Sept 9 (Mendelian Genetics I) [_/18]

Sept 9 (Mendelian Genetics I) [_/18]

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Who is Gregor Mendel and what did he do?

Gregor Mendel was an Austrian monk and scientist known as the “father of genetics.”
He studied pea plants and discovered the basic rules of heredity, explaining how traits are passed from parents to offspring through genes.

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Why was Mendel successful?

Mendel was successful because he carefully controlled his experiments, studied clear traits in pea plants, used large sample sizes, and kept detailed records of his results.

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Trait?

A specific physical characteristic or feature of an organism (such as eye color or plant height).

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True-breeding?

An organism that is homozygous and always produces offspring with the same trait when bred with another of the same type.

Example: A true-breeding purple-flower plant produces only purple-flower offspring.

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Monohybrid cross?

A mating experiment between two parents that focuses on tracking just one single trait.

Example: Crossing a purple-flower plant with a white-flower plant to study flower color.

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Phenotype?

The physical appearance or observable trait of an organism, which results from its genes.

Example: Purple flowers, blue eyes, or tall height.

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Genotype?

The genetic makeup (allele combination) an organism has for a trait.

Example: PP, Pp, or pp for flower color.

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Allele?

A different version of a gene that determines a trait.

Example: P = purple flowers and p = white flowers.

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Dominance / Recessiveness?

A dominant allele shows when at least one copy is present; a recessive allele usually shows only when two recessive copies are present.

Example: If P = purple flowers (dominant) and p = white flowers (recessive), then PP and Pp are purple, while pp is white.

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Law of Segregation?

The two alleles for a gene separate during gamete formation, so each gamete receives only one allele.

Example: A Pp plant produces gametes with either P or p.

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Homozygous?

Having two identical alleles, such as AA or aa.

Example: PP or pp.

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Heterozygous?

Having two different alleles for a trait.

Example: Pp.

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Dihybrid cross?

A genetic cross that looks at two traits at the same time.

Example: Crossing pea plants to study both seed color and seed shape.

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Define the Law of Independent Assortment? 

Alleles for different genes separate independently from each other when gametes are formed.

Example: A pea plant with genotype RrYy can produce RY, Ry, rY, and ry gametes because the seed shape and seed color alleles assort independently.

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What is a Test Cross?

A test cross is used to determine an organism’s unknown genotype by crossing it with a homozygous recessive organism.

Example: If a purple-flowered plant is P_ (either PP or Pp), cross it with pp to find out whether the purple plant is PP or Pp.

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What ratio do you expect from two heterozygotes in a monohybrid cross?

In a monohybrid cross between two heterozygotes (Aa × Aa), the expected genotype ratio is 1:2:1 and the phenotype ratio is 3:1.

• Genotype ratio (1:2:1) means the offspring are expected to be 1 AA : 2 Aa : 1 aa based on their genes.
• Phenotype ratio (3:1) means 3 offspring show the dominant trait for every 1 offspring showing the recessive trait based on how they look.

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What ratio in a test cross? What about a dihybrid cross?

In a test cross (Aa × aa), the expected phenotype ratio is 1:1, while in a dihybrid cross (AaBb × AaBb), the expected phenotype ratio is 9:3:3:1.

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What makes a particular pattern of inheritance Mendelian?

A pattern of inheritance is Mendelian when a trait is controlled by one gene with dominant and recessive alleles that follow Mendel’s laws of inheritance.