Sept 14 (Mendelian Genetics II) [_/13]

Sept 14 (Mendelian Genetics II) [_/13]

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What is a gene?

A section of DNA that contains instructions for a specific trait or function.

Example: A gene in a pea plant can help determine flower color, such as purple or white.

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What is an allele?

A different version of a gene.

Example: For a flower-color gene, P is the purple allele and p is the white allele.

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What is a test cross (draw)?
 

Test cross: A cross used to determine an organism’s unknown genotype by breeding it with a homozygous recessive organism.

Example: Cross an unknown purple plant (P_) with a white plant (pp) to find out whether the purple plant is PP or Pp.

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What makes a particular pattern of inheritance Mendelian?

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

Example: In Mendel’s pea plants, purple flowers (P) are dominant over white flowers (p), so PP and Pp are purple, while pp is white.

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What is a monohybrid cross?

Monohybrid cross: A genetic cross that studies the inheritance of one trait.

Example: Crossing two pea plants (Pp × Pp) to study only flower color.

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What types of gametes are made in a monohybrid cross?

In a monohybrid cross, each gamete carries one allele for the single gene being studied.

Example: A heterozygous Pp parent makes two types of gametes: P and p.

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What gametes in a dihybrid cross?

In a dihybrid cross, gametes contain one allele from each of the two genes being studied.

Example: An AaBb parent can make 4 types of gametes: AB, Ab, aB, and ab.

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[Pedigrees] What does a circle denote? What does a square denote?

In a pedigree:

○ Circle = Female

□ Square = Male

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How do we label generations?

In a pedigree, generations are labeled with Roman numerals:

I = 1st generation

II = 2nd generation

III = 3rd generation

IV = 4th generation

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What do generations show us?

Generations indicate different levels of a family over time, such as grandparents → parents → children.

Example: I = grandparents, II = parents, III = children.

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What is meant by a filled shape? What about an unfilled shape? [Pedigree]

● / ■ Filled shape = the person has the trait being studied.

○ / □ Unfilled shape = the person does not have the trait being studied.

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Homozygous dominant pedigree?
 

Homozygous dominant: The person has two dominant alleles (AA).

Example: If the pedigree tracks a dominant trait, an AA person is affected (filled).

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Homozygous recessive pedigree?

Homozygous recessive: The person has two recessive alleles (aa).

Example: If the pedigree tracks a recessive trait, an aa person is affected (filled).