week 8 Flashcards

1
Q

What is genetic sex determination and how does it differ among species?

A

Genetic sex determination is a system where sex is determined by specific chromosomes. In most mammals, males are XY (male heterogametic), while females are XX. In birds, males are ZZ (female heterogametic), and females are ZW. African pigmy mice use a single-locus polygenic system, and African cichlid fish have a multi-locus polygenic system.

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2
Q

What chromosome typically determines male development in mammals and what gene is crucial for this process?

A

In mammals, the Y chromosome typically determines male development, with the SRY gene encoding a transcription factor that induces testicular development.

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3
Q

What is genetic sex determination and how does it differ among species?

A

Genetic sex determination is a system where sex is determined by specific chromosomes. In most mammals, males are XY (male heterogametic), while females are XX. In birds, males are ZZ (female heterogametic), and females are ZW. African pigmy mice use a single-locus polygenic system, and African cichlid fish have a multi-locus polygenic system.

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4
Q

How does sex determination work in birds?

A

In birds, sex determination is the opposite of most mammals, with males being the homogametic sex (ZZ) and females the heterogametic sex (ZW).

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5
Q

What is unique about sex determination in African pigmy mice and cichlid fish?

A

African pigmy mice use a single-locus polygenic system where sex determination can vary, and in African cichlid fish, sex determination is based on a multi-locus polygenic system which can also be affected by environmental factors.

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6
Q

What are the costs and benefits of sexual reproduction?

A

The costs of sexual reproduction include maintaining the molecular machinery for the process, the need to find a mating partner, and decreased reproductive capacity. The benefits include high genetic variability aiding evolution, the combination of advantageous alleles, and the ability for paired chromosomes to mask deleterious mutations.

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7
Q

describe gastrulation in frogs?

A
  • On one side of the blastula, cells change their shape and cell adhesion properties and start to move inward(involution), forming the dorsal lip.
  • Cells of the animal pole spread out across the surface and will form the ectoderm.
  • Cells of the vegetal pole move inwards where they will form the endoderm and mesoderm.
  • The process of gastrulation leads to formation of the gastrula
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8
Q

What are early embryonic cell divisions referred to and characterized by?

A

Early embryonic cell divisions are referred to as cleavage. They are very rapid, do not increase the overall size of the embryo, and involve a modified cell cycle that skips the G1 and G2 phases.

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9
Q

What drives the rapid cell divisions known as cleavage?

A

Cleavage is driven by continuously high cyclin-CDK activity that focuses on S and M phases.

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10
Q

What is the result of cleavage in early embryonic development?

A

cleavage results in the formation of the blastula, which is a hollow sphere of cells.

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11
Q

how does cleavage in mammals differ from other species?

A

cleavage in mammals occurs more slowly, is asynchronous and rotational, leading to the formation of the blastocyst.

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12
Q

What are the components of the blastocyst and their contributions to development?

A

The inner cell mass of the blastocyst will form the embryo, the trophoblast will contribute to the placenta and umbilical cord, and the blastocyst cavity contains factors for cellular differentiation.

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13
Q

What is gastrulation?

A

Gastrulation is the process where the blastula is transformed into an embryo with distinct tissue layers and body axes, involving extensive cell movements to establish the three germ layers.

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14
Q

What are the three germ layers formed during gastrulation and their associated tissues?

A

The neural ectoderm (outer layer) gives rise to the nervous system and the ectoderm gives rise to skin, the mesoderm (intermediate layer) to muscles and the skeletal system, and the endoderm (inner layer) to the digestive and respiratory systems.

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15
Q

Describe the process of gastrulation in sea urchins.

A

Gastrulation in sea urchins involves several key steps:

The vegetal pole of the blastula flattens.
Some cells at the vegetal pole change shape and move inward to form the beginnings of the archenteron.
Other cells break free, becoming primary mesenchyme, which will contribute to the embryo’s internal structures.
More cells break free as secondary mesenchyme, and thin filopodia from these cells attach to the overlying ectoderm.
The archenteron elongates through the contraction of mesenchymal filopodia and cell rearrangement.
The mouth of the sea urchin forms where the archenteron meets the ectoderm.
The blastopore, the initial opening that forms during gastrulation, will develop into the anus of the mature animal.

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16
Q

What is epiboly?

A

epiboly describes the flattening and spreading of cells that occurs on the outside of the blastula during gastrulation.

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17
Q

Given that each human gene has multiple alleles, how many possible genotypes are there?

A

If each of the 23,000 human genes has two alleles, the number of possible genotypes would be 2 raised to the power of 23,000, a figure far greater than the number of atoms in the universe.

