Question of the Day

Draw a Punnett Square for the following cross: Aa X Aa

Punnett Square

Agenda

• MET Videos

• Quiz

• Prove me wrong

Fig. 14-3-1EXPERIMENT

P Generation

(true-breeding parents) Purple

flowers Whiteflowers

Fig. 14-3-2EXPERIMENT

P Generation

(true-breeding parents) Purple

flowers Whiteflowers

F1 Generation

(hybrids) All plants hadpurple flowers

Fig. 14-3-3EXPERIMENT

P Generation

(true-breeding parents) Purple

flowers Whiteflowers

F1 Generation

(hybrids) All plants hadpurple flowers

F2 Generation

705 purple-floweredplants

224 white-floweredplants

Allele for purple flowers

Locus for flower-color gene

Fig. 14-4

Allele for purple flowers

Homologouspair ofchromosomes

Locus for flower-color gene

Allele for white flowers

Definitions

• Homozygous—two of the same alleles– Purple and Purple alleles– White and White alleles

• Heterozygous—two different alleles– One Purple and one white allele

• Genotype—combination of alleles

• Phenotype—expression of alleles

Fig. 14-5-1P Generation

Appearance:Genetic makeup:

Gametes:

Purple flowers White flowersPP

P

pp

p

Fig. 14-5-2P Generation

Appearance:Genetic makeup:

Gametes:

Purple flowers White flowersPP

P

pp

p

F1 Generation

Gametes:

Genetic makeup:Appearance: Purple flowers

Pp

P p1/21/2

Fig. 14-5-3P Generation

Appearance:Genetic makeup:

Gametes:

Purple flowers White flowersPP

P

pp

p

F1 Generation

Gametes:

Genetic makeup:Appearance: Purple flowers

Pp

P p1/21/2

F2 Generation

Sperm

Eggs

P

PPP Pp

p

pPp pp

3 1

Dominance in Humans

• Tongue rolling dominant to non-rolling

• Cleft chin dominant to smooth chin

Dominance in Humans

• Widows peak dominant to straight hairline

• Unattached earlobes dominant to attached earlobes

Law of Segregation

1. Different alleles cause variation in a popluation

2. For each trait, an organism inherits two alleles…one from each parent

3. If the two alleles differ, then one, the Dominant allele is fully expressed

4. The two alleles for each trait separate prior to sex

The Law of Segregation cont’d

• The two alleles for each trait are separated prior to sex

• Example: Heterozygote• Purple color is separated from white color

and each allele is passed on separately to the baby

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

The Law of Independent Assortment

• When chromosomes are ripped apart prior to sex, the traits are sorted independently from one another

• Example:– Having a cleft chin does not mean that you

will always have attached earlobes

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Dominantly Inherited Disorders

• Some human disorders are caused by dominant alleles

• Dominant alleles that cause a lethal disease are rare and arise by mutation

• Achondroplasia is a form of dwarfism caused by a rare dominant allele

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Fig. 14-17

Eggs

Parents

Dwarf Normal

Normal

Normal

Dwarf

Dwarf

Sperm

Dd dd

dD

Dd dd

ddDd

d

d

How can two dwarfs have children that are not dwarfs?

• Homozygous dominant is lethal

• Heterozygous in non-lethal

• Homozygous recessive is non-dwarf

Punnett Square

Autosomes vs. Sex Chromosomes

1 st g en e ra tio n

2 n d g en e ra tio n

3 rd g en e ra tio n

1 2

1 2 3 4 5

1 2 3 4

K ey

n o rm a l m a le

n o rm a l fem a le

m a le w ith co n d itio n

fem a le w ith co n d itio n

Sex chromosomes

• Sex determined by XX and XY

• Sex linked traits– Hemophilia

• X linked recessive

Hemophilia Punnett Square

Based on the diagram below, what do you know about individual III-2's

mother?

Objectives

• Demonstrate content knowledge of genetics

• Work collaboratively with your peers

• Discuss ideas and form a consensus

• Self-evaluate your work