Chapter 6 and 7: Matter of Sex and Complex Traits PDF

1 CHAPTER 6: MATTER OF SEX Growth of the penis and testicles Deepening of the voice Growth of facial and body hair...

1 CHAPTER 6: MATTER OF SEX Growth of the penis and testicles Deepening of the voice Growth of facial and body hair Increased muscle mass Increased bone density Development of a sex drive ESTROGEN (XX CHROMOSOME) Estrogen triggers the development of female secondary sex characteristics during puberty, including breast growth widening of the hips Y chromosome growth of pubic and underarm hair. SRY gene: It triggers the development Estrogen plays a crucial role in regulating the of the gonads into testes, which in turn produce menstrual cycle, stimulating the growth of the male hormones (like testosterone), leading to uterine lining and preparing the body for male physical characteristics. potential pregnancy. Estrogen levels increase during pregnancy, X chromosome contributing to the thickening of the uterine FOXL2: This gene is essential for ovarian lining and the development of the placenta. development and function. properly. FIGLA: This gene is involved in the formation Social and Cultural influences of primordial follicles, the precursors of eggs. ✓ Gender Roles: Society often assigns specific This gene is associated with X-linked forms of roles and ovarian dysgenesis. expectations to individuals based on their perceived gender. These roles can influence behavior, interests, and aspirations. ✓ Cultural Norms: Different cultures have varying definitions of masculinity and femininity, impacting how individuals are raised, treated, and expected to behave. ✓Socialization: From a young age, individuals are socialized into gender roles through family, peers, media, and other social institutions. Psychological factors ✓ Gender Identity: This refers to a person's Testosterone (XY CHROMOSOME) internal sense of being male, female, or ✓ Responsible for development of male something else. It is a deeply personal and characteristics subjective experience. ✓ Essential for sperm production in the testes. ✓ Gender Expression: This refers to how ✓ triggers the development of male secondary individuals express their gender identity through sex characteristics: Created by: @pgbamms  2 clothing, behavior, and other outward ANATOMY OF THE Y CHROMOSOMES expressions. ✓ Sexuality: Sexual orientation is separate from gender identity, but it can be influenced by social and cultural factors. Arms: The X chromosome has two arms: Short arm (p arm): This arm is smaller and contains fewer genes. Long arm (q arm): This arm is longer and contains more genes. ✓ Y chromosome has a very short arm and a Regions: long arm. Pseudoautosomal Region (PAR): Located at ✓ With Pseudoautosomal regions the tips of both the X and Y chromosomes, the ✓ PAR 1 and PAR2 PAR is a homologous region that undergoes ✓ They can cross over with the counterparts on recombination during meiosis. It contains the X chromosomes essential genes required for both male and ✓ 5% of the total Y chromosomes with genes female development. that encode proteins that function in both sexes. X-Linked Region: This region comprises the ✓ Control bone growth, cell division, immunity, majority of the X chromosome and contains fertility, energy metabolism, hormone synthesis genes that are specific to the X chromosome. ✓ Most of the Y chromosome region are male These genes are involved in a wide range of specific region between the two functions, including: Pseudoautosomal region Sex Determination:. ✓ Includes gene essential for male fertility, Cognitive Development SRY gene Immune System Function Blood Clotting Many Other Functions Created by: @pgbamms  3 Sex Ratio Traits Inherited on Sex Chromosomes The proportion of males and females in a human Y linkage population -Refers to genes located on the Y chromosomes -Genes that are only inherited by males ✓ Stages of Sex Ratio: ✓ Sex ratio at conception: Primary Sex Ratio X linkage ✓ Sex Ratio at Birth: Secondary Sex Ratio - Refers to genes located on the X chromosomes ✓ Sex Ration at maturity: Tertiary sex Ratio -These genes can be inherited by both males and females but expression can differ depending on ✓Sex ratio can change markedly with age due the sex of the individual. to illness and environmental factors that affect - Males needs only single copy of the X-linked the sexes differently such as participation in allele to express the trait or the illness (recessive wars and giving birth. or dominant) ✓ Altering the sex ratio intentionally will have - Females need single copy of the allele for a drastic effect to the society. Dominant while two copies for recessive Importance of SEX RATIO Population Dynamics: Reproduction: A balanced sex ratio is essential for successful reproduction. A skewed ratio can lead to difficulties in finding mates and ultimately affect population growth. Age Structure: The sex ratio at different age groups can influence the overall age structure of a population. For example, a higher proportion of males in younger age groups could indicate a potential for rapid population growth. Social and Economic Implications: Gender Roles: Sex ratio imbalances can influence traditional gender roles and expectations, potentially impacting family structures and societal norms. Labor Market: A skewed sex ratio can impact the labor