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Questions and Answers
What process involves planting seeds from fertilized eggs to grow new plants?
What ratio represents the phenotypic ratio in Mendel's F2 generation?
Which type of alleles are represented by lowercase letters in Mendel's notation?
What does the presence of a dominant allele imply in a genetic cross?
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What is the initial step in Mendel's cross-pollination procedure?
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What is the term used for the observable features of an individual?
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Which statement correctly defines a dominant allele?
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Which of the following describes a homozygous individual?
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Why did Gregor Mendel use pea plants as his model organism?
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What is the role of an allele?
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What term describes the transmission of traits from parent to offspring?
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What is the primary significance of Mendel's work with pea plants?
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Which of the following best defines a recessive allele?
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How many of the children from a BB (homozygous dominant) father and a bb (homozygous recessive) mother will have blue eyes?
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What is the probability of two heterozygous parents having a child with blue eyes?
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Which of the following genotypes represents a child with blue eyes?
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If two parents are heterozygous for brown eyes (Bb), what is the expected phenotypic ratio of their offspring?
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A father with BB and a mother with bb contribute which alleles to their offspring?
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Which statement correctly describes the alleles for a child with brown eyes from two heterozygous parents (Bb)?
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What describes the relationship between dominant and recessive traits in eye color?
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In a genetic cross between two heterozygous parents with regard to a recessive trait, what genotypic ratio can be expected?
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What is the phenotypic ratio resulting from a cross between two heterozygous snapdragons?
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What best describes codominance?
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Which of the following is an example of multiple alleles?
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What defines polygenic inheritance?
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Which trait is most influenced by polygenic inheritance?
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What does a bell curve indicate about genetic traits in a population?
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How does within species variation contribute to evolution?
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What role does each gene play in quantitative traits?
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What is the genotypic ratio resulting from a monohybrid cross?
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In a dihybrid cross involving traits for seed color and texture, what is the phenotypic ratio?
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What does the law of independent assortment imply about trait inheritance?
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What is the purpose of a test cross?
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What is the genotypic ratio for a dihybrid cross between two heterozygous parents?
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After performing a monohybrid cross, what ratio would indicate that 75% of the offspring display the dominant trait?
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In a test cross, which combination is used to identify the genotype of a dominant phenotype?
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What genotypic ratio should be expected if two individuals that are heterozygous for both traits are crossed?
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Study Notes
Genetics Terminology
- Genetics is the study of inheritance of traits.
- Heredity is the passing of traits from parents to offspring.
- A trait is a characteristic of an individual.
- A gene is a sequence of DNA that codes for a specific protein.
- An allele is a different version of a gene.
Genes and Inheritance
- Phenotype: Observable characteristics of an individual. Example is yellow seed or white flowers.
- Genotype: The alleles found within an individual, one from each parent.
- Genotype is denoted with letters, YY or Yy for yellow seeds.
Characterizing the Genotype
- Dominant allele: Allele that determines the phenotype of a heterozygous individual. Denoted with a capital letter. Example is Y or R.
- Recessive allele: Allele whose phenotype is only expressed in homozygous individuals. Denoted with a lowercase letter. Example is y or r.
- Homozygous: Having two identical alleles of a certain gene. Example: YY or yy
- Heterozygous: Having two different alleles of a certain gene. Example: Yy or Rr
Father of Genetics
- Gregor Mendel (1822-1884): Austrian monk who studied inheritance of traits in pea plants.
- He used pea plants as a model organism and tested the leading hypothesis of blended inheritance which was incorrect.
- His discovery was recognized after his death.
Model Organisms
- Organisms that are easy to care for and can be used to make inferences about many other similar species.
- Small, short-lived, inexpensive to care for, produce a large number of offspring, can be manipulated experimentally.
Life Cycle of the Pea Plant
- Self-pollination occurs when pollen from the male anthers falls on the female stigma of the same plant.
- Fertilization occurs when sperm from the pollen fertilizes the plant’s eggs.
- Germination happens when the seed is planted and grown into a new plant.
- Development occurs as seedlings develop into mature seed plants.
Mendel’s Procedure: Cross Pollination
- Peel back closed petals of a pea plant.
- Pull out the pollen-bearing stamens with tweezers.
- Gather pollen from a green-seed plant with a paintbrush.
- Rub pollen grains on the stigma of the first plant.
Mendel’s First Test
- Letters represent alleles from parents.
- Paired chromosomes equal two alleles.
- Dominant alleles represented by capital letters. Example is Y.
- Recessive alleles represented by lowercase letters. Example is y.
Using a Punnett Square
- Used to predict the outcome of a cross between two individuals.
Mendel’s 2nd and 3rd Generations
- F1 generation self-pollinated.
- F2 generation results in a 3:1 phenotypic ratio.
- F2 generation also results in a 1:2:1 genotypic ratio.
- Return of green phenotype in F2 generation.
Check Your Understanding
- Cross between a man (BB) with brown eyes and a woman (bb) with blue eyes. All children will have brown eyes because they will all have an allele for brown eyes (B).
Check Your Understanding
- Cross between a man and woman who are both heterozygous (Bb) for brown eyes. There is a 25% chance that they will have a child with blue eyes.
Check Your Understanding
- Cross between a man and a woman who are both heterozygous (Bb) for brown hair.
- Genotypic ratio is 1 Homozygous dominant: 2 Heterozygous: 1 Homozygous recessive
- Phenotypic ratio is 3 Brown: 1 Blond.
Monohybrid and Dihybrid Crosses
- Monohybrid cross: Cross between parents that are heterozygous for a single gene. Phenotypic ratio is 3:1 and genotypic ratio is 1:2:1.
- Dihybrid cross: Genetic cross between parents that are heterozygous for two genes. Phenotypic ratio is 9:3:3:1 and genotypic ratio is 1:2:2:1:4:2:1:2:1.
Test Cross
- Cross a homozygous recessive individual with an unknown genotype that displays the dominant phenotype.
Determining the Gametes for Dihybrid Cross
- Independent Assortment: One trait does not influence the inheritance of another trait.
- All traits are inherited independently of one another.
Check Your Understanding
- Dihybrid cross between two individuals that are heterozygous for both hair color (Bb) and eye color (Ee).
- Phenotypic ratio is 9:3:3:1.
Codominance
- When two alleles of a given gene have different phenotypic effects, with both effects present in organisms heterozygous for the particular gene.
- Example is blood type.
Multiple Alleles
- When three or more alleles exist for the same gene within a population.
- Increased diversity of population.
- Example is blood types.
Polygenic Inheritance
- Several genes determine the phenotype with each gene having a small additive effect on the trait.
- Example is human height, eye color, weight.
Quantitative Traits
- Phenotype depends on the cumulative actions of many genes.
- Quantitative traits vary among individuals to produce a continuous distribution of phenotypes.
- Examples include human height and skin color.
Polygenic Inheritance
- Example is skin color.
Within Species Variation
- Basis for evolutionary change.
Genetic Variation and Evolution
- Average beak depth in Galapagos finches shifted toward thicker beaks after a drought.
- Thicker billed individuals were better at eating larger seeds of drought tolerant plants.
Check Your Understanding
- Cross between two red roses that are both heterozygous (Rr).
- Phenotypic ratio is 3 Red: 1 White.
- Genotypic ratio is 1 Homozygous dominant: 2 Heterozygous: 1 Homozygous recessive.
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Description
Test your knowledge on key genetics concepts such as traits, genes, and inheritance. This quiz covers essential terminology including dominant and recessive alleles, as well as genotype and phenotype distinctions. Perfect for students studying genetics and heredity.