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18
Q

What is convergent extension?

A

Convergent extension is the process where cells intercalate and extend in the direction of movement, driving involution and contributing to the elongation of the embryo.

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19
Q

How is gastrulation initiated in the embryo?

A

Gastrulation is initiated by a rotation of the cortical cytoplasm following fertilization, leading to the formation of the gray crescent in the embryo.

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20
Q

What is the significance of the gray crescent in embryonic development?

A

Hans Spemann’s experiments with newt embryos showed that the gray crescent is required for proper gastrulation.

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21
Q

Who discovered the concept of the organizer and what was its significance?

A

Hans Spemann and Hilde Mangold discovered the organizer, evidenced by transplantation of the dorsal lip that induced host cells to act as dorsal cells, playing a key role in embryonic development. They were awarded the Nobel Prize in 1935 for this discovery.

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22
Q

How is the organizer established in the embryo?

A

The organizer is established through the dorsal enrichment of β-catenin, a transcription factor that regulates the activity of Organizer genes, following fertilization.

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23
Q

What is neurulation and why is it important?

A

Neurulation is the process where the ectoderm folds to create the neural tube, marking the first step in organogenesis and the formation of the nervous system.

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24
Q

What are somites and what do they induce?

A

somites are segments of mesodermal tissue forming along the length of the neural tube, and their formation induces body segmentation.

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25
Q

What is the function of Hox genes in embryonic development?

A

Hox genes control the body plan of an embryo along the anterior-posterior axis, and their DNA order reflects their expression sequence and location in the developing animal.

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26
Q

How do Hox genes influence the development of an embryo?

A

Hox genes have been extensively studied in Drosophila and are critical for ensuring that the correct body parts develop in the right place, directing the correct cell fates within each segment.

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27
Q

What are the two meristems in plant development, and what is their role?

A

The two meristems are regions containing undifferentiated cells that continue to give rise to new tissues and orchestrate growth throughout the plant’s life.

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28
Q

How many permanent tissue layers do plants have, and what are they?

A

Plants have three permanent tissue layers: dermal, ground, and vascular tissues.

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29
Q

What is the function of dermal tissue in plants?

A

Dermal tissue covers and protects the plant, controls gas exchange, and in roots, is responsible for water absorption.

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30
Q

What roles does ground tissue serve in plants?

A

Ground tissue provides structural support, carries out photosynthesis, and stores water and nutrients.

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31
Q

What is the purpose of vascular tissue in plants?

A

Vascular tissue transports water, minerals, and sugars to different parts of the plant.

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32
Q

How is tissue morphology determined in plants?

A

Tissue morphology in plants arises from the regulation of cell division and cell elongation.

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33
Q

Why don’t plant cells use cell migration to organize tissues?

A

Plant cells do not migrate to organize tissues due to their rigid cell walls, which keep cells fixed relative to their neighbors.

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34
Q

What is meiosis and how does it relate to sex determination in humans?

A

Meiosis is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, crucial for sexual reproduction. In humans, it separates homologous chromosomes, ensuring that offspring inherit one set of chromosomes from each parent, including the sex chromosomes which determine the sex of the individual.

35
Q

What is the karyotype of a female human diploid cell?

A

The karyotype of a female human diploid cell contains 23 pairs of chromosomes, including two X chromosomes (XX), differentiating from the male karyotype, which includes one X and one Y chromosome (XY).

36
Q

Describe the process of meiosis in human females.

A

In human females, meiosis begins before birth with the formation of oogonia, which develop into primary oocytes and arrest in prophase I. After puberty, meiosis resumes, leading to the development of secondary oocytes which arrest in metaphase II and only complete meiosis upon fertilization, resulting in a fertilized egg.

37
Q

How does sex determination vary across different species?

A

Sex determination mechanisms can vary widely:

In most mammals, the presence of a Y chromosome determines maleness.
Birds use a ZW system, with males being ZZ (homogametic) and females ZW (heterogametic).
African pygmy mice and African cichlid fish exhibit polygenic sex determination systems, with multiple alleles influencing sex, often including environmental factors.

38
Q

How does the environment influence sex determination in some species?

A

: In certain species, sex determination can be influenced by environmental factors, such as temperature, which affects the expression or repression of critical genes like Sox9 during sensitive periods of development.

39
Q

What is the SRY gene and what does it do?

A

The SRY (sex-determining region Y) gene, located on the Y chromosome, encodes for a transcription factor that induces male (testicular) development and triggers the expression of the Sox9 transcription factor, driving male development.

