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Copy of AP Bio- Genetics Chap 15: Chromosomal Basis of Inheritance

3 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.
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Paul Saia

on 15 November 2013

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Transcript of Copy of AP Bio- Genetics Chap 15: Chromosomal Basis of Inheritance

Chromosomal Basis of Inheritance
Sex-Linked
Big Questions
Make Sure You Can
How are traits inherited?

How are traits expressed?

What is the relationship between genetics and human health?
Interpret pedigrees and use them to identify the mode of inheritance for particular traits.

Identify each of the examples in this presentation as belonging to particular modes of inheritance.

Use data from crosses involving linked genes to determine the distance between linked genes on a chromosome (in map units).

Explain how each of the examples discussed in this presenation affects human physiology at the molecular, cellular and organismal levels of organization.
X-Linked Recessive
X-Linked
Dominant

Y-Linked
Most common sex-linked inheritance pattern in humans.

Tend to show up in males due to hemizygosity.
Hemophilia
A defect in the proteins involved in blood clotting.

2 different forms are X-linked recessive conditions.

Can lead to death from hemorrhage (not typical in modern times).
Red-Green Color Blindness
A defect in the proteins that detect particular wavelengths of light.

Harmless...unless you want to be a pilot.
Not particularly common...

...but make sure you can spot it on a pedigree
Even less common than X-linked Dominant (the Y chromosome has almost no genes on it).
Duchenne Muscular Dystrophy
Due to an abnormality in the dystrophin protein.

Early onset muscle degeneration disease.

Symptoms appear by age 6, terminal by mid-20's
Inheritance of Hemophilia in a European Royal Lineage.
The Dystrophin protein is encoded in the longest gene in the human genome (2.4 MB)
An example of a vision test given to children to determine color-blindness.

Non-Mendelian Inheritance

Epigenetics
Extra-nuclear genes
Some traits aren't on chromosomes
Mitochondria and Chloroplasts have their own chromosomes.

These are inherited "
matrilineally
"

In males, the Y-chromosome is inherited "
patrilineally
"*
* not technically "Extra-nuclear", but still...
Varriegated 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
Methylation
Some traits are only expressed if the gene is inherited from one parent or the other.
Methyl groups (
-CH3
) 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

Linkage

Sex-Linkage
Gene Linkage
Some genes travel together
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
Several possible sex-linked transmission situations
Note: Gigantificated!
Actual Size
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