lecture 13: mendelian genetics Flashcards
What did Mendel study? (2)
Heredity and how are traits passed on from parents to offspring?
—> Gave basics of genetics and explain a big part of them
What are the 2 hypotheses for heredity?
- Blending hypothesis
2. Particulate hypothesis
What is the blending hypothesis?
Idea that genetic material from the two parents blends together to produce a trait
What is the particulate hypothesis?
Idea that parents pass genetic material as discrete heritable units (now known as “alleles”) that interact to produce a trait —>correct hypothesis
What are the 5 aspects of Mendel’s study?
- Used pea plants as model organism
- Many varieties of these plants with distinct traits for various heritable characters
- Matings are controlled: take sperm and egg from white/purple or contrary
- Matings produce many offsprings
- Track many characters in either-or manner (two traits)
Mendel’s Experiment Design?
- Parental generation (P): true-breeding (of 1 trait) X true-breeding (of trait 2) —> purple flower X white flower
- 1st first filial generation offspring (F1)
- Self-pollination (self-fertilization) of F1
- 2nd filial generation offspring (F2)
What is true-breeding?
Plants that produce offspring of the same variety when they self-fertilize
What are Mendel’s three principles of inheritance?
- Segregation
- Dominance
- Independent Assortment
What happened at the F1 generation? (hybrids)
All hybrid plants of F1 were purple
What happened at F2 generation?
3:1 ratio of purple to white flowers
Mendel conclusion?
- Observed same pattern of inheritance in six other pea plant characters (3:1 ratio)
- Results support particulate hypothesis of heredity
What is Mendel’s model? (5)
- For each character, an organism inherits one heritable factor (gene) from each parent
- Alternative versions (alleles) of these heritable factors account for variations in inherited characters
- One allele is dominant while the other is recessive
- The heritable factors (genes). are segregated (separated) during gamete formation and are packaged into different gametes
- Sex of parent passing on the allele does not affect the inheritance pattern —> give same results
What is a Punnett square?
Matrix which predicts the probability of an offspring’s genotype and phenotype for a particular set of parents
What are the phenotypic ratios and genotypic ratios in Mendel’s study?
Genotypic Ratio: 3:1 purple vs white
Phenotypic Ratio: 1 homozygous dominant (PP), 2 heterozygous (Pp), 1 homozygous recessive (pp)
What makes an allele dominant and what makes it recessive?
Dominant: when effects of an allele can detected regardless of the alternative allele
Recessive: if the effect of an allele is masked in the heterozygous condition
How can mendelian traits in humans be disorders?
- Disorders caused by one gene (monogenic disorders)
- Can be inherited as a recessive or dominant trait depending on the allele involved in the disorder
What are carriers?
Heterozygotes that have a disorder inherited in a recessive fashion
What is albinism?
- Problem with pigmentation of skin and hair
- A recessive disorder (aa) —> homozygous recessive
What is achondroplasia (dwarfism)?
- Dominant disorder (Dd; heterozygous or homozygous dominant)
- Only possibility to be “normal” = dd = homozygous recessive) —> so impossible to be a carrier and have dwarfism —> so two no-dwarf parents cannot have a dwarf child
Does dominance have to do with frequency in population?
No, the dominant allele is not the most prevalent in population
- Concerns only the alleles
What is a monohybrid cross and a dihydrid cross?
Hybrid following a single character
What are the two characters that Mendel studied for his dihybrid crosses?
Colour (yellow and green) and shape (round and wrinkled)
What were the dominant and recessive traits in Mendel dihybrid crosses?
Dominant: Yellow and Round
Recessive: Green and Wrinkled
What are the 2 hypotheses of Mendel’s dihybrid crosses?
- Dependent Assortment
2. Independent Assortment
