week 8 Flashcards
What is genetic sex determination and how does it differ among species?
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.
What chromosome typically determines male development in mammals and what gene is crucial for this process?
In mammals, the Y chromosome typically determines male development, with the SRY gene encoding a transcription factor that induces testicular development.
What is genetic sex determination and how does it differ among species?
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.
How does sex determination work in birds?
In birds, sex determination is the opposite of most mammals, with males being the homogametic sex (ZZ) and females the heterogametic sex (ZW).
What is unique about sex determination in African pigmy mice and cichlid fish?
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.
What are the costs and benefits of sexual reproduction?
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.
describe gastrulation in frogs?
- 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
What are early embryonic cell divisions referred to and characterized by?
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.
What drives the rapid cell divisions known as cleavage?
Cleavage is driven by continuously high cyclin-CDK activity that focuses on S and M phases.
What is the result of cleavage in early embryonic development?
cleavage results in the formation of the blastula, which is a hollow sphere of cells.
how does cleavage in mammals differ from other species?
cleavage in mammals occurs more slowly, is asynchronous and rotational, leading to the formation of the blastocyst.
What are the components of the blastocyst and their contributions to development?
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.
What is gastrulation?
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.
What are the three germ layers formed during gastrulation and their associated tissues?
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.
Describe the process of gastrulation in sea urchins.
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.
What is epiboly?
epiboly describes the flattening and spreading of cells that occurs on the outside of the blastula during gastrulation.
Given that each human gene has multiple alleles, how many possible genotypes are there?
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.
What is convergent extension?
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.
How is gastrulation initiated in the embryo?
Gastrulation is initiated by a rotation of the cortical cytoplasm following fertilization, leading to the formation of the gray crescent in the embryo.
What is the significance of the gray crescent in embryonic development?
Hans Spemann’s experiments with newt embryos showed that the gray crescent is required for proper gastrulation.
Who discovered the concept of the organizer and what was its significance?
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.
How is the organizer established in the embryo?
The organizer is established through the dorsal enrichment of β-catenin, a transcription factor that regulates the activity of Organizer genes, following fertilization.
What is neurulation and why is it important?
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.
What are somites and what do they induce?
somites are segments of mesodermal tissue forming along the length of the neural tube, and their formation induces body segmentation.
What is the function of Hox genes in embryonic development?
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.
How do Hox genes influence the development of an embryo?
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.
What are the two meristems in plant development, and what is their role?
The two meristems are regions containing undifferentiated cells that continue to give rise to new tissues and orchestrate growth throughout the plant’s life.
How many permanent tissue layers do plants have, and what are they?
Plants have three permanent tissue layers: dermal, ground, and vascular tissues.
What is the function of dermal tissue in plants?
Dermal tissue covers and protects the plant, controls gas exchange, and in roots, is responsible for water absorption.
What roles does ground tissue serve in plants?
Ground tissue provides structural support, carries out photosynthesis, and stores water and nutrients.
What is the purpose of vascular tissue in plants?
Vascular tissue transports water, minerals, and sugars to different parts of the plant.
How is tissue morphology determined in plants?
Tissue morphology in plants arises from the regulation of cell division and cell elongation.
Why don’t plant cells use cell migration to organize tissues?
Plant cells do not migrate to organize tissues due to their rigid cell walls, which keep cells fixed relative to their neighbors.