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Heredity Review
Asexual reproduction
Hydra (related to jelly-fish
Single celled eukaryotes like
this protist
Zygote (2n) - diploid
n chromosomes
Independent Assortment
Codominance
Incomplete Dominance
Epistasis
Thomas Hunt Morgan
Discovered sex-linked traits
• The recessive mutations s (scute bristles) and rb (ruby
eyes) identify two linked autosomal genes of Drosophila
melanogaster. When females heterozygous for these genes
were crossed with scute bristled, ruby eyed males, the
following classes and numbers of progeny (out of 1000)
were obtained:
• wildtype bristles, wildtype eyes 188
• scute bristles, wildtype eyes 307
• wildtype bristles, ruby eyes 313
• scute bristles, ruby eyes 192
Based upon these results, the map distance between the s and
rb genes is estimated to be:
• A. 31.3 map units
• B. 38 map units
• C. 30.7 map units
• D. greater than 50 units because all four classes of
offspring were observed
DNA (pattern done by Rosalind Franklin,
Model completed by Watson and Crick)
Promoter includes the TATA box; has the core DNA sequence 5'-TATAAA-3' or a
variant, which is usually followed by three or more adenine bases. It is usually
located 25 base pairs upstream to the transcription site. The sequence is
believed to have remained consistent throughout much of the evolutionary
process, possibly originating in an ancient eukaryotic organism.
G 5” cap and Poly A tail and reomval of introns
Conjugation
• Histone acetylation
– Seems to loosen chromatin structure and thereby
enhance transcription
Unacetylated histones
Figure 19.4 b
Acetylated histones
(b) Acetylation of histone tails promotes loose chromatin structure that
permits transcription
Evolution of Genes with Related Functions: The
Human Globin Genes
• The genes encoding the various globin proteins
– Evolved from one common ancestral globin gene, which
duplicated and diverged
Ancestral globin gene
Duplication of
ancestral gene
Mutation in
both copies
Transposition to
different chromosomes



Further duplications
and mutations


Figure 19.19


  2  2 1 
1
-Globin gene family
on chromosome 16



G

A

 -Globin gene family
on chromosome 11


• The similarity in the amino acid sequences of
the various globin proteins
– Supports this model of gene duplication and
mutation
• Subsequent duplications of these genes and random mutations
– Gave rise to the present globin genes, all of which code for oxygen-binding
proteins
Genomic library
Bands form due to SNP’s
-Single nucleotide
polymorphisms
A single nucleotide polymorphism (SNP, pronounced snip), is a DNA sequence variation occurring when a single
nucleotide - A, T, C, or G - in the genome (or other shared sequence) differs between members of a species (or
between paired chromosomes in an individual). For example, two sequenced DNA fragments from different
individuals, AAGCCTA to AAGCTTA, contain a difference in a single nucleotide. In this case we say that there are
two alleles : C and T