Reproduction
Resumen
Pull a strawberry plant out of a bed in late summer and you will find it trailing a thin horizontal stem across the soil, with a small rooted plant at the far end. That little plant had no other parent. Every base in its DNA came from the plant you are holding. A few metres away, a bee is carrying pollen between two flowers, and the seed that results from that visit will carry instructions from two different individuals. Both events are reproduction, and the difference between them shapes almost everything that follows in genetics.
This lesson takes the two forms apart. You will see what a gamete is and what actually happens when two of them fuse, why that fusion produces offspring that resemble their parents without copying either of them, and why reproduction from a single parent gives you offspring so alike that biologists call them clones. Then you will weigh the two against each other the way an examiner does: not asking which is better, but asking which one wins in a particular field, on a particular farm, in a particular changing climate.
Objetivos
- There are two forms of reproduction: sexual reproduction - the joining (fusion) of male and female gametes. The mixture of the genetic information from two parents leads to variety in the offspring; asexual reproduction - no fusion of gametes and only one individual is needed as the parent. There is no mixing of genetic information and so no genetic variation in the offspring. These genetically identical individuals are known as clones.
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Nota de la lección
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Felicitaciones por completar la lección del Reproduction. Ahora que has explorado el conceptos e ideas clave, es hora de poner a prueba tus conocimientos. Esta sección ofrece una variedad de prácticas Preguntas diseñadas para reforzar su comprensión y ayudarle a evaluar su comprensión del material.
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- Which statement about asexual reproduction is correct? A. Two parents are needed B. Male and female gametes fuse C. The offspring are genetically identical to the parent D. The offspring show a wide range of genetic variation Answer: C
- A human body cell contains 46 chromosomes. How many chromosomes are in a human sperm cell? A. 11 B. 23 C. 46 D. 92 Answer: B
- What is a clone? A. A cell formed when two gametes fuse B. A group of genetically identical individuals produced from one parent C. A sex cell with a single set of chromosomes D. An offspring produced from two parents of different varieties Answer: B
- Which of these is produced by sexual reproduction? A. A potato plant grown from a tuber B. A strawberry plant at the end of a runner C. A seedling grown from a seed D. A shrub grown from a cutting Answer: C
- Why can a population of genetically identical plants be destroyed completely by a new disease? A. The plants are always grown close together B. The plants have no way of reproducing C. No individual differs from the others, so none is likely to be resistant D. Cloned plants grow more slowly than plants grown from seed Answer: C
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