40
Q

How does meiosis explain Mendel’s laws of inheritance?

A

Meiosis explains Mendel’s laws of inheritance by demonstrating how homologous chromosomes line up independently at the metaphase plate during meiosis I and segregate randomly, contributing to the law of independent assortment.

41
Q

Do genes on the same chromosome always follow the law of independent assortment?

A

Genes on the same chromosome are said to be linked and typically do not follow the law of independent assortment, though complete linkage is rare due to crossing over.

42
Q

What is crossing over during meiosis?

A

Crossing over occurs during meiosis I when homologous chromosomes exchange DNA segments, resulting in recombinant chromatids with a mixture of genetic information from both chromosomes.

43
Q

What are the consequences of crossing over?

A

Crossing over leads to incomplete linkage, which means that alleles on the same chromosome are not always inherited together, creating recombinant phenotypes in offspring.

44
Q

What does recombination frequency indicate, and how is it measured?

A

Recombination frequency indicates the distance between genes on a chromosome, with 1 centimorgan (1 cM) equalling a 0.01 frequency of recombination. However, this frequency is not linear to physical distance, and crossover rates vary along the chromosome.

45
Q

How does X-linked inheritance work in males?

A

Males are hemizygous for X-linked genes and inherit their X chromosome from their mother, resulting in distinct inheritance patterns for X-linked traits compared to females.

46
Q

What is aneuploidy?

A

Aneuploidy is the presence of an abnormal number of chromosomes in a cell, often due to non-disjunction, which is the failure of chromosomes to separate properly during meiosis.

47
Q

What are some syndromes resulting from autosomal chromosome aneuploidy?

A

Examples include Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13).

48
Q

hat are some syndromes resulting from sex chromosome aneuploidy?

A

Examples include Klinefelter syndrome (XXY), XYY syndrome, Triple X syndrome (XXX), and Turner syndrome (XO), which is the only viable human monosomy.

49
Q

Why is a nervous system needed in multicellular organisms?

A

A nervous system is needed for communication between different areas of the organism, to control the functions of the organism, such as movement, and to regulate responses to conditions or sensory stimuli, contributing to homeostasis.

50
Q

What are neurons and what is their function?

A

Neurons are nerve cells that are excitable and capable of producing and transmitting electrical impulses known as action potentials. These impulses propagate along neurons like a “Mexican Wave” and are the basis of neuronal communication.

51
Q

What is an action potential?

A

An action potential is a transient change in the potential difference (voltage) across the membrane of a neuron, which flows down the neuron and forms the basis of communication between different areas of the organism.

52
Q

What is the structure of a typical neuron and its components?

A

A typical neuron consists of many dendrites, a cell body (soma) with a nucleus, a single axon insulated by a myelin sheath, and axon terminals. The soma integrates incoming signals, dendrites receive inputs, and the axon transmits impulses to the next neuron.

53
Q

What is a synapse?

A

A synapse is the connection between neurons that transmits signals from one cell to the next. It is unidirectional, typically going from the axon terminal of one neuron to the dendrite of another.

54
Q

How do synapses contribute to the functioning of neurons?

A

Each neuron can make a vast number of connections with many other neurons through synapses. With approximately 100 billion neurons and many more synapses in the human brain, the capacity for integration and pattern determination is immense.

55
Q

Why is neurotransmitter removal important in synaptic communication?

A

Neurotransmitter removal is crucial because it ensures that nervous system signaling is rapid and dynamic. It prevents the continuous activation of postsynaptic receptors, which allows the synapse to reset and be ready for the next signal.

56
Q

What are the three mechanisms of neurotransmitter removal from the synapse?

A

Neurotransmitters are removed from the synapse by:

Reuptake into presynaptic neurons or glial cells for reuse.
Breakdown by enzymes.
Diffusion out of the synaptic cleft.

57
Q

What is divergence in the context of synaptic connections?

A

Divergence occurs when synaptic signals are spread out throughout the nervous system, enabling a single neural pathway to amplify and distribute the signal to multiple regions.

58
Q

What is convergence in synaptic connections?

A

Convergence is the process by which signals from multiple presynaptic neurons are channeled down to a smaller number of postsynaptic neurons or a specific nerve tract, focusing the input.

59
Q

What are afferent neurons and what is their role?

A

Afferent neurons, or sensory neurons, carry information from the periphery into the central nervous system and convert sensory stimuli into action potentials using specialized receptors.

60
Q

What are efferent neurons and their function?

A

Efferent neurons, or motor neurons, transmit commands from the central nervous system to effectors such as glands and muscles, instigating a response or action.

