chromosomal patterns of inheritance

7/29/2019 Chromosomal Patterns of Inheritance

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Mader: Biology 8th Ed.

Chromosomal Patterns of Inheritance


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Outline

X-Linked Alleles Human X-Linked Disorders

Gene Linkage

Crossing-Over Chromosome Map

Changes in Chromosome Number

Changes in Chromosome Structure

Human Syndromes


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Chromosomal Inheritance

All but one pair of chromosomes in malesand females are the same.

Autosomes - Nonsex chromosomes

The different pair, sex chromosomes,determines the sex of an individual.

X-linked (sex-linked) is the term used for

genes carried on the X chromosome.


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X-Linked Alleles

X-linked alleles have a different pattern ofinheritance than alleles on autosomesbecause the Y chromosome is blank forthese alleles.

Inheritance of a Y chromosome cannotoffset the inheritance of an X-linkedrecessive allele.


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Drosophila


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Human X-Linked Disorders

Color Blindness In humans, color vision receptors in the

retina are three different classes of conecells.

Only one type of pigment is present ineach class of cone cell.

The allele for blue-sensitive is

autosomal, but the red- and green-sensitive proteins are on the Xchromosome.


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Human X-Linked Disorders

Muscular Dystrophy Absence of protein dystrophin allows

calcium to leak into muscle cells.

Hemophilia Hemophilia A due to lack of clotting factor

IX and hemophilia B due to lack of clotting

factor VIII.



Hemophilia Pedigree



Gene Linkage

The existence of several alleles on the samechromosome.

Alleles on the same chromosome form a

linkage group because they tend to beinherited together.

Can be used to build a linkage map.



Constructing a Chromosome Map

A linkage map can also be called achromosome map because it tells the orderof gene loci on chromosomes.

If crossing-over occurs between twolinked alleles of interest, a dihybridproduces four types of gametes instead oftwo.



Crossing-Over



Linkage Data

The percentage of recombinant phenotypescan be used to map chromosomes because

there is a direct relationship between thefrequency of crossing-over and the distance

between alleles.

Assumed 1% crossing-over equals 1 mapunit.




Polyploidy Occurs when eukaryotes have more than

2n number of chromosomes.

Named according to number of sets ofchromosomes.

Major evolutionary force in plants.

Some estimate 47% of floweringplants are polyploids.




Monosomy and Trisomy Monosomy (2n - 1) occurs when an

individual has only one of a particular type

of chromosome. Trisomy (2n + 1) occurs when an

individual has three of a particular type of

chromosome.



Down Syndrome

Down syndrome (Trisomy 21) is caused by

three copies of chromosome 21.


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Changes in Sex Chromosome Number

An abnormal sex chromosome number isthe result of inheriting too many or too few Xor Y chromosomes.

Nondisjunction during oogenesis orspermatogenesis.


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Sex Chromosome Syndromes

Turner Klinefelter

(XO) (XXY)


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Sex Chromosome Syndromes

Poly-X Females

More than two X chromosomes and extraBarr bodies in the nucleus.

Range from tall and thin to tall and

severely retarded depending on numberof X chromosomes.

Jacobs Syndrome

XXY due to nondisjunction duringspermatogenesis.

Taller than average


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Deletion End of a chromosome breaks off, or two

simultaneous breaks lead to loss of an

internal segment. Translocation

Movement of a chromosome segment

from one chromosome to another, non-homologous chromosome.


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Duplication Presence of chromosomal segment more

than once in the same chromosome.

Known to occur as a result of aninversion in which segment is turned180o.


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Human Syndromes

Deletion Syndromes

Williams syndrome - Loss of segment of

chromosome 7.

Cri du chat syndrome (cats cry) - Loss ofsegment of chromosome 5.


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Review

X-Linked Alleles Human X-Linked Disorders

Gene Linkage

Crossing-Over Chromosome Map



Human Syndromes


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M d Bi l 8th Ed

chromosomal patterns of inheritance

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