Chapter 1 Flashcards
(115 cards)
1
Q
What is an embryo?
A
- a developing organism prior to birth or hatching
- in humans, the early stages of development, starting with the fertilized egg until the end of organogenesis (first 8 weeks of gestation)
2
Q
What is development?
A
- the process of progressive and continuous change that generates a complex multicellular organism from a single cell
- occurs throughout embryogenesis, maturation to the adult form, and continues into senescence
3
Q
What is a zygote?
A
- a fertilized egg with a diploid chromosomal complement in its zygote nucleus generates by the fusion of the haploid male and female pronuclei
4
Q
What is embryology?
A
- the study of animal development from fertilization to hatching or birth
5
Q
What is indeterminate growth?
A
- growth that is not halted, as opposed to determinate growth, which stops once a structure reaches a genetically predetermined size
- unlike animals, plants can have indeterminate growth
6
Q
What is metamorphosis?
A
- changing from one form to another, such as the transformation of an insect larva to a sexually mature adult or a tadpole to a frog
7
Q
What is oviparity?
A
- young hatch from eggs ejected by the mother, as in birds, amphibians, and most invertebrates
8
Q
What is viviparity?
A
- young are nourished in and born from the mother’s body rather than hatched from an egg, as in placental mammals
9
Q
What is ovoviviparity?
A
- young hatch from eggs held within the mother’s body where they continue to develop for a period of time, as in certain reptiles and sharks
10
Q
What is the holoblastic form of cleavage?
A
- from the Greek holos, “complete”
- refers to a cell division pattern in the embryo in which the entire egg is divided into smaller cells, as it is in echinoderms, amphibians, and mammals
11
Q
What is the meroblastic form of cleavage?
A
- from the Greek meros, “part”
- refers to a cell division pattern in zygotes containing large amounts of yolk, wherein only a portion of the cytoplasm is cleaved
- only part of the egg is destined to become the embryo, while the yolky portion serves as nutrition for the embryo, as in insects, fish, reptiles, and birds
12
Q
Why does the cleavage furrow not penetrate the yolky portion of the cytoplasm in meroblastic cleavage?
A
- the yolk platelets impede membrane formation
13
Q
What is differentiation?
A
- the process by which an unspecialized cell becomes specialized into one of the many cell types that make up the body
14
Q
What is morphogenesis?
A
- the organization of the cells of the body into functional structures via coordinated cell growth, cell migration, and cell death
15
Q
What is a stem cell?
A
- a relatively undifferentiated cell from the embryo, fetus, or adult that divides
- when it divides, it produces one cell that retains its undifferentiated character and remains in the stem cell niche and a second cell that leaves the niche and can undergo one or more paths of differentiation
16
Q
What is embryogenesis?
A
- the stages of development between fertilization and hatching (or birth)
17
Q
What is fertilization?
A
- the fusion of male and female gametes followed by the fusion of the haploid gamete nuclei to restore the full complement of chromosomes characteristic of the species
- initiation in the egg cytoplasm of those reactions that permit development to proceed
18
Q
What is a gamete?
A
- a specialized reproductive cell through which sexually reproducing parents pass chromosomes to their offspring
- an egg or a sperm
19
Q
What are pronuclei?
A
- the male and female haploid nuclei within a fertilized egg that fuse to form the diploid nucleus of the zygote
20
Q
What is a genome?
A
- the complete DNA sequence of an individual organism
21
Q
What is cleavage?
A
- a series of rapid mitotic cell divisions following fertilization in many early embryos
- divides the embryo without increasing its mass
22
Q
What is a blastomere?
A
- a cleavage-stage cell resulting from mitosis
23
Q
What is a blastula?
A
- an early-stage embryo consisting of a sphere of cells surrounding an inner fluid-filled cavity, the blastocoel
24
Q
What is gastrulation?
A
- the process involving movement of the blastomeres of the embryo relative to one another resulting in the formation of the three germ layers of the embryo
25
What is the gastrula stage?
- a stage of the embryo following gastrulation that contains the three germ layers that will interact to generate the organs of the body
26
What are germ layers?
- layers generated by the process of gastrulation that will form all of the tissues of the body, with the exception of the germ cells
27
What are the three germ layers in triploblastic organisms?
- ectoderm
- mesoderm
- endoderm
28
What are the two germ layers in diploblastic organisms?
- ectoderm
- endoderm
29
What is organogenesis?
- interactions between, and rearrangement of, cells of the three germ layers to produce tissues and organs
30
What is a larva?
