Human Genetics and Cell Division

Conception and Genetics

• A woman releases one ovum each month.
• If the ovum is not fertilized, it disintegrates.
• Sperm travels through the vagina, cervix, uterus, and fallopian tube to fertilize the ovum.
• Every human cell contains 23 pairs of chromosomes.
• Gametes (sperm and ova) contain 23 single chromosomes.
• At conception, the chromosomes combine to form a zygote.

Chromosomes, DNA, and Genes

• Chromosomes are threadlike structures composed of DNA.
• DNA has a double helix shape.
• Genes are short segments of DNA that contain genetic information.

Mitosis

• Mitosis is the process of cell division where the cell duplicates its nucleus, including the chromosomes, and then divides into two identical cells.

Meiosis

• Meiosis forms eggs and sperm (gametes).
• During meiosis, a cell duplicates its chromosomes but then divides twice, resulting in four cells with half the original genetic material.
• Each egg or sperm has 23 unpaired chromosomes.
• During fertilization, an egg and a sperm fuse to create a zygote.

Fertilization

• The 23 unpaired chromosomes from the egg and sperm combine to form 23 paired chromosomes in the zygote.

Determination of Sex

• Autosomes (22 pairs) contain genetic information.
• Sex chromosomes (23rd pair) determine sex.
• The X chromosome is large and carries many genes.
• The Y chromosome is small and carries few genes.
• Females have two X chromosomes (XX).
• Males have one X and one Y chromosome (XY).
• The sperm determines the sex of the individual.

Multiple Births

• Fraternal twins (dizygotic) develop from two separate ova and sperm.
• Identical twins (monozygotic) develop from one zygote that splits into two.

Genotype and Phenotype

• Genotype refers to the individual's unique genetic blueprint.
• Phenotype refers to the individual's actual set of characteristics.

Dominant and Recessive Genes

• A dominant gene strongly influences phenotype.
• Homozygous individuals have two identical genes (either both dominant or both recessive).
• Heterozygous individuals have one dominant and one recessive gene.

Polygenic Inheritance

• Many genes influence a single trait, such as skin color.

Multifactorial Inheritance

• Inheritance is influenced by both genes and the environment.

Genetic and Chromosomal Disorders

• Autosomal disorders are caused by genes located on autosomes.
• Sex-linked disorders are caused by genes on the X chromosome.

Chromosomal Errors

• Chromosomal errors occur when a child has too many or too few chromosomes.
• Errors happen during meiosis.

Pregnancy and Prenatal Development

• Pregnancy is the nurturing of a developing embryo or fetus.
• Prenatal development (gestation) transforms a zygote into a newborn.
• Pregnancy is divided into three trimesters.

First Trimester

• The zygote implants in the uterine lining.
• The zygote sends signals to stop menstruation.
• The cervix thickens and secretes mucus to protect the embryo.
• The baby's organs form during the first 8 weeks, making prenatal care critical.

Second Trimester

• Morning sickness subsides.
• The pregnant woman gains weight and her uterus expands.
• The woman begins to "show" during this trimester.

Third Trimester

• The fetus continues to grow rapidly.
• The woman's breasts may secrete colostrum, preparing for nursing.

Developmental Patterns

• Proximodistal pattern: development proceeds from the center of the body outward.
• Cephalocaudal pattern: development proceeds from the head downward.

Stages of Prenatal Development

• The germinal period (first two weeks): includes fertilization, cell division, and implantation in the uterine wall.

Embryonic Period

• The embryonic period (weeks 2 to 8): all major organs begin to form.

Problems in Prenatal Development

Environmental Hazards

• Substances like X-ray radiation can affect the developing fetus.

Maternal Emotions

• Stressful emotions like anxiety and depression can affect prenatal development.

Fetal Assessment and Treatment

• Ultrasonography is used to visualize the developing fetus.
• CVS (Chorionic Villus Sampling) and amniocentesis can detect chromosomal and genetic disorders.
• Fetoscopy allows for direct observation and surgical correction of fetal defects.

Explore the fundamental concepts of human genetics, including conception, chromosomes, DNA, and the processes of mitosis and meiosis. This quiz will test your knowledge of how genetic material is transmitted and the mechanics of cell division.