Principles of Biology I Meiosis and Sexual Life Cycles

Heredity

The transmission of traits from one generation to the next (Latin “heres” = heir).

Genetics

The study of heredity and inherited variation.

Genes

A unit of heredity as well as how offspring inherit traits from parents.

What is the transmission of genes the result of?

It is the result of replication of DNA (DNA synthesis), making copies of genes to pass to offspring.

Gametes

Eggs and sperm though which genes are passed to offspring.

Zygote

A single cell embryo that is formed when sperm and egg intersect.

Locus (Loci)

The specific location on a chromosome where each gene is found.

Asexual Reproduction

A single parent passes all of its genes to its offspring without the fusion of gametes.

Clones

A group of genetically identical individuals (or cells) from the same parent (or cell).

Sexual Reproduction

Two parents give rise to offspring that have unique combinations of genes from both parents, therefore the offspring are genetically different from parents and each other.

Life Cycle

A sequence of stages in the reproductive history of an organism, from conception to production of its own offspring.

Somatic Cells

Non-reproductive cells that from a given species have the same number of chromosomes.

Karyotype

A display of condensed chromosomes (from a cell in mitosisI as seen under a microscope.

Homologous Chromosomes (Homologs)

Chromosomes that come in pairs that have the same visual appearance and the same genes

What are not homologous chromosomes?

Sex Chromosomes (X and Y)

Ploidy

The number of entire sets of chromosomes that an organism or cell possesses.

Diploid

2n = 2 complete sets of chromosomes.

Haploid

n = 1 complete set of chromosomes.

Fertilization

The union of gametes (the sperm and the egg)

Zygote

The fertilized egg and it has one set of chromosomes from each parent.

What does the zygote produce?

Somatic cells by mitosis and develops into an adult.

what happens during meiosis?

At sexual maturity, the ovaries and testes produce haploid gametes.

Meiosis

A special type of cell division that produces gametes in sexually reproducing organisms.

Where does meiosis occur?

Only in reproductive cells

How are gametes formed?

Only by meiosis

How many rounds of cell division does meiosis have?

Two which are called meiosis I and meiosis II

How many rounds of replication (DNA synthesis) does meiosis have?

Just one with two rounds of cell division.

What is the result of meiosis?

Four haploid daughter cells with half as many chromosomes as the parent cell.

What happens during S phase that is the same as in mitosis?

Chromosomes are duplicated (replication/DNA synthesis)

What happens in the G2 Phase that is unique to meiosis?

The centrosomes are duplicated.

What happens in the G2 phase that occurs in both meiosis and mitosis?

The chromosomes are decondensed, therefore not individually visible.

Prophase I

Synapsis and crossing over occur

Metaphase I

Paired homologous chromosomes (homologs) line up on metaphase plate.

Anaphase I

Homologs separate (Sister chromatids do not separate)

Telophase I and Cytokinesis

Haploid daughter cells form (containing replicated chromosomes, i.e. with sister chromatids).