Reproduction (ANISCI 103 exam 1)

sex chromosome

mammals: determines the genetic sex of the offspring

3.8% more DNA on ____

an X sex chromosome

sperm sorting

1. DNA of sperm cells are stained with a fluorescent dye and then passed at 60mph through a flow cytometer as drops of liquid containing a single cell

2. X chromosome sperm fluoresce brighter which is detected and a charge is applied to the droplet

3. droplets with sperm pass through a magnetic field

positive drops (X) are deflected in 1 direction

negative drops (Y) are deflected in another direction

uncharged droplets pass straight through

sort through 8000 sperm/sec while maintaining a purity of 90%

point of sperm sorting

allows farmers to intentionally breed more females or more males

• higher costs

• lower conception rate

free martin

when a cow has twins and one is male and the other is female, the female is born sterile

fused portions of the placenta = shared blood supply

• fetal testes produce Mullerian Inhibiting Hormone which inhibits the development of the female reproductive tract

• heifer calf will look like a normal heifer but she will have under-developed internal organs or male seminal vesicles

  ex. small ovaries and uterus, no cervix, short vagina that ends blindly

Chimera

animal contains cells derives from 2 different zygotes

• each population of cells keeps its own character → an animal with mixed tissues

normal calf: 60 diff chromosomes in each cell

free martin: 60 chromosomes in her cells + 60 different chromosomes in the cells she received from her brother (containing XY chromosomes)

selecting breed stock: Swine

litter size = 5% heritability

birth weight = 20%

feed efficiency = 30%

percent lean cuts = 45%

percent fat cuts = 60%

nonadditive gene effect

only 1 or a few pairs of genes determine expression of a trait

ex. horned condition in cattle

P = polled/ no horns p = horned

additive gene effect

multiple genes determine expression of a trait

ex. milk production, carcass traits, weight gain

genetic testing

animals are tested for the presence/absence of specific genes that may lead to differences in disease susceptibility/production traits

Scrapie

neurodegenerative disorder

• transmissible spongiform encephalopathy

• progressive neurodegenerative brain disorder

scrapie prion (PrPSc) is a pathogenic isoform of a normal protein (PrPc) located on neurons

transmission: infected sheep carry the scrapie prion for life and can transmit it even if they’re asymptomatic

• most become infected from their moms at birth or soon after birth

clinical signs: after 2-5 years of incubation

• lethargic, hyperexcitable, high stepping/unusual hopping gait, fixed stare with the head held high, ataxia, blindness, trembling, convulsions when being handled

• death in 2 weeks - 6 months

• transmission & development of disease are both influenced by the host’s genotype

Scrapie susceptibility - genetic testing

susceptibility/resistance to the classical form is associated with the variations in PrP gene at codons 136, 154, 171

each sheep inherits 2 copies of each gene (1 from each parent)

AA RR - nearly resistant to scrapie

AA QR - rarely susceptible

AV QR - somewhat susceptible to some strains

QQ sheep → AA QQ, AV QQ, VV QQ - SUSCEPTIBLE

Male reproduction

1. produce spermatozoa (spermatogenesis)

2. produce hormones

3. deliver spermatozoa to the female at the appropriate time

female reproduction

1. produce eggs (oogenesis)

2. produce hormones (estrogen, progesterone, inhibin)

3. maintain pregnancy and deliver offspring

hypothalamus-pituitary- gonadal axis

reproduction regulated by hormones secreted by the hypothalamus, anterior pituitary gland, testes and ovaries

hormones: gonadotropin releasing hormone, luteinizing hormone, follicle stimulating hormone

male reproductive system made up of:

1. testes

2. duct system

3. accessory sex glands

4. urethra

5. penis

testes (function + location)

function: produce sperm and hormones

location: in the abdomen during fetal development then gradually pulled by the gubernaculum through the inguinal canal

cryptorchid (unilateral/bilateral)

retained/undescended testes

• very dangerous because the males will still produce the same amount of testosterone but will be sterile

scrotum

skin that houses the testes

functions: protector, thermosensor (nerves), cooler ( sweat glands)

testes are made up of:

seminiferous tubules

• where sperm production occurs (spermatogenesis)

leydig cells

• outside the seminiferous tubules

• produce testosterone

  • behavior/sex characteristics

Sertoli cells

• produce estrogen

• inside seminiferous tubules

spermatogenesis

• production of male sex cells/sperm ( haploid)

• in the seminiferous tubules

• begins at puberty and continues through life

• produced in large numbers

puberty - species variability

bull - 11 mon

stallion - 18 mon

stud dog - 9 mon

tom cat - 9 mon

ram - 7 mon

buck - 7-8 mon

boar - 7 mon

epididymis

immature sperm detach from sertoli cells and flow through ducts into the epididymis

• storage site

• maturation site

Vas deferens

• duct with thick, smooth muscle walls

sperm leaves epididymis and travels in the spermatic cords through the inguinal ring →connects with the urethra

spermatic cord

tubular structure extending from inguinal rings to testis

1. testicular artery and vein

2. pampiniform plexus

3. lymphatic vessels

4. nerves

5. ductus deferens

6. cremaster muscle

urethra

final outflow tract

collects spermatozoa from ductus deferens

collects secretions from accessory reproductive glands

accessory sex glands

glands that contribute to secretions to make sperm into semen

• varies by species

• development and maintenance depends on exposure to testosterone

bull + ram + stallion: ampulla, seminal vesicles, prostate, bulbourethral glands

boar: seminal vesicles, prostate, bulbourethral glands

Tom cat: prostate, bulbourethral glands

dog: prostate

path of sperm

testes/seminiferous tubules → ducts → epididymis → ductus deferens → urethra + accessory glands

female reproductive system

• ovaries

• oviducts

• uterine horns

• cervix

• vagina

• vestible

• vulva

oogenesis

process of creating an egg cell/ovum

ovulation

surge of luteinizing hormone causes a mature follicle to rupture which releasees the ovum

• ovum is then caught by the oviduct

corpus luteum

produces progesterone

• necessary for maintenance of pregnancy

• suppresses estrus behavior, mature follicle development, and ovulation

• makes the uterus ready for embryo

• closes the cervix

• encourages the mammary gland development

has fixed lifespan unless ovum is fertilized and resulting embryo implants in the uterus

female pregnant vs not pregnant

pregnant: corpus luteum has an extended lifespand and continues to produce progesterone

not pregnant: uterus releases Prostaglandin F2a to kill the corpus luteum in the ovary which leads to no more progesterone production

estrous cycle intervals

polyestrous: continously cycling through the year if not pregnant

• ex. cattle, pigs

seasonally polyestrous: cycle continously during certain season

• ex. ewes, doe, horses

monoestrous: 1 cycle per year

• dog

proestrous

follicles begin to develop and grow

• increased output of estrogen

estrous

period of sexual receptivity in the female

• estrogen production peaks

ovulation occurs near end of estrus in some species

induced ovulator species remain in a prolonged state of estrus if not bred (ex. cat, rabbit)

metaestrus - not all species

period where corpus luteum develops

• progesterone produced by corpus luteum temporarily inhibits follicular development in the ovary

lining of uterus prepared for implantation of a fertilized ovum

diestrus

corpus luteum at max size and exerting max effects → progesterone

pregnancy: corpus luteum retained

no pregnancy: Prostaglandin F2a is released by uterus to destroy corpus luteum

anestrus

temporary ovarian inactivity → ovaries shut down

seen in seasonally polyestrous, diestrous and monoestrous animals

mares: winter

does and ewes: summer