copyright © 2006 pearson prentice hall, inc. chapter 11 genetics – the study of heredity patterns...

Copyright © 2006 Pearson Prentice Hall, Inc.

Chapter 11

• Genetics – the study of heredity

• Patterns of Inheritance


11.1 What Is the Physical Basis of Inheritance?

• 11.1.1 Genes Are Sequences of Nucleotides at Specific Locations on Chromosomes

• 11.1.2 An Organism’s Two Alleles May Be the Same or Different– Figure 11.1 The relationships among

genes, alleles, and chromosomes (p. 168)


chromosome 1from tomato

pair ofhomologous

chromosomes


11.2 How Were the Principles of Inheritance Discovered?

• Figure 11.2 Gregor Mendel (p. 168)

• 1860’s

• Studied pea plants – parents pass to offspring the genetically heritable traits


11.2 How Were the Principles of Inheritance Discovered?

• 11.2.1 Doing It Right: The Secrets of Mendel’s Success– Figure 11.3 Flowers of the edible pea (p.

169)


intact pea flower flower dissected to showreproductive structures


Mendels Principles

• Alternative forms of genes exist (more than 1 color option etc.)

• 2 genes, 1 from each parent, determines…thus each parent contributes 1 for a (new) combination of 2 (principle of segregation)

• Dominant shows up first, what you see/expressed (recessive, unseen but there, i.e. masked)


Genetics “terms”

• Homozygous – same allele, “pure”

• Heterozygous – diff. allele

• Allele – alternatives forms of genes

• Phenotype – physical characteristic (seen/expressed)

• Wild Type – physical characteristic (phenotype) seen most commonly in nature

• Genotype – genetic (chromosomal) make up


11.3 How Are Single Traits Inherited?

• 11_UN01 Mendel's Peas: F1 Generation (p. 169)

• 11_UN02 Mendel's Peas: F2 Generation (p. 170)

• In a mono-hybrid (X1) cross (only 1 characteristic differs at a time when crossed)


pollen

pollen

cross-fertilize

true-breeding,purple-flowered

plant

all purple-floweredplants

true-breeding,white-flowered

plant

Parentalgeneration (P)

First-generationoffspring (F1)


self-fertilize

Firstgenerationoffspring (F1)

Secondgenerationoffspring (F2)

1/4 white3/4 purple



• 11.3.1 The Pattern of Inheritance of Single Traits Can Be Explained by the Inheritance of Alleles of a Single Gene– 11_UN03 Mendel's Peas: Gametes from a homozygous

parent (p. 170) – 11_UN04 Mendel's Peas: Gametes from a heterozygous

parent (p. 171) – 11_UN05 Mendel's Peas: Allele production (p. 171) – 11_UN06 Mendel's Peas: Heterozygote offspring from

dominant and recessive parents (p. 171) – 11_UN07 Mendel's Peas: F1 alleles to F2 generation (p. 171)


More terms

• Hybrid cross – offspring of 2 diff. varieties crossed. 1 = mono, 2= di

• P1 generation= parents

• F1 generation = offspring of P1 generation; next = F2


homozygous parent gametes

A A A A


heterozygous parent gametes

A a A a


purple parent

white parent

all P sperm and eggs

all p sperm and eggs

PP

pp

P P

p p


sperm eggs

or

F1

offspring

p

p Pp

Pp

P

P


sperm eggs

F2

offspring

Pp

P

gametes fromF1 plants

Pp

pp

PPP

P

P

p

p

p p



• 11.3.2 Simple “Genetic Bookkeeping” Can Predict Genotypes and Phenotypes of Offspring– Figure 11.4 The Punnett square method

(p. 172)


Pp

self-fertilize

eggs pp

P

p

Pp

pppP

PP 1

—4

1

—4

1

—4

1

—4

1

—2

1

—2

1

—2

1

—2

spe

rm


2 results w/ a monohybrid cross

• 3:1 ratio phenotype

• 1:2:1 ratio genotype

• Look the same!



