child and adolescent development | Quizlet

Heritability

hereditary perspective is seeking to determine how one's genotype is expressed as a phenotype

genotype

the genes that one inherits

phenotype

the ways in which a person's genotype is expressed in observable or measurable characteristics

conception

the moment of fertilization, when a sperm penetrates an ovum, forming a zygote (in the fallopian tube)

What happends after conception?

When a sperm cell penetrates the lining of the ovum, a biochemical reaction repels other sperm (preventing them from repeating the fertilization process)

How is a zygote formed?

few hours after conception the sperm cell begins to disintegrate, releasing its genetic material. The ovum also releases its genetic material, and a new cell nucleus forms around the hereditary information provided by the father's sperm and the mother's ovum.

zygote

a single cell formed at conception

from the union of a sperm and an

ovum

contains the biochemical material for the zygote's development from a single cell into a recognizable human being

What hereditary material is present in a human zygote?

46 chromosomes made up from genes (genes = basic units of heridity)

How many chromosomes does each parent contribute?

23 chromosomes to each of their children

Do genes on the chromosome also form pairs?

yes, the two members of each gene pair are located at the same sites on their corresponding chromosomes (DNA is a double helix)

How is it possible that zygote develops into a human?

DNA can duplicate itself

mitosis

the process in which a cell duplicates its chromosomes and then divides into two genetically identical daughter cells

What are the steps of mithosis?

1) original state

2) each chromosome splits lengthwise = producing a duplicate

3) duplicate sets of chromosomes move to opposite ends of original cell, which then begins to devide

4) cell completes its division = two new cells that have indentical sets of chromosomes

Does mitosis stop after growth?

No, it continues throughout life, generating new cells that enable growth and replacing old ones that are

damaged

With each division, the chromosomes are duplicated, every new cell contains an exact copy of the 46 chromosomes we inherited at conception.

gamets

reproductive cells, sperm cells and egg cells

produced in meiosis

meiosis

the process in which a germ cell

divides, producing gametes (sperm or

ova) that each contain half of the

parent cell's original complement of

chromosomes; in humans, the

products of meiosis contain 23

chromosomes.

steps of meiosis

1) each of the germ's cell's original

chromosomes duplicates itself, and the duplicate

remains attached

2) Crossing-over takes place among

adjacent chromosomes = new hereditary combinations

3) The original cell now divides to form two

new cells, each of which has 23 duplicated

chromosomes (some of which have been altered

by crossing over).

4) each chromosome and

its duplicate now split and segregate into

separate gametes (each gamete has

but half the chromosomes of its original cell)

crossing over

a process in which genetic material is

exchanged between pairs of

chromosomes during meiosis.

Brothers and sisters who have the same mother and father have inherited 23 chro-

mosomes from each of these parents. Why is it, then, that offspring of the same parents

sometimes barely resemble each other?

because meiosis makes us genetically unique

Why are crossovers important?

1) they increase genetic variability in human population = protection against congenital defects + environmental stresses

2) chiasma formed during cross over ties homologous chormosomes together = proper segregation during separation of meiosis

What happends to chromosome pairs not connected by a chiasma?

They drift independently and may end up in the same daughter cell = at the

end of meiosis, the resulting gametes will be aneuploid

Aneuploidy

Abnormal number of chromosomes (some sex cells will have too few chromosomes and some

too many)

What are consequences of aneuploidy?

It can cause spontaneous abortion,

congenital birth defects, and mental retardation

majority of zygotes having too few chromosomes

miscarry spontaneously

Most often it is trisomy (having more than the necessary

amount of chromosomes) that leads to congenital defects

and cognitive impairment such as Down syndrome

nondisjunction

improper separation of chromosomes

How are nondisjucntion and cross-overs related?

Nondisjuction is associated with low frequencies of cross-over

How is age related to cross-overs?

Decreasing

cross-over frequencies are

associated with increasing mater-

nal age

rate of trisomic pregnancies in

women 25 years old and younger

is 2% & 35% for women over the age of 40

What can cause nondisjunction in some chromosomes?

Nondisjunction may occur when chiasma form too close or too far from the centromere.

What did Lamb, Sherman, and Hassold (2005) investigate?

They investigated the location of nondisjunctions associated with pregnancies trisomic at chromosome 21 (linked to Down syndrome).

Where does nondisjunction typically occur in women under 29? And in 29 and older?

under 29: Very near to or very far from the centromere.

over 29: Nondisjunctions are distributed along the entire length of the chromosomal arm.

