Conception and Heredity

Forming a New Life: Conception and Heredity

• Development begins with the meeting of sperm and egg (conception), leading to a new individual with parental genetic information
• Post-fertilization development involves growth, differentiation, and preparation for independent life outside the womb

Fertilization (Conception)

• Fertilization is when a sperm and ovum combine to form one cell, a zygote
• The zygote is a single-celled organism that undergoes cell division to form a complete organism

The Female Reproductive Cycle

• High unpredictability of fertility
• Women begin with roughly 2 million immature ova in their ovaries
• Each ovum resides in a follicle, a small sac
• Ovulation involves a mature follicle rupturing and releasing an ovum, occurring approximately every 28 days in sexually mature women
• The ovum travels through the fallopian tube to the uterus, propelled by tiny hair-like cells (cilia)

The Male Reproductive Cycle

• Testicles produce hundreds of millions of sperm daily
• Sperm are released in semen during climax and travel to reach the ovum

Mechanics of Fertilization

• Fertilization typically occurs in the fallopian tube
• During fertilization:
  • Sperm move through the cervix and toward the ovum
  • Only a small portion of sperm reaches the ovum
  • Sperm use enzymes to penetrate the ovum and merge their nuclei
• Without fertilization:
  • The ovum and sperm cells die inside the woman's body
  • Sperm are absorbed by white blood cells
  • The ovum exits through the vagina

Multiple Births: Dizygotic Twins

• Dizygotic twins are fraternal, formed from two different eggs fertilized by two different sperm
• They are genetically similar to siblings, having the same or different sexes
• Multiple eggs are released at one time, may occur due to genetics

Multiple Births: Monozygotic Twins

• Monozygotic twins are identical, forming when one zygote divides after fertilization
• They are genetically similar

Factors Increasing Multiple Births

• Delayed childbearing
• Fertility drugs stimulate ovulation
• Assisted reproductive technology like in vitro fertilization

Mechanisms of Heredity

• Heredity involves passing on traits from parents to offspring

DNA: The Chemical Basis of Heredity

• Deoxyribonucleic Acid is the chemical basis of heredity
• DNA carries inherited instructions required for cellular development
• The chemical carries inherited guidelines for cellular life
• DNA has a double-helix structure, resembling a long, spiraling ladder

DNA: Chemical Base Pairs

• Adenine (A) pairs with Thymine (T)
• Cytosine (C) pairs with Guanine (G)
• The "letters" of the genetic code direct cellular processes

Chromosomes and Genes

• Chromosomes are coils of DNA, made up of smaller segments called genes
• Genes, located on chromosomes, serve as individual hereditary units
• Located in chromosome and contains thousands of bases

The Human Genome

• The Human Genome represents the complete sequence of genes
• A reference map, not a strict recipe, guiding gene locations
• Every person has a distinct genome

Gene Function and Protein Synthesis

• The sequence of bases in a gene instructs cells to produce proteins for various cellular functions
• Proteins carry out specific tasks

DNA as a Library Analogy

• DNA contains genes that are “books” with information to be used
• RNA Polymerase- readable and actionable format.
• Genes that are ‘read’ are based on environmental factors

Chromosomes and Cell Division

• Every cell in the normal human body, (excluding sex cells) contains 23 pairs of chromosomes-46 in total
• Meiosis: Sex cells undergo meiosis (cell division) ending with 23 chromosomes per sex cell.
• The sperm and ovum fuse at conception, they create a zygote with 46 chromosomes
• Mitosis: cell division after conception, DNA replicates forming identical genetic duplicates creating a new cell
• As cells divide they specialize leading to certain bodily functions

Mutation

• Mutation-Permanent alterations in genes can produce harmful traits that may also cause disease
• Genes guide growth and development
• Hormones and Environment: Hormonal levels can regulate genetic action and nutrition/stress that may influence genetic activity

Defining Biological Sex

• At conception, a zygote is formed from sperm (23 chromosomes) and egg cells (23 chromosomes)
• Autosomes (22 pairs): chromosomes that do not define sex
• Sex chromosomes are the pair of chromosomes that determine sex (X or Y)
  • Ovum always consists of X chromosome
  • Sperm can contain either the chromosome

Sex Determination: XX

• When the sperm contributes an X chromosome, it is a female
• The zygote inherits one X chromosome from the mother and one from the father

Sex Determination: XY

• Occurs when the sperm contributes the Y chromosome
• The zygote inherits an X chromosome from the mother and Y chromosome from the father

