BIOL 1102 - Lec 9 Reproduction I

Asexual Reproduction

Reproduction without sex. DNA comes from one individual.

Binary Fission

Cell splits to make Clones.

Budding

Clones grow on parent individuals

Fragmentation

Pieces break off and grow new individuals.

Parthenogenesis

Offspring from unfertilized eggs

Advantage /Disadvantage of Asexual Reproduction

Don’t have to find mates. No genetic variation in offspring

Sexual Reproduction

DNA comes from two different individuals.

Advantage /Disadvantage of sexual Reproduction

Have to find mates. Lots of genetic variation among offspring

Simultaneous Hermaphrodite

Has working male AND female reproductive organs. Do not usually self-fertilize.

Does not create genetic variation among offspring

Why not self-fertilize?

Sequential Hermaphrodite

Start life as one sex, but change to another.

Protandry

Born a male, change to a female Ex: clownfish

Protogyny

Born a female, change to a male. Ex: Wrasse

Genetic Sex Determination

Chromosomes determine sex of offspring.

Haplodiploidy

Females are Diploid, males are Haploid. Found in Bees, Ants, Wasps, other Hymenoptera.

XO system

Female is Homogametic (XX), Male has only one sex Chromosome (X). Found in Grasshoppers, Crickets, and Cockroaches, and many Arachnids (spiders).

ZW system

Female is the Heterogametic sex (ZW), Male is Homogametic (ZZ or ZZZ). Found in Birds, Butterflies, and Komodo Dragons. This is the opposite of the Human XY system.

Somatic Mosaic

One egg, but different populations of cells on the body express different genotypes.

Bilateral Gynandromorph

Half body is genetically male, half is genetically female.

Chimera

Body made from two different eggs that fused. Different genotypes.

XY system

Female is Homogametic (XX), Male is Heterogametic (XY). In Humans and Drosophila flies.

SRY Gene

Y-linked gene that blocks gene expression on X chromosome and allows ‘maleness’.

Androgen Insensitivity Syndrome

Syndrome: Problem with Androgen Receptors. Cells can’t receive male hormones; XY male can develop as a Phenotypic female. Can be partial or complete depending on the level of insensitivity to male hormones.

Environmental Sex Determination

The environment determines sex of offspring.

Temperature

Sex determined by nest temperatures (example: Crocodiles)

Environmental toxins

Farm chemicals can ‘feminize’ males in some amphibians, birds, and turtles.

Social environment

Some fish and frogs can change sex if one sex is rare (e.g., Clownfish and Wrasse)

Human Male Reproduction

Sperm are produced in the Testes

LH

Causes testes to release Testosterone

FSH

Causes Testes to make sperm and Ovaries to make eggs

Function of Scrotum

Keep the testes at the best temperature for sperm production. Unlike humans and most other mammals, some mammals, like Whales, Dolphins, and Elephants, have internal testicles.

Best temperature for Sperm production

In mammals, slightly below core body temperature.

Bulbourethral Gland

Make fluid to lubricate penis. Sometimes carries small amounts of sperm.

Prostate Gland

Activate sperm swimming. Makes 2 enzymes, one clumps sperm before ejaculation, another breaks it up right after. Make Prostaglandins hormone to move sperm toward egg.

Seminal Vesicles

Produce Fructose to feed swimming sperm. Makes Prostaglandins

Ovaries

where the eggs are produced

amount of eggs in ovary

At birth around 1 million,

At puberty 200,000 - 400,000

paused at Meiosis I

Human females have all of their eggs at birth?

Endometrium

Lining of uterus where fertilized egg will implant

Endometriosis

5-10% of Females. Endometrial cells grow outside uterus. Sometimes painful.

Causes of mensural cramps

Contractions of uterine muscles to remove unused endometrial cells from uterus.

Birth control pills

High levels of Estrogen or Progesterone fool body into thinking it’s pregnant to prevent ovulation.

relationship between body fat and menstruation

Females generally need at least 17% body fat in order to menstruate regularly.

Menopause

After about age 50, ovaries become less active and estrogen levels fall.

fertility drugs

Often large amounts of FSH, causing release of multiple eggs.