Sexual Reproduction

Sexual Reproduction Recall that sexual reproduction occurs when one haploid – the sperm – fuses together with another haploid – the egg. Each haploid contains 23 chromosomes. When they combine they produce a zygote (an offspring) with 46 chromosomes – or 23 pairs of chromosomes.

Advantage/ Disadvantage of Sexual Reproduction Offspring are genetically different from parents – variation allows for easier adaptation to environment Need to find a mate – this can be tricky and difficult for mammals. It promotes survival – you minimize the affects that diseases, viruses and bacteria have on the organism Produce fewer offspring – while fish can produce a large amount of offspring, only a handful do survive. Mammals can only hold few offspring inside the uterus It removes bad genes from the population – since crossing over happens, we can remove bad genes from the gene pool It takes time – Reproduction takes many months for most organisms. Asexual organism can reproduce in as little as 30 minutes.

Twins Identical (sometimes called Paternal or Maternal Twins) They're created from combining one egg and one sperm.  After a few days the one embryo will divide and create two identical babies. Fraternal (sometimes referred to as not-identical twins) are created from two eggs that get fertilized with two separate sperm.  Basically they are no more alike than any other brothers and sisters. Conjoined twins are created from one egg and one sperm, but the embryo does not fully separate .

Hermaphrodites A hermaphrodite is an organism that produces both male and female sex cells. Hermaphrodites can mate with any other member of its species, usually is CANNOT fertilize their own eggs with their own sperm. Earthworms and flowering plants are examples of hermaphrodites.

Earthworms When they meet, they attach to each other and fertilize each others eggs. They create a mucus ring called the clitellum - this can be found around the thicker part of the worm. The mucus ring will slip off the worm into the soil and act as a cocoon for the fertilized eggs. The offspring will hatch in a few days. After fertilization they will detach from each other.

Earthworms When they connect, they connect near the “genital pores” where they exchange each others sperm to fertilize each others eggs. The clitellum is where the eggs are fertilized, this is the mucus ring that will fall off in the soil.

Flowering Plants Stamen – contains the Anther and Filament. This is the male reproductive structure of the plant. Pistil – contains the Stigma, Style and Ovary. This is the female reproductive structure of the plant.

Flowering Plant Filament – is a stalk that supports the anther. Anther - is at the top of the stamen and produces pollen. The pollen grains contain the male gametes. Stigma – is at the top of the pistil that receives the pollen grains. The pollen grains travels down the style. The pollen fuses to to eggs in the ovary to create a zygote.

Flowering Plants Sometimes wind will move the pollen from one plant to another. Other times another organisms – like bees – will be attracted to the colour of the petals and the pollen attaches to them. These organisms then travel to another plant and deposit the pollen onto the pistil. This is known as cross contamination. The pollen then fertilizes the eggs in the ovary. The eggs turn into seeds that spread into the soil and grow.

Internal Fertilization In this form of reproduction, sperm is deposited inside the female in order to fertilize the egg. The embryo develops inside the mother until birth.

Mammals Mammals – are a warm-blooded animals that are distinguished by the possession of hair or fur, the secretion of milk by females for the nourishment of the young, and (typically) the birth of live young. Most mammals are ones that live on the land, examples can include: cats, dogs, apes, lions, bears, rabbits, elephants, squirrels, kangaroo, horses and humans. Mammals reproduce via internal fertilization.

Reptiles and Birds Reptiles and Birds live on land and in the sky. Reptiles – snakes, turtles, lizards, crocodiles Birds – owl, woodpecker, blue jay, robin, sparrow They have internal fertilization, but after fertilization occurs they lay their eggs and let the egg incubate. Reptiles lay their eggs and cover them with sand or other material to keep them warm while birds tend to sit on the egg to keep it warm.

Advantages and Disadvantages of Internal Fertilization Embryo protected from predators More % of offspring survive Disadvantages Requires more energy to find a mate Fewer zygotes produced than external fertilization

External Fertilization This is where the egg and the sperm cell unite outside the bodies of parents. The female lays the eggs and the male fertilizes it out in the open. The eggs are susceptible to the external environment.

Fish, amphibians Fish and amphibians spend all, or most of, their lives in the water. They have external fertilization. The male will fertilize the eggs after the female has released them. Fish – salmon, carp, goldfish, catfish, pike Amphibians – frogs, toads and newts

Advantages and Disadvantages of External Fertilization Little energy needed to find a mate Large number of offspring produced Disadvantages Most gametes do not survive. Regularly eaten by predators – low survival rate

Assignment Page 82 Questions - 1, 2, 4, 8, 10, 13