Inheritance

What type of cells are produced by meiosis?

Gametes—sperm and egg cells

How many chromosomes are in human gametes?

23 chromosomes (haploid)

Why is meiosis important for inheritance?

It allows offspring to inherit one set of chromosomes from each parent

What does meiosis help maintain across generations?

The diploid chromosome number (46 in humans)

How does meiosis increase genetic variation?

Through independent assortment and crossing over

What is a dominant allele?

expressed in the phenotype even if only one copy is present (represented by a capital letter, like A).

What is a recessive allele?

expressed when two copies are present (represented by lowercase letters, like aa).

Can a recessive allele be hidden?

Yes, it can be masked by a dominant allele in a heterozygous genotype (Aa).

Give an example of a dominant and recessive trait.

Dominant = brown eyes (B), Recessive = blue eyes (b)

What is a genotype?

genetic makeup of an organism

What is a homozygous dominant genotype?

A genotype with two dominant alleles (e.g., AA).

What is a homozygous recessive genotype?

A genotype with two recessive alleles (e.g., aa).

What is a heterozygous genotype?

A genotype with one dominant and one recessive allele (e.g., Aa).

What is a phenotype?

The observable physical trait or characteristic that results from the genotype (e.g., eye color, blood type).

What is the relationship between genotype and phenotype?

The genotype determines the phenotype. Dominant alleles are expressed in the phenotype if present.

What is complete dominance?

A pattern where the dominant allele completely masks the recessive allele in the phenotype.
🧬 Example: AA or Aa both show the dominant trait.

What is incomplete dominance?

A pattern where the heterozygous phenotype is a blend of both alleles.
🧬 Example: Red flower (RR) + White flower (WW) = Pink flower (RW)

What is codominance?

A pattern where both alleles are fully and separately expressed in the phenotype.
🧬 Example: AB blood type (both A and B are expressed)

What does sex-linked mean?

A trait controlled by a gene located on a sex chromosome, usually the X chromosome.
🧬 Example: Colorblindness is more common in males because they only have one X.

What is a Punnett square used for?

To predict the possible genotypes and phenotypes of offspring from a genetic cross.

What is a monohybrid cross?

A cross that examines one gene with two alleles (e.g., A and a).

What are the parent genotypes in a typical monohybrid cross?

Aa × Aa (heterozygous parents)

What is the genotype ratio for Aa × Aa?

1 AA : 2 Aa : 1 aa

What is the phenotype ratio for Aa × Aa (if A is dominant)?

3 dominant : 1 recessive

What does each box in a Punnett square represent?

A possible genotype of an offspring.

If “A” is dominant for brown eyes and “a” is recessive for blue eyes, what % of offspring would have brown eyes from Aa × Aa?

75% would have brown eyes (AA or Aa)