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Transcript of Mendel
History of Genetics
studied physics, chemistry, and mathematics at the University of Vienna
He didn't know it, but peas are an excellent model organism. Why?
Characteristics of Model Organisms:
1) rapid development with short life cycles
2) small adult size
3) readily availabile
4) easily distinguishable characteristics
5) simple to care for
Law of Segregation
Law of Dominance
Law of independent assortment
Cross and Testcross
Blending of Inheritance
(The acquisition of traits genetically transmitted from parents to offspring)
Brunn, Austria = Brno, Czech Republic
Mendel determined that one form of the trait is
over the other
one form of a hereditary trait dominates or prevents the expression of the recessive trait.
Mendel determined that since peas reproduce sexually, there must be two “characters” (now called alleles) that influence each trait. (one from the egg and one from the sperm)
– the dominant or recessive form of a gene
*Law of Independent Assortment
*Law of Dominance
*Law of Segregation:
each characteristic is controlled by two factors, which separate and go to different gametes when an organism reproduces.
Practice, Part I:
Mendelian Genetics Hand-out
Practice, Part II:
during gamete formation, the genes for one trait are not inherited along with the genes for another trait.
characterized by blending of phenotypes.
What would be the phenotypes of the offspring of two pink parents?
Both traits show. Calico cats and roan coats are examples.
and multiple alleles:
Deletion, Inversion, Translocation, Polyploidy, Nondisjunction
Tall (T) is dominant to short (t).
I crossed a tall plant with a short plant and the resulting offspring were 24 tall and 21 short. Draw a Punnet square to determine the
of both parents.
2. What is the
ratio of the offspring in a
(Tt x Tt)? The genotypic ratio?
Mendelian Genetics in Humans: Pedigrees
1. Why are all daughters of hemophiliac fathers carriers?
2. Extension: Why don't all genes follow the law of independent assortment?
Sex-Linked Recessive Mutations
- inability to break down the amino acid
-Cyctic fibrosis - 1 in 25 in the U.S. are carriers.
-Tay-Sachs disease - inability to break down lipids necessary for brain
function, common in Ashkenazi Jews
-Huntington's Disease - degenerative disease of the nervous system
Hint...why do some genes tend to be inherited together?
*How is this different than the blending of inheritance theory?
Can you calculate the frequency of alleles in a population?
Yes, but the population must be stable.
What can knowing the frequencies of alleles in a population tell you?
It can tell you if a population is evolving!
1. The breeding population must be large
2. Mating must be random
3. There are no mutations of alleles
4. No migrations occur (immigration or emigration)
5. There is no natural selection
Tristan de Cunha
Founder Effect: Differences in the gene pool of a small colony compared to the original population.
1814: 15 British Settlers, 1 Individual was a carrier for a form of blindness (retinitis pigmentosa).
1960: 240 inhabitants. 4 had retinitis pigmentosa and 9 were carriers (allele frequency is 10x normal).
a population can lose or gain alleles (due to migration). Tends to reduce differences between populations.
or allelic drift is the change in the frequency of a gene variant (allele) in a population due to random events.
Genetics vs. the environment
Genes can be turned on (expressed) and turned off
Drugs, chemicals, temperature, and light
Northern Elephant Seal