market, potentially leading to higher unemployment rates for one gender or a shift in economic opportunities. Social Stability: Extreme imbalances in the sex ratio could contribute to social unrest and political instability, as groups with differing interests compete for power and resources. Created by: @pgbamms  4 Example: Pattern baldness: This trait is dominant in males but recessive in females. This means that a male with one copy of the baldness allele will be bald, while a female needs two copies of the baldness allele to be bald. X-INACTIVATION A crucial process in female mammals that ensures proper gene dosage balance. Females have two X chromosomes, while males have one X and one Y chromosome. If both X chromosomes in females were active, they would produce twice the amount of gene products from X-linked genes compared to males. Sex-Limited and Sex-Influenced Traits This would lead to an imbalance in gene expression, potentially causing SEX LIMITED TRAITS developmental problems. ✓ Inheritance pattern of a trait that appears in only one sex. X inactivation ensures that females have ✓ The inheritance of pattern of a sex-limited the same dosage of X-linked genes as trait follows the typical mendelian principles, males, preventing this imbalance. but its expression is limited to one sex due to hormonal or anatomical differences X inactivation is an epigenetic change because it ✓ Governed by genes that can reside on turns off genes on one X chromosome without autosomes (non-sex chromosomes) or sex altering the DNA itself. It does this by chromosomes. The expression of these genes is modifying the chromosome's structure, which is influenced by the individual's sex hormones. passed on to new cells. SEX-INFLUENCED TRAIT Changes to the structure of histones, the proteins ✓ Traits that is expressed differently in males that package DNA, which can affect gene and females, even though both sexes carry the expression. same gene. ✓ The expression of the trait is influenced by the hormonal environment of the individual. ✓Governed by genes that can reside on autosomes (non-sex chromosomes) or sex chromosomes. Created by: @pgbamms  5 Possible Affect of X-Inactivation to histone modifications. These modifications alter Phenotype of Mammals the accessibility of DNA to transcription factors, effectively switching genes on or off. Mosaicism Because females randomly inactivate Genomic imprinting one X chromosome in each cell, they can have A fascinating epigenetic phenomenon where the different versions of X-linked genes active in expression of a gene depends on whether it was different parts of their body, leading to variations inherited from the mother or the father in traits like skin color or disease susceptibility. Example: Incomplete Inactivation Insulin-like Growth Factor 2 (IGF2) Sometimes, not all genes on the gene inactive X chromosome are completely silenced. Involved in growth and development This means females might have higher levels of only expressed from the paternal allele. certain proteins from those genes compared to Overexpression can result to gigantism males, leading to differences in how they look or Excessive growth and can also disrupts function. other aspects of development. Variable Expression CHAPTER 7: COMPLEX TRAITS Because X inactivation is random, females carrying a recessive gene on the X SINGLE GENE TRAITS chromosome might show symptoms if a large Determined by the alleles of a single gene. portion of their cells inactivate the healthy X These traits often exhibit simple inheritance chromosome, leaving the faulty one active. patterns Cystic fibrosis: Caused by a mutation in CFTR PARENT OF ORIGIN EFFECTS gene In Mendel's pea experiment, it didn't Sickle cell anemia: Caused by a mutation in matter whether a trait came from the HBB gene male or female. POLYGENIC TRAITS For certain genes in mammals, parental Influenced by multiple genes, often interacting origin influences age of onset of a with each other. disease or symptom severity. Height: Growth hormone Receptor gene, Fibroblast Growth Factor Receptor 3 (FGFR3), Two mechanisms of parent-of-origin Insulin-like Growth Factor 1 (IGF1), Bone effects Morphogenetic Proteins (BMPs) -Genomic imprinting - Differences between the developmental timetables of sperm and oocyte The chemical basis of silencing one parent's genetic contribution involves epigenetic modifications, primarily DNA methylation and Created by: @pgbamms  6 HEIGHT The inheritance of susceptibility genes combined with exposure to environmental factors, like carcinogens, is a clear explanation of a complex trait. Susceptibility genes: DNA repair genes ( BRCA2 or NER pathway); Detoxification genes (CYP1A1 and GST (glutathione S- transferase), TP53 ☐ Environmental factors: Smoking, Air pollution Growth hormone Receptor gene, Fibroblast Growth Factor Receptor 3 (FGFR3), Insulin-like Growth Factor 1 (IGF1), Bone Morphogenetic Proteins (BMPs) Nutrition Protein Polygenic Traits are Continuously Varying Minerals (calcium) Vitamins (vit. D) Socioeconomic status Health and Diseases kwashiorkor and marasmus LUNG CANCER Skin color varies widely among individuals, from very light (pale) to very dark (deep brown or black), with numerous shades in between. Created by: @pgbamms  7 Skin color can be quantified using various scales and tools, such as the Fitzpatrick scale, which classifies