REPRODUCTION

• Reproduction – The process of producing offspring– Two parents – similar looking offspring– One parent – identical looking offspring

• Two Types– Asexual– Sexual

ASEXUAL REPRODUCTION

• A single parent passes a complete copy of its genetic information to each of it’s offspring– Offspring are identical to parents

• Four different types of asexual reproduction

Binary Fission• Prokaryotes (bacteria)

• DNA is replicated

• DNA Attaches to the cell membrane

• Cell splits – each having the same DNA

FRAGMENTATION

• Body breaks into several pieces, some or all of the fragments regrow missing parts and develop into adults

• Ex. Starfish, some worms, some plants

BUDDING

• New individuals split off from existing ones

• Ex. Hydra, potatoes, jellyfish, corals

PARTHENOGENESIS

• Process by which females make a viable egg that grows into an adult without fertilization

• Ex. Water fleas, some worms, some bees

SEXUAL REPRODUCTION

• Meiosis

• Purpose is to produce cells that are genetically different from parents

• Offspring has traits from each parent, but is different

• Male – sperm

• Female - egg

Meiosis

• Genes are located on chromosomes

• Each species has a specific number of chromosomes– Mosquitoes = 6– Chimpanzees = 48– Humans = 46

• Each egg and sperm have 22 autosomes and 1 sex chromosomes and when they come together we have 46

Haploid vs.Diploid• Diploid = two sets of chromosomes (46)

• Haploid = one set of chromosomes (23)

• Homologous chromosomes = identical to each other

• Autosomes = chromosomes that do not determine sex

• Sex chromosomes- determine sex (XX-females, XY-males

Meiosis I

• Meiosis I – 1st nuclear division

• Follows a period of interphase - cell growth

• Divided into 4 phases

• Prophase I – chromosomes form from DNA strands, spindle fibers appear, homologous pairs line up and form a tetrad

• Crossing over may occur – which is when chromosomes exchange portions of their chromatids, resulting in an exchange of genes

Heterogenous chromosomes

• Metaphase I – tetrads move to the center of the cell

• Anaphase I – homologous pairs of chromosomes separate. Each chromosome is still composed of two chromatids joined by a centromere

• Telophase I – cytoplasm divides, forming 2 daughter cells

Meiosis II (2nd nuclear division)

• Occurs in each cell formed during meiosis I, and is not preceded by DNA replication

• Divided into 4 phases

• Prophase II – new spindle fibers form

• Metaphase II – chromosomes move to the center of the cell

• Anaphase II – the centromeres joining the chromatids divide freeing the sister chromatids from each other, and the chromatids move to opposite poles of the cell

• Telophase II – spindle dissolves, nuclear membrane forms, and cytokinesis occurs. Produces four daughter cells

• Formation of egg and sperm – forms gametes (sexual reproductive cells)

• Meiosis in males produces 4 sperm

• Meiosis in females produces 1 egg and 3 polar bodies which will disintegrate

• Meiosis allows for genetic recombination. This allows for variation between parent and offspring

GENETIC VARIATION• Advantageous for a population in order to

survive in their environment– Polar bears with a gene for thick fur vs. those with a

gene for thin fur. ( Who would survive?)

• Only made possible by sexual reproduction due to rearranging of genes

• Read pages, 253 – 254 with a partner together summarize the 3 keys to genetic variation

MULTICELLULAR LIFE CYCLES

• Life Cycle – all the events in the growth and development of an organism

• Two types of life cycles– Diploid– Haploid

DIPLOID LIFE CYCLE

• Most animals have this

• Diploid cells go through meiosis and forms gametes (sperm and egg) which join together during fertilization

• Result is the haploid gamete

HAPLOID LIFE CYCLE

• Occurs in fungi and some protists

• A zygote goes through meiosis immediately after it is formed and makes new haploid cells

• Haploid cells divide by mitosis and create new individuals

Alternation of generations

• Plants and multicellular organisms that alternate between diploid and haploid

• Sporophyte; diploid phase of a plant – produces spores through meiosis

• Gametophyte; haploid phase that produces gamete by mitosis