Biology 2107 > Unit 4 > Flashcards

Unit 4 Flashcards

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1
Q

What was the blending hypothesis?

A

The idea that genetic material from parents mixes, like paint colors blending (disproven).

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2
Q

Why did Mendel choose pea plants for his experiments?

A

Easy to cultivate, fast growth, many offspring, clear traits, and ability to control mating.

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3
Q

What is a character?

A

A heritable feature (e.g., flower color).

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4
Q

What is a trait?

A

A variant of a character (e.g., purple or white flowers).

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5
Q

What is hybridization?

A

Mating two contrasting true-breeding varieties.

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6
Q

What is an allele?

A

Different versions of a gene.

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7
Q

What is the law of segregation?

A

Alleles separate during gamete formation; each gamete gets one allele.

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8
Q

Segregation corresponds to what part of meiosis?

A

Separation of homologous chromosomes in anaphase I.

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9
Q

What is the law of independent assortment?

A

Allele pairs segregate independently during gamete formation.

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10
Q

When does independent assortment apply?

A

To genes on nonhomologous chromosomes or those far apart on the same chromosome.

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11
Q

What is the phenotypic ratio of a dihybrid cross (AaBb × AaBb)?

A

9:3:3:1

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12
Q

What is a monohybrid?

A

Heterozygous for one character (Aa).

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13
Q

What is a monohybrid cross?

A

Aa × Aa.

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14
Q

What is a dihybrid?

A

Heterozygous for two characters (AaBb).

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15
Q

What is a dihybrid cross?

A

AaBb × AaBb.

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16
Q

What is a testcross?

A

Crossing an organism with dominant phenotype to a homozygous recessive to determine its genotype.

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17
Q

What result of a testcross indicates the unknown is heterozygous?

A

Any recessive offspring appear.

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18
Q

What is the multiplication rule?

A

Probability of independent events occurring together (“AND”).

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19
Q

What is the addition rule?

A

Probability of mutually exclusive events (“EITHER/OR”).

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20
Q

What is complete dominance?

A

When a heterozygote has the same phenotype as the homozygous dominant individual.

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21
Q

What is incomplete dominance?

A

The heterozygote shows an intermediate phenotype between the two homozygotes.

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22
Q

What is codominance?

A

Both alleles in a heterozygote are fully and simultaneously expressed.

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23
Q

How can the level at which a phenotype is observed affect dominance?

A

Dominance relationships may differ at anatomical, physiological, or molecular levels.

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24
Q

What is pleiotropy?

A

When a single gene influences multiple phenotypic traits.

