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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