• 11.3.3 Mendel’s Hypothesis Can Predict the Outcome of New Types of Single-Trait Crosses


Seedshape

Seedcolor

Podshape

Podcolor

Flowercolor

Flowerlocation

Plantsize

smooth

yellow

inflated

green

purple

at leafjunctions

tall(1.8 to2 meters)

wrinkled

green

constricted

yellow

white

at tips ofbranches

dwarf(0.2 to 0.4meters)


11.4 How Are Multiple Traits Inherited?

• 11.4.1 Mendel Concluded That Multiple Traits Are Inherited Independently– Figure 11.6 Predicting genotypes and

phenotypes for a cross between parents that are heterozygous for two traits (p. 173)

– Figure 11.7 Independent assortment of alleles (p. 174)


What if 2 characteristics are different?

• Di-hybrid cross

• 2 characteristics differ simultaneously…

• You get independent assortment – separate out individually during gamete formation, do not effect each other

• Result: 9:3:3:1 genotype


Sy

SsYy

SY sY sy

self-fertilize

eggs

SY

Sy

sY

sy

SSYY SSYy SsYY SsYy

SSyY

sSYY

sSyY

SSyy

sSYy

sSyy

SsyY

ssYY

ssyY

Ssyy

ssYy

ssyy

1—4

sper

m

1—4

1—4

1—4

1—4

1—4

1—4

1—4

1—16

1—16

1—16

1—16

1—16

1—16

1—16

1—16

1—16

1—16

1—16

1—16

1—16

1—16

1—16

1—16


pairs of alleles on homologouschromosomes in diploid cells

chromosomes replicate

replicate homologouspair during metaphaseof meiosis I,orienting like this or like this

meiosis I

meiosis II

SY sy Sy sY

independent assortment produces four equallylikely allele combinations during meiosis


11.5 How Are Genes Located on the Same Chromosome

Inherited?• 11.5.1 Genes on the Same

Chromosome Tend to Be Inherited Together– 11_UN08 Pair of homologous

chromosomes (p. 175)


flower color gene pollen shape gene

purpleallele, P

longallele, L

redallele, p

roundallele, I


11.5 How Are Genes Located on the Same Chromosome

Inherited?• 11.5.2 Crossing Over Can Create New

Combinations of Linked Alleles


11.6 How Is Sex Determined?

• Figure 11.8 Photomicrograph of human sex chromosomes (p. 175)

• Figure 11.9 Sex determination in mammals (p. 176)


Y chromosome

X chromosome


female parent

male parent

male offspring

female offspring

spe

rm

eggs


11.8 Do the Mendelian Rules of Inheritance Apply to All

Traits?• No!

• Incomplete Dominance Produces Intermediate Phenotypes– Figure 11.10 Incomplete dominance (p.

177)


P:

F1:

F2:

RR R´R´

RR´RR´

R´R

R

R´

RR RR´

R´R´RR´

eggs

sper

m

1—2

1—2

1—2

1—2

1—4

1—4

1—4

1—4

Incomplete dominance =Pink flowers,a combo ofRed and white.Thus heterozygous alleles areboth dominantand effect equally.Phenotype +Genotype =1:2:1



Traits?• 11.8.2 A Single Gene May Have

Multiple Alleles– Figure E11.1 Cystic fibrosis (p. 179) – Table 11.1 Human Blood Group

Characteristics (p. 178)


2 alleles effect 1 trait – codominance, both phenotypes expresseedIn heterozygous cross



Traits?• Other exceptions…

• 11.8.5 The Environment Influences the Expression of Genes– Figure 11.11 Environmental influence on

phenotype (p. 178)

– NATURE vs. NURTURE debates


Others…

• Pleiotropy – 1 gene effects lots of characteristics (sickle cell anemia)

• Polygenic inheritance – additive effect of 2+ genes = continuum, skin color

• Sex linked genes – (law of independent assortment is not ALWAYS the case) i.e. color blindness example (men)

• What can we do – amniocentisis, pedigree charts…

copyright © 2006 pearson prentice hall, inc. chapter 11 genetics – the study of heredity patterns...

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