3 4 Heredity Our Genetic Background Heredity Genes
3. 4 Heredity: Our Genetic Background
Heredity, Genes, and Chromosomes • Parents and children have similar traits, or characteristics, because parents pass traits down to their children through genes, which are the sections of information that make up DNA. • DNA is like a body's master plan, and genes are the individual instructions for building each piece. • The passing down of traits in the form of genes from parents to their children is called heredity. Every living thing has a DNA master plan that they inherit from their mom and dad.
• Genes are the basic building blocks of heredity. • All genes come in pairs, just like shoes. But unlike shoes, each gene in a pair can be different. One might be a sneaker, while the other is a high heel. • Your mom and dad each have two genes for every trait, but they each only passed one on to you, to make up your set of two. It's gene math: 1 from mom + 1 from dad = 2 for you! • My friend Sam has green eyes, but his brother Bill has blue eyes. How did that happen? Well, their mom and dad each have two genes for the trait of eye color. One of the genes has the instructions for blue eyes and the other has the instructions for green eyes. Sam's mom and dad both happened to pass down their green eye gene to Sam, but their blue eye gene to Bill. Just like that, you have variation between the brothers!
• Chromosome: composed of deoxyribonucleic acid (DNA). • 46 chromosomes into 23 pairs. • In each 23 pairs one chromosome comes from the father and other from the mother. • Instructions for the development of particular traits in the individual. • Mutations, which are random changes in the instructions genes carry, also create variation. Since genes are like recipes for body parts, changing the instructions can lead to recipes for new and different traits. A mutation adds instant variety to an individual's genes. Some mutations can be passed on to an individual's children, while some cannot.
Nature and Nurture • Nature: inherit • Biological groundwork that prepares a person to develop in certain ways. • Physical appearance, intelligence, and abilities in certain areas like math or the arts of language. • Nurture: environmental factors what a person is exposed to in life. • Variety of factors such as family, education, culture, living conditions, experience. • Are you who you are because of genetics or because of how you grew up? This old question of how much of a trait is genetically determined versus environmentally determined is referred to as the nature versus nurture debate. Nature generally refers to genes, while nurture refers to environment.
Kinship Studies • Degree in which people are related-the more closely related. • Twin Studies • Indentical twins, or monozygotic twins, if one of her eggs is fertilized and then splits into two genetically identical parts before the embryo starts to develop. • Each part will then develop into separate embryos. Identical twins share the same exact DNA because of this. Because they share 100% of their DNA, identical twins will always be the same sex. Though it's not always the case, identical twins will also often share a placenta and develop in the same embryonic sac. • If the twins are not identical, they would be considered dizygotic, or fraternal twins. This type of twin develops when two separate eggs are fertilized by different sperm and implant in the uterus at the same time. These twins will have the same genetic connection as any other siblings and will share 50% of the same DNA. Fraternal twins can be the same sex, or there can be one male and one female.
Adoptee Studies • Psychologists look for the relative similarities between children and their adoptive and biological families.
Twins Reared Apart • Kinship study • Identical twins reared apart constitute two individuals with the same genetic constitution (genotype) reared in two different environments. The study of a series of such twins allows us to estimate the influence of genetic and environmental factors on measured characteristics (phenotypes) of the twins
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