gregor mendel austrian monk studied at the university of vienna discovered the basic principles of...
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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 LAWS1. 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 CROSSESGiven: T- tall R - round
t – dwarf 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
Predict the gametes
• 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 agentsNorms of reaction broadest for polygenic traits
like skin color. Multifactorial characters: both genetic & environmental influences.
Mendelian Inheritance in Humans
• Recessive Disorders– Cystic fibrosis - PKU– Tay-Sachs disease– Sickle-cell disease
• Dominant Disorders– Achondroplasia -Polydactyly– Huntington’s disease
• Multifactorial Disorders
SICKLE CELL DISEASE
• Pleiotrophy – one disorder, multiple effects
• Incomplete dominance
• Heterozygotes – sickle cell trait, advantage (resistant to malaria)
PEDIGREES
INHERITANCE PATTERN?
FETAL TESTING
THE CHROMOSOMAL
BASIS OFINHERITANCE
The Chromosomal Basis of Mendel’s Laws
Segregation
R & r alleles Segregate
Only one long chromosomeIn each gamete
Fertilization recombines the R & r alleles
IndependentAssortment
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 Carrier passes Carrier w/ afflicted
transmits to all trait to ½ sons male; 50% of
daughters ½ daughters children afflicted
Sons 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
Sex linked Recessive Disorders in Humans
• Duchenne Muscular Dystrophy
• Hemophilia
• Red/Green Color blindness
X Inactivation
NONDISJUNCTIONleads to aneuploidy (trisomy, monosomy, polyploidy)
CHROMOSOMAL MUTATIONS
Human Chromosomal Disorders
• 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