CHAPTER 9 Patterns of Inheritance

BIOLOGYCONCEPTS & CONNECTIONS

Fourth Edition

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor

From PowerPoint® Lectures for Biology: Concepts & Connections

CHAPTER 9Patterns of Inheritance

Modules 9.1 – 9.10


• Genetics is the science of heredity

• These black Labrador puppies are purebred—their parents and grandparents were black Labs with very similar genetic makeups

– Purebreds often suffer from serious genetic defects

Purebreds and Mutts — A Difference of Heredity


canine hip dysplasia


• The parents of these puppies were a mixture of different breeds

– Their behavior and appearance is more varied as a result of their diverse genetic inheritance


• The science of heredity dates back to ancient attempts at selective breeding

• Until the 20th century, however, many biologists erroneously believed that

– characteristics acquired during lifetime could be passed on

– characteristics of both parents blended irreversibly in their offspring

MENDEL’S PRINCIPLES

9.1 The science of genetics has ancient roots


• The inheritance of acquired characters (or characteristics) is the hereditary mechanism by which changes in physiology acquired over the life of an organism (such as muscle enlarged through use) are purportedly transmitted to offspring. It is also commonly referred to as the theory of adaptation equated with the evolutionary theory of French naturalist Jean-Baptiste Lamarck (1744-1829).


Genetic Disproof

• There are many formulations of the genetic disproof, but all have roughly the same structure as the following:

• Acquired traits do not affect an organism's genome.

• Only the genome is passed to the offspring.

• Therefore, acquired traits cannot be passed to the offspring.


• Modern genetics began with Gregor Mendel’s quantitative experiments with pea plants

9.2 Experimental genetics began in an abbey garden

Figure 9.2A, B

Stamen

Carpel



• Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation

Figure 9.2C

• This illustration shows his technique for cross-fertilization

1 Removed stamensfrom purple flower

White

Stamens

Carpel

PurplePARENTS(P)

OFF-SPRING

(F1)

2 Transferred pollen from stamens of white flower to carpel of purple flower

3 Pollinated carpel matured into pod

4 Planted seeds from pod


• Mendel studied seven pea characteristics

Figure 9.2D

• He hypothesized that there are alternative forms of genes (although he did not use that term), the units that determine heredity

FLOWER COLOR

FLOWER POSITION

SEED COLOR

SEED SHAPE

POD SHAPE

POD COLOR

STEM LENGTH

Purple White

Axial Terminal

Yellow Green

Round Wrinkled

Inflated Constricted

Green Yellow

Tall Dwarf


Punnett Squares

• Professor Reginald Crundall Punnett, FRS (June 20, 1875 – January 3, 1967) was a British geneticist who co-founded, with William Bateson, the Journal of Genetics in 1910. Punnett is probably best remembered today as the creator of the Punnett square, a tool still used by biologists to predict the probability of possible genotypes of offspring. His Mendelism (1905) is sometimes said to have been the first textbook on genetics; it was probably the first popular science book to introduce genetics to the public.



• From his experimental data, Mendel deduced that an organism has two genes (alleles) for each inherited characteristic

– One characteristic comes from each parent

9.3 Mendel’s principle of segregation describes the inheritance of a single characteristic

P GENERATION(true-breedingparents)

F1 generation

F2

generation

Purple flowers White flowers

All plants have purple flowers

Fertilization among F1 plants(F1 x F1)

3/4 of plantshave purple flowers

1/4 of plantshave white flowers

Figure 9.3A


• A sperm or egg carries only one allele of each pair– The pairs of

alleles separate when gametes form

– This process describes Mendel’s 1. Law of segregation

– 2. Alleles can be dominant or recessive

GENETIC MAKEUP (ALLELES)

P PLANTS

F1 PLANTS(hybrids)

F2 PLANTS

PP pp

All P All p

All Pp

1/2 P 1/2 p

EggsP

p

P

PPp

Sperm

Pp Pp

pp

Gametes

Gametes

Phenotypic ratio3 purple : 1 white

Genotypic ratio1 PP : 2 Pp : 1 pp

Figure 9.3B


• Alternative forms of a gene (alleles) reside at the same locus on homologous chromosomes- One allele is dominant over the other with regard to Mendelian Traits.

