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Biology 1B > Genetics > Flashcards

Genetics Flashcards

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1
Q

Q: What role does DNA sequence variation play in biology?

A

A: DNA variation underlies the majority of biological diversity, including differences in traits, disease susceptibility, and evolution.

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2
Q

Q: What kinds of biological questions can genetic analysis answer?

A

A:

What causes genetic diseases?

How do organisms evolve?

How do drugs affect individuals differently?

What is the composition of the microbiome?

How can we conserve biodiversity?

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3
Q

Q: What is a genotype?

A

A: The genetic makeup of an organism — the alleles it possesses for a particular trait (e.g., AA, Aa, or aa).

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4
Q

Q: Define dominant and recessive alleles.

A

A:

Dominant: An allele that masks the effect of a recessive one when heterozygous (e.g., A in Aa).

Recessive: An allele that is only expressed when homozygous (e.g., aa)

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5
Q

Q: What is a one-factor cross?

A

A: A genetic cross involving a single trait with two alleles (e.g., flower color: Pp × Pp).

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6
Q

Q: How does Mendel’s First Law relate to meiosis?

A

A: During Anaphase I, homologous chromosomes (and their alleles) separate, ensuring each gamete gets one allele per gene.

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7
Q

Q: What is Mendel’s First Law (Law of Segregation)?

A

A: Each individual has two alleles for a gene, which segregate during meiosis, so each gamete receives only one allele.

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8
Q

Q: What is Mendel’s Second Law?

A

A: The Law of Independent Assortment: alleles of two (or more) unlinked genes segregate independently during meiosis.

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9
Q

Q: How does Mendel’s Second Law relate to meiosis?

A

A: During Metaphase I, homologous chromosome pairs align independently, so genes on different chromosomes assort randomly into gametes.

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10
Q

Q: What is a two-factor cross?

A

A: A genetic cross involving two traits, each controlled by a different gene (e.g., AaBb × AaBb).

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11
Q

Q: What genotypic ratio is expected in the offspring of a dihybrid cross (AaBb × AaBb)?

A

A: 9:3:3:1 (if genes assort independently)

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12
Q

Q: Why do X-linked recessive traits appear more frequently in males?

A

A: Males have only one X chromosome, so a single recessive allele will result in the trait being expressed.

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13
Q

Q: How does linkage affect Mendel’s laws?

A

A: Linked genes do not assort independently, so Mendel’s second law does not apply unless recombination occurs.

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14
Q

Q: What is the meiotic basis of allele segregation for linked genes?

A

A: Linked genes stay together on the same chromosome unless crossing over occurs between them during Prophase I of meiosis.

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15
Q

Q: What is the role of meiotic recombination?

A

A: It can break linkage by exchanging DNA between homologous chromosomes, creating new allele combinations.

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16
Q

Q: How is recombination frequency related to genetic loci?

A

A: The greater the distance between two genes, the higher the chance of a recombination event occurring between them.

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17
Q

Q: What determines biological sex in humans?

A

A: The presence of the Y chromosome (specifically the SRY gene) determines male development; absence = female (XX).

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18
Q

Q: What karyotype is associated with Klinefelter syndrome?

A

A: XXY — a male with an extra X chromosome; may have reduced fertility and secondary sexual characteristics.

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19
Q

Q: What is Turner syndrome?

A

: A female with only one X chromosome (XO). Often shorter in stature and may have fertility issues.

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20
Q

Q: What is sex-linked inheritance?

A

A: Inheritance of genes located on the X or Y chromosomes. Patterns differ in males and females due to sex chromosome composition

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21
Q

Q: What is the molecular basis of X-linked haemophilia?

A

A: Caused by loss-of-function mutations in genes coding for blood clotting factors (e.g., Factor VIII or IX).

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22
Q

Q: Name some common X-linked disorders.
A:

A

Haemophilia A & B

Red-green colour blindness

Duchenne muscular dystrophy

Fragile X syndrome

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23
Q

Q: What’s the inheritance pattern of an X-linked recessive trait?

