1. Chapter 3: Heredity and the Environment
The Genetic Code
DNA (deoxyribonucleic acid)
Molecule that contains the chemical instructions for cells to manufacture various proteins.
Chromosome
a molecule that contains protein and DNA.
Humans have 46 chromosomes (23 pairs), and about 25,000 genes.
Genome
the code for making a human being
Every person has a slightly different code, but the human genome is 99.5% the same for any 2 people.

2. What Genes Are
Genes are as section of chromosomes and the basic unit for the transmission of heredity, consisting of a string of chemicals that code for the manufacture of certain proteins.

3. The Beginnings of Life Development begins at conception
Each human reproductive cell, or gamete, contains 23 chromosomes.
Human reproductive cells = sperm or egg (ova)
Two human gametes join together to form a cell with 46 chromosomes, a new individual.
There is incredible diversity possible.

4. The Beginnings of Life zygote genotype
the single cell formed from the fusing of the nucleus of a sperm and the nucleus of an ovum.
In human beings this occurs in the fallopian tubes.
genotype
An organism’s entire genetic inheritance, or genetic potential contained on the chromosomes from mom and dad.
Genotype = an individual’s genetic potential

5. The Beginnings of Life
Male or Female?

6. phenotype
the observable characteristic of a person, including appearance, personality, intelligence, and all other traits
Depends on the interaction of biology, environment and experiences.
Phenotype = actual expression of genetic inheritance.

7. Exactly how to our genetic instructions influence the specific traits that a given offspring inherits?
Most traits are polygenic, they are affected by many genes. Regulator genes regulate the genetic interaction which makes a great deal of difference.
and
Multi-factorial
refers to a trait that is affected by many factors, both genetic and environmental

8. Additive Heredity Additive genes
A gene that has several alleles (alleles = slight variations of the gene) each of which contribute to the phenotype.
All additive genes contribute something to the phenotype

9. Dominant-Recessive Heredity
the interaction of a pair of alleles in such a way that the phenotype reveals the influence of one allele (the dominant gene) more than that of the other (the recessive gene)
Dominant gene = code is expressed (sometimes dominant gene completely controls characteristic)
Recessive gene = code is not expressed in the presence of a dominant gene (sometimes recessive genes are not completely hidden)
a special case of the dominant-recessive pattern occurs with genes that are x-linked, located on the x chromosome

10. Twins and Clones dizygotic (fraternal) twins
result from two sperm penetrating two ova, and share 50% of their genes
monozygotic (identical) twins
originate from one zygote, and share 100% genes
Can also have identical quadruplets or octuplets
a clone
originates from a live organism
Artificially created

11. From One Cell to Many More Complications
A small alteration in the sequence of base pairs or several extra repetitions in one triplet ma be inconsequential or may cascade to create a major problem

12. Concepts accepted by all Developmentalists
Genes affect every aspect of human behavior, including social and cognitive behavior. Every trait, action and attitude has a genetic component.
Most environmental influences on children raised in the same home are not shared

13. Each child’s genes elicit other people’s responses, and these responses shape development. In other words, a child’s environment is partly the result of his or her genes.
Children, adolescents, and especially adults choose environments that are compatible with their genes (called niche-picking), and thus genetic influences in adulthood

14. Chromosomal and Genetic Abnormalities
abnormalities caused by identifiable problems such as an extra chromosome or a single gene
Why is the study of these problems relevant to the study of development?
provids insight into the complexities of nature and nurture
Knowledge of their origins helps limit these effects
information combats the prejudice that surrounds such problems

15. Chromosomal and Genetic Abnormalities
Not Exactly 46 Chromosomes
Extra chromosomes in all cells
Missing a chromosome in all cells
Mosaicism = having a mixture of cells, some normal and some with an number of chromosomes or a series of missing genes (a problem of duplication)
What causes this?

16. Chromosomal and Genetic Abnormalities
Down Syndrome
a condition in which a person has 47 chromosomes instead of the usual 46, with three rather than two chromosomes at the 21st position
(also called Trisomy-21).
people with Down Syndrome typically have distinctive characteristics, including unusual facial features, heart abnormities, and language difficulties

19. Chromosomal and Genetic Abnormalities
Abnormalities of the 23rd Pair
Every human has at least 44 autosomes and one X chromosome
an embryo cannot develop without an X chromosome
Only condition where an embryo with 45 chromosomes can survive is a girl with Turner Syndrome (45X or X0). 1 in 2,500 births.
Underdeveloped female organs
Short or broad chest, webbed neck
Poor spatial skills, delayed social skills
Prone to heart, kidney and thyroid problems

22. Abnormalities of the 23rd pair
Can have additional sex chromosomes
Trisomy X Syndrome (47XXX)
Girls born with an extra X chromosome
1 in 1,000 girls
Phenotypically normal with slightly lower intelligence, quiet and passive with delayed speech and motor skills

24. Kleinfelter’s Syndrome (47XXY)
Boys born with an extra X chromosome
Little slow in elementary school
Double X keeps the penis from growing and fat begins to accumulate around breasts, sterile
Long limbs, lack of body hair
Hormones can alleviate symptoms

27. Abnormalities of the 23rd Pair
XYY Syndrome
Boys with one or more extra Y chromosomes
Could be 47XYY or 48XYYY
Caused by cell division problems during sperm production
Normal phenotype
Tall, severe acne, poor coordination, impulsive behavior, lower intelligence
1 in 1,000 births

29. Chromosomal and Genetic Abnormalities
Dominant-Gene Disorders
everyone carries genes or alleles that could produce serous diseases or handicaps in the next generation
Severe dominant disorders are rare because individuals with them do not reproduce
Exceptions
Huntington’s Disease which usually doesn’t develop until late in life so reproduction has already occurred
Tourette’s Syndrome which is not disabling so people are able to reproduce.
7,000 single-gene disorders
their dominant effects are apparent in the phenotype

30. Chromosomal and Genetic Abnormalities
Fragile X Syndrome
a genetic disorder in which part of the X chromosome seems to be attached to the rest of it by a very thin string of molecules
the actual cause is too many repetitions of a particular part of a gene’s code
Males are more likely to be affected than females
Causes mental deficiency or mental retardation

32. Chromosomal and Genetic Abnormalities
Recessive-Gene Disorder
most recessive disorders are not X-linked
double recessive patterns are lethal…one recessive gene is protective
sometimes a person who carried a lethal gene has many descendants who marry each other… the genetic disease then becomes common in that group

33. Carrier
a person whose genotype includes a gene that is not expressed in the phenotype…such an unexpressed gene occurs in half of the carrier’s gametes and thus is passed on to half of the carrier’s children, who will most likely be carriers, too…
Generally, only when the gene is inherited from both parents does the characteristic appear in the phenotype.