sexual reproduction and heredity

purpose of sexual reproduction

→ provide for the continued existence of a species

→ replication of living organism

cells involved in reproduction

→ reproductive sex cells called gametes

→ sperm (male), egg (female)

chromosomes in sex cells

→ sex cells contain 1/2 the amount of chromosomes ordinary cells in the body contain

→ 23

product of fertilisation

zygote, which contains 46 chromosomes

heredity

passing down of genetic material from one generation to the next during sexual reproduction

biological traits

→ physical traits such as shape of nose, shape of eye

→ behavioural traits such as anxiety, aggression

DNA

→ genetic material that cells contain

→ why humans inherit certain traits from their parents

sexual reproduction

→ involves two parents

→ involves the passing on of 1/2 of each parent’s genetic material to the offspring

→ involves the production of gametes by the organisms

→ offsprings are genetically similar to their parents

→ involves fusion of gametes during fertilisation

penis

→ erectile organ that deposits sperm into vagina during intercourse

→ blood vessels in the erectile tissue found in this organ becomes filled with blood during sexual arousal

testes

→ produces sperm (male sex cell)

→ produces male hormones

scrotum

→ regulates testes temperature for efficient sperm production

→ protects the testes

epididymis

→ narrow coiled tube

→ where inactive sperms are stored before they enter the sperm duct

sperm duct

→ long narrow tube

→ transports the sperm from the testes, and epididymis to urethra

urethra (male)

→ tube that passes through the centre of the penis to the exterior

→ excretes urine and semen at different times

kidney

→ produces urine

→ manages waste materials in the body

urinary bladder

→ stores urine from the kidney until ready for expulsion

→ controls the release of urine

male sex glands

→ produces enzymes and nutrients to help the sperm swim actively

ureter

→ transports urine from kidney to urinary bladder

urethra

→ short narrow short tube

→ transports urine out of the body

vagina

→ where sperm is deposited during sexual intercourse

uterus

→ has thick, muscular, elastic walls

→ where foetus develops during pregnancy

→ inner lining is spongy and covered in blood capillaries in prep for implantation of fertilised egg

cervix

→ circular ring of muscle

→ dilates to allow passage of baby during birth

oviduct / fallopian tube

→ site of fertilisation

→ muscular tube from ovary to uterus

→ transports mature egg every month

menstrual cycle

→ each cycle lasts 28 days

→ recurring process

→ may range from 21 to 33 days due to ..

* natural variations
* factors such as stress, poor diet, malnutrition

day 1 to 5

menstruation

menstruation

→ takes place when no fertilisation occured in the previous cycle

→ thick uterine wall supplied with blood capillaries breaks down together with unfertilised ovum

→ discharged out of the female’s body through the vagina

day 6 - 13

beginning of thickening of uterine lining

beginning of thickening of uterine lining

uterine lining begins to thicken and blood vessels form inside the lining

ovulation

→ ovary releases mature ovum

→ ovum can survive 12-24 hours after ovulation

→ sperm deposited into the vagina can last up to 3 days inside the female

→ if no fertilisation occurs, ovum will die and disintegrate

fertile period

→ days 11-17 (3 days before and 3 days after ovulation)

day 15 - 28

→ prep for fertilisation

→ lining of uterus at its thickest

→ if no fusion between sperm and ovum, thick uterine lining begins to break down

→ if fertilisation occurred, uterine lining is maintained to support foetus development

gamete

→ the only naturally occurring haploid in humans

→ sex cells (sperm and egg)

haploid

cell that only contains one complete set of chromosomes (23c)

diploid

cell that contains two sets of chromosomes

fertilisation

→ sperm is deposited into vagina, sperm swims up vagina, uterus then oviduct. sperm meets egg and fertilisation will take place

