Biological Beginings

Genetic Foundations of Child Development

• Genes are the basic unit of heredity in a living cell; genes are made up of DNA and contained chromosomes.

• Chromosomes- The 25,000 or so genes in the human body are called chromosomes.

• Genes are made up of DNA. Humans have 23 pairs.

• Mitosis- the process in which each chromosome in the cell’s nucleus duplicates itself.
• Meiosis- the process where each pair of chromosomes separates; one member going to each gamete. 
• Fertilization- the process in which a sperm fertilizes an egg to form a zygote.

Genetic Basis of Individual Traits

• Allele- Genes located at the same point on corresponding chromosomes and related to the same physical characteristic.
• Dominant gene- A gene that overrides any competing instructions in an allele pair.
• Recessive gene- A gene that influences growth and development primarily when the other gene in the allele pair is identical to it.

Chromosome and Gene-Linked Abnormalities

Often times problems occur in the genetic instructions that children receive. There are two primary types of genetic disorders, chromosome abnormalities and single-gene defects.  Chromosome abnormalities occur in 4% of births.

• Down syndrome- caused by an extra copy of chromosome 21. It is associated specific physical characteristics and mental limitations.
• Klinefelter syndrome- a sex-linked abnormality found in males who have an extra X-chromosome. It affects both primary and secondary sexual characteristics.
• Turner syndrome- a disorder in which females are missing either an X-chromosome or part of one of their X-chromosome. It can be associated with possible infertility.

Prenatal Development
 The period of growth between conception and birth. It is divided into three phases: the periods of the zygote, embryo, and fetus.

• Zygote- a one celled being, divides multiple times and becomes a ball of cells that burrows into the uterus. 
• Embryo- from week 2 through 6 after conception, the embryo grows rapidly, forming structures needed to sustain future growth and developing organs and body parts .
• Fetus- between week 9 and birth, the fetus continues to grow quickly; puts the finishing touches on the body and brain and becoming sufficientyl heavy and strong to live in the outside world.