Download Mendel Notes

› 1. Are traits inherited?
› 2. If so, from whom?
› 3. What are some examples of inherited traits
that you see in yourself or in classmates?
› 4. Human Inheritance Lab…

https://www.youtube.com/watch?v=Me
hz7tCxjSE
An Austrian monk who was important in
our understanding of biological
inheritance. (1822)
 Genetics – scientific study of heredity
 Studied pea plants
 Terms you should know:

› Character – a heritable feature (eye color)
› Trait – a variety of a character (brown eyes)

Flowers are used for reproduction
› Male part (stamen) produces pollen
› Female part (carpel) produces eggs

Normally self-pollinate
› Fertilize themselves

True-breeding: if allowed to selfpollinate, they would have offspring
identical to themselves  a tall plant
would produce tall plants
Peas can cross-pollinate.
 Mendel prevented self-pollination by
removing the male parts of a flower,
then he dusted the flower with pollen
from another plant.

› Produced crosses of the two plants
› Crosses between parents with different traits
are called “hybrids”
Each character Mendel studied had 2
possible traits
 He called the original pair of plants the P
(“parental”) generation and the
offspring from the crosses the F1 (“first
filial”) generation


In the F1 generation, all the plants looked
like just one of the parents.
› It appeared that one trait had disappeared!

Two conclusions:
› 1. Biological inheritance is determined by
factors that are passed from one generation
to the next
 Today these factors are called “genes”
 Different forms of a gene are called “alleles”

Two conclusions (continued)
› 2. The principle of dominance: some alleles
are dominant and others are recessive

Segregation
› To discover if the recessive alleles were still
present in the F1 generation, Mendel allowed
the F1 plants to self-pollinate and produce
an F2 generation
› Result: The traits controlled by the recessive
allele reappeared!
› How? Alleles had been separated
(“segregated”) from each other during
gamete (sex cell) formation

Segregation (continued)
› The F1 plants inherited one allele from one
parent and one allele from the other.
› Example: If a short parent (tt) was crossed with a
tall parent (TT), the offspring inherited one short
allele (t) and one tall allele (T). Since it had a
dominant and a recessive allele, the dominant
trait (tall) was expressed. The F1 can produce
two different types of gametes (those with an
allele for tallness “T” and those with an allele for
shortness “t”).