→ only one sperm cell can fertilise the egg

formation of embryo

→ zygote continually divides, forming the embryo which is a ball of cells

→ zygote goes through cell division

hormonal control over uterine lining

→ embryo embeds itself in the uterine lining and develops after fertilisation

→ embryo secrets hormone to prevent lining from breaking down

→ placenta produces the hormone later on

birth control / contraception

→ used to disrupt stages of sexual reproduction

* fertilisation of an ovum by sperm
* implantation of the embryo into the lining of the uterus
* killing sperms
* ovulation

→ practiced by people who don’t want to have children but still wish to partake in sexual intercourse

measures of birth control

→ temporary

→ permanent

temporary contraception

→ temporarily disrupts sexual reproduction

→ if a person wishes to have children, they can stop using contraceptions as and when they like

permanent contraception

→ effects are irreversible

→ couple will not be able to have children at all anymore

rhythm method

→ avoidance of sexual intercourse during the fertile period (days 11 to 17, or 3 days before and 3 days after ovulation)

spermicide

→ chemical that kills / disables sperm from entering the uterus

diaphragm

→ dome shaped rubber cap with elastic rim

→ inserted into the vagina, over the cervix

→ prevents sperm from entering past the cervix, impermeable

→ prevents fertilisation

condom

→ thin rubber tube used to cover erect penis during sexual intercourse

→ impermeable to sperms, prevents sperm from entering the uterus

→ impermeable to bacteria and virus

→ prevents fertilisation

→ can protect user from STIs

intra-uterine device (IUD)

→ piece of plastic or metal (usually copper) inserted into the uterus by a doctor

→ prevents implantation of an embryo onto the uterine lining

contraceptive pills

→ contain certain female sex hormones which prevent ovulation

→ disrupts the function of the ovary, no mature egg is released

sterilisation

→ vasectomy and tuber ligation

→ permanent birth control

vasectomy

→ involves cutting and tying the sperm ducts of the male during surgery

→ no sperms will be deposited during sexual intercourse and male is unable to get his partner pregnant

→ prevents fertilisation

tuber ligation

→ involves cutting and tying of the fallopian tubes / oviducts during surgery

→ egg is prevented from meeting the sperm

→ female cannot get pregnant

→ prevents fertilisation

abortion

→ deliberate termination of a pregnancy by removal / expulsion of an embryo / foetus

→ not a form of birth control

miscarriage

→ spontaneous abortion

→ occurs without intervention

Sexually Transmitted Infections (STI)

→ infections that spread primarily by close sexual contact or / and sexual intercourse

→ can be either viral or bacterial

→ can jeopardise one’s health and fertility if left untreated

viral STIs

→ possible to remain asymptomatic for periods of time

→ virus remains dormant, can go unnoticed

→ possible to pass to another person without realisation

→ generally cannot be treated, symptoms can be managed

→ example: HIV

bacterial STIs

→ needs to be treated with antibiotic or antimicrobial medication

→ examples: gonorrhoea, syphilis

Acquired Immunodeficiency Syndrome (AIDS)

→ blood borne disease

→ caused by HIV (human immunodeficiency virus)

→ HIV develops into AIDS

→ currently no cure

Transmission of AIDS

→ sexual intercourse with infected person

→ sharing hypodermic needles with infection person (eg. for drugs, and tattooing, acupuncture or piercings if needles are not sterile / stained with blood)

→ blood transfusion with blood from an infected person that contains HIV

→ infection from infected mother to foetus across the placenta through the umbilical cord during pregnancy

→ through breastfeeding

Protection against AIDS

→ abstinence (don’t have sex)

→ keep to one partner

→ usage of condoms

→ do not abuse drugs

→ do not share instruments that may prick the skin and be contaminated with blood (eg. toothbrush, razor)

Gonorrhoea

→ bacterial STI

→ transmitted by:

* having unprotected sex with infected person
* childbirth from infected mother to unborn baby
* infected fluid contact

→ can be treated with antibiotics if detected early

Syphilis

→ bacterial STI

→ transmitted by:

* direct contact with syphilis sore
* sexual intercourse with infected partner
* mother to foetus

→ can be treated with antibiotics if detected early

untreated STI

→ can cause infertility

→ can cause internal organ damage