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Genetics: A Monk a Pea and a Fly. Mendel and His Peas. Born in Czech Republic in 1822 Studied math in Vienna Was in charge of the monastery garden Conducted controlled breeding between true-breeding pea plants to study inheritance. Garden Peas : Tasty and Educational. Easy to grow - PowerPoint PPT Presentation
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Genetics: A Monk a Pea and a Fly
Mendel and His Peas• Born in Czech
Republic in 1822• Studied math in
Vienna• Was in charge of the
monastery garden• Conducted controlled
breeding between true-breeding pea plants to study inheritance
Garden Peas : Tasty and Educational
• Easy to grow• Fast growing• Number of easily
recognized traits• Lots of offspring
(each seed)• Easy to control
crossing
Mendel’s Crosses
Dominant and Recessive Traits
• Noticed traits in the F1 were not a blend of the parents but, instead favored one parent
• Trait that shows up the F1 generation is Dominant the trait that is masked is Recessive
• Today : Traits chemical factors = Genes Forms of a trait = Alleles
The F1 Cross• Mendel then crossed the F1 plants and the
recessive trait reappeared!• What happened? *Segregation : Alleles on homologous
chromosomes separate when sex cells are produced
Think about the logic here
Genotypes and Phenotypes
• Genotype : expression of alleles present Dominant alleles : Capital first letter of
the dominant trait Recessive alleles : Lower case script of
the first letter of the dominant trait Homozygote : Two of the same allele Heterozygote : Two different alleles• Phenotype : Actual visible trait
• Example : Flower colorPurple (P) is dominant to white (p)Cross a pure breeding plant with purple
flowers with a pure breeding plant with white flowers.
1) Determine genotypes 2) Segregate alleles 3) Perform cross
Probability and Genetics• Chance of an event occurring : probability• Does not indicate something will happen
only the likelihood that it can happen• Allele combinations follow rules of
probability• Probabilities in genetics can be
determined using simple math or Punnett squares
Mr. Curry’s Never Miss, Easy, Solves Every Type of Genetics Problem Method
1. Define alleles2. Define phenotypes associated with genotypes3. Write out cross4. Produce gametes5. Perform cross (Punnett square)6. Determine genotypic and phenotypic ratios of
offspring7. Answer the problem
Typical Monohybrid • Homozygous Dominant X Homozygous
Recessive P= F1= F2=
Two Traits at Once : Dihybrid Cross
• How do you determine inheritance for two traits at once?
- Dihybrid Cross• Just remember : Segregation and
Independent Assortment (For now, these genes exist on separate chromosomes)
• In the fruit fly Drosophila melanogaster, vestigial wings and hairy body are produced by two recessive alleles carried on different chromosomes. The normal alleles, long wings and hairless body, are dominant. If a vestigial-winged, hairy male is crossed with a female homozygous for
• both of the normal traits, what would be the phenotypes and genotypes of their progeny? If the
• F1 generation was allowed to mate randomly among themselves, what phenotypes and genotypes would be expected among the F2’s, and in what proportions?
• In some breeds of dogs, a dominant allele controls the characteristic of barking while trailing. In
• these dogs, another, independent gene controls ear shape, erect ears being dominant over floppy ears.
• If a dog breeder wants to produce a true-breeding strain of floppy-eared dogs that bark on the trail,
• how should she proceed, knowing that the alleles for erect ears and silent trailing are present in her
• kennels?
• P cross = Homozygous Dominant X Homozygous Recessive
P= F1= F2=
Other Types of Inheritance
• Not all genes are dominant or recessive• Sometimes get both alleles, a modified
form or the dominant or something new altogether
Incomplete Dominance• Two alleles produce three phenotypes• Third phenotype is a muted version of the
“dominant”• Example 4 O’clock flowersRR = RedRW= PinkWW = White
Codominance• When two alleles are both equally
expressed in the heterozygote• Example : ABO bloodtypesIAIA, IAi =A type bloodIBIB, IBi = B type bloodIAIB = AB type bloodii = O type blood
Sex Determination• In all animals : Sex is determined by the
combination of sex chromosomes (23rd pair in humans)
• XX = female• Xy = male
Polygenic Inheritance• Traits are governed by more than one
gene• Most traits are polygenic• Each gene may have two or more alleles• Many genes can be codominant or
incompletely dominant• Heterozygotes are intermediate in
phenotype
• A recessive gene combination will effect the phenotype
Multiple Alleles
The Fruit Fly
Drosophila melanogaster Homo sapiens