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Copy of Chapter 3: Forming A New Life
Transcript of Copy of Chapter 3: Forming A New Life
How does conception occur?
The process by which sperm and ovum - male and female sex organs, combine a create a single cell called zygote.
The zygote which then duplicates itself again and again by cell division to produce all the cells that make up a baby. This process is called mitosis.
Conception does not alway end with a birth.
Dizygotic Twins; Fraternal Twins
Women's Body releases two ova within a short period of time and both are fertilized.
Monozygotic Twins; Identical Twins
A single fertilized ovum split into two.
Mechanisms Of Heredity
What is heredity?
The inborn factors inherited from one's biological parents that affect development.
The "stuff" of heredity is a chemical called DNA
Chromosomes are coils of DNA that consist of smaller segments called genes, the functional units of heredity.
Composition of the Zygote:
What determines the sex?
22 out of the 23 pairs of chromosomes are autosomes, that means they are not related to sexual expression.
The 23rd pair are sex chromosomes- one from the father and one from the mother.
sex chromosome are either X or Y
Babies born with birth defects are at high risk of dying at or shortly after birth or during infancy and childhood.
Affects only about 3% of live births.
Leading cause of infant death in the United States.
Most Common Abnormalities
Cleft Lip or Cleft Palate.
Dominant & Recessive Inheritance
When one parent has one dominant abnormal gene and one recessive normal gene and the other parent has two recessive normal genes, each of their children has a 50-50 chance of inheriting an abnormal gene.
If a dominant gene is lethal at an early age, the affected children would likely die before reproducing. That gene would not be passed on to the next generation and would soon disappear from the population.
Recessive defects are expressed only if the child is homzygous (having the same alleles) which means a child must inherit a copy of the recessive gene from each parent to be affected.
Certain ethnic groups are more likely to carry some recessive genes.
People with only one sickle cell allele and one normal allele don't have sickle cell, but show some symptoms of the condition.
Some Birth Defects
Cystic fibrosis - Overproduction of mucus. (1 in 2,000 white births)
Hemophilia - Excessive bleeding, usually affects males. (1 in 10,000 families with a history of hemophilia)
Spina bifida - Incompletely closed spinal canal, resulting in muscle weakness or paralysis. (1 in 1,000)
Sickle-cell anemia - Deformed, fragile red blood cells that can clog the blood vessels. (1 in 500 African Americans.