NRSG 200 Lecture 2 - Biological and Environmental Influences on Development

Genotype

the unique and complex blend of genes from both parents that determine our unique characteristics

Phenotype

the observable characteristics of your unique genetic make up

Genome

complete set of genes in a cell or organism

Alleles

one or more alternative forms of a gene

Heterozygous

2 different copies of the same gene (also called carriers)

Homozygous

2 identical copies of the same gene

Where does DNA exist in the cell?

Nucleus

Sex cells (gametes)

specific chromosomes that determines sex of organism (Male XY, Female XX)

Somatic (body) cells

all other cells in the body (besides sex chromosomes)

Autosome

genes located in chromosome pairs 1-22

Sex chromosomes

X and Y chromosomes

Dominant

that are expressed when one copy is present

Recessive

genes that are expressed when two copies are present

Mitosis

cell division process that produces two identical daughter cells from one mother cell

Meiosis

cell division process that produces four haploid daughter cells from one diploid mother cell

Two phases of meiosis

Meiosis I and meiosis II

When does the cell become haploid in meiosis?

after meiosis I

Zygote

How many chromosomes does a zygote contain?

46 chromosomes (23 pairs from both mom and dad)

What determines whether the zygote will dvelop into a female or a male?

Sex chromosomes

What sex chomosome do the egg and sperm contain?

- All ova (eggs) contain one X chromosome

- Sperm carry either a X chromosome or a Y chromosome

What is the most common type of twin?

Dizygotic (fraternal)

How do dizygotic twins occur?

Occurs when released ova (eggs) are fertilized individually by two different sperm

How do dizygotic twins appear?

Usually look different

Genetic similarity of dizygotic twins

Genetically, no more similar than siblings born separately

How do monozygotic twins occur?

Occurs when the same ovum is fertilized by one sperm, but splits during the fertilization process

How do monozygotic twins appear?

Look the same

Genetic similarity of monozygotic twins

Share the same exact genotype

Mendelian (simple) inheritance

inheritance of traits controlled by a single gene with two alleles

4 patterns of inheritance

1. Autosomal dominant

2. Autosomal recessive

3. X-linked dominant

4. X-linked recessive

Autosomal dominant inheritance

- Located on the non-sex genes (autosomal) and one requires one copy of the gene to display genetic condition

- v

Are males and females affected equally or unequally in autosomal dominant inheritance?

Equally

Example of autosomal dominant condition

Marfan syndrome

Marfan syndrome

disorder of connective tissue

4 symptoms of Marfan syndrome

1. Tall, thin body

2. Extremities disproportionately long for trunk

3. Heart problems

4. Skin and eye problem

What types of individuals have autosomal recessive conditions?

Occurs in homozygous individuals only

Parents of individuals affected with autosomal recessive conditions

Affected individuals may or may not have an affected parent

Offspring of 2 carrier parents for autosomal recessive inheritance

Offspring have 25% chance of having gene with 2 carrier parents

Are males and females affected equally or unequally in autosomal recessive inheritance?

Yes

Example of autosomal recessive condition

Cystic fibrosis

Cystic fibrosis

disorder that causes buildup of thick, sticky mucus and affects the lungs and digestive system

4 cystic fibrosis symptoms

1. Frequent lung infections

2. Chromic cough

3. Poor weight gain

4. Bulky, greasy stools

X-linked dominant inheritance

Dominant gene on X chromosomes

Offspring of affected parents in X-linked dominant inheritance

- Affected males produce all affected daughters

- If mom is affected, 50% chance to either son or daughter

Example of X-linked dominant condition

Fragile X syndrome

Fragile X syndrome

most common inherited cause of intellectual disability

Does fragile X syndrome affect males or females more severely?

Males

2 sympotoms of fragile X syndrome

1. Large ears and head

2. ADHD/autism/language and learning delays

Offspring in X-linked inheritance with affected father

- All daughters are carriers

- Sons are unaffected

Example of X-linked recessive condition

Hemophilia A and B

Hemophilia

absence of clotting factors and prolonged bleeding time

Incomplete dominance

genetic inheritance pattern in which both alleles influence the characteristic

Polygenic inheritance

most traits are a function of the inheritance of many genes (height, skin color, intelligence, etc.)

Genomic imprinting

expression of a gene is determined by whether it is inherited from the mother or the father

Example of genomic imprinting

Prader-Willi syndrome (father)/Angelman syndrome (mother)

How are genes/alleles expressed in genomic imprinting?

Only one copy of gene is expressed in imprinting

What may genomic imprinting indirectly influence?

