Transcript Document 7433661

GREGOR MENDEL
•
•
•
•
Austrian monk
Studied at the University of Vienna
Discovered the basic principles of heredity
Worked with breeding garden peas
– Self pollinating
– Perfect flowers
– Artificially cross pollinated
Mendel’s Pea Plants
• True breeding – all offspring
same variety
• Hybridization – crossing 2
contrasting true breeding
varieties
• P generation – parental
generation (true breeding)
• F1 – first filial (hybrids)
• F2 – second filial (from self
pollinating F1s)
Mendel tracked heritable characters for 3
generations
MENDEL’S LAWS
1. Alternative versions of genes (alleles) account for
variations in inherited characters.
2. For each character, an organism inherits two
alleles, one from each parent.
3. If the 2 alleles differ, then one, the dominant allele
is fully expressed in the organism’s appearance;
the recessive allele has no noticeable effect on the
organism’s appearance
4. The 2 alleles for each character segregate during
gamete production.
Law of Segregation
• Letters represent alleles
(upper case for dominant
alleles & lower case for
recessive alleles)
• P generation – true
breeding plants, matching
alleles (PP or pp)
• Gametes contain only one
allele
• Fusion of gametes → hybrid
F1s
• When hybrids produce
gametes, the 2 alleles
segregate
• Half the gametes receive
the P allele and half
receive the p allele
• Punnett squares show
possible combinations of
alleles in gametes
• Each square is a possible
offspring
VOCABULARY
TEST CROSS
DIHYBRID CROSSES
Given: T- tall
t – dwarf
R - round
r - wrinkled
PROBABILITY LAWS
1. CHANCE HAS NO MEMORY
2. RULE OF MULTIPLICATION: the chance
of 2 independent events occurring together
is the product of their individual
probabilities.
3. RULE OF ADDITION: the probability of an
event that can occur in 2 or more different
ways is the sum of the separate
probabilities.
PROBABILITY PRACTICE
1) If a coin is tossed 7 times and lands heads
all seven times, what is the chance of
getting heads again?
2) A couple has 3 girls; what is the chance
that their fourth child will be another girl?
3) In a deck of 52 cards, what is the chance
of drawing:
a) Any red card?
b) Any ace?
c) Any heart?
PROBABILITY PRACTICE
1. From a normal deck of cards, what is the
chance of drawing the Jack of Hearts?
2. When tossing 2 dice, what is the
probability of getting a “6” up on both?
3. What is the probability of 2 parents, with
genotypes AabbCc x AaBBCc, having a
child with the genotype AaBbCc?
AaBbRr x Aabbrr
• What fraction of the offspring will have the
following genotypes?
– aabbrr
- AaBbRr
- aaBbrr
• What fraction of the offspring will have at least
two recessive phenotypes?
a) list all possible genotypes
b) calculate probabilities (rule of multiplication)
c) pool probabilities (rule of addition)
AaBbRr x Aabbrr







