journal

Biological and

Environmental

Foundations

Biological and Environmental Foundations

• Genetic Foundations

• Heredity, Environment and Individual Differences

The Genetic Process —

Beginning Life As A Single Cell

GENETIC FOUNDATION

• The foundations of development are heredity and environment. Heredity supplies our genotype (genetic makeup), while heredity and environment combine to form the phenotype (observable characteristics).

• Each of us is made up of trillions of cells. Chromosomes in the nucleus of the cell store and transmit genetic information.

The Genetic Process — Beginning Life As A Single Cell

• DNA and the collaborative gene

– DNA — deoxyribonucleic acid, DNA molecules make up chromosomes.

– Chromosomes — thread-like structures

– Genes — units of hereditary information, A gene is a segment of a DNA molecule which contains instructions for making proteins.

Genetic Foundations

Cells, Chromosomes, Genes, and DNA

Genetic Foundations

Nucleus (center of cell) contains chromosomes

and genes

Chromosomes are threadlike structures

composed of DNA molecules

Gene: a segment of DNA (spiraled double chain)

containing the hereditary code

The Genetic Code • Mitosis is the process of cell duplication in

which each new cell receives an exact copy

of the original chromosomes.

The Genetic Code

• The process of Meiosis produces the sex cells.

• Sex cells are the sperm

in males and the

ova in females

Sex Cells

• Meiosis is the process of cell division through which sex cells are formed. It halves the number of chromosomes so each gamete contains 23.

• In meiosis, the chromosomes pair up and exchange segments in a process called crossing over, so that genes from one are replaced by genes from another. Then chance determines which member of each pair will gather with others and end up in the same sex cell.

• Meiosis leads to variability among offspring. When sperm and ovum unite at conception, the resulting zygote has 46 chromosomes—23 from each parent.

The Genetic Process

• Genes and chromosomes

– Meiosis — specialized form of cell division

– Fertilization — egg and sperm fuse together will result in a zygote with 46 chromosomes (23 from each parent)

– Genetic variability in the population

– Next Slide – Boy or Girl, the X and Y chromosomes

Genetic Foundations

Boy or Girl? • The 22 pairs of matching chromosomes within a human

cell are called the autosomes.

• The twenty-third pair consists of sex chromosomes. Females have an XX pair of sex chromosomes; males have an XY pair.

The sex of the new organism is determined by whether an X-

bearing or a Y-bearing sperm fertilizes the ovum.

• Who determines the sex of the child?

Multiple Births

• Fraternal, or dizygotic, twins result when two separate ova are fertilized by two separate sperm.

• Identical, or monozygotic, twins result when a single zygote that has started to duplicate separates into two clusters of cells that develop into two individuals. Monozygotic twins have the same genetic makeup.

• During their early years, children of single births are often healthier and develop more rapidly than do twins

Patterns of Genetic Inheritance

• Dominant–recessive inheritance is a pattern where, in a heterozygous situation, only one gene’s influence is exhibited.

• The gene that is dominant is expressed; the gene that is recessive is not expressed.

• An individual who is heterozygous is a carrier who can pass a recessive gene to his or her children.

Patterns of Genetic Inheritance

• If the genes from both parents are alike, the child is homozygous and will display the inherited trait.

• If they are different, then the child is heterozygous, and relationships between alleles determine the trait that will appear.

Laura Berk, 2016

Disorder of Genes

What is PKU?

PKU (Phenylkentonuria) – Recessive • Phenylketonuria or PKU is one of the most frequently occurring

recessive disorders.

• Inability to metabolize the amino acid phenylalanine, contained in many proteins, causes severe central nervous system damage in the first year of life.

• A diet low in phenylalanine = normal mental development. Even small amounts of phenylalanine interfere with brain functioning – less cognitive and motor development appears in childhood into adulthood.

• Dominant genes rarely transmit serious diseases from one generation to the next, since the individual usually does not live long enough to pass the gene to the next generation. An exception is Huntington disease.

What is Huntington Disease?

• Huntington Disease – Dominant

• Central nervous system degeneration leads to muscular coordination difficulties, mental deterioration, and personality changes.

• Symptoms usually do not appear until age 35 or later.

Patterns of Genetic Inheritance

• Codominance is a pattern of inheritance in which both influence the person’s characteristics.

• –The sickle cell trait is a heterozygous condition present in many black Africans, Latin, Arabs, India, Italians as Caucasians

• –Sickle cell anemia occurs in full form when a child inherits two recessive genes.

Patterns of Genetic Inheritance X–linked inheritance occurs when a recessive allele is carried on the

X chromosome. Males are more likely to be affected, since the Y chromosome is not as long as the X and may not have a corresponding dominant gene to override the recessive gene. – Red-green color blindness is one example of an X-linked

recessive trait.

