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Fetal Development
• Create a timeline outlining the stages of human development
• Label a diagram of the stages of human development
KEY WORDSImplantation Embryo Trimester
Fetus
Haploid gametes contain 23 total chromosomes – 22 regular chromosomes and 1 sex chromosome.
Two types of sex chromosomes- called X and Y
• Sperm can have either one X OR one Y.
• Eggs always have one X chromosome.
• Every male body cell has one X and one Y.
• Every female body cell has two X.
MEIOSIS– MALES
46 ChromosomesDIPLOID 2n
HAPLOID 1n
x y
xx yyxx yy
Female sperm Male sperm
MEIOSIS– FEMALES
46 ChromosomesDIPLOID 2n
HAPLOID 1n
x x
xx xxxx xx
Female egg
x xx
y
Female zygote Male zygote
x xx
y
Egg and sperm meet in the oviduct - fertilization.
Sex is determined by the male at fertilization.
Nuclei are joined to produce a single diploid cell called a zygote.
2 stages of development - fertilization to birth:1. Embryo stage: first eight weeks.2. Fetus stage: from eight weeks to birth.
1. Embryo StageZygote implants in endometrial lining and begins togrow (divide) by mitosis for first eight weeks.
Once implanted – called an embryo.
Cleavage: mitotic divisions begin, changing zygote to a multicellular embryo.
2. Fetus StageDeveloping embryo forms bone cells around the ninth week of pregnancy.
Once bone forms - called a fetus until born.
Placenta - exchanges waste and nutrients through umbilical cord.
Amnion – protective sac filled with fluid.
Pregnancy can also be divided in 3 trimesters:
1st trimester – conception to 3rd month
• development of all body systems and organs.• sex can be determined• embryo movements not perceptible to the
woman. she may not know that she is pregnant
• At end - fetus weighs 28 grams, 7.5 mm long.• fetus is particularly sensitive to alcohol,
smoking and other drugs.
1st trimester
2nd trimester – 4th to 6th months
• period of rapid and continuous growth.• Only brain and lungs still developing.• embryo movements can be felt.• At end - fetus weighs 650 grams, 30 cm long.
• If born prematurely:Might survive with great medical assistance. Most do not survive.
2nd trimester
3rd trimester – 7th to 9th (birth) month
• fetus kicks, stretches and moves freely.• Eyes sense light, fingerprints have formed.• At end – fetus weighs 3300 grams, 35 cm long. • Dangers include complications during delivery
and lifestyle choices.
3rd trimester
And then, before you know it...
• Zygote at fertilization.• Embryo at implantation to endometrium.• Fetus after bone development.• Baby at birth.
• Fertilization to birth can be separated into 2 stages – embryo and fetus.
• Pregnancy can be separated into 3 trimester.
Homologous chromosomes are similar but NOT identical.
Homologous means that the chromosomes contain the same types of genes.
Gene - piece of DNA with instructions for a specific trait – hair colour, height, eye colour…
A diploid cell will contain two variations of each gene.
1 – mom1 – dad