Chap 2 - Heredity, Prenatal, Birth

• Genes are specific sequences of nucleotides and are recipes for making proteins
• Normal human cells contain 46 chromosomes (or 23 pairs; one from each parent) in the nucleus of the cells
• Mitosis is defined as the cell’s nucleus making an exact copy of all the chromosomes and splitting into two new cells
• In meiosis, the gamete’s chromosomes duplicate, and then divide twice resulting in four cells containing only half the genetic material of the original gamete
• Genotype refers to the sum total of all the genes a person inherits
• Phenotype refers to the features that are actually expressed
• We may receive either the same version of a gene from our mother and father, that is, be homozygous for that characteristic the gene influences
• If we receive a different version of the gene from each parent, that is referred to as heterozygous
• Some genes are dominant, meaning they express themselves in the phenotype even when paired with a different version of the gene, while their silent partner is called recessive
• Recessive genes express themselves only when paired with a similar version gene
• Geneticists refer to different versions of a gene as alleles
• Most characteristics are polygenic, meaning they are the result of several genes
• Sometimes the dominant gene does not completely suppress the recessive gene; this is called incomplete dominance
• To inherit a disorder, a person must receive the recessive gene from both parents. Those who have inherited only one recessive gene are called carriers and should be unaffected by this recessive trait
• Monozygotic or identical twins occur when a fertilized egg splits apart in the first two weeks of development
• When two eggs or ova are released and fertilized by two separate sperm, the result is dizygotic or fraternal twins
• Some genetic disorders are sex-linked; the defective gene is found on the X-chromosome
• Recessive Disorders (Homozygous): The individual inherits a gene change from both parents. If the gene is inherited from just one parent, the person is a carrier and does not have the condition
• Sickle Cell Disease (SCD) affects the ability of the blood to transport oxygen
• Cystic Fibrosis (CF) affects breathing and digestion due to thick mucus building up in the body
• Phenylketonuria (PKU) is a metabolic disorder in which the individual cannot metabolize phenylalanine, an amino acid
• Tay Sachs Disease is caused by enzyme deficiency resulting in the accumulation of lipids in the nerve cells of the brain
• Albinism is when the individual lacks melanin and possesses little to no pigment in the skin, hair, and eyes
• Autosomal Dominant Disorders (Heterozygous): In order to have the disorder, the individual only needs to inherit the gene change from one parent
• Huntington’s Disease affects the individual’s nervous system
• Tourette Syndrome results in uncontrollable motor and vocal tics as well as body jerking
• Achondroplasia is the most common form of disproportionate short stature
• Sex-Linked Disorders: When the X chromosome carries the mutated gene, the disorder is referred to as an X-linked disorder
• Fragile X Syndrome occurs when the body cannot make enough of a protein it needs for the brain to grow
• Hemophilia occurs when there are problems in blood clotting causing both internal and external bleeding
• Duchenne Muscular Dystrophy is a weakening of the muscles resulting in an inability to move, wasting away, and possible death
• A chromosomal abnormality occurs when a child inherits too many or two few chromosomes
• Trisomy 21 or Down syndrome occurs when there are three rather than two 21st chromosomes
• Trisomy 13 is caused by an extra chromosome 13
• Trisomy 18 is caused by an extra chromosome 18
• When the abnormality is on the 23rd pair, the result is a sex-linked chromosomal abnormality
• Turner syndrome occurs when part or all of one of the X chromosomes is lost
• Klinefelter syndrome (XXY) results when an extra X chromosome is present in the cells of a male
• A service that assists individuals identify, test for, and explain potential genetic conditions that could adversely affect themselves or their offspring is referred to as genetic counseling
• Behavioral Genetics is the scientific study of the interplay between the genetic and environmental contributions to behavior