Chapter 6 - Section 6.2 - Study Guide - Assess Your Learning Outcomes - Page 199: 6

Differences in hair texture (straight, wavy, curly) and hair color are primarily determined by genetic and structural factors. Here's an explanation of the basis for these differences: **Hair Texture (Straight, Wavy, Curly):** Hair texture is mainly influenced by the shape and cross-sectional structure of the hair shaft, as well as the arrangement of protein molecules within the hair shaft. The key factors that contribute to different hair textures are: 1. **Hair Follicle Shape:** Hair follicles have a significant impact on hair texture. The shape of the hair follicle, which is determined by genetics, dictates the angle at which the hair emerges from the scalp. - **Straight Hair:** Round hair follicles typically produce straight hair. - **Wavy Hair:** Slightly oval or elliptical hair follicles produce wavy hair. - **Curly Hair:** Curved or flattened hair follicles produce curly hair. 2. **Cross-Sectional Shape:** The cross-sectional shape of individual hair strands can also vary: - **Round or circular cross-section:** This typically results in straight hair. - **Oval or elliptical cross-section:** This often leads to wavy hair. - **Flattened cross-section:** This contributes to curly or coiled hair. 3. **Protein Structure (Keratin):** The arrangement of keratin proteins in the hair shaft can affect its flexibility and curliness. The more disulfide bonds between keratin proteins, the curlier the hair tends to be. **Hair Color:** Hair color is determined primarily by the presence and type of pigments within the hair shaft. There are two main types of pigments responsible for hair color: 1. **Melanin:** Melanin is the primary pigment responsible for hair color. It is produced by melanocytes, specialized cells located within the hair follicles. The amount and type of melanin in the hair determine its color. - **Eumelanin:** This type of melanin produces black or brown hair. - **Pheomelanin:** Pheomelanin is responsible for red and yellow hair colors. 2. **Genetics:** Hair color is inherited from one's parents. The combination of genes inherited from each parent determines the specific type and amount of melanin in the hair. - **Multiple Genes:** Several genes, including those associated with melanin production and distribution, contribute to the wide range of hair colors observed in humans. - **Dominant and Recessive Alleles:** Dominant alleles for melanin production typically result in darker hair, while recessive alleles lead to lighter hair colors. **Environmental and Age Factors:** While genetics play a significant role, environmental factors such as exposure to sunlight, chemical treatments (dyeing, bleaching), and age-related changes can also influence hair color. For example, graying of hair occurs as melanocytes gradually produce less melanin over time. In summary, differences in hair texture (straight, wavy, curly) are primarily determined by the shape of hair follicles, the cross-sectional shape of the hair strand, and the arrangement of keratin proteins. Hair color is mainly influenced by the presence and type of pigments (melanin) within the hair shaft, with genetics being a key factor in determining the specific color.

Differences in hair texture (straight, wavy, curly) and hair color are primarily determined by genetic and structural factors. Here's an explanation of the basis for these differences: **Hair Texture (Straight, Wavy, Curly):** Hair texture is mainly influenced by the shape and cross-sectional structure of the hair shaft, as well as the arrangement of protein molecules within the hair shaft. The key factors that contribute to different hair textures are: 1. **Hair Follicle Shape:** Hair follicles have a significant impact on hair texture. The shape of the hair follicle, which is determined by genetics, dictates the angle at which the hair emerges from the scalp. - **Straight Hair:** Round hair follicles typically produce straight hair. - **Wavy Hair:** Slightly oval or elliptical hair follicles produce wavy hair. - **Curly Hair:** Curved or flattened hair follicles produce curly hair. 2. **Cross-Sectional Shape:** The cross-sectional shape of individual hair strands can also vary: - **Round or circular cross-section:** This typically results in straight hair. - **Oval or elliptical cross-section:** This often leads to wavy hair. - **Flattened cross-section:** This contributes to curly or coiled hair. 3. **Protein Structure (Keratin):** The arrangement of keratin proteins in the hair shaft can affect its flexibility and curliness. The more disulfide bonds between keratin proteins, the curlier the hair tends to be. **Hair Color:** Hair color is determined primarily by the presence and type of pigments within the hair shaft. There are two main types of pigments responsible for hair color: 1. **Melanin:** Melanin is the primary pigment responsible for hair color. It is produced by melanocytes, specialized cells located within the hair follicles. The amount and type of melanin in the hair determine its color. - **Eumelanin:** This type of melanin produces black or brown hair. - **Pheomelanin:** Pheomelanin is responsible for red and yellow hair colors. 2. **Genetics:** Hair color is inherited from one's parents. The combination of genes inherited from each parent determines the specific type and amount of melanin in the hair. - **Multiple Genes:** Several genes, including those associated with melanin production and distribution, contribute to the wide range of hair colors observed in humans. - **Dominant and Recessive Alleles:** Dominant alleles for melanin production typically result in darker hair, while recessive alleles lead to lighter hair colors. **Environmental and Age Factors:** While genetics play a significant role, environmental factors such as exposure to sunlight, chemical treatments (dyeing, bleaching), and age-related changes can also influence hair color. For example, graying of hair occurs as melanocytes gradually produce less melanin over time. In summary, differences in hair texture (straight, wavy, curly) are primarily determined by the shape of hair follicles, the cross-sectional shape of the hair strand, and the arrangement of keratin proteins. Hair color is mainly influenced by the presence and type of pigments (melanin) within the hair shaft, with genetics being a key factor in determining the specific color.