Chromosomes and Inheritance .... by hashim

8/3/2019 Chromosomes and Inheritance .... by hashim

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Chromosomes and Inheritance

Since genes are carried

on chromosomes,knowledge of

chromosome number

and structure has far-

reaching implications

for basic genetics,human health, and

evolution.

A normal human malekaryotype.


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X-linked InheritanceWhen Men and Woman Play by Different Rules

Behind the 8-ball? Colorblindness is an X-linked recessive trait.


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X-linked Inheritance

There are many X-linked recessive traits.


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Pedigree Analysis is a Key Tool in Human Genetics

Analyzing a pedigree is like puzzle-buildingyou try things (assigning

potential genotypes) until the pieces fit (youre as certain as you can be about

genotypes and modes of transmission (autosomal vs. X-linked; dominant vs.

recessive).


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A Pedigree of a Recessive Human Trait

Note that the trait can appear in offspring of parents without the trait.

Heterozygotes who do not show the trait are termed carriers.


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A Pedigree of a Dominant Human Trait

Note that the trait appears in every generation and the offspring

of an affected heterozygote are expected to show the trait.


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Changes in Chromosome Number and Structure

Changes in chromosome number and structure are important for health and

evolution.

Down syndrome is caused by a change in chromosome number.


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Aneuploidy occurs when one of the chromosomes is present inan

abnormal number of copies.

Aneuploidy

Trisomy and monosomy are two forms of aneuploidy.


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Down Syndrome is Caused by

Trisomy for Chromosome 21

Aneuploidy is remarkably common, causingtermination of at least 25% of human

conceptions.

Aneuploidy is also a driving force in cancer

progression (virtually all cancer cells are

aneuploid).


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Chromosome Non-Disjunction in Meiosis Causes Aneuploidy


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The Frequency of Chromosome Non-Disjunction And Down

Syndrome Rises Sharply with Maternal Age

The phenomenon is clearthe explanation isnt.


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Sex Chromosome Aneuploid Conditions are Common

Klinefelter syndrome


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Polyploidy

Polyploidy occurs when all the chromosomes are present inthreeor more copies.

Polyploidy is common in plants and rare in animals.


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Polyploids Are Created When Chromosome Number Doubles

A common way for this to occur is for the mitotic spindle to fail,

leaving all chromosomes in one cell.


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Polyploidy is a Major Force in Plant Evolution

Roughly 35% of flowering plants (the most familiar plant

species) arose through polyploidization.


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Most Crop Species are Polyploid

Polyploids, like the one on the left, are larger than their diploid

progenitors (strawberry on right).


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There are 4 types of

chromosome structural change

all of them associated with

human disorders

Chromosome Structural Changes


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A Boy with Cri-du-Chat Syndromea Debilitating Disorder

Caused by Chromosome Deletion


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Cri-du-Chat is Caused by the Loss of the Short Arm of One Copy

of Chromosome 5


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Translocations Lead to a Number of Human Cancers

In Burkitts lymphoma, a chromosome translocation

causes a cell cycle-promoting gene to always beactive.


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Searching for Chromosomal Defects - Amniocentesis and Chorionic

Villus Sampling

Many new

techniques forlearning about

individual genes

rather than whole

chromosomes are

available or under

development.


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Searching for Chromosome and Gene DefectsPre-Implantation

Genetic Diagnosis (PGD)

Removing a cell for

diagnosis from a humanembryo.

The diagnosis: trisomy

21 (Down syndrome).

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Chromosomes and Inheritance .... by hashim