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25
How many alleles determine human ABO blood type?
Three: Iᴬ, Iᴮ, and i.
26
What is epistasis?
One gene masks the phenotypic expression of another gene at a different locus.
27
Epistatic vs. hypostatic gene?
Epistatic gene: does the masking. Hypostatic gene: gets masked.
28
What defines polygenic inheritance?
A single trait controlled by the additive effect of many genes.
29
What type of traits often show polygenic inheritance?
Quantitative traits like human skin color and height.
30
What is a pedigree?
A chart showing inheritance of traits across generations.
31
What is a carrier?
A heterozygote who carries a recessive allele but is phenotypically normal.
32
What causes sickle-cell disease?
A single amino acid substitution in hemoglobin.
33
Why is heterozygosity for sickle cell advantageous in some regions?
Carriers (heterozygotes) have resistance to malaria.
34
Why are lethal dominant alleles rare?
Affected individuals usually die before reproducing.
35
What does the chromosome theory of inheritance state?
Mendelian genes have specific loci on chromosomes, and chromosomes undergo segregation and independent assortment.
36
What organism did Morgan use for genetic studies?
Drosophila melanogaster (fruit fly).
37
What is a wild-type phenotype?
The typical, most common phenotype in natural populations.
38
What chromosomes do male mammals have?
XY.
39
What chromosomes do female mammals have?
XX.
40
What gene on the Y chromosome determines male development?
SRY (Sex-determining Region of Y).
41
What does SRY do?
Encodes a transcription factor that triggers testes formation.
42
What are X-linked genes?
Genes located on the X chromosome.
43
Why are X-linked recessive traits more common in males?
Males are hemizygous (only one X).
44
Why is dosage compensation needed?
Males have only one X chromosome, so they produce half as much X-linked gene product as females.
45
What mechanism equalizes expression in females?
X-inactivation → formation of Barr bodies.
46
What are linked genes?
Genes located near each other on the same chromosome.
47
Do linked genes assort independently?
No — they are inherited together.
48
What causes recombination between linked genes?
Crossing over during prophase I of meiosis.
49
What is the maximum recombination frequency between two genes?
50%.
50
How do you calculate recombination frequency?
Recombinants ÷ Total offspring.
51
Who developed the first genetic map?
Alfred Sturtevant.
52
What is a map unit (m.u.)?
1% recombination frequency = 1 map unit.
53
What does recombination frequency indicate about gene distance?
Greater distance → higher chance of crossover → higher RF.
54
What is the genome?
The genetic material transmitted from parents to offspring.
55
What is the whole genome shotgun approach?
A sequencing method starting with cloning and sequencing random DNA fragments, then using computer programs to assemble the overlapping sequences into a continuous sequence.
56
What is Sanger sequencing?
A method of DNA sequencing that uses dideoxyribonucleoside triphosphates (ddNTPs) to terminate DNA synthesis at specific bases.
57
Why do ddNTPs terminate DNA synthesis?
They lack a hydroxyl (–OH) group at their 3′ end, preventing the addition of the next nucleotide.
58
What is Next-Generation Sequencing (e.g., Illumina)?
"High-throughput" methods that sequence many DNA fragments simultaneously, making the process faster and less expensive than older methods.
59
Is genome size correlated with the number of genes?
No. For example, C. elegans has a smaller genome but more genes than Drosophila. Humans have a huge genome (3,000 Mb) but only ~20,000 genes.
60
What is the Human Genome Composition (Coding vs. Non-coding)
Only 1.5% codes for proteins, rRNA, or tRNA. The rest (98.5%) is non-coding DNA.
61
What are pseudogenes?
Former genes that have accumulated mutations and are now nonfunctional.
62
What is repetitive DNA?
DNA sequences present in multiple copies in the genome. It makes up about 44% of the human genome (mostly transposable elements).
63
What are short tandem repeats (STRs)?
A series of repeating units of 2 to 5 nucleotides (e.g., GATC). The number of repeats varies among individuals, making them useful for DNA profiling.
64
What are transposable elements?
DNA segments that can move from one location to another within the genome. First discovered by Barbara McClintock.
65
What are transposons?
Eukaryotic transposable elements that move by a "cut and paste" or "copy and paste" method involving DNA directly.
66
What are retrotransposons?
Eukaryotic transposable elements that move by means of an RNA intermediate. They leave a copy behind and require reverse transcriptase to convert RNA back to DNA.
67
What are multigene families?
Collections of identical or very similar genes (e.g., genes for rRNA or globins).
68
What is unequal crossing over?
An error during prophase I of meiosis that can result in one chromosome with a deletion and another with a duplication of a particular gene.
69
What is the smallest unit of evolution?
A population. Natural selection acts on individuals, but only populations evolve over time.
70
What is a population?
A group of individuals of the same species that live in the same area and interbreed, producing fertile offspring.
71
What is a fixed allele?
An allele is considered fixed if all individuals in a population are homozygous for the same allele.
72
What is the Hardy-Weinberg Equilibrium?
A state in which allele and genotype frequencies in a population remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work.
73
What is natural selection?
Differential success in reproduction that results in certain alleles being passed to the next generation in greater proportions. It is the only mechanism that consistently causes adaptive evolution.
74
What is genetic drift?
A process where allele frequencies fluctuate unpredictably from one generation to the next due to chance events. It is most significant in small populations.
75
What is the founder effect?
A type of genetic drift that occurs when a few individuals become isolated from a larger population, establishing a new gene pool that differs from the source population.
76
What is the bottleneck effect?
A type of genetic drift resulting from a drastic reduction in population size (e.g., due to a natural disaster). The surviving gene pool may not reflect the original population's makeup.
77
What is directional selection?
Occurs when conditions favor individuals at one extreme of a phenotypic range, shifting the population's frequency curve in one direction.
78
What is disruptive selection?
Occurs when conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes.
79
What is stabilizing selection?
Occurs when conditions favor intermediate variants and act against extreme phenotypes, reducing variation.
80
What is sexual selection?
Natural selection for mating success. It can lead to sexual dimorphism (marked differences between sexes).
81
What is intrasexual selection?
Intrasexual: Competition among individuals of one sex (usually males) for mates.
82
What is intersexual selection?
Intersexual: Individuals of one sex (usually females) are choosy in selecting their mates (mate choice).
Biology 2107
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