- the sexually immature stage of an organism
- often of significantly different appearance than the adult
- frequently the stage that lives the longest and is used for feeding or dispersal
31
What are germ cells?
- a group of cells set aside for reproductive function
- become the cells of the gonads (ovary and testis) that undergo meiotic cell divisions to generate the gametes
32
What are somatic cells?
- cells that make up the body
- all cells in the organism that are not germ cells
33
What is gametogenesis?
- the production/development of gametes
34
What is the sporophytic stage?
- the diploid growth stage in the alternating life cycle of plants and algae
35
What is the gametophytic stage?
- the haploid stage of the alternating life cycle in plants and algae that produce gametes (eggs and sperm)
- the sexual phase
36
What is the blastopore?
- the invagination point where gastrulation begins
- in deuterostomes, this marks the site of the anus
- in protostomes, this marks the site of the mouth
37
What is the neurula?
- refers to the embryo during neurulation
38
What is the neural tube?
- the embryonic precursor to the central nervous system (brain and spinal cord)
39
What are somites?
- segmental blocks of mesoderm formed from paraxial mesoderm adjacent to the notochord (the axial mesoderm)
40
What is meiosis?
- a unique division process that in animals occurs only in germ cells, to reduce the number of chromosomes to a haploid complement
41
How is meiosis different from mitosis?
- cells undergo two cell divisions without an intervening period of DNA replication
- homologous chromosomes (each consisting of two sister chromatids joined at a kinetochore) pair together and recombine genetic material
42
What are cotyledons?
- the embryonic leaves contained within the seed of a plant, which provide nutrients that support embryogenesis and germination of the seedling
- during germination, they emerge from the seed before true leaves are formed
43
What is the root apical meristem? (RAM)
- in plants, the meristem at the tip of a growing root
44
What is the shoot apical meristem? (SAM)
- in plants, the meristem at the tip of a growing shoot that is the source of stem cells for all plant organs above ground, such as leaves and flowers
45
What is dermal tissue?
- in animals, the tissue (the dermis) that underlies the epidermis; together, they make up the skin
- in plants, the tissue that makes up the outer layer (the epidermis) of the plant; epidermal cells and guard cells that surround stomata are cell types found in this
46
What is vascular tissue?
- the conducting tissue in plants that transports fluids and nutrients
- major components are the xylem and phloem
47
What is the xylem?
- in vascular plants, the conduits for bringing water and nutrients up through the plant
48
What is the phloem?
- in vascular plants, the conduits that carry sugars produced by photosynthesis, along with other metabolites, from sources to sinks - primarily from the leaves to the non-photosynthetic parts of the plant
49
What is the vegetal pole?
- the yolk containing end of the egg or embryo, opposite of the animal pole
50
What is the animal pole?
- the pole of the egg or embryo where the concentration of the yolk is relatively low; opposite end of the egg from the vegetal pole
51
What does it mean for an egg to be isolecithal?
- from the Greek, "equal yolk"
- sparse, equally distributed yolk particles, as in sea urchins, mammals, and snails
52
What does it mean for an egg to be centrolecithal?
- such as those of insects, has yolk in the center and undergoes superficial cleavage
53
What is superficial cleavage?
- the divisions of the cytoplasm of centrolecithal zygotes that occur only in the rim of the cytoplasm around the periphery of the cell
- due to the presence of a large amount of centrally-located yolk, as in insects
54
What does it mean for an egg to be telolecithal?
- such as those of birds and fish, only one small area at the animal pole of the egg that is free of yolk
55
What is discoidal cleavage?
- meroblastic cleavage pattern for telolecithal eggs, in which the divisions occur only in the small blastodisc, as in birds, reptiles, and fish
56
What is invagination?
- the infolding of a region of cells, much like the indenting of a soft rubber ball when it is poked
57
What is involution?
- inturning or inward movement of an expanding outer layer so that it spreads over the internal surface of the remaining external cells
58
What is ingression?
- migration of individual cells from the surface layer into the interior of the embryo
- cells become mesenchymal (they separate from one another) and migrate independently
59
What is delamination?
- the splitting of one cellular sheet into two more or less parallel sheets
60
What is epiboly?
- the movement of epithelial sheets (usually of ectodermal cells) that spread as a unit (rather than individually) to enclose the deeper layers of the embryo
61
How does epiboly occur?
