Genetics_Zoology_Part_2

7/30/2019 Genetics_Zoology_Part_2

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Mendelian InheritancePart 2


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Multiple Alleles

More than two forms of an allele exist in a

population

An individual only has two of the alleles


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A allele for making the A antigen on redblood cells

B allele for making the B antigen on redblood cells

O allele for NOT making the A or B antigenon red blood cells

Multiple Blood Alleles


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AA or AO = Type A blood

BB or BO = Type B blood

AB = Type AB blood

OO = Type O blood

Three alleles give four blood types


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Codominance: Blood Type


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California Court Case

1946 the California supreme court ruled

that Charlie Chaplin was the biological

father of a child he claimed was not his.

His defense was that the baby had type B

blood. He had type A and the woman who

sued him had type O (These may not be the actualblood types, but it illustrates the point)

Was the court correct?


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O

O

A AO

OO

AO

OO

O

AA, AO = Type A

BB, BO = Type B

AB = Type AB

OO = Type O


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Mutation

Change in a gene

nucleotide sequence is often altered

Produce abnormal protein

Cause a disease (sickle cell anemia)

Resistance to a disease (AIDS)


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Levels of Mutation

Molecular level

Deletion of nucleotides

Addition of nucleotides

Substitution of nucleotides

Chromosomal level

Change in structure

Change in number of chromosomes


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Hemoglobin

Protein molecule made

of 4 globin chains

2 alpha chains with 141amino acids

2 beta chains with 146

amino acids


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Sickle Cell Anemia

Gene for making

hemoglobin is

changed from normal


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Normal Hemoglobin Beta ChainFirst six amino acids

CTC

Valine Histidine Thre.

.

Leucine Glutamic acidProline

CAC

Valine Histidine Thre..

Leucine ValineProline

Hemoglobin S Beta ChainFirst six amino acids

One nucleotide has changed


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Hemoglobin S

Forms long rod like molecules that stretchRBC into a sickle shape

Sickled cells obstruct circulation of blood

Allele for hemoglobin S is recessive

SS = Normal

Ss = Carrier

ss = Sickle cell anemia


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Why is the s allele more

common in Blacks than Whites?

Ancestors of Blacks lived in areas where

malaria was present

Malaria parasite cannot survive onhemoglobin S

Even Ss are immune to malaria

The s allele is beneficial in an environmentwhere malaria is present


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Beta Globin Mutations

Over 300 different mutations!


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Causes of Mutations

Spontaneous Random

About 1/100,000 chance of a gene mutating

Induced Caused by mutagens

X-raysbreak DNA

UV radiation.Thymine dimers

LSDBreak chromosomes

Cigarette smokedamages tumor suppressorgenes


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Spontaneous Mutation

Two people of normal height have a childwith dwarfism

Bacteria become resistant to antibiotics Cold virus mutates every year

Immunity for this years cold will not protectyou from next years cold

AIDS virus (HIV)mutates too fast to makea conventional vaccine


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Ultraviolet LightCauses adjacent Thymines to bond together

ACA TT CT G

ACA TT

CT

G


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Excision Repair EnzymeRemoves small section of DNA

ACA TT

CT

G


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Excision RepairRemoves small section of DNA

CA T C

ACA TT CT G

DNA Polymerase fills in missing nucleotides


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Xeroderma Pigmentosum

Skin blisters from sun

exposure

Develop skin canceras children

Recessive gene does

not produce DNArepair enzyme


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Sunlight Exposure Increases

the Risk of Skin Cancer

DNA repair enzymes do not always fix the

damage that sunlight inflicts on DNA of skincells.

The more a person is exposed to sunlight, the

greater the risk of skin cancer


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Homologous chromosomes line up

in a double file in metaphase I of

meiosis


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Homologous Pairs

Separate


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Four Gametes With Single

Chromosomes


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Fertilization


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Nondisjunction

One pair of chromosomes fails to

separate during meiosis


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Trisomy

Zygote ends up with 3chromosomes instead of

2 for a given

chromosome pair.


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Karyotype

Often arranged

with autosomes

in descending

order and sex

chromosomes

separate


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Normal

Male


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Normal

Female


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Trisomy 21Down Syndrome


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Down Syndrome

Large tongue

Flat face

Single crease across

palm

Slanted eyes

Mental retardation

Some are not


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Maternal Age &Down Syndrome


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Trisomy 18Edward Syndrome


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Edward Syndrome

Heart defects

Displaced liver

Abnormal hands

Low-set ears

Severe retardation

98% abort

Lifespan < 1 year

Trisomy 13


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Trisomy 13Patau Syndrome


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Patau Syndrome

Cleft lip and palate

Extra fingers & toes polydactylism

Defects Heart

Brain

Kidney

Most abort

Live span < 1 month


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Klinefelter Syndrome


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Klinefelter Syndrome

Breast

development

Small testes Sterile

Low intelligence

Not retarded


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Turner Syndrome


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Turner Syndrome

Short

Not go through

pruberty

Produce littleestrogen

Sterile

Extra skin on neck

Ab l Ch


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Abnormal Chromosome

Numbers Aneuploidy

Missing or extra

chromosome

Polyploidy Extra set of

chromosomes

Usually lethal

Common in cancer Common in plants

Fetal testing can determine


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Fetal testing can determineabnormal karyotypes

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