A

A:
more males
Affected males inherit from carrier mothers, affected male passed affected x to daughter

Carrier females may have affected sons, and daughters who are carriers,
no father-son transmission, can skip gens

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24
Q

Q: Can females be affected by X-linked recessive diseases?

A

A: Yes, but it’s rare. Happens when:

They inherit two mutant alleles, or

Due to X-inactivation skewing.

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25
Q: What is aneuploidy?
A: Aneuploidy is a condition in which an individual has an abnormal number of chromosomes, such as having an extra or missing chromosome.
26
Q: How can genetic disease arise from aneuploidy?
A: Abnormal chromosome numbers can disrupt gene dosage, leading to developmental issues and disorders like Down syndrome or Turner syndrome.
27
Q: What causes Down syndrome (Trisomy 21)?
A: It is caused by non-disjunction during meiosis, resulting in an individual having three copies of chromosome 21
28
Q: What is the molecular basis of sickle cell anaemia?
A: A missense mutation in the β-globin gene changes codon GAA (glutamic acid) to GTA (valine), altering red blood cell shape and function.
29
Q: How does the sickle cell mutation cause disease?
A: The altered haemoglobin polymerises under low oxygen, deforming red blood cells, blocking blood flow, and causing pain and organ damage.
30
Q: How does the sickle cell allele protect against malaria?
A: Heterozygous individuals (carriers) have some sickled cells that resist Plasmodium infection, offering protection without full disease symptoms.
31
Q: What is parthenogenesis?
A: A form of asexual reproduction where an embryo develops from an unfertilized egg.
32
Q: What is apomixis?
A: A form of asexual reproduction in plants where seeds are produced without fertilization, bypassing meiosis.
33
Q: How do Daphnia use asexual and sexual reproduction based on environmental conditions?
A: In favorable conditions, Daphnia reproduce asexually. When conditions worsen, they switch to sexual reproduction to create hardy, genetically diverse offspring.
34
Q: What are the costs of asexual reproduction?
A: Lack of genetic diversity, making populations more vulnerable to disease and environmental change.
35
Q: What is the role of sex in generating recombinant genotypes?
A: Sexual reproduction combines parental alleles, creating new combinations that may enhance survival under natural selection.
36
Q: Why is the loss of sexual reproduction considered an evolutionary dead end?
A: Asexual species accumulate harmful mutations and lack genetic diversity, making them less adaptable and more prone to extinction.
37
Q: What is a key feature of modern banana cultivation?
A: Modern bananas (like the Cavendish) are clonally propagated, meaning all plants are genetically identical clones.
38
Q: What was the banana cultivar wiped out by Panama disease in the 1950s?
A: The Gros Michel variety.
39
Q: What is Panama disease?
A: A deadly fungal disease affecting bananas, caused by Fusarium oxysporum f. sp. cubense.
40
Q: Why are clonal banana cultivars highly vulnerable to Panama disease?
A: Because they lack genetic diversity, making all individuals equally susceptible to infection.
41
Q: What is the Red Queen Hypothesis?
A: An evolutionary theory stating that species must continuously evolve to survive against evolving pathogens—“it takes all the running you can do to stay in the same place.”
42
Q: Why might pathogens evolve faster than their hosts?
A: Pathogens often have shorter generation times, higher mutation rates, and larger populations, speeding up evolution.
43
Q: Name a human pathogen that has evolved within living memory.
A: HIV evolved from simian immunodeficiency virus; others include SARS-CoV-2 and antibiotic-resistant bacteria like MRSA.
44
Q: How was the SRY gene identified?
A: By studying individuals with Klinefelter syndrome (XXY) and Turner syndrome (XO), researchers found that the presence of a specific region on the Y chromosome determined maleness. The SRY gene in this region was identified as the key sex-determining gene.
45
Q: What is the SRY gene?
A: A gene on the Y chromosome that encodes a transcription factor triggering male development.
