Chapters 11 & 12: Meiosis and Inheritance

What happens in Meiosis I

Homologous chromosomes separate; crossing over and independent assortment occur.

What happens in Meiosis II

Sister chromatids separate, similar to mitosis.

Crossing over

The exchange of genetic material between homologous chromosomes during prophase I of meiosis; increases genetic diversity.

Random arrangement

Independent assortment of chromosomes during metaphase I of meiosis; leads to genetic variation.

Errors in meiosis

Nondisjunction or improper chromosome separation can lead to conditions like Down syndrome or other chromosomal disorders.

Alleles

Variants of a gene that determine specific traits.

Dominant allele

An allele that expresses its trait even if only one copy is present.

Recessive allele

An allele that only expresses its trait if two copies are present.

Homozygous

An organism with two identical alleles for a gene (e.g., AA or aa).

Heterozygous

An organism with two different alleles for a gene (e.g., Aa).

Genotype

The genetic makeup of an organism (e.g., Bb, tt).

Phenotype

The physical traits or characteristics expressed by the genotype (e.g., brown eyes, tall plant).

Punnett squares

Diagrams used to predict genetic outcomes of a cross.

Monohybrid cross

A cross involving one gene with two alleles.

Dihybrid cross

A cross involving two genes, each with two alleles.

Sex-linked inheritance

Traits controlled by genes on the X or Y chromosome; often affects males more if on the X chromosome.

Environmental factors that determine sex

In some species, temperature or environmental conditions during development determine the sex of the offspring.

Incomplete dominance

A genetic situation in which neither allele is dominant, resulting in a blended phenotype (e.g., red + white = pink).

Codominance

Both alleles are fully expressed in the phenotype (e.g., AB blood type).

Pleiotropy

A single gene affects multiple traits.

Polygenic Inheritance

Multiple genes influence a single trait, often seen in traits like height or skin color.

Mitosis produces _______

two identical diploid cells

Meiosis produces _______

four genetically unique haploid cells

What is meiosis for?

sexual reproduction

What is mitosis for?

growth, repair, and asexual reproduction.

Number of divisions after meiosis

2 divisions

Number of divisions after mitosis

1 divisions