Chapter 3: Principles of Genetics

Who formed the foundational work on genetics?

Gregor Mendel

What did Mendel’s experiment show?

That traits are inherited through discrete units (genes), not by blending.

What did Mendel’s P1 generation show?

The P1 (parental) generation were purebred plants that produced offspring showing only one parental trait.

What happened when Mendel crossed yellow and green peas?

The F1 generation all showed yellow peas, indicating yellow is dominant over green.

What is Mendel’s Law of Segregation?

Each organism carries two alleles for each trait, which segregate during gamete formation.

What is a punnett square?

A chart that predicts the probability of offspring genotypes and phenotypes from parental crosses.

How are punnett squares used in biotechnology?

To predict genetic outcomes and inheritance patterns in breeding or genetic studies.

What is the Law of Independent Assortment?

Genes for different traits separate independently during gamete formation.

Why is the Law of Independent Assortment important in biotechnology?

It helps predict how multiple traits are inherited and combined in organisms.

What is a testcross?

A cross between an individual with an unknown genotype and a homozygous recessive to determine genotype.

What is homozygous?

Having two identical alleles for a particular gene (e.g., AA or aa).

What is heterozygous?

Having two different alleles for a particular gene (e.g., Aa).

Why are testcrosses important in biotechnology?

They help identify unknown genotypes and verify purebred lines.

What is incomplete dominance?

A form of inheritance where the heterozygote shows an intermediate phenotype.

What does incomplete dominance show in biotechnology?

It reveals gene interactions that produce new, blended traits.

What is codominance?

Both alleles are fully expressed in the heterozygote (neither is dominant).

What is an example of a trait determined by codominance?

Human blood type AB (both A and B alleles are expressed).

Why is codominance important in biotechnology?

It helps understand gene interactions and design genetic models.

What is polygenic inheritance?

When multiple genes influence a single trait

What is a classic example of polygenic inheritance?

Human skin color or height

What type of results does polygenic inheritance produce?

A continuous range of variation rather than distinct categories

How is sex determined?

By specific chromosomes (XX for female, XY for male in humans)

Why is sex determination important in biotechnology?

It’s essential for breeding programs and understanding genetic disorders

How are sex-linked traits determined?

By genes located on sex chromosomes (usually the X chromosome)

Why are males more likely to express X-linked disorders?

Because they have only one X chromosome, so recessive traits are expressed directly

How do females express sex-linked disorders?

Only if they inherit two copies of the recessive allele, one from each parent

Why is it important to understand sex-linked inheritance in biotechnology?

To identify carriers and manage genetic conditions in populations

What are chromosomal alterations?

Structural changes in chromosomes, such as deletions, duplications, inversions, or translocations

What is deletion?

The loss of a chromosome segment

What is inversion?

A chromosome segment breaks off, flips around, and reattaches

What is translocation?

A chromosome segment attaches to a nonhomologous chromosome

What is duplication?

A chromosome segment is copied and repeated

What is crossing over?

The exchange of genetic material between homologous chromosomes during meiosis

Why is crossing over important in science and biotechnology?

It increases genetic diversity and aids in gene mapping

When does crossing over occur?

During prophase I of meiosis

What is nondisjunction?

The failure of chromosomes to separate properly during meiosis

What is the result of nondisjunction?

Gametes with abnormal chromosome numbers, leading to disorders

What diseases does nondisjunction help explain?

Down syndrome, Turner syndrome, and Klinefelter syndrome

What is Down’s syndrome?

A genetic disorder caused by trisomy 21 (extra copy of chromosome 21)

What is Turner syndrome?

A condition in females with only one X chromosome (XO)

What is Klinefelter syndrome?

A condition in males with an extra X chromosome (XXY)