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Chapter 2: Heredity, Prenatal Development, and Birth

2.1: Heredity

The basic building block of nature perspective is the gene.

  • Genes - the recipes for making proteins; located on the chromosomes

  • Proteins - influence the structure and function of cells

There are 20,500 genes estimated in humans.

Normal human cells contain 46 chromosomes; 23 pairs from each parent.

Cells of the body are created by Mitosis AFTER conception.

  • Mitosis - cell’s nucleus making an exact copy of all chromosomes and splitting into new cells

Cells used in sexual reproduction are called Gametes (sperm or ova); are formed in Meiosis instead.

  • Meiosis - the gamete’s chromosomes duplicate, then divide twice resulting in four cells containing half the genetic material of the original gamete

Each Sperm and Egg possesses only 23 chromosomes separately, which they then combine to create 46.

Only 22 of the 23 pairs are similar in length. The 23rd chromosome is either the XY or XX chromosome.

  • XY - Male

  • XX - Female

2.2 Genotypes and Phenotypes

  • Genotype - sum total of all inherited genes

  • Phenotype - the features that are actually expressed that can be observed

  • Homozygous - a person who has inherited two identical versions of the same gene. One inherited from each parent.

  • Heterozygous - a person who has two different versions of the same gene

Dominant V. Recessive Genes

  • Dominant - heavily expressed in the phenotype even when paired with different versions

    • EX: dimples, curly hair, normal vision, normal dark hair

    • Incomplete dominance - when the dominant gene doesn’t completely suppress the recessive gene

  • Recessive - express themselves only when paired with a similar version

    • EX: red hair, nearsighted, straight hair

    • can cause abnormality in the shape of red blood cells

Alleles are different versions of a gene.

Polygenic genes are characteristics that are the result of several genes.

Carriers are those who have inherited only one recessive-gene.

Monozygotic V. Dizygotic twins

  • Monozygotic (Identical) Twins - when one egg separate in the first two weeks of development; creating two separate genetically identical offspring

  • Dizygotic (Fraternal) Twins - developed from two different eggs but share the same amount of genetic material

2.3: Genetic Disorders

Most genetic disorders are dominant gene-linked.

Since males only have one X chromosome, they are at greater risk for sex-linked disorders.

  • EX: Hemophilia, Color-blindnes, and baldness

2.4: Chromosomal Abnormalities

Chromosomal Abnormality occurs when a child inherits too many or two few chromosomes.

Most common cause is age of the mother due to ovum long term exposure.

Most common abnormalities is on pair 21: Trisomy 21 or Down Syndrome

  • Down Syndrome - when there is an extra 21st chromosome of the existing two

Sex Linked Chromosomal Disorders

  • Occurs on chromosome pair #23

2.5: Behavioral Genetics

Behavioral Genetics is the scientific study of how genetic and environmental factors interact to influence individual differences in behavior and traits.

    Some environmental circumstances can trigger symptoms of a genetic disorder.

Genotype-Environment Correlation

The processes by which genetic factors contribute to variations in the environment

  • Passive Genotype-Environment Correlation - when children passively inherit the genes and the environments their family provides (like being naturally athletic)

  • Evocative Genotype-Environment Correlation - how the social environment reacts to individuals based on their inherited characteristics (interest or hobbies)

  • Active Genotype-Environment Correlation - when individuals seek out environments that support their genetic tendencies

2.6: Prenatal Development

  • The Germinal Period

    • Last about 14 days; from conception to implantation of the egg in lining

    • Zygote / 2-cell stage / 4-cell stage / 8-cell uncompacted morula / Early Blastocyst / Late-stage blastocyst / Implantation of blastocyst

  • The Embryonic Period

    • Starting the third week the blastocyst has implanted in the uterine wall; Is now an Embryo

    • When an embryo is formed, blood vessels grow to form the placenta

    Placenta - a structure connected to the uterus that nourishes the embryo

  • The Fetal Period

    • Ninth week until birth; referred to as fetus

    • Developing body parts and bodily functions

    • First chance of survival outside the womb is known as the age of viability; reached at about 24 weeks

    • Around 36 weeks the fetus is almost ready for birth

    • 40 weeks is around full-term development and birth is imminent

2.7: Teratogens

Teratology - the study of factors that contribute to birth defects

Teratogens - environmental factors that can contribute to birth defects

2.8: Maternal Factors

  • Gestational Diabetes

  • High Blood Pressure

  • Rh Disease (anemia)

  • Weight Gain

  • Stress

  • Depression