Susceptibility to illness

Chromosomal abnormalities

- occur when cells have too few or too many copies of a chromosome

- Any chromosomal number that is not an exact multiple of haploid number (ex. 45 or 47)

Monosomy

Monosomy (45) on autosomes is incompatible with life

Trisomy

Trisomy (47) of certain autosome are compatible with life

Example of trisomy

down syndrome (trisomy 21)

How do chromosomal abnormalities occur?

Occur when chromosomes are damaged or altered (pieces of chromosome may be deleted or added through non-disjunction)

Edwards syndrome chromosomal abnormality

Trisomy 18

Edwards syndrome prognosis

Only 5% live past the first year

5 manifestations of Edwards syndrome

1. Microcephaly

2. Micrognathia

3. Cleft palate

4. Cardiac defects

5. Intellectual disabilities

Down syndrome chromosomal abnormality

Trisomy 21

What is down syndrome associated with?

Advanced maternal age

6 manifestations of down syndrome

1. Flat nasal bridge

2. Small mouth/protruding tongue

3. Low set ears

4. Shortened fingers

5. Cardiac defects

6. Intellectual disabilities

Turner's syndrome chromosomal abnormality

Affects only women - missing an X chromosome

4 manifestations of Turner's syndrome

1. Small stature

2. Cardiovascular problems

3. Amenorrhea

4. Webbed neck

Klinefelter syndrome chromosomal abnormality

Affects only men - extra X chromosome

3 manifestations of Klinefelter syndrome

1. Tall stature

2. Learning disabilities

3. Androgen deficiency at puberty resulting in small testes and reduced body hair

Mutation

sudden changes and abnormalities in structure of genes - may involves one or many genes

2 ways that mutations may occur

1. Spontaneously

2. Exposure to environmental toxins

Genetic counseling

a medical field that helps prospective parents determine the risk that their children will inherit genetic defects and chromosomal abnormalities

4 prenatal diagnosis methods

1. Ultrasounds

2. Amniocentesis

3. Chorionic villus sampling

4. Noninvasive prenatal testing

3 environmental influences on development

1. Families

2. Neighborhoods

3. Schools

How do families influence children's development?

- First relationships - learn about norms, values, etc.

- Source of learning skills

Direct influence of families on chidlren's development

parents' demeanor and parenting style directly influences the child's psychological wellbeing

Indirect influence of families on children's development

parents' interactions with each other will also indirectly influence the child's psychological wellbeing

How do neighborhoods influence children's development?

Offer resources and social ties - i.e. church, urban (more crime and violence) vs. rural environments (less resources)

How do schools influence children's development?

Transmit knowledge and skills; social system: funding of schools and economic stability of their neighborhoods has an effect on academic

2 ways that cultural context can influence children's development

- Affect child-rearing practices, family interactions, and activities

- Caring for grandparents or elderly relatives can affect parenting and the child psychological wellbeing

Social determinants of health (SDOH)

- conditions in which people are born, grow, work, worship, live, and age, which affects health and quality-of-life

- Complex, integrated and overlapping social structures and economic systems that are responsible for most health inequities

5 SDOH

1. Economic stability

2. Health care and quality

3. Neighborhood and built environment

4. Social and community context

5. Education quality and access

How do we define poverty?

Federal Poverty Level

How many US children live in poverty?

1 in 4

Poverty has a profound effect on (these 6 factors)

1. Health outcomes

2. Environmental exposures

3. Nutrition

4. Safety/injury

5. Parenting challenges

6. Exposure to toxic stress (prolonged stress response)

Behavioral genetics

field of study that examines how genes and experiences come to influence the diversity of human traits, abilities, and behaviors

Twin studies

compare identical and fraternal twins to estimate how much of a trait or behavior is attributable to genes

Adoption studies

compare the degree of similarity between adopted children and their biological parents whose genes they share (50%) and their adoptive parents with whom they share no genes

What two factors lead to a wide range of potential expressions of a genetic trait?

Environmental opportunities and constraints

Why do certain individuals respond differently to the same environment?

Genetic make-up

Epigenetics

- environmental factors can influence the expression of genetic traits

- Modification in the expression of genes rather than in the genetic code itself

2 factors that can influence epigenetic change

1. Lifestyle factors

2. Environment

Epigenetics before birth

Prenatal environmental factors can affect risk of certain diseases and conditions

Lifestyle factors can influence risk for what 2 diseases?

1. Cancer

2. Alzheimer's disease

2 epigenetic mechanisms

1. DNA methylation

2. DNA histone modification

DNA methylation

addition of a methyl group to the DNA that affects transcription/modifies function of gene

DNA histone modification

histones help package DNA