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AP Bio- Mendelian Genetics 2: Extensions to Mendelian Genetics

2 of 3 of my Mendelian Genetics Unit. Image Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The Internet Provided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. By David Knuffke.

Jessica Gregerson

on 30 January 2015

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Transcript of AP Bio- Mendelian Genetics 2: Extensions to Mendelian Genetics

Extensions to Mendelian Genetics




Non-Mendelian Inheritance


Incomplete Dominance
Multiple Alleles
More Than 2 Choices
The interactions among genes and the organism can be highly variable.
Variable Effects
Gene Linkage
Extra-nuclear genes
Polygenic Inheritance
When the heterozygous condition expresses a third phenotype, different from either homozygous condition.
When the heterozygous condition expresses both of the homozygous conditions simultaneously.
Example: Carnation Color
w w
w R
How does this alter ratios?
Example: Human A, B, & AB Bloodtypes
Very few traits are expressed in simple Dominant/Recessive relationships
The body makes anti-blood type antibodies for any carbohydrate that is not on the surface of it's own bloodcells.

These antibodies cause blood cells that have particular carbohydrates to agglutinate (clump)

with the wrong blood type will kill a person.
Many traits are controlled by more than two alleles or one locus
When there are more than two alleles for a gene.
When more than one gene contributes to the expression of a particular trait
Example: Human A,B, & O alleles
Three blood type alleles = six possible genotypes, and four different phenotypes.
Example: Human Skin Color
Interactions at three(?) different loci leads to a wider variation for the trait (distributed along a bell curve).
When one gene has multiple effects on the physiology of an organism
When two or more genes control the expression of a single trait.
Example: Sickle-cell anemia
Example: Coat color in Laborador Retrievers
One locus has wide-ranging effects on the entire physiology of the organism.
The E/e allele controls whether pigment will be produced or not.

If at least one E allele is present, the B/b locus determines the color of the pigment produced

__ee - golden lab
bbE_ - chocolate lab
B_E_ - black lab
Some genes travel together
Some traits aren't on chromosomes
Linkage was first studied in the early 1900's by Thomas Hunt Morgan, a biologist who worked at Columbia University.

His lab (and its grad. students) laid the foundation for physically locating genes on chromosomes
Refers to genes that are on a sex chromosome.

Males will show sex-linked traits at a higher frequency than females (why?)

First discovered in fruit flies.
The white eye mutation is on the fruit fly X chromosome
The X chromosome in humans has many genes. The Y chromosome has very few
Map of Y Chromosome...
Different modes of sex determination (fruit flies are essentially like us)
Drosophila melanogaster
The "Fruit Fly": An awesome model organism for genetics (why?)
Refers to any genes that are on the same chromosome

Usually linked genes will travel together during meiosis.

When might they separate?
How linkage affects transmission of genes
Linkage Mapping
Since linked genes are only separated by crossing over events, the higher the frequency of recombinant offspring for any two genes, the greater the likelihood of there being a crossing over event between them.

This correlates to a greater distance between the genes on a chromosome.

This information can be used to generate a "
linkage map
" of genes on a chromosome.

Map units
": indicate distance between genes on a linkage map.

1 map unit = 1% chance of crossover (and recombinant offspring)
A linkage map of a Drosophila chromosome
Mitochondria and Chloroplasts have their own chromosomes.

These are inherited "

In males, the Y-chromosome is inherited "
* not technically "Extra-nuclear", but still...
Variegated Leaves: A trait conferred by a chloroplast gene
Mapping of Y-Chromosome mutations informs our understanding of historical human migration.
Refers to any heritable trait that is not determined by DNA sequences
Genomic Imprinting
Some traits are only expressed if the gene is inherited from one parent or the other.
Methyl groups (
) are added to DNA to inactivate it.

Some evidence to suggest this methlation pattern may be heritable, and affect phenotype.

Might explain phenomena like genomic imprinting
Big Questions
Make Sure You Can
"Dominance Hierarchy":
I = I > i

How does this alter ratios?
How does this alter ratios?
How does this alter ratios?
The likelihood of a genotype expressing a phenotype in an organism (or population)
The extent to which a trait is expressed in an organism.
Down's Syndrome is a genetic condition with total penetrance, but highly variable expressivity.
Several possible sex-linked transmission situations
The interaction of an organism's genome and its environment leads to complex patterns of gene expression.
The flower color of some species of hydrangea depends upon the pH of the soil (more acidic = bluer)
The coat color of Arctic Hare's changes on a seasonal basis.
How much of a human is a product of genes?
How able are scientists to separate themselves from their culture and biases?
Summing It Up:
How are traits inherited?

How are traits expressed?
Note: Gigantificated!
Describe how each of the situations that is discussed in this presentation extends Mendelian understanding of genetics.

Use your understanding of these situations to analyze/predict data from experiments and genetics problems.

Provide examples of each of the situations described in this presentation.

Explain why most traits result from the interplay between an organism and its environment.

Illustrate how genetics sheds light on the relationship between science and society.
Actual Size
Meiosis...makes gametes
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