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Genetics #1: Mendelian Genetics

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Tom Chester

on 15 March 2011

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Transcript of Genetics #1: Mendelian Genetics

GENETICS The scientific study of heredity Gregor Mendel
The Father of Modern Genetics This Austrian monk developed these ideas
in a monastery in present-day Czech Republic.
Pea plants! Why?
Easy to grow
Many easy traits to pick out
Self-fertilize! Mendel worked with these plants
until he knew they were true-breeding.

Once he had these plants, he performed a
TO CREATE A HYBRID -Generation Parent Generation 1 -Generation The Hybrid offspring + P-generation All plants have purple flowers.
Why? F generation 1 To start off with, Mendel started
This means the plants he crossed were
different in only one trait. Generation 1 Generation 2 F Generation 1 fertilization among F plants 1 ! ! F Generation 2 3/4 of plants have purple flowers
1/4 of plants have white flowers
Why? From this, he discovered these groundbreaking ideas:
There are different forms of the same gene that enable variations.
An organism inherits two of these alleles for each characteristic --one from each parent.
If the two alleles are different, the one that determines appearance is called dominant (the other is recessive).
A sperm/egg carries only one allele for each inherited trait because they separate during meiosis. #1 - There are different forms of the same gene that enable variations. These alternative versions are called ALLELES. Alleles are located at specific locations on specific chromosomes (seen below). There can be multiple different alleles for one gene. #2 - An organism inherits two of these alleles for each characteristic -one from each parent.

If you inherit two identical alleles, you are HOMOZYGOUS for that gene.

If you inherit two different alleles, you are HETEROZYGOUS for that gene. #3 - The allele that, for example, determines your appearance is the DOMINANT allele. The allele that has no noticeable effect is called the RECESSIVE allele, BUT there are many types of dominance. (In other words, there are exceptions to every rule in science.) Dominance? Wrong! Dad Mom + = YOU! (aww) #4 - Remember Meiosis?
When gametes are formed, each gamete will receive only one allele of each gene. So alleles separate from each other in meiosis. This is called the LAW OF SEGREGATION. GENOTYPE -
the genetic makeup
The specific combination
of alleles an organism has. - PHENOTYPE
the physical traits
The appearance
of an organism Part 2 -Generation The DI-HYBRID CROSS -Generation 1 + -Generation 2 1 2 3 4 5 6 7 8 9 1 2 3 1 2 3 1 1 9/16 Yellow & Round
3/16 Yellow & Wrinkled
3/16 Green & Round
1/16 Green & Wrinkled Phenotypic ratio
9:3:3:1 LAW OF INDEPENDENT ASSORTMENT Each pair of alleles segregates independently of the other pairs of alleles during gamete formation (meiosis). Time for some "Lab" work, get it? (What is this guy's deal with dogs?) Black coats are dominant over chocolate coats. Progressive retinal atrophy is a genetic disease that causes vision loss common in labrador retrievers. The allele that causes this is recessive. Perform a cross between these two labs. This dog has PRA. (progressive retinal atrophy) WAIT A SECOND!?
What is the black lab's genotype? How would you find out? It's called performing a TESTCROSS. It is mating the individual with the unknown genotype with a homozygous recessive individual. How would this work? bbnn BbNn Now, perform a cross between these labs. Exceptions to Complete Dominance:
(When heterozygotes don't look like either homozygotes.)
Incomplete dominance - both alleles blend together
Codominance - both alleles are expressed, but don't blend x RR rr Rr x R W RW x O
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