Formula 2n (n = # of heterozygous pairs)
AA → 20 →1 gamete type (A)
Aa → 21 → 2 gametes (A or a)
AABb → 21 →2 gametes (AB or Ab)
AaBb → 22 → 4 gametes (AB, Ab, aB, ab)
AaBbDd → 23 → 8 gametes
AaBbDdFf → 24 →16 gametes
AaBbDd
AaBbDdFf
Incomplete Dominance
• Alleles for red and white,
neither is dominant.
• Hybrids are a blend of the
two alleles and are
phenotypically pink
• There is NO allele for pink,
therefore NO true breeding
pink flowering plants.
• Codominance: both alleles
equally expressed. Human
blood type, cow coloring
MULTIPLE ALLELES
EPISTASIS
• Gene at one locus
alters the phenotypic
expression of a gene
at a second locus
• Gene for fur color:
(B) black (b) brown
• 2nd gene deposition of
pigment: (C) color (c)
white
Polygenic Traits
 Skin color and height
in humans
 Additive effect of 2
or more genes on 1
phenotype
 Quantitative
characters –
variation along a
continuum
 Dots represent
“units” of darkness
NATURE and NURTURE
The product of a genotype is a range of phenotypic
possibilities over which there may be variation due
to environmental influence. Norm of reaction
- Hydrangea flower color and pH (blue-pink)
- Human blood typing: little range (genotype
mandates phenotype.
- Human blood counts: vary with altitude,
fitness, infectious agents
Norms of reaction broadest for polygenic traits like
skin color. Multifactorial characters: both genetic
& environmental influences.
Mendelian Inheritance in Humans
• Recessive Disorders
– Cystic fibrosis
– Tay-Sachs disease
– Sickle-cell disease
- PKU
• Dominant Disorders
– Achondroplasia
– Huntington’s disease
• Multifactorial Disorders
-Polydactyly
SICKLE CELL DISEASE
 Pleiotropy – one
disorder, multiple
effects
 Incomplete
dominance
 Heterozygotes –
sickle cell trait,
advantage (resistant to
malaria)
PEDIGREES
INHERITANCE PATTERN?
FETAL TESTING
THE
CHROMOSOMAL
BASIS OF
INHERITANCE
The Chromosomal Basis of Mendel’s Laws
Segregation
R & r alleles
Segregate
Only one long
chromosome
In each
gamete
Fertilization
recombines
the R & r
alleles
Independent
Assortment
Long and short
chromosomes;
Arranged in 2
equally likely
ways
They assort
independently
Fertilization
9:3:3:1 ratio
THOMAS HUNT MORGAN





Worked with Drosophila
Wild type – phenotype most common in the wild.
Red eyes, gray, normal wings
Mutant phenotypes – white eyes, ebony, vestigial
wings
Discovered sex linkage
Sex linked genes – on sex chromosomes
Sex Linked Inheritance
 Sex linked genes: on the X or Y
chromosome
 X & Y NOT homologous
 X-linked genes: males being XY
have only one copy/allele,
females XX have two
copies/alleles
 X-Linked recessive – more
common in males
 X-Linked dominant – more
common in females
SEX DETERMINATION
 Humans – sex determined
by presence or absence of Y
chromosome; XX-female;
XY-male
 Fruit flies – # of X
chromosomes; XX-female;
XY-male; XXY-female
 Birds – females are
heterogametic
Transmission of Sex-Linked Recessive Traits
Father w/ trait
transmits to all
daughters
Carrier passes
trait to ½ sons
½ daughters
Sons afflicted
Carrier w/ afflicted
male; 50% of
children afflicted
LINKAGE
 Law of Linear Order: genes on the same
chromosome are linked and are inherited in
a block.
 Drosophila – 2 linked genes; inherited
together
 body color (G gray, g ebony)
 wing size (L long, l vestigial)
 Test cross by Morgan produced unexpected
results
CROSSING OVER
MAPPING
 Linkage map – genetic map based on recombination
frequencies
 Map units – one map unit = 1% recombination frequency
 Cytological maps – locate genes with respect to
chromosomal features like stained bands
Recombination frequencies:
used to construct genetic map
The probability of a crossover between 2 loci is proportional to
the distance separating the loci
MAPPING PRACTICE
• AC = 22%
BC = 7%
AB = 15%
• Yellow /white = .5% white miniature = 34.5 %
yellow miniature = 35.4 %
• AB = 8%
AC = 28%
AD = 25%
BC = 20%
BD = 33%
– What is the distance between C and D?
Sex linked
Recessive Disorders in Humans
• Duchenne Muscular Dystrophy
• Hemophilia
• Red/Green Color blindness
X Inactivation
NONDISJUNCTION
leads to aneuploidy (trisomy, monosomy, polyploidy)
CHROMOSOMAL MUTATIONS







Down Syndrome (Trisomy 21)
Turner Syndrome (XO, monosomy X)
Klinefelter syndrome (XXY)
XYY, XXX
Cri du chat (cry of the cat) deletion in #5
CML (chronic myeloid leukemia) translocation of #
22
Down Syndrome due to translocation of #21
Genomic Imprinting
• Prader-Willi Syndrome:
– Mental retardation, obesity, short
stature, small hands & feet (father)
• Angelman Syndrome:
– Spontaneous laughter, jerky
movements, other motor and
mental symptoms (mother)
• Same cause – partial deletion of
chromosome #15
• Genomic Imprinting – gene on
one chromosome silenced