Genetic Crosses

Introducing: The Mendaliens!

Phenotype vs. Genotype

Phenotype – what the organism looks like

Red protein

Red protein

+

Red flower

White protein

White protein

+White flower

Phenotypes

Phenotype vs. Genotype

Genotype – what alleles does the organism have?Red protein

Red protein

+

Red flower

White protein

White protein

+White flower

Genotypes

Use letters for convenience

“R” for red allele

“W” for white allele

RR WW RW

homozygous homozygous heterozygous

Time to have kids!

A parent gives ONE from each pair of chromosomes to a child.

In your cells

In your egg (or sperm)

RW

Plant babies could get:

RW

Plant parents:

RR RW

WR WW

+

+

Use “T” for tall plant (capital letter because it’s dominant

over the other allele)

Use “t” for short plant (lowercase letter because it’sRecessive to the other allele)

TT

Plant babies could get:

tt

Plant parents:

Tt Tt

Tt Tt

Tt

Plant babies could get:

Tt

Plant parents:

TT Tt

Tt tt

Genotypes¼ TT½ Tt¼ tt

Phenotypes¾ tall

¼ short

TT Tt

Tt tt

To make life easier may I introduce:The Punnett square!

Option 1 from mom

Option 2 from mom

Option 1 from dad

Option 2 from dad

Kid Kid

Kid Kid

T

TT Tt

Tt tt

t

T

t(Tt)

(Tt)

What about two traits at once?

Genotype RWfor color

Tt Genotypefor height

Phenotype:Pink and tall

Remember, a egg (or sperm) gets one of each pair of chromosomes, but it’s a crapshoot as to

which of the pair will be chosen

R W

T t

RT

Rt

WT

Wt

RT

RT

Rt

WT

Wt

Rt WT Wt

RRTT RRTt RWTT RWTt

RRTt Rrtt RWTt RWtt

RWTT RWTt WWTT WWTt

RWTt RWtt WWTt WWtt

Mendalien Problem #1

In MendAliens, normal head top is dominant to Bart head top, in which the top of the head is jagged. Suppose a MendAlien homozygous for normal head shape is crossed with one homozygous for Bart head shape.

H h

HH hh

H

Hh Hh

Hh Hh

H

h

h(hh)

(HH)

H

HH Hh

Hh hh

h

H

h(Hh)

(Hh)

(HH)

(Hh)

H

H

H

h

HH Hh

Hh hh

(hh)

(Hh)

H

h

h

h

Hh hh

Hh hh

GE

ge

ge

ge

ge

GE GE GE

(SSEE)

(ggee)

GgEeGgEeGgEe

GgEe

GgEe

GgEe

GgEe

GgEe

GgEe

GgEe

GgEe

GgEe

GgEe

GgEe

GgEe

GgEe

GE

GE

Ge

gE

ge

Ge gE ge

(GgEe)

(GgEe)

GgEeGGEeGGEE

GGEe

GgEE

GgEe

GGee

GgEe

Ggee

GgEe

ggEE

ggEe

Ggee

GgEe

ggEe

ggee

Phenotypes

GGEEGgEE (x2) GgEe (x4)GGEe (x2)

9 out of 16

ggEEggEe (x2)

3 out of 16

GGeeGgee (x2)

3 out of 16

GGEE

1 out of 16

(GgEe)

(ggee)

GE Ge gE ge

ge

ge

ge

ge

GgEe

GgEe

GgEe

GgEe

Ggee

Ggee

Ggee

Ggee

ggEe

ggEe

ggEe

ggEe

ggee

ggee

ggee

ggee

E = no ears (dominant)

E = ears (recessive)

XeY

XeY

XEY

X XXE XXE XE?

XE Xe?

XE XEXE

XeXE

Y

XE Xe

XE Xe

XE Y Xe Y

E = no ears (dominant)

e = ears (recessive)

XeY

XE XeXe

XeXE

Y

XE Xe

Xe Xe

XE Y Xe Y

What if?

Where did the a and the come from?