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Sexual reproduction Two parents- each parent contributes half of its genetic information to the offspring Maintains variety within a species.

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Presentation on theme: "Sexual reproduction Two parents- each parent contributes half of its genetic information to the offspring Maintains variety within a species."— Presentation transcript:

1 Sexual reproduction Two parents- each parent contributes half of its genetic information to the offspring Maintains variety within a species

2 Review- chromosomes are found in pairs called homologous chromosomes
Diploid chromosomes number – both chromosomes from each pair are present in the cell

3 Monoploid chromosome number- only one chromosome from each pair is present in the cell.
(also called haploid chromosome number)

4 Meiosis Occurs only in the gonads
Produces gametes with a monoploid (n) chromosome number


6 Gonads- specialized structures where meiosis occurs
Testes ovaries

7 Gametes- specialized cells with a monoploid chromosome number
Sperm Ova (eggs)

8 Spermatogenesis Is Meiosis in the male Produces sperm
Occurs in the testes All sperm have an adaptation that allows them to travel to the egg

9 Oogenesis Is meiosis in the female Produces eggs (ova)
Occurs in the ovaries

10 Sperm + Egg= Zygote n+n=2n
Fertilization Sperm + Egg= Zygote n+n=2n

11 External fertilization
Occurs outside the female body Fish and amphibians Many ova are released at one time. Sperm are deposited over the eggs

12 Internal fertilization
Occurs inside the female body Sperm is introduced into the moist environment of the female reproductive tract where they unite with the ovum (egg)



15 External development Occurs outside the female body Amphibians, fish:
develop in water Yolk provides food Little or no parental care Birds, reptiles: fertilization occurs before shell forms yolk, nest



18 Internal development Occurs inside female body

19 Non-placental mammals

20 Marsupials Have an underdeveloped placenta

21 Give birth to premature offspring that climb in a pouch (marsupium) to finish their development


23 External development vs. Internal development

24 Human Reproduction Males-

25 Testes- male gonads; lie outside the body in the scrotum where the temp. is 2-4o lower than body temp. Sperm produced continuously from puberty to old age. Epididymis- coiled tube that stores and nourishes sperm; flagellum (tail) grows

26 Vas deferens- sperm duct that leads from the epididymis to the urethra
Seminal vesicles, Cowper’s gland & prostate- all produce fluid which becomes semen



29 Females

30 Ovaries – female gonads; where ova are produced; 1 ½ inches long; in lower abdominal cavity
Fallopian tubes (oviduct)- lead from ovary to uterus * Fertilization occurs here!!!! Uterus- pear-shaped organ, thick walled, muscular. Development of fetus occurs here

31 Cervix- muscular ring between uterus and vagina
Vagina- muscular tube leading from uterus to outside the body. (birth canal)



34 Menstrual cycle Female releases one gamete (ovum) once a month from puberty to menopause Controlled by hormones 4 stages

35 Follicle stage Follicle – structure in the ovary where the ovum is prepared to be released Last days FSH (follicle stimulating hormone) from the pituitary causes the formation of the follicle Follicle begins to release the hormone estrogen which shuts off the production of FSH Estrogen triggers the thickening of the uterine lining


37 Ovulation Ovum is released from the ovary
Luteinizing hormone (LH)- triggers ovulation



40 Corpus luteum Follicle fills with yellow cells that produce a hormone called progesterone Progesterone maintains the thickening of the uterine lining in case fertilization occurs

41 Menstruation Uterine lining is shed if fertilization does not occur

42 Fertilization Occurs in the upper part of the Fallopian tube
Sperm and egg unite; diploid chromosome number is restored






48 Embryonic Development
Embryology- study of embryo development

49 Terms in embryology Zygote – fertilized egg
Cleavage- rapid cell division in zygote; division of zygote into a solid ball of cells Morula- solid ball of cells

50 morula

51 Blastula- hollow ball of cells-
differentiation begins in this stage of development Differentiation – cells become specialized in structure and function

52 blastula

53 Gastrula- formation of 3 primary germ layers

54 gastrulation



57 3 primary germ layers These 3 layers of cells develop into the structures of the new organism

58 endoderm Inner most layer of cells Produces digestive tract
Respiratory system Liver Pancreas thyroid

59 mesoderm Middle layer of cells Produces Skeleton Muscles
Circulatory system Excretory system gonads

60 ectoderm Outer layer of cells Produces Nervous system Skin Hair

61 Life in the uterus Placenta forms from embryonic cells
Exchange of materials between mother and fetus Mother sends oxygen, food, antibodies to fetus Fetus sends waste to mother (Carbon dioxide, urea) No exchange of blood

62 Umbilical cord forms between the 4th and 8th week



65 Amnion- membrane that holds amniotic fluid (protection)
Umbilical cord- connects placenta to fetus






71 4 weeks

72 8 weeks

73 3 months

74 6 months

75 6 months



78 Multiple births More than one child born at a time



81 Identical Twins One egg is fertilized by one sperm and in early embryonic development the morula splits into two individual group of cells. Can identical twins be two different genders?

82 Fraternal twins Two eggs are fertilized by two different sperm

83 Caesearn section Surgery is performed to remove the fetus from the uterus.







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