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Inheritance and Evolution
• More about inheritance – Aneuploidy – X inactivation – Cytoplasmic inheritance – Genomic imprinting (briefly)
– Epistasis – Multiple genes
• Start evolution (if time) – Stories about Darwin and
Wallace
20 February 2019
Alleles on the same chromosome tend to be inherited together.
D
F E A
B C e
d
f c b a
(Especially if they are located near each other on the chromosome).
Gray body, normal wings Black body, vestigial wings
b+ vg+
b+ vg+
b+ vg+
b vg
b vg
b vg
b vg
b vg
b vg
b vgb vg
b vg
b+ vg+
b+ vg b vg+
b vg
After Meiosis I
After Meiosis II
Eggs Sperm
b+ vg+ b vg b+ vg b vgb vg+
Female is heterozygous for both genes
Male is homozygous recessive for both, so there is only one kind of gamete After DNA replication
The Down�s syndrome phenotype is the result of an extra copy of chromosome 21.
Aneuploidy: an extra or missing chromosome
Meiosis I
Nondisjunction can happen in either meiosis 1 or meiosis 2
Meiosis II
Gametes
n + 1 n + 1 n + 1 n – 1 n – 1 n – 1 n n
Aneuploidy is more common in plants
6
e.g. Datura fruits, with an extra copy of each chromosome
2
Why are calico & tortiseshell cat always female?
7
Chromosome rearrangements
8 Indian Muntjac Chinese Muntjac
Cytoplasmic Inheritance
Mitochondria and chloroplasts are inherited only from the mother
Epistasis: interactions among loci
Gene E determines whether dark pigment is deposited or not
Gene B determines color of pigment (Black or brown)
Black or Brown
pigment or no pigment
Yellow base color
B-E- Black bbE- Brown --ee Yellow
If no pigment is deposited (ee), it doesn�t matter what allele is present at the B locus
What phenotype ratio of offspring do you expect if you cross two heterozygous black labs (BbEe x BbEe)?
BE Be bE be BE BBEE BBEe BbEE BbEe
Be BBEe BBee BbEe Bbee
bE BbEE BbEe bbEE bbEe
be BbEe Bbee bbEe bbee
Multiple Genes
Eggs
Sperm
Phenotypes: Number of dark-skin alleles: 0 1 2 3 4 5 6
1/64 6/64 15/64 20/64 15/64 6/64 1/64
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8
AaBbCc AaBbCc
×
3
Human height is controlled by many genes
14
Descent with Modification
Charles Darwin Alfred Wallace
Fig. 22-5
NORTH AMERICA
EUROPE
AFRICA
AUSTRALIA
GREAT BRITAIN
SOUTH AMERICA
ATLANTIC OCEAN
PACIFIC OCEAN Cape of
Good Hope
Tierra del Fuego Cape Horn
Tasmania New Zealand
And
es
Equator
The Galápagos Islands
Pinta
Marchena Genovesa
Santiago Daphne Islands
Pinzón Fernandina
Isabela San
Cristobal
Santa Fe
Santa Cruz
Florenza Española
Darwin�s voyage on the Beagle
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Alfred Wallace
17
Darwin in 1859
1st printing sold out in a single day!
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