Lecture 29
Inheritance
Importance of geneticsImportance of genetics• Understanding hereditary diseases and to Understanding hereditary diseases and to
develop new treatmentsdevelop new treatments• Donor matchesDonor matches• PaternityPaternity• ForensicsForensics• EvolutionEvolution
Genetic TestingWould you want to know?
• Ethical concerns• Cost• Insurance companies
Difference between Meiosis and MitosisDifference between Meiosis and Mitosis
Meiosis IMeiosis I
Interphase Prophase I Metaphase I Anaphase I Telephase I
Crossing Over of Nonsister Chromatids between Homologous Chromosomes
Meiosis IIMeiosis II
Prophase II Metaphase II Anaphase II Telephase II
Genetic Testing
Gel electrophoresis
• PCR way of copying specific DNA fragments from small sample DNA material "molecular photocopying"
• It’s fast, inexpensive and simple
Polymerase Chain Reaction
Genetic Testing
Paternity Test $99
$299, looks at specific diseases
23 and me
• Genes- genetic material on a chromosome that codes for a specific trait
• Genotype- the genetic makeup of the organism
• Phenotype- the expressed trait• Allel- an alternative form of a
gene
Genetic Definitions
Dominance Mechanism
• Two alleles are carried for each trait
• In true-breeding individuals, both alleles are the same (homozygous).
• Hybrids, on the other hand, have one of each kind of allele (heterozygous).
• One trait is dominant, the other trait is recessive
Homunculus
How is “heredity passed on:
Spermist vs Ovists
Spermist conception of a
human sperm
Homunculus
Leeuwenhoek’s black male and white female rabbit experiments: spermist “proof”
Mendel’s Three Principles
• Dominance
• Segregation
• Independent Assortment
The foundation of “classical” scienceThe foundation of “classical” science
(1822-1884)
Dominance
• Traits of both parents inherited, but one shows over the other
• Traits are not blended
Dominance Mechanism
• Two alleles are carried for each trait
• In true-breeding individuals, both alleles are the same.
• Hybrids, on the other hand, have one of each kind of allele.
• One trait is dominant, the other trait is recessive
Segregation
• Half the gametes (egg or sperm) will carry the traits of one parent and half the traits for the other parent
Pairs of alleles are separated (=segregated) during meiosisPairs of alleles are separated (=segregated) during meiosis
Two different parental characteristics will be inherited independently of one another during gamete formation.
Independent Assortment
Example: flower color and leaf shape
Genetic Information
Genes are traits
“Eye color”
Ear lobe connectedness
Genes produce proteins
Enzymes are proteins
Homologous Chromosomes
gene: location
allele: specific trait
Allele Example
Gene = “eye color”
Alleles
brownbluegreenlavender
Allele Examples
appearance
eye color:homozygous
Allele Examples
appearance
eye color:heterozygous,brown dominant over blue
Genotype vs Phenotype
homozygous(dominant)
heterozygous
homozygous(recessive)
genotype phenotype
appearanceappearance
Punnett Square
If male & female are heterozygous for eye color
X
brown: 3/4 offspringblue: 1/4 offspring
male
female
PKUEach parent carries one gene for PKU.
P p
P pX
P
p
pP
P
P
P
p
p
P
p
p
Possible genotypes: 1PP 2Pp 1pp
Possible phenotypes:no PKU PKU
Compare this to what would have happened if one parent was homozygous for sickle cell.
HbA HbA
HbS HbS
X
HbS
HbS
HbAHbA
HbA
HbS
HbA
HbS
HbS
HbA
HbS
HbA
all offspring are carriers of sickle cell trait
Where Does Genetic Diversity Come From?
Where Does Genetic Diversity Come From?
• Mutation• Chromosomal Aberrations• Genetic Recombination
(e.g., from sexual reproduction)
• Mutation• Chromosomal Aberrations• Genetic Recombination
(e.g., from sexual reproduction)
mutationmutation
Sickle Cell Mutation
CTG ACT CCT GAG GAG AAG TCTLeu Thr Pro Glu Glu Lys Ser
CTG ACT CCT GAG GTG AAG TCTLeu Thr Pro Glu Val Lys Ser
NORMAL Hb
SICKLE CELL
Autosomes and Sex Chromosomes
Red-Green Color BlindnessSex-linked trait
XC Y
XC Xc
X
XC
Xc
YXC
XC
XC
XC
Y
Xc
XC
Y
Xc
Normal male
Normal female recessive gene
Possible outcomes: XCXC XCXc XCY XcYNormal female
Normal Female(carrier)
Normal male
Color-blind male
E unconnected earlobee connected earlobeE unconnected earlobee connected earlobe
alleleallele genegene
P EE x ee
gametes E e
F1 Ee
unconnected
connected
F1 Ee x Ee
gametes1/2 E 1/2 e1/2 E 1/2 e
E
e
E e
EE Ee
Ee ee
F2 1 EE 2 Ee 1 ee
PunnettSquare
Genotypes Phenotypes
Experiment to determinedominant vs. recessiveExperiment to determinedominant vs. recessive
Genetic Sleuthing
My eye color phenotype is brown.
What is my genotype?
Complexities
• Multiple genes for one trait
• Example: eye color
• Blended traits (“incomplete dominance”)
• Influence of the environment (UV, smoking, alcoholism)
Complexities
• Co-dominance-neither allele is recessive and the phenotypes of both alleles are expressed.
• Blood types- AB (not O); sickle cell anemia
heterochromia
Disorders
Down’s Syndrome (chrom 21)
Huntington’s (chrom 4)
Alzheimer’s (chrom 1, 10, 14, 19, 21)
Tongue RollerTongue Roller
R = Tongue Rollerr = Unable to Roll Tongue
Widow’s Peak
W = Widows Peakw = Lack of Widow’s Peak
Free Ear Lobe Attached Ear Lobe
E = Free Ear Lobee = Attached Ear Lobe
Hitchhiker’s Thumb
Hi = Straight Thumbhi = Hitchhiker’s Thumb
Bent Little FingerBent Little Finger
Bf = Bent Little Fingerbf = Straight Little Finger
Mid-digital Hair
M = Mid-Digital Hairm = Absence of Mid-Digital Hair
Dimples
D = Dimplesd = Absence of Dimples
Short Hallux
Ha = Short Halluxha = Long Hallux
Short Index Finger
Ss = Short Index FingerS1 = Long Index Finger
*Sex-Influenced Trait*Sex-Influenced Trait
http://www.youtube.com/watch?v=gCPuHzbb5hA