skin color based on response to UV light, or the Pantone Skin Tone Guide, which provides a range of skin color swatches. the distribution of shades often follows a normal (bell-shaped) curve. Height can take on a wide range of values within a population, rather than falling into distinct categories. Height can vary significantly among Empiric Risk individuals. The probability of developing a disease based on When plotted on a graph, the the incidence in a particular population relying distribution of heights in a large in the real-world data and observations, population often follows a normal (bell- considering both genetic and environmental shaped) distribution. factors contributing to the disease. Height is typically measured in a quantitative manner, such as in Empiric risk increases with: centimeters or inches. severity of the disease, number of affected members how closely related a person is to affected members As an example, consider using empiric risk to predict the likelihood of a child being born with a neural tube defect (NTD). In the United States, the overall population risk of carrying a fetus Eye color typically falls into distinct categories, with an NTD is about 1 in 1,000 (0.1 percent). such as brown, blue, green, hazel, and gray. For people of English, Irish, or Scottish ancestry, the risk is about 3 in 1,000. However, if While there can be variations within these a sibling has an NTD, no matter what the ethnic categories (like light blue vs. dark blue), they are group, the risk of recurrence increases to 3 still classified into broad groups rather than percent, and if two siblings are affected, the risk existing on a smooth gradient. to a third child is even greater. By determining whether a fetus has any siblings with NTDs, a When plotting eye color distributions in a genetic counselor can predict the risk to that population, you often see peaks at specific fetus, using the known empiric risk. colors (e.g., the most common eye colors) rather than a smooth bell curve typical of continuous traits. Created by: @pgbamms  8 Coefficient of Relatedness Heritability The proportion of genes that two people related in a certain way share. A measure of the genetic similarity between two individuals Genetic counselors use the designations Primary (1), Secondary (2) and tertiary (3) relatives when calculating risk. Concordance Refers to the probability that two individuals will both have a particular trait, given that one of them already has the trait. It's a way to measure the similarity of traits between individuals. Concordance is super important when Designated H, estimates the proportion of the studying twins phenotype variation for a trait that is due to Concordance is like a score that tells us genetic differences in a certain population at a how likely both twins are to have the certain time. same trait. High concordance in identical twins Refers to the extent to which genetic differences means that the trait is probably mostly contribute to the variation of a trait, not the controlled by genes. If both twins have proportion of the trait itself that is determined by the same trait, even if they were raised genes. apart, it's a strong hint that genes are a big player. Focuses on the genetic component of the Lower concordance in fraternal twins variation in a trait compared to identical twins also points to a genetic influence. If fraternal twins are less likely to share the trait than identical twins, it suggests that genes are Created by: @pgbamms  9 more important than environment for that trait. ✓ By identifying genetic variants linked to Methods to Investigate Complex Traits disease risk or treatment response, GWAS can Understanding heritability and concordance is inform the development of targeted therapies crucial for determining the relative influence of tailored to specific patient subpopulations. genetics and environment on a particular trait or condition. ✓GWAS results can be used to tailor treatments to an individual's genetic makeup, leading to 1. Knowing whether a trait is primarily genetic more effective and personalized healthcare. or environmental helps us understand its cause and development ✓GWAS provide valuable insights into disease patterns, risks, and susceptibilities, informing 2. Understanding the genetic basis of a condition public health initiatives and strategies for allows for personalized medicine prevention and intervention. 3. Understanding the complex interplay between genes and environment is essential for advancing research in various fields, including medicine, psychology, and public health. GENOME-WIDE ASSOCIATION STUDIES A powerful tool in genetics research that aim to identify genetic variants associated with specific traits or diseases. The basic principle of Genome-Wide Association Studies (GWAS) involves comparing the frequency of specific genetic variations (SNPs) in individuals with a trait or disease to those without it. If a certain SNP is more common in those with the trait, it suggests a potential association and increased risk for that condition. IMPORTANCE OF IDENTIFYING GWAS ✓ GWAS help us understand the complex interplay of genes and their contributions to various traits and diseases. ✓ GWAS pinpoint specific variations in DNA sequences (SNPs) that are associated with increased risk for certain conditions. Created by: @pgbamms