Podcast
Questions and Answers
In an individual with a dominant phenotype, what type of cross would determine if they are homozygous or heterozygous for that trait?
In an individual with a dominant phenotype, what type of cross would determine if they are homozygous or heterozygous for that trait?
- Cross with a homozygous dominant individual.
- Cross with a homozygous recessive individual. (correct)
- Cross with a heterozygous individual.
- Self-cross (cross with itself).
If a plant with round and yellow seeds (RRYY) is crossed with a plant with wrinkled and green seeds (rryy), what will be the genotype of the F1 generation?
If a plant with round and yellow seeds (RRYY) is crossed with a plant with wrinkled and green seeds (rryy), what will be the genotype of the F1 generation?
- rryy
- RrYy (correct)
- RrYY
- RRYY
Which of Mendel's laws states that genes for different traits are inherited independently of each other?
Which of Mendel's laws states that genes for different traits are inherited independently of each other?
- Law of Uniformity
- Law of Segregation
- Law of Dominance
- Law of Independent Assortment (correct)
In a species of flower, red petals (R) are dominant over white petals (r). If two heterozygous plants (Rr) are crossed, what is the probability of producing a plant with white petals?
In a species of flower, red petals (R) are dominant over white petals (r). If two heterozygous plants (Rr) are crossed, what is the probability of producing a plant with white petals?
In cattle, coat color exhibits codominance. If a homozygous brown cow is crossed with a homozygous white cow, what will the phenotype of the offspring be?
In cattle, coat color exhibits codominance. If a homozygous brown cow is crossed with a homozygous white cow, what will the phenotype of the offspring be?
A man who is a carrier for an autosomal recessive disorder has children with a woman who has the disorder. What is the probability that their child will have the disorder?
A man who is a carrier for an autosomal recessive disorder has children with a woman who has the disorder. What is the probability that their child will have the disorder?
In humans, skin color is an example of polygenic inheritance. How does polygenic inheritance affect the phenotype?
In humans, skin color is an example of polygenic inheritance. How does polygenic inheritance affect the phenotype?
Which event during meiosis can lead to genetic recombination, creating new combinations of alleles on the same chromosome?
Which event during meiosis can lead to genetic recombination, creating new combinations of alleles on the same chromosome?
Flashcards
Gene
Gene
Hereditary factors that determine traits, located on chromosomes.
Allele
Allele
A variant form of a gene (e.g., for flower color: purple or white).
Dominant Allele
Dominant Allele
The allele that is always expressed when present.
Recessive Allele
Recessive Allele
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Genotype
Genotype
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Phenotype
Phenotype
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Homozygous
Homozygous
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Heterozygous
Heterozygous
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Study Notes
- Gregor Mendel is known as the father of genetics.
- Mendel studied inheritance using pea plants.
- Mendel proposed hereditary factors, now known as genes.
Mendel’s Experiments
- In his first experiment, Mendel crossed pure purple (PP) and pure white (pp) pea plants.
- The F₁ generation was 100% purple (Pp), indicating purple is dominant.
- In the F₂ generation, the ratio was 3 purple : 1 white, showing the recessive trait reappearing.
- In his second experiment, Mendel crossed round yellow (RRYY) and wrinkled green (rryy) pea plants.
- The F₁ generation was 100% round yellow.
- The F₂ generation showed a 9:3:3:1 ratio, meaning traits inherit independently.
Mendel’s Laws
- Law of Uniformity: Offspring of purebred parents show only the dominant trait.
- Law of Segregation: Each individual has two alleles per gene, which separate randomly during gamete formation.
- Law of Independent Assortment: different traits inherit independently unless they are linked.
Key Genetic Terms
- Gene: A DNA segment that codes for a trait.
- Allele: A different form of a gene (e.g., P = purple, p = white).
- Dominant (P) traits are always expressed.
- Recessive (p) traits are only expressed if no dominant allele is present.
- Genotype: Genetic makeup (PP, Pp, pp).
- Phenotype: Physical appearance (purple, white).
- Homozygous: Two same alleles (PP, pp).
- Heterozygous: Two different alleles (Pp).
Test Cross
- A test cross determines if an individual with a dominant phenotype is homozygous (PP) or heterozygous (Pp).
- It involves crossing with a recessive homozygote (pp) and analyzing the offspring.
Beyond Mendel: Non-Mendelian Inheritance
- Incomplete Dominance: Results in a blended phenotype (e.g., Red × White = Pink flowers).
- Codominance: Both traits appear (e.g., Brown × White cattle = Brown & white patches).
- Polygenic Inheritance: Multiple genes control a trait (e.g., skin color).
- Multiple Alleles: More than two alleles exist (e.g., Blood types A, B, O).
Chromosomal Theory of Inheritance
- Genes are located on chromosomes.
- Thomas Hunt Morgan (1910) proved the gene-chromosome link using fruit flies.
- Alfred Sturtevant (1913) created the first genetic map.
Linked Genes & Genetic Recombination
- Genes on the same chromosome are inherited together.
- Crossing over during meiosis can create new gene combinations.
Sex Determination
- XX = Female, XY = Male.
- The father determines the sex (passes X or Y chromosome).
Mendelian Inheritance of Disorders
- Autosomal Dominant: AA, Aa = affected.
- Examples: Achondroplasia (dwarfism) and Huntington’s disease (brain degeneration).
- Autosomal Recessive: aa = affected, Aa = carrier.
- Examples: Albinism (lack of melanin) and Sickle-cell anemia (defective hemoglobin).
X-Linked Disorders
- Males (XY) need only one affected X to express the disorder.
- Females (XX) need two copies to be affected; one copy makes them a carrier.
- A father cannot pass X-linked traits to his sons.
- Examples include Haemophilia (blood clotting disorder) and color blindness (difficulty distinguishing colors).
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Description
Explore Gregor Mendel's experiments on pea plants, revealing the principles of inheritance. Learn about the Law of Uniformity, Segregation, and Independent Assortment. Understand dominant and recessive traits.
