Transmission (Classical, Mendelian) Genetics Ch 11 Gregor Mendel –Experiments in Plant...
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Transcript of Transmission (Classical, Mendelian) Genetics Ch 11 Gregor Mendel –Experiments in Plant...
Transmission (Classical, Mendelian) Genetics Ch 11
• Gregor Mendel– Experiments in Plant Hybridization, 1865
• Controlled experiments, mathematical analysis
Pisum sativum, the garden pea
• What makes this a good model organism?
• easy to grow
• hundreds of offspring per cross
• short generation time
• can self fertilize or cross– Paint pollen (sperm) from one plant onto the
female parts of another (emasculated plant)
Mendel’s conclusions
1. Genes are physical units– 2 alleles for each gene– 1 allele inherited from each parent
Genes and alleles of Pisum sativum
Gene Alleles• Pea color ?• Flower color white, purple• Pod shape constricted, inflated• Pea surface ?• Stem height tall, dwarf
2. Principle of Dominance- One allele dominant, the other recessive- The dominant allele is expressed in the phenotype
Gene for flower color
P allele = purple
p allele = white
GENOTYPES PHENOTYPE
Homozygous dominant =
Heterozygous =
Homozygous recessive =
3. Random segregation of alleles into gametes – gamete receives ONE allele per gene– random segregation of alleles 50/50
PP pp
What is the phenotype of all offspring in F1 generation?
P generation
P P
p
p
Note that the P generation is true breeding
Genotype
Phenotype
How did Mendel do it? The Monohybrid cross
Which allele is dominant?What is the genotype of the f1 generation?
YY yy
Cross 2 f1 plants (or let one self-fertilize)
What is the ratio of phenotypes?
Results of Mendel’s monohybrid crosses
Parental Strains F2 progeny RatioTall X dwarf 787 tall, 277 dwarfRound seeds X wrinkled 5474 round, 1850 wrinkledYellow seeds X green 6022 yellow, 2001 greenViolet flowers X white 705 violet, 224 whiteInflated pods X constricted 882 inflated, 299 constrictedGreen pods X yellow 428 green, 152 yellowAxial flowers X terminal651 axial, 207 terminalgene = ?alleles = ?
In mice, black fur is dominant over white fur
Cross heterozygous mouse with homozygous recessive mouse B = black b = white
Test cross (one gene)
• A mouse has black fur, what are its 2 possible genotypes?
Test cross mouse to homozygous recessive mouse
If black mouse is BB If black mouse is Bb
A mouse was test crossed and 7 offspring black, 2 white. What is mouse’s genotype?
All possible one gene crosses
Parents ratio offspring
Pedigree Analysis Ch 11
Autosomal recessive inheritance (bb)
• unaffected parents can have affected offspring
• May “skip” a generation• Two affected parents cannot
have an unaffected child• Not sex related
Autosomal recessive traits
• Sickle cell disease
• Albinism
• Cystic fibrosis
• O blood type
Phenylketonuria (Ch.4)
• PKU (1/12,000) Mutation in gene encoding phenylalanine hydroxylase enzyme needed for phe metabolism
Chromosome 1212q24.1
missing phenylalanine hydroxylase enzyme
If plasma phe level is too high, phe is converted into a phenylpyruvate toxic to brain tissue
Why are these babies normal when born?
Pleiotropic effectsno tyrosine (little melanin)slow growthretardationblue eyeslow adrenaline
No nutrasweetlow phe diet ($5K/yr)
1902 Archibald Garrod: One gene: one enzyme“Inborn errors of metabolism”PKUAlbinismAlkaptonuriaTyrosinemia
Black urinearthritis
Ch 4
Fill in genotypes. If II,1 and II, 4 mate, what is the chance of offspring having PKU?
II, 1 X II, 4 p(aa)
•p(aa AND a girl)?
How do we know this is autosomalrecessive?
If III-3 and II-1 mate p (normal child)
Product rule:
p (affected boy)?
All people have harmful recessive alleles, small chanceThat 2 people with same rare alleles will mateConsanguinous marriage increases the chance
Bedoin intermarriage
Autosomal dominant disordersAa and AA =affectedaa =unaffected
•Tend to show up in every generation•2 affected parents can have unaffected child•2 unaffected parents cannot have an affected child
Dominant pedigree
Achondroplasia -1/20,000 births
• Mutation in FGFR3 gene Chromosome 4• Affects cartilage growth needed for bone
lengthening• Affected individuals Aa why not AA?
• Most cases spontaneous (associated with increasing paternal age)
what is the genotype of parents in this case?
P(III, 3 and III, 5 have a child of normal height)
P ( II, 3 and III, 7 have a boy with achondroplasia)
• Mutation in dog FGF4 gene