– Hemophilia, a disorder in which the blood fails to clot normally, is also an X-linked disease.

– Besides X-linked disorders, many sex differences reveal the male to be at a disadvantage.

Genetic Principles

• Chromosome abnormalities – Down syndrome

• Sex-linked chromosome abnormalities

– Klinefelter syndrome

– Fragile X syndrome

– Turner syndrome

– XYY syndrome

Chromosomal Abnormalities

• Abnormalities of the Chromosomes including Sex Chromosomes

– Sex chromosome disorders usually result in fewer problems than defects of the autosomes and are often not recognized until adolescence.

– A variety of myths about individuals with sex chromosome disorders exist. For example, it is often erroneously believed that males with XYY syndrome are more aggressive and antisocial than XY males. Researchers were trying to link aggressive behavior to chromosomal abnormalities.

– Research indicates that adding to or subtracting from the usual number of X chromosomes results in specific types of intellectual deficits.

What if We Have Too Many or Too Few Chromosomes?

• Meiosis is the cell division process that produces cells that will become the egg and sperm cells of an organism.

• Cells produced by meiosis have half the normal number of chromosomes (each meiotic cell has one copy of each chromosome), so that when an egg and sperm fuse at fertilization, the resulting zygote has the two copies of each chromosome it needs for proper development.

• Sometimes during the course of normal meiosis, chromosomes are not correctly distributed from a dividing cell into the two daughter cells.

• When this happens, one daughter cell has twice the number of copies of that particular chromosome and the other daughter is left with no copies of that chromosome.

• If such a cell is later used in a fertilization event, the resulting zygote will have either a total of one of that type of chromosome (monosomy) or have three of that type of chromosome (trisomy).

Trisomy 21

Down's Syndrome Karyotype

• Down syndrome, caused by the presence of three copies of chromosome 21, is the most commonly observed imbalance in the number of non-sex chromosomes (1 in 800 live births).

• Medical problems associated with Down syndrome include mental retardation, congenital organ defects, respiratory infections, and leukemia

Trisomy 21

Down's Syndrome Karyotype

XYY Syndrome

• Occurrence - 1:1,000 men

• Most common indicators are developmental delay and/or behavior problems Average final height approximately 7cm above average Normal body build, Comparatively low weight relative to stature Larger craniofacial dimensions than in non-XYY males, severe acne in adolescence

Abnormal number of chromosomes

• Abnormal numbers of chromosomes are very often incompatible with life. In general, the human body can tolerate excess genetic material more easily than it can tolerate missing genetic material.

• In certain cases, such as Turner's Syndrome, if individuals are identified soon enough they can be successfully treated with hormones to reduce the effects of the chromosome imbalance.

Turner's Syndrome Karyotype (X0)

Individuals with Turner's syndrome have a single X chromosome (and no Y) as their sex chromosome. They develop as girls, but are sterile, small in stature, and have a pattern of major and minor malformations.

Klinefelter's Syndrome Karyotype (XXY)

• Individuals with Klinefelter's Syndrome have XXY sex chromosomes. They develop as males, with subtle phenotypic anomalies.

• The XXY chromosomes are marked with a box in the karyotype below.

What is Fragile X? • Fragile X is a family of genetic conditions, which can

impact individuals and families in various ways (x-linked genetic disorder.

• Fragile X Syndrome is the most common cause of inherited mental impairment. This impairment can range from learning disabilities to more severe cognitive or intellectual disabilities. (Sometimes referred to as mental retardation.)

• FXS is the most common known cause of autism or "autistic-like" behaviors. Symptoms also can include characteristic physical and behavioral features and delays in speech and language development.

• This diagram displays fragile X syndrome. This occurs in about 1 in 1500 males. Affected female carriers are typically normal. Most of the affected males have mental retardation, and their testes are larger than normal.

• fragile X-associated tremor ataxia syndrome (FXTAS), a condition which affects balance, tremor and memory in some older male gene carriers.

• Fragile X-related premature ovarian failure (POF), a problem with ovarian function which can lead to infertility and early menopause in some female gene carriers.

Sex-Linked Chromosome Abnormalities

Klinefelter’s

Syndrome

Males have an extra X chromosome

Fragile X Syndrome

Abnormality in the X chromosome

Turner’s Syndrome

Females missing an X chromosome

XYY Syndrome

Males have an extra Y chromosome

Thank you

Berk, Laura E., (2016). Infants, Children, and Adolescents.

Boston, MA: Pearson. EIGHTH EDITION