B15 Flashcards
What did Mendel do
Medel carried out breeding experiments involving peas. He cross bred different types of peas and realised that characteristics were inherited by the offspring of the peas in clear ,predictable patterns
What conclusions did mendel come to from his experiments with cross breeding peas
Mendel reached three important conclusions about heredity(passing of genes from parents to offspring) in plants:
- He said characteristics in plants are determined by “hereditary units”
- He then sias hereditary units are passed onto the offspring unchanged from both parents , one unit from each parent
- He then also said a hereditary unit can be dominant or recessive and that if an individual has a dominant and recessive herditary unit the dominant characteristic will be expressed
What discoveries then came following Mendels conclusions
- In the late 1800’s scientists became familiar with chromosones.They were able to observe how the chromosones behaved during cell division
- In the early 20th century it was discovered that there were striking similaries between the way that chromosones and mendels units acted .Based on this it was proposed that the units were found on chromosones . These units are now known as genes
- In 1953 , the structure of DNA was determined . This allowed scinetists to discover exactly how genes work
Why were mendels theories not widely accepted
Mendels theories were not widely accepted as genes and chromosones had nit yet been discovered so people simply didnt understand his theory
How do populations become isolated
- The most common way for populations to become isolated is by geographical isolation. This is where two populations become physically isolated by a geographical feature e.g a new mountain range, a new river or area of land becoming an island
- Some populations also become environmentally isolated e,g when the climate changes in one area where a populations live but not in other
What are fossils
Fossils are the remains of organisms from millions of years ago that are preserved in rock, ice and other places
What is one way that a fossil might form
A fossil may form if a plant or animal does not decay after it has died
Why might a animal not decay
An animal or plant may not decay if one or more of the conditions needed for decay are not there . For example
- -An animal or plant might not decay if there is too little or no oxygen present
- -A poisonous gas may kill off the bacteria that cause decay
- -Temperatures may be too low for decay to occur
How else are fossil formed
Many fossils are formed when harder parts of animals and plants are replaced by minerals as they decay , causing them to become part of the rock
What other types of fossil are there
Some fossils are not of animals but of preserved traces of animals that have been left behind
