HUMAN GENETICS

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)

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

II.Studying human geneticsA.Difficult because

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

B.Methods for studying humans1.Pedigrees: record that

shows how a trait is inherited within a family

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

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

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

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

Vitiligo=AutoImmune

Piebaldness=Genetic

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

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)

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

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

Example punnet squares for type A dad and type B mom

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

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

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

7.Color visiona)XC=Color Vision,

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

(XcXc)

Normal

Red-Green

Total

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

is colorblind?

Hemophilia in the Royal Families of Europe

IV.Genetic disordersA.Nondisjunction: failure of

chromosomes to separate during meiosis1.Normal = 23

chromosomes2.Abnormal = 22 or 24

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

female with only 1 X chromosome

b)Short stature, sterile

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

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

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

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

blood in adults, amnio for baby

Normal Trisomy 21

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

B. DNA fingerprinting1. Analysis of DNA

sequences to determine identity

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