46
Q: What is the function of transcription factors?
A: They are proteins that regulate gene expression by binding to specific DNA sequences, turning genes on or off.
47
Q: What does “indifferent gonad” mean in development?
A: It refers to the early gonadal structure in embryos that is not yet male or female and can develop into either testes or ovaries.
48
Q: What happens to the indifferent gonad if SRY is present?
A: It develops into testes, which produce testosterone and anti-Müllerian hormone (AMH).
49
Q: What happens to the indifferent gonad if SRY is absent?
A: It develops into ovaries, which produce estradiol and follow the default female pathway.
50
Q: What anatomical changes occur during male gonad development?
A: Testes form and secrete testosterone (promotes male genitals) and AMH (causes regression of Müllerian ducts, preventing female reproductive tract).
51
Q: What anatomical changes occur during female gonad development?
A: Ovaries form, no AMH is produced, so Müllerian ducts develop into uterus, fallopian tubes, and upper vagina.
52
Q: What do the Wolffian ducts develop into?
A: In males, they become the vas deferens, epididymis, and seminal vesicles, under the influence of testosterone.
53
Q: What structures arise from the indifferent external genitals in males and females?
A: Genital tubercle → Penis (male) / Clitoris (female) Urogenital folds → Penile urethra (male) / Labia minora (female) Labioscrotal swellings → Scrotum (male) / Labia majora (female)
54
Q: What hormone drives male external genital development?
A: Dihydrotestosterone (DHT), derived from testosterone.
55
Q: Which adult structures in females derive from the Müllerian ducts? =
A: Uterus, fallopian tubes, and upper vagina.
56
Q: What are the main steps of fertilisation? A:
Sperm binds to egg membrane Fusion of sperm and egg membranes Entry of sperm nucleus into egg Egg activation & prevention of polyspermy Fusion of male and female pronuclei
57
Q: What is polyspermy?
A: Fertilisation of one egg by more than one sperm, leading to abnormal chromosome numbers (e.g. triploidy), which is lethal in humans.
58
Q: How is polyspermy prevented?
A: Fast block: change in membrane potential Slow block: cortical granule reaction modifies zona pellucida, preventing more sperm entry
59
Q: What are the key stages of early animal development?
A: Zygote Cleavage divisions Blastula formation Gastrulation Formation of ectoderm, endoderm, and mesoderm
60
Q: What is gastrulation?
A: A major developmental event where the blastula reorganises into a gastrula, forming three germ layers: Ectoderm Mesoderm Endoderm
61
Q: What does the ectoderm give rise to?
A: Skin Nervous system Sensory organs
62
Q: What does the mesoderm give rise to?
A: Muscles Bones Blood Kidneys Reproductive organs
63
Q: What does the endoderm give rise to?
A: Gut lining Liver Pancreas Lungs (inner parts)
64
Q: What is the trophoblast?
A: The outer layer of the blastocyst in mammals that contributes to placenta formation and helps with implantation into the uterus.
65
Q: How is the trophoblast different in placental mammals compared to animals without placentas?
A: In placental mammals, the trophoblast plays a critical role in forming the placenta, unlike in egg-laying animals.
66
Q: What are the main functions of the placenta?
A: Exchange of gases, nutrients, and waste Produces hormones (e.g. hCG) Protects the fetus via immune modulation
67
Q: Define determination.
A: The process by which a cell becomes committed to a specific fate, even if it has not yet begun to show the features of that cell type.
68
Q: Define morphogenesis.
A: The biological process that gives rise to the shape and structure of tissues, organs, and the organism as a whole.
69
Q: What is a cell lineage?
A: The developmental history of a cell, including the sequence of divisions and differentiation steps that led to its current state.
70
Q: Why is the fruit fly (Drosophila melanogaster) important in developmental biology?
A: It’s a model organism that helped uncover genetic principles of development, including homeotic genes and body plan formation.
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Biology 1B (14 decks)

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