copyright © 2010 pearson education, inc. chapter 7 dna detective complex patterns of inheritance...

Copyright © 2010 Pearson Education, Inc.

Chapter 7 DNA Detective

Complex Patterns of Inheritance and DNA Fingerprinting


DNA Detective

1918: the Romanovs and four servants were murdered by Communists

1991: shallow grave containing bones of at least nine people dug up

Were any of these the Romanovs? If so, which ones?


7.1 Forensic ScienceForensic Science

The study of evidence discovered at a crime scene and used in a court of law.

Bones seemed to belong to six adults and three children

Sexing was inconclusive, due to decomposition of pelvises

Skeletons might be the Romanovs. Could resemblance among relatives be useful?


7.2 Dihybrid Crosses

Dihybrid crosses = crosses involving two genes simultaneously

Mendel’s peas: seed color and seed shape are on different chromosomes.

Y = yellow seed color; y = green seed color; R = smooth seeds; r = wrinkled seeds

Cross between two double heterozygote parents: YyRr x YyRr

The following Punnett square shows expected numbers of genotypes and phenotypes:


7.2 Dihybrid Crosses - Punnett Square

Figure 7.1

Possible typesof pollen

Possible types of ovules

Phenotype

RrYy RrYy

RRYYround, yellow

RRYyround, yellow

RrYYround, yellow

RrYyround, yellow

RRYyround, yellow

Rryyround, green

RrYyround, yellow

Rryyround, green

RrYYround, yellow

RrYyround, yellow

rrYYwrinkled, yellow

rrYywrinkled, yellow

RrYyround, yellow

Rryyround, green

rrYywrinkled, yellow

Rryywrinkled, green

Genotype

9

3

3

1

Round, yellow

Round, green

Wrinkled, yellow

Wrinkled, green

RRYY, RrYY, RRYy, RrYy

Rryy, Rryy

rrYY, rrYy

rryy



The Tsar and Tsarina were both heterozygotes for hair texture and eye color.

Due to random alignment of chromosomes and independent assortment, they could form the following gametes:



Figure 7.2a–b

Meiosis

Meiosis

Two types of gametes

Two other types of gametes

TsarinaCc Dd

Wavyhair

Darkeyes

TsarinaCc Dd

(b) Another possible Metaphase I alignment

Wavyhair

Darkeyes

(a) One possible Metaphase I alignment



Their gametes could then potentially produce the following offspring:

Figure 7.2c

Tsar ccDd(straight hair,dark eyes)

Tsarina CcDd(wavy hair,dark eyes)

ccDdStraight hair

Dark eyes

cD

cd

Possible types of sperm

Possible types of eggs

CcDdWavy hairDark eyes

ccDdStraight hair

Dark eyes

ccddStraight hair

Blue eyes

CcDdWavy hairDark eyes

CcddWavy hairBlue eyes

ccDDStraight hair

Dark eyes

(c) Punnett square for the mating of the Tsar and the Tsarina

CcDDWavy hairDark eyes


7.3 Extensions of Mendelian GeneticsExtensions of Mendelian Genetics More complex patterns of inheritance

Incomplete dominance: two copies of the dominant allele are required to see the full phenotype; heterozygote phenotype is intermediate to the homozygotes (e.g., flower color in snapdragons)

Figure 7.3

x =

Flower color in snapdragons

Red = RR White = rr Pink = Rr


7.3 Extensions of Mendelian Genetics Codominance: neither allele is dominant

to the other; heterozygote shows both traits at once (e.g., coat color in cattle)

Polygenic Traits = affected by multiple genes and the environment Height, weight, etc

Figure 7.4


7.3 Extensions of Mendelian Genetics

Blood typing can be used to exclude potential parents.

ABO blood group as three alleles of one gene: Multiple allelism IA and IB are codominant to each

other; i is recessive to both other alleles.

An individual will have two of these alleles.



Blood typing with Rh factor An RBC cell membrane protein Simple mendelian two gene complete dominance Indicated as + or – after ABO blood type



Blood Transfusions O- is universal donor AB+ is universal receiver


7.4 Sex Determination and Sex Linkage

Prince Alexis suffered from hemophilia, the inability to clot blood normally due to the absence of a clotting factor. Gene for this clotting factor is on the X

chromosome.

Alexis inherited the hemophilia allele from his mother.



Sex Determination and Sex Linkage

Humans have 22 pairs of autosomes and one pair of sex chromosomes Women: two X

chromosomes Men: one X and one Y

chromosome

Figure 7.6

MaleXY

FemaleXX

Meiosis

Fertilization

Possible sperm Possible eggsX Y X X

XY XXThis zygote willdevelop into a male.

This zygote willdevelop into a female.


7.4 Sex Determination and Sex LinkageSex-linked genes: genes located on the sex

chromosomes X-linked: located on the X chromosome Y-linked: located on the Y chromosome

Males always inherit their X from their mother Males are more likely to express recessive X-linked

traits than females Only females can be carriers of X-linked recessive

traits.



Figure 7.8

Crosses of carriers for hemophilia



Figure 7.8

Other X-linked recessive traits•Red-Green Color Blindness•Duchenne muscular dystrophy



X Inactivation Early female embryos

randomly inactivate one of the X chromosomes in each cell.

Inactivation is irreversible and inherited during cell division.

It is caused by RNA wrapping around the X chromosome.

Figure 7.9



Tortoiseshell Cats Result is patches of tissue in adult female

with different X chromosomes active.