61
Q

What are interneurons and what is their significance in the nervous system?

A

Interneurons, also known as circuit or relay neurons, form connections and circuits between other neurons. They typically link afferent and efferent neurons, contribute to the complexity of the nervous system, are involved in information processing and storage, and are predominantly found within the central nervous system.

62
Q

How do specialized neurons in the retina function in terms of dendrites and inputs?

A

Specialized neurons in the retina have fewer dendrites and deal with a limited scope of inputs, focusing solely on visual information.

63
Q

What is the role of neurons with a large number of dendrites, such as those in the cerebellum?

A

Neurons in the cerebellum have a multitude of dendrites to handle extensive inputs, controlling intricate and complex movements.

64
Q

Describe neurons in the cortex in terms of their dendritic branching and axon length.

A

Neurons in the cortex often feature branched dendrites and long axons, facilitating broad and long-distance communication within the brain.

65
Q

What is the purpose of reflexes, and how does the withdrawal reflex work?

A

Reflexes are rapid, automatic responses to stimuli that protect the body from harm. The withdrawal reflex, a simple reflex, involves an afferent neuron, an interneuron, and an efferent neuron, allowing for a quick reaction without input from the brain, but rather through the spinal cord.

66
Q

What initiates the withdrawal reflex?

A

The withdrawal reflex begins when heat activates skin receptors, which are connected to afferent neurons, generating an action potential.

67
Q

Describe the path of an action potential in the withdrawal reflex.

A

he action potential travels along the afferent neuron into the spinal cord, activates the interneuron, and is then relayed to the efferent neuron, which triggers muscle contraction and moves the affected body part away from the source of harm.

68
Q

What are simple nerve nets and where are they found?

A

Simple nerve nets consist of lengthy projections with a few connections, permitting basic responses and functions such as contraction and relaxation. They are found in simple organisms like sea anemones.

69
Q

How do more complex nerve networks function in organisms like earthworms?

A

In earthworms, segmented innervation with ganglia in each segment coordinates movement through segmental nerves. The anterior ganglia function like a primitive brain, orchestrating complex behaviors and responses.

70
Q

Describe the nerve network in squid and its capabilities.

A

Squids have a more specialized and organized pattern of nerve networks, with specialized ganglia coordinating specific functions, such as intricate movement patterns. Their sensory systems, particularly for vision, are more developed and coordinated by large visual ganglia within the brain.

71
Q

What makes the human nerve network the most complex?

A

Humans have a vast number of nerve cells, ganglia, and processing centers. The nervous system is divided into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which serves as an information relay and communication system between the periphery and the CNS.

72
Q

What are the two components of the human nervous system?

A

The two components of the human nervous system are:

Central Nervous System (CNS): Comprising the brain and spinal cord, it acts as the main processing center and is protected by bone.
Peripheral Nervous System (PNS): It functions as the communication system, relaying information to and from the CNS to the rest of the body.

73
Q

what is epistasis?

A

Epistasis is where one gene alters the phenotypic expression of another gene

74
Q

what is mutation?

A

Mutation is a heritable change in the genetic information of a cell or organism

75
Q

what is a synonymous mutation?

A

Synonymous (silent) mutations occur because 64 codons exist but only 20 amino acids exist so there is a redundancy in the code so some nucleotide changes don’t alter the amino acid sequence

76
Q

what is a missense mutation?

A

Missense mutations occur if the point mutation changes a codon into one that specifies a different amino acid so the amino acid sequence is changed

77
Q

what is a nonsense mutation?

A

Nonsense mutations occur when the point mutation changes a codon that specifies an amino acid into a stop codon so translation is prematurely terminated

78
Q

what is a frame shift mutation?

A

Frame-shift mutations occur when an insertion or deletion occurs which alters the reading frame of the entire rest of the sequence so so the whole amino acid sequence changes too

79
Q

what is a silent mutation?

A

Silent mutations don’t alter the amino acid sequence or the mutation causes a change in amino acid sequence that has no effect on the protein’s function

80
Q

what is a loss of function mutation?

A

Loss-of-function mutations result in a change of the amino acid sequence that impairs normal protein function

81
Q

what is a gain of function mutation?

A

Gain-of-function mutations result in a change in the amino acid sequence that leads to an abnormally functioning protein

82
Q

what is RAS

A

-RAS is a small GTPase that cycles between active and inactive states and can suffer from a mutation that affects its activity resulting in constitutive activation

-Constitutively active RAS promotes survival and proliferation of tumour cells

83
Q
A