1

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

16

Alfred Wallace

17

Darwin in 1859

1st printing sold out in a single day!