- by the cells dividing
- by the cells changing their shape
- by several layers of cells intercalating into fewer layers
- often, all three aforementioned mechanisms are used
62
What is the anterior-posterior (anteroposterior or AP) axis?
- the body axis defining the head versus the tail (or mouth versus anus)
- when referring to the limb, this refers to the thumb-pinkie axis
63
What is the dorsal-ventral (dorsoventral or DV) axis?
- the plane defining the back versus the belly
- when referring to the limb, this axis refers to the knuckles and palms
64
What is the right-left axis?
- specification of the two lateral sides of the body
65
What are the pharyngeal arches?
- paired bars of mesenchymal tissue (derived from paraxial mesoderm, lateral plate mesoderm, and neural crest cells), covered by endoderm internally and ectoderm externally
- found near the pharynx of the vertebrate embryo, they form gill supports in fish and many skeletal and connective tissue structures in the face, jaw, mouth, and larynx in other vertebrates
- also called branchial arches
66
What is the neural crest?
- a transient band of cells, arising from the lateral edges of the neural plate, that joins the neural tube to the epidermis
67
What are neural crest cells?
- cells that detach during the formation of the neural tube and migrate to form a variety of cell types and structures
- cell types and structures include sensory neurons, enteric neurons, glia, pigment cells, and (in the head) bone and cartilage
68
What are epithelial cells?
- cells that are tightly linked together on a basement membrane to form a sheet or tube with little extracellular matrix
69
What are mesenchymal cells?
- unconnected or loosely connected cells that can act as independent migratory units; in contrast to epithelial cells
70
What is apoptosis?
- programmed cell death
- an active process that prunes unneeded structure (e.g. frog tails, male mammary tissue)
- controls the number of cells in particular tissues
- sculpts complex organs (e.g., palate, retina, digits, and heart)
71
What is the blastema?
- a group of undifferentiated progenitor cells that form in some organisms at the site of an amputation
- able to grow and differentiate to replace the amputated tissue
72
What are fate maps?
- diagrams based on having followed cell lineages from specific regions of the embryo in order to "map" larval or adult structures onto the region of the embryo from which they arose
- the superimposition of a map of "what is to be" onto a structure that has yet to develop into these organs
73
What are vital dyes?
- stains used to label living cells without killing them
- when applied to embryos, used to follow cell migration during development and generate fate maps of specific regions of the embryo
74
What are fluorescent dyes?
- compounds that emit bright light at a specific wavelength when excited with ultraviolet light
- such as fluorescein and green fluorescent protein (GFP)
75
What is a chimeric embryo?
- an embryo made from tissues of more than one genetic source
76
What is green fluorescent protein? (GFP)
- a protein that occurs naturally in certain jellyfish
- emits bright green fluorescence when exposed to ultraviolet light
- the gene that encodes the protein is widely used as a transgenic label for cells in developmental and other research, since cells that express the protein are easily identified by a bright green glow
77
What is a transgene?
- exogenous DNA or a gene introduced through experimental manipulation into a cell's genome
78
What is the phylotypic stage?
- the stage that typifies a phylum, such as the late neurula or pharyngula of vertebrates, and which appears to be relatively invariant and to constrain its evolution
79
What is the last universal common ancestor? (LUCA)
- The ancient common ancestor to all life on Earth
80
What does it mean to be homologous?
- structures and/or their respective components whose similarity arises from their being derived from a common ancestral structure
- example: the wing of a bird and the forelimb of a human
81
What does it mean to be analogous?
- structures and/or their respective components whose similarity arises from their performing a similar function, as opposed to their arising from a common ancestor
- example: the wing of a bird and the wing of a butterfly
82
What does it mean to be mesendodermal?
- pertaining to mesendoderm, which develops into mesoderm and endoderm
- a synonym for endomesodermal
83
What is multicellularity?
- consisting of multiple cells
84
What is the colonial theory?
- the theory, originally proposed by Ernest Haeckel in 1874, that multicellular organisms arose through the symbiosis of unicellular organisms of the same species
85
What is a choanocyte?
- found in sponges, it is a type of cell that contains a central flagellum surrounded by a collar of microvilli
- power the unidirectional flow of water through a sponge and also function as multipotent stem cells during sponge regeneration
86
What are choanoflagellates?
- a group of unicellular and colonial free-living eukaryotes
- the cells of these eukaryotes have the same basic structure as choanocytes of sponges, with a central flagellum surrounded by a collar of microvilli
- the ancient unicellular, colonial, free-living eukaryotes are considered to have been the common ancestor of all metazoans
87
What does it mean to be extant?
