusively males that exhibit symptoms, but the phenotype skips generations even when all members of the generation are male. What the heck is going on here? What type of inheritance is this?
X-linked recessive disorder (G6PD deficiency).
Males (XY) inherit it from carrier mothers, skipping generations.
Why is O blood type called the universal donor? Explain from a genetic standpoint. Based on both antibody and antigen production, how could an individual of type A or B blood accept blood from a type O individual? (hint, the answer to the second question is only partly genetic).
Type O has no A/B antigens, so it won’t trigger an immune response.
Type A or B individuals lack anti-O antibodies, making O blood compatible.