The Y Chromosome’s Role: The SRY Gene

• Critical region that contains the SRY gene
• Key towards the development of male characteristics that produces testoerone
• Triggers for testes formations and male development

Early Stages of Sex Organ Development

• Male and Female embryos are near identical to another

Sexual Differentiation: Male

• Between 6-8 weeks’ gestation, genetically male embryos begin producing testosterone
• This sustained high levels of testosterone supports male reproductive organs and body figures
• Activation of the SRY gene begins
• Development starts development of reproductive cells
• Teste cell production occurs with no SRY Activation

Sexual Differentiation: Female

• Complex and doesn’t depend on the SRY gene
• Key role with the Wnt-4 Signaling molecule-causes abnormal female masculinization

X-Inactivation

• Thought to inactivate most genes on the second X chromosome
• Research shows 75% of “extra” X chromosomes are inactivated and genes present in some but not all women contribute to individual differences
• Women’s chromosomes can act as backups
• Healthier overall

Genetic Transmission: Alleles

• Alleles are alternative forms of gene that occupies paired chromosomes and affect a trait.
• Person inherits one allele, maternal and paternal

Genetic Transmission: Homozygous

• when traits inherit identical alleles at a certain point
• includes two dominant and recessive alles

Genetic Transmission: Heterozygous

• traits inherit different traits from their parents
• includes one dominant or recessive allele

Genetic Transmission: Dominant Inheritance

_ The child passes different alleles and only expresses one Expresseion is always visible Homozygous or Herterozygous makes trait appear Dominant allels masks the recessive allele

Genetic Transmission: Recessive Inheritance

• Recessive allele only expresses its trait when expressing the “dd(same traits
• The child must receive both identical recessive alleles for the traits manifest
• Traits don’t show when paired with dominant alleles and can manifest when paired will recessive alles
• Person with ‘no dimples’ would need tow recessive allele

Polygenic Inheritance

• Genes to influence a trait or behavior require a combination
• Genetics are small but identifiable
• Traits often fall into spectrum (eg. intelligence)

Genotype vs Phenotype

Phenotype

• Observable characteristics and traits of an individual or behavior
• Behavior and enviromental factor (nutrition and upbringing)
• Potential for tallness might not reach the height is suffering from malnutrition from chilfdhood

Genotype

• Individual underlining genetic makeup
• Inherited and constant

Hidden Alleles

• Recessive allele can hide when paired with a dominant
• Stay hidden for generations until carriers that get passed down
• EX: Having or Not having dimples

Two Heterozygous Parents

When both parents are heterozygous that inherit D or d Outcomes of parents can receive Has dimples or No Dimples

Multifactorial Transmissions

• Combination of genetic and environmental factor
• Genes are modified b/c of environmental factors, causing variance in traits
• Potential (genetic) may not always be visible in correct enviromental support
• Ex. Influenced by nutrition and lifestyle and education
• Genetic interactions and presdipositions

Epigenetics: Defintion and Action

• Genes that will/won't lead expression of genes and structures
• Can only turn on/ off due to body/environmental stressors
• Means ‘above the genome’ affecting gene outside of generic cole
• Altering a cell in the gene alters and manipulates how genes are ready

Health Implications of Epigenetics

• Helps to identify where some twins may develop same conditions at different ages
• Epigenetic changes may link to disease like cancer

Modified Imprinting

• Vulnerable cells during critical periods like puberty/pregnancy make women respond to hormones that can influence the diet health and environment
• Age can be heritable and linked during transmission to offspring but sperm cells can also pass to offspring
• Nutrition and good health during a women during her lifetime can improve child's long term health

Genetic/Genomic Imprinting

Differential gene expression and whether the trait is from the father/mother

• Some genes are affected by their origin
• Unlike parental genes the genes can activate mother/fatjer version
• Regulates to grow/develops by allocating resources and development tissues
• Improper can cause fetal/growth birth defects, and disrupted imbalances

Genetic and Chromosal Aberrations

Affect approximately 3% of birth Leading cause for infants in us

Dominant and Recessive Traits

Cleft Lip/Plate and Down syndrome are common defects Gene Defects - Not less likely to be lethal at death and survival for production 50% chance individuals face for an abnormal gene Huntingtons disease for dominant

Gene Defect Recessive

Recessive defects are only inheritable and when having 2 copies of the “aa” More likely to be lethal when the carries (Aa) often dont show sympotoms

Characteristics of Recessive Defects

They can persist across generations because heterozygous carriers can reproduce Parents won't suspect that child has risk to unless they have a defective gene Inherited when both parents Aa This shows