The Developing Person Through the Life Span 8e by Kathleen Stassen Berger Chapter 3 – Heredity and Environment PowerPoint Slides developed by Martin Wolfger and Michael James Ivy Tech Community College-Bloomington Reviewed by Raquel Henry Lone Star College, Kingwood

The Genetic Code What Genes Are DNA (deoxyribonucleic acid) Molecule that contains the chemical instructions for cells to manufacture various proteins Promotes growth and sustains life

What Genes Are Chromosomes: Molecules of DNA DNA consists of 46 chromosomes arranged in 23 pairs

What Genes Are Genes Specific sections of a chromosome carry instructions via four chemicals. Chemicals organized in four pairs (A-T, T-A, C-G, G-C). Each person has about 3 billion pairs.

What Genes Are Allele A variation that makes a gene different in some way from other genes for the same characteristics Many genes never vary; others have several possible alleles Genome The full set of genes that are the instructions to make an individual member of a certain species

The Beginnings of Life Gametes Reproductive cells (sperm and ova) Each consists of 23 chromosomes. Zygote Two gametes (sperm and ovum) combine and produce a new individual with 23 chromosomes from each parent.

The Beginnings of Life

Matching Genes Genes are passed down from generation to generation Genotype An organism’s genetic inheritance, or genetic potential Unique for each organism

Matching Genes Homozygous Two genes of one pair that are exactly the same in every letter of their code. Heterozygous Two genes of one pair that differ in some way. Typically one allele has only a few base pairs that differ from the other member of the pair.

Male or Female? Humans usually possess 46 chromosomes. –44 autosomes and 2 sex chromosomes termed the 23 rd pair –Females: XX –Males: XY –Sex of offspring depends on whether the father’s Y sperm or X sperm fertilizes the ovum.

Male and Female

The Beginnings of Life The zygote begins duplication and division then differentiation and specialization occur. Cells change from being stem cells, those from which any other specialized type of cell can form, to being only one kind of cell.

Twins Monozygotic (identical) twins Originate from one zygote that splits very early in development Same genotype Dizygotic (fraternal) twins Result from fertilization of two separate ova by two separate sperm Incidence is genetic and varies by ethnicity and age.

Assisted Reproduction Assisted reproductive technology (ART) a general term for the techniques that help infertile couples conceive and sustain a pregnancy In vitro fertilization (IVF) takes place outside a woman’s body involves mixing sperm with ova surgically removed from the woman’s ovary if a zygote is produced, it is inserted into a woman’s uterus, where it may implant and develop into a baby.

From One Cell to Many Phenotype The observable characteristics of a person, including appearance personality, intelligence, and all other traits Intimately connected with genotype Almost every trait is: polygenic (affected by many genes) multifactorial (influenced by many factors)

Epigenetics Referring to environmental factors that affect genes and genetic expression

Gene-Gene Interactions Human Genome Project International effort to map the complete human genetic code Essentially completed in 2001; analysis is ongoing Found “only” about 20,000 genes in humans Exact number is unknown

Additive Heredity Additive genes Genes that add something to some aspect of the phenotype Effects of additive genes add up to make the phenotype Example: Height is affected by the contributions of about 100 genes

Dominant-Recessive Heredity Dominant-recessive pattern - Dominant gene is more influential than the recessive gene (non-additive). –Dominant gene can completely control the phenotype with no noticeable effect of recessive gene. –Genes for blood type B and Rh-positive blood are dominant.

Carrier: a person whose genotype includes a gene that is not expressed in the phenotype –Unexpressed gene occurs in half of the carrier’s gametes and is passed on to half of the carrier’s offspring –Offspring can be carrier or express the gene in the phenotype (e.g. when unexpressed gene is inherited by both parents) Dominant-Recessive Heredity

X-linked: A gene carried on the x chromosome

Alcoholism Alcoholism probably has a genetic basis –Genes can cause an overpowering addictive pull in some people –Environmental conditions can modify the genetic effects –Nature and nurture combine to create an alcoholic

Nearsightedness Termed myopia Low nearsightedness runs in families and is associated with minor variations in the Pax6 gene Environment also plays a role –Increase in nearsightedness among East Asian schoolchildren –Increased schoolwork may have caused nearsightedness in children with a Pax6 allelle

Heritability Statistical term that indicates what portion of the variation in a particular trait within a particular population is inherited. –Example: 90% of the height differences among children of the same age is genetic. Environment can affect the expression of inherited genes.

Not Exactly 46 Down Syndrome (Trisomy-21) –Three copies of chromosome 21 –Specific facial characteristics (thick tongue, round face, slanted eyes) –Hearing losses, heart abnormalities, muscle weakness, short stature –Slow to develop language –Accelerated aging (cataracts, dementia, certain forms of cancer common at age 40)

Gene Disorders a)Dominant-Gene Disorders Half of the offspring of parents with a dominant disorder will have the disorder. Most dominant disorders begin in adulthood (fatal dominant childhood conditions cannot be passed on). Many dominant disorders have relatively mild or variable symptoms. Tourette syndrome –Some who inherit the dominant gene exhibit uncontrollable tics and explosive outbursts –Most have milder, barely noticeable symptoms

b)Recessive Disorders Fragile X syndrome –Most common form of inherited mental retardation –Additional symptoms include muscle weakness, shyness, and poor social skills Sickle-cell trait –Offers some protection against malaria –African carriers are more likely than non-carriers to survive Gene Disorders

Genetic Problems

Genetic Counseling and Testing Genetic Counseling Consultation and testing by trained professionals Enables prospective parents to learn about their genetic heritage, including harmful conditions that may be passed on to their offspring Ethical Guidelines Test results are kept confidential Decisions regarding sterilization, adoption, abortion, or carrying a pregnancy to term are made by the clients

Genetic Counseling and Testing Phenylketonuria (PKU) Recessive condition Results in inability to metabolize phenylalanine (amino acid found in many foods) Buildup of phenylalanine causes brain damage, progressive mental retardation, and other symptoms Early testing and a special diet usually results in normal development