Meiosis 1 Reproduction Reproduction is the process of

Meiosis 1

Reproduction • Reproduction is the process of producing offspring • Some offspring are produced by two parents • Some offspring are produced by just one parent • Whether an organism is identical or similar to its parent is determined by the way that the organism reproduces

Asexual Reproduction • When a single “parent” passes a complete copy of its genetic information to each of its offspring • An individual formed by asexual reproduction is genetically identical to its parent

Types of Asexual Reproduction • Binary Fission: Reproduction performed by most prokaryotes

Types of Asexual Reproduction • Fragmentation: A kind of reproduction in which when the body of an organism breaks into several pieces, some or all of these fragments re-grow missing parts and develop into complete adults

Types of Asexual Reproduction • Budding: In budding, new individuals split off from existing ones

Types of Asexual Reproduction • Parthenogenesis: A process in which a female makes an egg that grows into an adult without being fertilized by a male

Sexual Reproduction • Practiced by most eukaryotic organisms • In sexual reproduction, two parents give genetic material to produce offspring that are genetically different from their parents • Each parent produces a gamete (reproductive cell) • Gamete from one parent fuses with gamete from another parent to form a zygote • This process is called fertilization

Germ Cells & Somatic Cells • Germ cells are cells that are specialized for sexual reproduction (sperm & egg) • Somatic cells are all other body cells. They DO NOT participate in sexual reproduction

Asexual vs. Sexual Reproduction • Asexual reproduction – Advantages: Very efficient - can reproduce a lot in a short period of time – Disadvantages: Organisms can die off easily if the environment changes

Asexual vs. Sexual Reproduction • Sexual reproduction – Advantages: Produces genetically different organisms so a population could survive in a changing environment – Disadvantages: It could take a lot of energy to find a mate

Chromosome Number • Genes are located on Chromosomes • Each chromosome has thousands of genes that play an important role in determining how an organism develops and functions • Each species has a unique number of chromosomes (mosquitoes = 6; humans = 46; ferns = 500) • If an organism has too many or too few chromosomes, the organism may not develop and function properly

Chromosome Number • When fertilization occurs, two cell combine to form a zygote • The gametes that form a zygote have only ONE copy of each chromosome (not two, like somatic cells) • This ensures that the resulting zygote has the correct number of chromosomes

Haploid vs. Diploid • Cells that are diploid (somatic cells) have two sets of chromosomes (2 n) • Cells that are haploid (gametes) have one set of chromosomes (n)

Homologous Chromosomes • Each diploid cell has pairs of chromosomes made up of two homologous chromosomes • Homologous chromosomes are chromosomes that are similar in size, in shape, and in the kinds of genes they contain • Each chromosome in a homologous pair comes from one of the two parents

Autosomes and Sex Chromosomes • Autosomes are chromosomes that do not determine the sex of an individual • Sex chromosomes have genes that determine the sex of an individual • All humans receive an X chromosome from their mother • If they receive an X chromosome from their father, the human is a girl (XX) • If they receive a Y chromosome from their father, the human is a boy (XY)

Meiosis • During meiosis, a diploid cell goes through two divisions to form four haploid cells

Mitosis vs. Meiosis • Mitosis creates 2 daughter cells that are genetically identical • Meiosis creates 4 daughter cells that are genetically different • Mitosis makes cells that are used during growth and repair – happens in body cells • Meiosis produces cells that allow an organism to reproduce sexually – only happens in reproductive structures

Genetic Variation • Genetic variation is advantageous for a population • It can help a population survive a major environmental change • Genetic variation is made possible by SEXUAL reproduction