HUMAN GENETICS

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HUMAN GENETICS. Introduction 46 chromosomes in each cell (23 pairs) Autosomes : all chromosomes except sex chromosomes (22 pairs) Sex chromosomes: determine gender (1 pair). Sex determination XX = female XY = male - PowerPoint PPT Presentation

Transcript of HUMAN GENETICS

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I. IntroductionA.46 chromosomes in each

cell (23 pairs)B.Autosomes: all

chromosomes except sex chromosomes (22 pairs)

C.Sex chromosomes: determine gender (1 pair)

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1.Sex determinationa)XX = femaleb)XY = male

2.During meiosis, each egg from the female gets an X; 1/2 male sperm get X, 1/2 get Y

3.Males determine gender of offspring!a)Except in birds and

reptiles where female is XY and male is XX

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II.Studying human geneticsA.Difficult because

1.Long generations (25 yrs)2.Single births3.Ethical concerns

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B.Methods for studying humans1.Pedigrees: record that

shows how a trait is inherited within a family

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2.Population sampling1.Selecting a small # of

people to represent an entire population

2.Must be a random sample3.Ex: through random

sampling, researchers discovered that 65% of people in US taste PTC, 35% cannot

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3.Identical twin studiesa)Identical genetic codesb)Separated at birth: study

which traits are genetic(Nature) & which are environmental (Nurture)

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III.Inheritance of human traitsA.Dominant traits

1. Polydactyly - extra fingers & toes

2. Dwarfism - small size3. Curly hair4. Huntington disease -

nervous disorder5. Piebaldness - white

patches of hair

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Vitiligo=AutoImmune

Piebaldness=Genetic

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B.Recessive traits1.Straight hair2.Freckles3.Albino4.Cystic fibrosis - lung disorder5.Deafness6.PKU - nervous disorder

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C.Codominance1.Sickle cell anemia -

irregularly shaped red blood cells• O allele = healthy(HH)• 1 allele = mild case(HS),

resistant to malaria• 2 alleles = severe case(SS)

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D.Multiple alleles1.3 or more alleles which

code for a single trait2.Human blood type

a) 3 possible alleles: IA, IB, iO

b)IA & IB are codominant, iO is recessive

c)41% of US is Type O -- o allele is most common

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Blood Type Genotypes Antigens

AIAIA

IAiO A

BIBIB

IBiO B

AB IAIB A & B Universal acceptor

O iOiO None Universal donor

5.Possible blood types

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Example punnet squares for type A dad and type B mom

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E.Polygenic traits1.Controlled by 2 or more

genes2.Skin color - the more

genes, the more melanin darker skin color

3.Height - more dominant alleles taller

4. Eye Color

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F.Sex-linked traits1.Genes located on X

chromosome2.Males only have one X, so

only have one allele controlling these genes

3.Males more likely to have disorders that are sex-linked because they only need 1 recessive allele

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4.Carrier: someone who has one allele for a disorder -- does not have the disease but can pass it on to children

5.Only women can be carriers for sex-linked traits

6.Examples: hemophilia, muscular dystrophy, colorblindness

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7.Color visiona)XC=Color Vision,

Xc=colorblindb)Males - 8% colorblind (XcY)c)Females - 1% colorblind

(XcXc)

Normal

Red-Green

Total

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What are the chances for a healthy dad and a mom who is a carrier for colorblindness to have a child that

is colorblind?

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Hemophilia in the Royal Families of Europe

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IV.Genetic disordersA.Nondisjunction: failure of

chromosomes to separate during meiosis1.Normal = 23

chromosomes2.Abnormal = 22 or 24

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3.Monosomy: too few chromosomes, one chromosome left unpaireda)Turner syndrome:

female with only 1 X chromosome

b)Short stature, sterile

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4.Trisomy: too many chromosomes, extra copy of onea)Down’s syndrome:

trisomy 21b)1 in 1400 when mother

under age 25, 1 in 100 by age 40

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B.Detecting genetic disorders1.Physical characteristics -

features, disabilities2.Ultrasound - pictures of

baby in utero using sound waves

3.Amniocentesis - sample of fluid from around baby, can examine baby’s cells

http://www.biology.iupui.edu/biocourses/n100/2k4csomaldisordersnotes.html

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http://www.katie.com/babyblog/archives/000538.html

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4.Karyotype: picture of a person’s cromosomes • taken from any cells --

blood in adults, amnio for baby

Normal Trisomy 21

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V. BiotechnologyA. Genetic engineering:

manipulating the DNA of an organism

1. Select useful traits, such as resistance to diseases

2. Transgenic organisms: contain a gene from another organism

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B. DNA fingerprinting1. Analysis of DNA

sequences to determine identity

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C.Gene therapy1. Once we know which genes

code for specific proteins and cause disorders

2. Insert a normal gene into a chromosome to replace a dysfunctional gene

3. On hold until more research can be completed

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