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Development of chromosome theory of inheritance
•~1900 “rediscovery” of Mendel’s work
• 1902 similarity of mendelian transmission and chromosome behavior in
mitosis & meiosis (T. Boveri; W. Sutton)
• 1905 observations of sex-limited heteromorphic chromosomes (N. Stevens)
• 1910 discovery of sex-linked gene (T.H. Morgan)
• 1916 sex chromosome non-disjunction proof (C. Bridges)
Development of chromosome theory of inheritance
•~1900 “rediscovery” of Mendel’s work
• 1902 similarity of mendelian transmission and chromosome behavior in
mitosis & meiosis (T. Boveri; W. Sutton)
• 1905 observations of sex-limited heteromorphic chromosomes (N. Stevens)
• 1910 discovery of sex-linked gene (T.H. Morgan)
• 1916 sex chromosome non-disjunction proof (C. Bridges)
replication
mitosis
Fig. 3-1
replication
meiosis
Drosophila melanogaster has a heteromorphic chromosome pair
•Males have one of each member (XY)
•Females have two of one member of the pair (XX)
Fig. 3-5
Morgan’s white gene analysis
white-eye male
F1
F2
X
red-eye female
all red-eye
½ males red-eye
½ males white-eye
all females red-eye
red = w+ allele
(wildtype)
white = w allele
(mutant)
Morgan’s white gene analysis
Reciprocal cross
white-eye male
X
red-eye female
red-eye male
X
white-eye female
F1
all red-eye
F1
all males white-eye
all females red-eye
F2
½ males red-eye
½ males white-eye
all females red-eye
F2
½ males red-eye
½ males white-eye
½ females red-eye
½ females white-eye
Sex-dependent transmission & expression
(sex-linkage)
Morgan’s white gene analysis - INTERPRETATION
Reciprocal cross
white-eye male
Xw/Y
X
red-eye female
Xw+/Xw+
F1
all red-eye Xw+/Y
Xw/Xw+
F2
½ males red-eye
Xw+/Y
½ males white-eye Xw/Y
all females red-eye Xw+/Xw
Xw+/Xw+
red-eye male
Xw+/Y
X
white-eye female
Xw/Xw
F1
all males white-eye Xw/Y
all females red-eye Xw/Xw+
F2
½ males red-eye
Xw+/Y
½ males white-eye Xw/Y
½ females red-eye Xw+/Xw
½ females white-eye Xw/Xw
Sex-linkage indicates locus on a sex-limited chromosome
Sex linkage can be the reverse (e.g., lepidopterans, birds)
Females have the heteromorphic chromosome pair (ZW)
•Are the heterogametic sex
Fig. 3-6
Males are ZZ
•Are the homogametic sex
C. Bridges’ cross of red males (w+/Y) and white females (w/w) produced rare
• white female (must be w/w = gets two X chromosomes from mother?)
• red male (must be w+) = gets father’s X chromosome?
C. Bridges’ cross of red males (w+/Y) and white females (w/w) produced rare
• white female (must be w/w = gets two X chromosomes from mother?)
• red male (must be w+) = gets father’s X chromosome?
Explanation: chromosome nondisjunction
Fig. 3-7
•Confirmed chromosome theory
•Discovered general class of rare, recurring mutation with significant consequences
•Demonstrated why geneticists should “treasure your exceptions”
The sizes and densities of genes differs considerably among organisms
Fig. 3-13
Due to: spacing between genes
introns, relative number and sizes
other stuff
Genic organization of two small regions of human chromosome 21
Fig. 3-12
Karyotype of
Indian muntjac
(2n+6)
Fig. 3-8
Conventional cytogenetic markers for karyotype analysis
• Chromosome number (n, 2n, etc.)
Conventional cytogenetic markers for karyotype analysis
• Chromosome number (n, 2n, etc.)
• Chromosome size (large → small)
• Centromere location:
central (metacentric)
terminal (telocentric)
in-between (acrocentric)
• Chromatin differential compaction
• Euchromatin (lightly staining, lower density of DNA, most genes)
• Heterochromatin (densely staining, highly compacted,usually centromeric)
• Banding patterns (localized, alternating high/low compaction regions)
Human karytype (female)
using G-banding technique
Fig. 3-17
Drosophila karyotype in diploid and
polytene cells
(larval salivary gland cells)
Fig. 3-18
Conventional cytogenetic markers for karyotype analysis
• Chromosome number (n, 2n, etc.)
• Chromosome size (large → small)
• Centromere location:
central (metacentric)
terminal (telocentric)
in-between (acrocentric)
• Chromatin differential compaction
• Euchromatin (lightly staining, lower density of DNA, most genes)
• Heterochromatin (densely staining, highly compacted,usually centromeric)
• Banding patterns (localized, alternating high/low compaction regions)
• Special structures (nucleolus organizers, constrictions)
Stylized corn chromosomes
Fig. 3-19
In situ hybridization
with a fluorescently
labelled probe for a
single-copy muscle protein gene
Fig. 3-1
3-11
In situ hybridization with
a 3H-labelled probe for a
mouse satellite DNA
Fig. 3-14
In situ hybridization with a
fluorescently labelled
telomeric DNA sequence
(human fibroblast)
Fig. 3-16
Repeated from Cell Biology (must read/review)
Pages 88-90: chromosome/chromatin structure
Pages 90-95: mitosis & meiosis
Pages 96-97: life cycles of haploid and diploid organisms
Overview of allele
transmission through
mitosis and meiosis
Fig. 3-35
Overview of allele
transmission through
chromatid formation/
DNA replication
Fig. 3-36
Euglena genomes
• nuclear (red)
• mitochondrial (yellow)
Fig. 3-40
Fig. 3-41
Neurospora nuclear (ad) and mitochondrial (poky) genes
display distinctive sexual transmission patterns
(maternal inheritance)
Fig. 3-42
Organellar genes can show cytoplasmic segregation during asexual growth
Fig. 3-43
Typical inheritance of a human mitochondrial disease
Fig. 3-45
Fig. 3-1