Heredity & Environment: Chapter 3 Human Development & Learning

Hail Mary, full of grace! The Lord is with thee; blessed art thou among women, and blessed is the fruit of thy womb, Jesus. Holy Mary, Mother of God, pray for us sinners now and at the hour of our death. Amen.

The Genetic Process Each of us carries a “genetic code” that we inherited from our parents. The nucleus of each human cell contains chromosomes made up of DNA. DNA is a complex molecule, shaped like a double helix, that contains genetic info.

Genetic process cont. Genes, the units of heredity information, are short segments of DNA that 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.

A silly, but effective way that I remember the relationship between genes, chromosomes and DNA is using a sweater analogy. Genes are the individual fibers in the yarn. DNA is the yarn itself, comprised of many genes. Chromosomes are the sweater, comprised of many strands of DNA. This is certainly not detailed and accurate enough for a biology class, but if you find yourself mixing up things like relative size and complexity, it works!

What do genes do? Genes direct cells to reproduce themselves and assemble proteins. Proteins form cells and regulate the body’s processes.

Genes and Chromosomes With 1 exception, all of the cells in the human body contain 46 chromosomes arranged in 23 pairs. These cells reproduce by mitosis. Mitosis: Cells duplicate themselves and then divide. The two resulting cells contain the same 23 pairs of chromosomes, paired identically to the original cell.

The exception to the rule Gametes: Sperm and egg cells These cells divide by a process called meiosis. A cell duplicates its chromosomes and then divides 2 times, resulting in four new cells each with only 23 unpaired chromosomes. During fertilization, an egg cell and a sperm cell pair up to create a single cell, a zygote.

Meiosis vs. Mitosis

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 Zygote 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.

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 Heterozygous 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 23rd pair Females: XX Males: XY Sex of offspring depends on whether the father’s Y sperm or X sperm fertilizes the ovum.

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 Dizygotic (fraternal) 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.

How genes translate into traits Phenotype: What you can observe about the trait Example: A person’s weight Phenotype influenced by: Genotype (genes) Environment So: “Final product” usually influenced by heredity AND environment

Epigenetics Referring to environmental factors that affect genes and genetic expression

Gene-environment correlations Passive correlation: Biological parents create an environment that fosters the traits they passed on. Evocative correlation: A child’s genetic traits shape it’s environment. Active (niche-picking) correlation: Children seek out environments that are amenable to their dispositions.

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.

Dominant-Recessive Heredity 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)

X-linked: A gene carried on the x chromosome

Mendelian Inheritance Table

Genetics of Eye Color Eye-color is a very common example of a simple dominant-recessive gene, but the reality is that eye-color is much more complicated than that. It may be very helpful for you to remember the example of the Brown eyes + Blue eye example, but if you want to know more about eye color, this site will help.

Genotype to Phenotype Almost every trait is: polygenic (affected by many genes) multifactorial (influenced by many factors)

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 statistical variation in a particular trait within a particular population is “explained” by genetics. Example: 90% of the variation in height among children of the same age is statistically explained by genetics. Environment can affect the expression of inherited genes. Heritability is a tricky concept because it is actually a statistical term that requires an understanding of statistics that is not generally included with statement regarding the heritability of this and that. If 90% of the variation in height is “heritable,” it does not mean that the height of each individual person is 90% determined by their genes. What would that even mean? In fact, it gets a little confusing. Check this out: http://www.somsd.k12.nj.us/cms/lib7/NJ01001050/Centricity/Domain/218/A.P._Psychology_3-C_(C)_-_Heritability_and_Molecular_Genetics_2.pdf If 8 people are genetically identical (they are octuplets or clones), and they all grow to different heights, then zero percent of the variation in their heights is due to genetics. This doesn’t mean that genes have nothing to do with height. It means that, because they are genetically identical, 100% of the variation in their heights must be due to something other than their genes. Conversely, if scientists were somehow able to expose people to perfectly identical conditions (e.g., surroundings, food, etc.) then 100% of the variation in their height would be attributable to genetics and 0% to environment. In reality, genes interact with environment.

Concordance rates What are concordance rates? The proportion of a “random sample” that shares a trait. Twin-studies, adoption-studies, sibling-studies, etc. Why are twins reared apart of particular interest?

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)

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

Recessive Gene 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

Page 80 and 81 in your book.

Genetic Counseling and Testing 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

Hi! If you are seeing this, then it is likely that you are finished with the majority, if not all, of your Week 1 readings. If you found any of this a bit tedious, remember that the really cool stuff starts in Week 2!