DNA, Genes, Chromosomes and Heredity
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DNA, Genes, Chromosomes and Heredity
- 2. DNA, RNA, and Protein Deoxyribonucleic acid (DNA) The genetic material of cells; made of chemical building blocks called nucleotides arranged in a double- stranded helix. DNA contains all of the instructions needed to direct the activities of cells.
- 3. Genes and Heredity Gene—a segment of a DNA molecule; genes are the basic building blocks of inheritance Chromosome—a strand of DNA containing a number of genes Mitosis—the process by which somatic cells duplicate themselves, resulting in genetically identical cells with 46 chromosomes
- 4. • Base Pairs • Adenine • Guanine • Cytosine • Thymine • The combination and sequence of these base pairs is the basic code of life on planet earth
- 6. Patterns of Heredity Alleles —pairs of corresponding genes located at specific positions on specific chromosomes Homozygous—a condition in which an individual has a pair of identical alleles at a particular position Heterozygous—a condition in which an individual has a pair of non-identical alleles at a particular position
- 7. Genotype and Phenotype Genotype—a person’s genetic makeup as determined at the moment of fertilization Phenotype—the observable expression of a person’s genotype
- 11. Polygenic Inheritance • Many traits such as height, shape, weight, color, and metabolic rate are governed by the cumulative effects of many genes. • Polygenic traits are not expressed as absolute or discrete characters, • Polygenic traits are recognizable by their expression as a gradation of small differences
- 12. Skin Color • Human skin color is a good example of polygenic (multiple gene) inheritance. • Capital letter genes (A, B and C) control dark pigmentation. • Lower case (a, b & c) control light pigmentation • All "dominant" genes (AABBCC) has the maximum amount of melanin and very dark skin. • All "recessive" small case genes (aabbcc) has the lowest amount of melanin and very light skin.
- 15. The Genetic Difference Between Males and Females
- 16. Sex Linked Traits • Some genes that cause certain phenotypes are located on the X and Y chromosome • These chromosomes are not identical so there are some interesting inheritance patterns for these sex linked traits • Mothers are XX so they can only give an X • Fathers are XY so if they give an X the child will be a girl; a Y and the child is a boy. • If the child is a Boy we can be certain he got his X from his mother.
- 18. Dominant and X-Linked Patterns
- 21. Chromosomal Disorders Down Syndrome—Trisomy 21 an extra chromosome exists on the 21st pair Turner Syndrome—females with Turner Syndrome and missing an X chromosome Fragile X Syndrome—the most common cause of intellectual disability in males
- 22. Fragile X • It is the most common cause of genetically- inherited mental impairment. • Abnormality on the X chromosome which is restricted or broken • Retardation, Autism, Hyperactivity, Tactile Sensitivity
- 23. Copyright © 2017 Pearson, Inc. All Rights Reserved Fragile X Syndrome
- 24. X Y Abnormalities • Klinefelter’s Syndrome • An extra X chromosome in a male. • At puberty the body does not know whether to mature as a male or female. • Breasts may form, underdevelopment of male genitals and marked weight gain can be some of the symptoms.
- 25. Genetic Counseling Provides guidance for parents about the possibility of genetic disorders in their future children based on an extensive health history of both parents’ families over as many generations as possible
- 26. Copyright © 2017 Pearson, Inc. All Rights Reserved Genes and Environment in Human Behavior Colorado Adoption Study Results
- 27. Copyright © 2017 Pearson, Inc. All Rights Reserved Gene–Environment Transactions Three Types of Gene–Environment Correlations
- 28. Copyright © 2017 Pearson, Inc. All Rights Reserved Gene–Environment Transactions DNA Methylation: An Epigenetic Mechanism
- 29. Genetic (Genomic) Imprinting • The phenomenon of parent-of- origin gene expression. The expression of a gene depends upon the parent who passed on the gene. • They are due to deletion of the same part of chromosome 15. • Father = Prader-Willi • Mother = Angelman Syndrome.
Editor's Notes
- Key question 2: How are traits passed from generation to generation?
- LO 2.3: Explain how genes get passed from generation to generation and produce variability in human development. Figure 2.3: PKU Transmission PKU transmission is revealed sequentially via a vertical click and reveal widget.
- LO 2.2: Explain the indirect pathway by which genes affect human behavior, using the example of fragile X syndrome. Figure 2.2: Fragile X Syndrome Figure 2.2 illustrates the pathway from gene to behavior. Fragile X example is revealed sequentially via a vertical click and reveal widget. The pathway involves the four levels in the developmental systems model discussed at the end of this chapter (genes, neural activity, behavior/cognition, and the environment). Figure 2.2 gives you a feeling for the ways in which pathways from genes to behavior work for one genetic disorder. However, scientists are still filling in the steps in these pathways for the more than 4,000 rare single-gene disorders found in the human population.
- LO 2.5: Explain how scientists identify genetic and environmental contributions to complex traits such as IQ. Figure 2.4: Colorado Adoption Study Results Parent–offspring correlations were obtained for general cognitive ability at ages 3, 4, 7, 9, 10, 12, 14, and 16 years for three groups: biological mothers and adopted-away children (BM-AC), adoptive parents and adopted children (AP-AC), and control parents and control children (CP-CC). The correlations are the weighted average of mothers and fathers for the latter two groups. Ask students to interpret the findings of the graph. How do they explain the results here?
- LO 2.8: Describe how the three types of gene–environment correlations help explain findings of twin and adoption studies. In gene–environment correlations, genetic variations among people influence the environment to which they are exposed. Passive gene–environment correlations result when children inherit genotypes associated with family environment. Evocative gene–environment correlations occur when individuals evoke reactions from the environment based on genetic predispositions. Active gene–environment correlations occur when the individual seeks out environments that support genetic predispositions. Research evidence supports the roles of passive, evocative, and active correlations in development.
- LO 2.10: Describe evidence from animal and human studies that environments influence gene expression. Epigenesis refers to chemical processes that surround the gene to control expression of the gene. Unlike genetic mutations, epigenetic effects do not alter the DNA sequence in activating or silencing gene expression. Epigenesis works in humans by attaching methyl groups to DNA, reducing expression of some genes (Szyf & Bick, 2013). Evidence for the effects of epigenetic changes comes from twin studies (Fraga et al., 2005; Petronis, 2006) and studies of the impact of stress in the first four years of life (Essex et al., 2013; Romens, McDonald, Svaren & Pollack, 2015). Chemicals known as methyl groups (Me) can attach at various points to the DNA strand, reducing the activity of genes in those locations.