Chapter 15 AP

8/3/2019 Chapter 15 AP

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Chapter 15: The Chromosomal Basis of Inheritance


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Word Roots:

aneu- = without

cyto- = cell

hemo- = blood

mono- = one

non- = not

dis- = separate

poly- = many

re- = again

com- = together

bin- = two at a time

trans- = across

tri- = three

soma- = body

Nondisjunctionan accident ofmitosis or meiosis in which both

members of a homologous

chromosomes or both sister

chromatids fail to move apart.Recombinantan offspring whose

phenotype differs from that of the

parents.


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Thomas Hunt Morgan Drosophilamelanogaster

Fruit Fly

Small

Rapid reproduction

Multiple offspring

Controllable mating

4 Chromosome pairs

3 autosome pairs

1 sex chromosome pair

www.chem.rochester.edu


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Support for the Chromosomal Theory of Inheritance

Eye color experiment

Wildtype red eyes w+

Mutantwhite eyes w


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Correlation between

trait and chromosome

Discriminate betweenautosomal and sex-

linked inheritance

Provided support for

Mendelian inheritance


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Linked Genes Inherited Together

Linkedgenes

Parental

Recombinant

Genetic recombination

Recombinantfrequency

50% - unlinked

Independent assortment

< 50% - linked

Non-independent

assortment


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Recombination of Linked Genes Crossing Over

Crossing over

Recombinant frequency

# recombinants/total

offspring x 100%

Close to 50% -many cross overs

Genes far apart

Far from 50% - fewcross overs

Genes close

together


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Linkage Mapping

Alfred H. Sturtevant

Genetic map

Crossing over is random

Genes far apart more

crossing over

Genes close together

less crossing over

LinkageMap

Map units 1unit = 1%

centimorgans


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Physically linked but

genetically unlinked

Far apart on chromosome

Map - add recombinantfrequencies of other traits in

between

Further evidence for

chromosomal inheritance

4 groups of linkages

4 chromosomes

Cytogeneticmaps

Chromosomal features

Sequence maps

Nucleotide sequences


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Sex-linked Genes


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X0 system

XX female

X0 male

Z-W system

ZW female

ZZ male

Haplo-diploid system

Diploid female

Haploid - male


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Sexual Anatomy

Sexually amorphic embryo

Hormones control physical

outcomes

Y-chromosome

SRY gene

Protein transcription

factor for other genes

Sex-linked gene

X-linked gene


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Sex-linked Disorders

Duchenne Muscular Distrophy

1 in 3,500 males

Muscle weekness, loss of

coordination, death by 20s

Hemophilia

18,000 in US (mostly males)

Prolonged bleeding

Color blindness

8%-12% males; 1% females

Differing ability to see color


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X Inactivation

Barr Body

Random for each cell

Mary Lyon

Mosaic

Heterozygous carrier

Some cells with disorder,

others without

XISTX-inactive specific

transcript


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Alteration of Chromosome Number

NondisjunctionAnaphase I and II

Aneuploidy

Trisomic

Monosomic

Nondisjunction Anaphase

Zygote development

Polyploidy

Triploidy

Tetraploidy

Common in plants


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www.bbc.co.uk

www.cricyt.edu.ar


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Alterations of Chromosome Structure

Deletion lost chromosomal fragment

Duplication lost fragment attached to sister chromatid

Inversion reattachment of fragment backwards

Translocation fragment joins non-homologous chromosome


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Human Disorders due to Chromosomal Alterations

Frequency of aneuploid

Spontaneous abortion

Syndrome

Diagnosis before birth

Amniocentesis

Chorionic Villus Sampling

www.genetics.com.au


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Trisomy 21 Down Syndrome

1 in 700

Characteristic facial features

Short stature

Heart defects

Increased respiratory infection

Mental retardation

Prone to:

Leukemia

Alzheimers


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Kleinfelter Syndrome

XXY

1 in 2,000

Male

Small testes

Sterile

Breast enlargment

Normal intellegence

www.aafp.org

www.tokyo-med.ac.jp


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XYY Super Male

Taller

Increases aggression

Reduced IQ


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Trisomy X

1 in 1,000

No distinguishing

characteristics

bb.westernu.edu


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Monosomy X - Turner Syndrome

1 in 5,000

Only known monosomy

Sterile

Treatment hormone replacement


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Disorders Caused by Structurally Altered Chromosomes

Cri du chat

Deletion in chromosome 5

Mental retardation

Small head, unusual facial features

Distressed cat cry

Death in infancy


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Chronic Myelogenous Leukemia

Reciprocal translocation

9 and 22Philadelphia chromosome


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Genomic Imprinting

Gene expression

Dependent on parent

Occurs during gamete formation

Transmitted to all body cells

Consistent through generations

Insulin-like growth factor Igf2

Pn Mnwild type

Pn Mmwildtype

Pm Mn - dwarf

Methylation

Inactivation

Activation

Igf2


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Extranuclear Genes

Maternal inheritance

Mitochondria

ETC and ATP synthase

Mitochondrial myopathy

Energy deprivation in muscles and nerves

Diabetes

Heart disease

Plastids

Variegation of leaves

Chapter 15 AP

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