- still in existence, such as a species
88
What is a choanoblastaea?
- considered to be the ancestor of all metazoans (multicellular animals)
- thought to have been a sphere of choanocytes that lived in the open ocean
89
What are embryophytes?
- land plants; named as such because they all undergo embryogenesis
90
What is the last eukaryotic common ancestor? (LECA)
- the hypothetical ancestor to all plants, animals, and fungi
- thought to have been a unicellular protist that had flagella and mitochondria
91
What are plastids?
- organelles found in plant cells that perform many functions, including photosynthesis
- example: chloroplasts
92
What is autotrophy?
- the process found in organisms such as plants and bacteria of synthesizing complex organic compounds using inorganic substances and light or chemical energy
93
What was the Cambrian explosion?
- the rapid diversification of life in the Cambrian period (approximately 541 million years ago) during which most major animal groups appeared, including those with species living today
94
What are Charophytic algae?
- a group of freshwater green algae
- an ancient member of which is thought to have been the common ancestor of all terrestrial plants
95
What is a phytohormone?
- a hormone, such as auxin, found in plants
96
What is the cell wall?
- an extracellular layer outside the cell membrane and surrounding the cells of plants, fungi, and many prokaryotes
- in land plants, they are rigid, containing cellulose, and other polymers
- they inhibit cell movement and restrict the planes of cell division
97
What does it mean to be apical?
- at the apex, or top
- this layer of your epidermis is the outermost layer, facing the external environment
98
What does it mean to be basal?
- at the base, or bottom
- this layer of epidermal cells is the lowest layer, which sits on the basal lamina
99
What are plasmodesmata?
- cytoplasmic channels that form between adjacent plant cells, allowing for direct transport of substances between the cells
100
What are stomata?
- in plants, the pores in the epidermis of leaves and other organs that allow for gas exchange
- each pore is bordered by two guard cells that control the size of the pore, opening and closing this in response to environmental conditions
101
What is a phragmoplast?
- a structure found in plants during cytokinesis that forms between the two daughter nuclei
- made up of cellulose-filled fusing vesicles, microtubules, microfilaments, and endoplasmic reticulum
- it builds the cell wall between the two daughter cells
102
What is the alternation of generations?
- in plants, a life cycle in which a haploid multicellular gamete-producing stage (the gametophyte) alternates with a diploid multicellular spore-producing stage (the sporophyte)
103
What is quiescence?
- a period of inactivity or dormancy
- usually affiliated with a period of stem cell behavior
104
What is dormancy?
- in seed plants, a prolonged period of quiescence that a seed can undergo prior to germination
105
What are malformations?
- abnormalities caused by genetic events such as gene mutations, chromosomal aneuploidies, and translocations
106
What is a syndrome?
- from the Greek, "happening together"
- several malformations or pathologies that occur concurrently
- genetically-based ones are caused either by (1) a chromosomal event (such as trisomy 21) where several genes are deleted or added, or (2) by one gene having many effects
107
What is a disruption?
- an abnormality or congenital defect caused by exogenous agents (teratogens) such as plants, chemicals, viruses, radiation, or hyperthermia
108
What are teratogens?
- from the Greek, "monster-formers"
- exogenous agents that cause disruptions in development resulting in the formation of congenital defects
109
What is teratology?
- the study of birth defects and of how environmental agents disrupt normal development
110
What are some of the common considerations in choosing a good model system?
- size
- generation time
- embryo accessibility
- feasibility of genomic interrogation
- organism type and phylogenetic position
- ease of experimental manipulation
111
What are the variations in cellular processes that bring about morphogenesis?
- direction and number of cell divisions
- cell shape changes
- cell migration
- cell growth
- cell death
- changes in the composition of the cell membrane or secreted products
112
What is the first law of vertebrate embryology? (Von Baer)
- the general features of a large group of animals appear earlier in development than do the specialized features of a smaller group
- all developing vertebrates appear very similar right after gastrulation; it is only later in development that the distinctive features of class, order, and finally species, emerge
113
What is the second law of vertebrate embryology? (Von Baer)
- less general characteristics develop from the more general, until finally the most specialized appear
114
What is the third law of vertebrate embryology? (Von Baer)
- the embryo of a given species, instead of passing through the adult stages of lower animals, departs more and more from them
- ex. mammals never go through a fishlike stage
115
What is the fourth law of vertebrate embryology?
- the early embryo of a higher animal is never like a lower animal, but only like its early embryo