9.4 Homologous chromosomes bear the two alleles for each characteristic

GENE LOCI

Figure 9.4

P a B

DOMINANTallele

RECESSIVEallele

P a b

GENOTYPE: PP aa Bb

HOMOZYGOUSfor thedominant allele

HOMOZYGOUSfor therecessive allele

HETEROZYGOUS


• By looking at two characteristics at once, Mendel found that the alleles of a pair segregate independently of other allele pairs during gamete formation

– This is known as:

3. Principle of independent assortment

9.5 The principle of independent assortment is revealed by tracking two characteristics at once


Figure 9.5A

HYPOTHESIS: DEPENDENT ASSORTMENT

HYPOTHESIS: INDEPENDENT ASSORTMENT

PGENERATION

F1

GENERATION

F2

GENERATION

RRYY rryy

Gametes RY

Yellowround

ry

RrYy

Eggs SpermRY

ry

RY

ry

1/21/2

1/21/2

Actual resultscontradict hypothesis

RRYY rryy

RY ryGametes

RrYy

Eggs RY

rY

1/4

1/4

Ry

ry

1/4

1/4

RY

rY

Ry

ry

1/4

1/4

1/4

1/4

RRYY

RrYYRrYY

RRYy rrYY RrYy

RrYyRrYyRrYyRrYy

rrYy RRyy rrYy

Rryy Rryy

rryy

9/16

3/16

3/16

1/16

Greenround

Yellowwrinkled

Yellowwrinkled

ACTUAL RESULTSSUPPORT

HYPOTHESIS


• Independent assortment of two genes in the Labrador retriever

Figure 9.5B

PHENOTYPES Black coat, normal vision

B_N_

Blind

GENOTYPES

MATING OF HETEROZYOTES(black, normal vision)

PHENOTYPIC RATIO OF OFFSPRING

Black coat, blind (PRA)

B_nn

Chocolate coat, normal vision

bbN_

Chocolate coat, blind (PRA)

bbnn

9 black coat,normal vision

3 black coat,blind (PRA)

3 chocolate coat,normal vision

1 chocolate coat,blind (PRA)

Blind

BbNnBbNn


http://www.athro.com/evo/gen/punexam.html


A dihybrid cross


The Female Calico Cat-X-Linked Calico coloring is a mix of phaeomelanin based colors (red) and eumelanin based color (black, chocolate and cinnamon). Cats of this coloration are believed to bring good luck in the folklore of many cultures.[1]

The spotting gene causes white patches to cover the colored fur


4 Sex-Linked Traits:

1. Normal Color Vision: A: 29, B: 45, C: --, D: 26

2. Red-Green Color-Blind: A: 70, B: --, C: 5, D: --

3. Red Color-blind: A: 70, B: --, C: 5, D: 6

4. Green Color-Blind: A: 70, B: --, C: 5, D: 2


• The offspring of a testcross often reveal the genotype of an individual when it is unknown

9.6 Geneticists use the testcross to determine unknown genotypes

TESTCROSS:

B_GENOTYPES bb

BB Bbor

Two possibilities for the black dog:

GAMETES

OFFSPRING All black 1 black : 1 chocolate

B

b

B

b

b

Bb Bb bb

Figure 9.6


• Most such disorders are caused by autosomal recessive alleles

– Examples: cystic fibrosis, sickle-cell disease

9.9 Connection: Many inherited disorders in humans are controlled by a single gene

Figure 9.9A

D D

d d

NormalDd

NormalDd

DDNormal

DdNormal(carrier)

DdNormal(carrier)

ddDeaf

Eggs Sperm

PARENTS

OFFSPRING


• Inheritance follows the rules of probability

– The rule of multiplication and the rule of addition can be used to determine the probability of certain events occurring

9.7 Mendel’s principles reflect the rules of probability

F1 GENOTYPES

Bb female

F2 GENOTYPES

Formation of eggs

Bb male

Formation of sperm

1/2

1/2

1/2

1/21/4

1/41/4

1/4

B B

B B

B B

b

b b

b

b b

Figure 9.7


• The inheritance of many human traits follows Mendel’s principles and the rules of probability

9.8 Connection: Genetic traits in humans can be tracked through family pedigrees

Figure 9.8A

OMIM-

http://www.ncbi.nlm.nih.gov/sites/entrez?db=omim


• Family pedigrees are used to determine patterns of inheritance and individual genotypes

Figure 9.8B

DdJoshuaLambert

DdAbigailLinnell

D_Abigail

Lambert

Female

DdElizabeth

Eddy

D_JohnEddy

? D_HepzibahDaggett

?

?

ddDdDdDdddDdDd

MaleDeaf

Hearing

ddJonathanLambert


• A few are caused by dominant alleles

Figure 9.9B

– Examples: achondroplasia, Huntington’s disease

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CHAPTER 9 Patterns of Inheritance

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