Figure 7.10

(a)

Genotype

Orange male Black female Tortoise shell female

(b)Random Xchromosomeinactivation

Tortoiseshell catwith patches oforange and black

MitosisMitosis

Inactive Xchromosome

Active Xchromosome

Allele fororange fur

Allele forblack fur

x =

Early embryo

Phenotype

X inactivation



Y-Link Genes Passed only from father to son But few genes on Y-chromosome

SRY gene



Figure 7.10

Animation—X-Linked Recessive TraitsPLAY


7.5 Pedigrees

Pedigree: a family tree, showing the inheritance of traits through several generations

Pedigrees reveal modes of inheritance

Symbols commonly used in pedigrees:

Figure 7.11

Female

Male

Marriage or mating

Offspring inbirth order(from left to right)

Affected individuals

Known or presumedcarriers

or

or

Pedigree analysis symbols


7.5 Pedigrees

Pedigree for an autosomal dominant trait: Polydactyly

Figure 7.12a

(a) Dominant trait: Polydactyly

Two unaffectedindividualscannot haveaffected offspring.

Two affectedparents canhaveunaffectedoffspring.

pp

Pp

pp

pp

PpPpPp

pp pp pp

Pp


7.5 PedigreesPedigree for an autosomal recessive trait: Attached earlobes

Figure 7.12b


7.5 PedigreesPedigree for an X-linked trait: Muscular

dystrophy

Figure 7.12c


7.5 Pedigrees

Romanov Pedigree Pedigree analysis

reveals that Queen Victoria’s mother must have had a mutation for the hemophilia allele, which was ultimately passed on to Prince Alexis Romanov.

Figure 7.13


7.6 DNA Fingerprinting

DNA Fingerprinting No two individuals are genetically identical

(except for MonoZygotic twins) Therefore, individuals have small differences

in nucleotide sequences of their DNA

This is the basis for DNA fingerprinting Unambiguous identification of people



Steps in DNA fingerprinting: overview DNA isolated from tissue sample DNA cut into fragments with enzymes

DNAs of different sequences produce fragments of different sizes

Fragments separated on basis of size and visualized

Each person’s set of fragments is unique



DNA Fingerprinting: using small samples Small amounts of DNA can be amplified

using PCR (polymerase chain reaction) DNA is mixed with nucleotides, specific

primers, Taq polymerase, and then is heated

Heating splits the DNA molecules into two complementary strands

Taq polymerase builds a new complementary strand

DNA is heated again, splitting the DNA and starting a new cycle.


7.6 DNA Fingerprinting In each cycle of PCR, the DNA doubles.

Figure 7.14

5

4

3

2

1

Primer

Double stranded DNA

Primer Polymerase

PCR is used toamplify, or makecopies of, DNA.During a PCRreaction, primers(free nucleotides)and DNA are mixedwith heat-tolerantpolymerase.

As the mixturecools, the primersbond to the DNAtemplate and thetwo polymeraseuse the primers toinitiate synthesis.

A copy of theDNA template isassembled.

The mixture isheated again. Theprocess is repeatedmany times,doubling the DNAamount each time.

The DNA is heatedto separate, ordenature, the twostrands.



Cut DNA into fragments DNA is cut into

fragments using restriction enzymes, which cut around DNA sequences called VNTRs (variable number tandem repeats)

Figure 7.15

Variablenumbertandemrepeat(VNTR)

4 VNTRs

5 VNTRs

Student 1

6 VNTRs

3 VNTRs

Homologouschromosomes

Student 2

=



Visualize Fragments Gel electrophoresis separates DNA

fragments on basis of their sizes Electric current is applied to an agarose gel Smaller fragments run faster through the gel

Fragments are transferred to a sheet of filter paper

Labeled probe reveals locations of fragments containing VNTRs

These steps are illustrated in the next slide



Figure 7.16



DNA Fingerprint Each person will have a

unique pattern of bands.

Figure 7.17



Animation—Polymerase Chain Reaction (PCR)PLAY



Romanovs DNA fingerprinting analysis DNA fingerprinting showed that 9 persons

were buried in the Ekaterinburg grave. Romanovs would be more similar in

pattern to each other than to nonrelatives. All of a child’s bands must be present in

one or both of the parents.



Figure 7.18

Hypothetical DNA pattern from Romanov graves



Figure 7.18

Pretenders to the Romanov throne



But were remains in grave really Romanovs? To see if parents and their children were

Romanovs, DNA fingerprints were prepared for relatives of tsar and tsarina.



Pedigree of Romanov family

Figure 7.20

Tsar’sbrotherGeorge

Tsar TsarinaCarrier of

hemophiliaallele

Tsarina’ssister

Not a carrierof hemophilia

allele

Tsarina’sniece Alice

Tsarina’sgrandnephewPrince Philip

QueenElizabeth II

Lady Diana Charles

Olga Tatiana Maria Anastasia AlexisHemophilia

William Henry

DNA evidence

Members of Romanov family executed in 1918

DNA evidence

Anne TimothyLawrence

Peter Zara

Andrew SarahFerguson

Beatrice LouiseEugenie

Edward SophieRhys-Jones



But were remains in grave really Romanovs? Adult male skeleton (related to the

children) was related to George, the tsar’s brother.

Adult female skeleton (related to the children) was related to Prince Philip, the tsarina’s grand-nephew.

Conclusion: the grave contained the tsar, tsarina, three of their children, and four servants.

copyright © 2010 pearson education, inc. chapter 7 dna detective complex patterns of inheritance...

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