Why are younger women's gametes vulnerable to improper chromosome separation?

They are vulnerable at universally vulnerable sites due to their specific locations on chromosome 21.

How does aging affect a woman's meiotic machinery?

It accumulates environmental and age-related damage, making it less efficient and more error-prone.

What are other crossover mistakes besides nondisjunction?

Misalignment of paternal and maternal chromosomes (causing nonhomologous exchanges) and exchanges between a chromosome arm and its duplicate.

What cellular mechanisms help prevent crossover mistakes?

Mechanisms that promote crossover between homologues and suppress crossover between chromosomes and their duplicates.

How do scientists study meiosis and its errors?

Through direct observations of meiosis in progress and indirect analyses of genotype data in families; they reveal mechanisms and errors that create genetic variety across generations.

What is the independent assortment principle?

each pair of

chromosomes segregates indepen-

dently of all other chromosome pairs

during meiosis

How many different genetic combinations can a human parent produce in their sperm or ova? An a couple?

human --> more than 8 milion

couple --> 64 trilion (8 million from the father × 8 million from the mother)

Why are the odds of two siblings having identical genes even smaller than 1 in 64 trillion?

Because crossing-over during meiosis alters the genetic composition of chromosomes, increasing genetic variation beyond the 8 million combinations from segregation alone.

How does crossing-over affect genetic variation?

It increases the number of possible genetic combinations in an individual's gametes beyond what would occur with simple chromosome segregation.

What makes each individual genetically unique?

The random segregation of chromosomes and the genetic variation introduced by crossing-over during meiosis.

monozygotic (identical) twins

same genotype, form when zygote splits into two they should show very similar developmental progress if genes have much effect on human development.

Dizigotic (fraternal) twins

result when a mother releases two ova at the same time and

each is fertilized by a different sperm; are

born together, they have no more genes in common than any other pair of siblings.

What are karyotypes?

Chromosomal portraits that reveal the structure and number of chromosomes in an individual.

How many pairs of human chromosomes are there, and what are the first 22 pairs called?

There are 23 pairs of chromosomes; the first 22 pairs are called autosomes.

Which chromosome pair determines a person's sex?

The 23rd pair, known as the sex chromosomes.

What are the sex chromosomes in males?

One X chromosome (elongated) and one Y chromosome (short and stubby).

What are the sex chromosomes in females?

Two X chromosomes.

Who determines the sex of a child, the mother or the father?

The father, because his sperm can carry either an X or a Y chromosome. All ova (egg cells) carry only the X chromosome

What is the biological injustice in blaming mothers for not bearing male children?

It's unjust because fathers determine the child's sex based on whether their sperm carries an X or Y chromosome.

How do genes promote development at the biochemical level?

Genes call for the production of amino acids, which form enzymes and other proteins necessary for the formation and functioning of new cells.

What is an example of genes regulating a specific trait?

Genes regulate the production of melanin in the iris, affecting eye color—brown eyes have more melanin, while blue or green eyes have less.

How do genes guide cell differentiation?

Genes determine which cells become parts of the brain, circulatory system, bones, skin, etc., influenced by surrounding biochemical environments during development.

What role do regulatory genes play in development?

Regulatory genes "turn on" or "turn off" other genes at specific points in the life span, such as initiating growth spurts in adolescence and stopping growth in adulthood.

How can environmental factors influence genetic expression?

Environmental factors like nutrition, temperature, or exposure to toxins can affect how genes function, influencing traits like height even if a person has genes for tall stature.

How does the internal cellular environment affect gene expression?

The environment within the cell's nucleus and the surrounding cellular environment can influence how genes are expressed.

What are experience-expectant interactions?

Environmental effects experienced by all humans, necessary for normal development (e.g., exposure to language for language development).

What are experience-dependent interactions?

Environmental effects that are unique to individuals, shaping specific traits based on personal experiences (e.g., learning a musical instrument).

What is the key takeaway about how genes influence human characteristics?

Genes do not simply "code" for traits; they interact with the environment at many levels to produce proteins that influence development and characteristics.

What are major patterns of genetic inheritance?

The ways in which parents' genes are expressed in their children's phenotypes.

What are the four main patterns of genetic expression?

Simple dominant-recessive inheritance, codominance, sex-linked inheritance, and polygenic (multiple gene) inheritance.

What is polygenic inheritance?

The determination of traits by the interaction of many genes working together.

What is simple dominant-recessive inheritance?

A pattern where a characteristic is influenced by one pair of genes (alleles), with one dominant and one recessive allele. So that only

its phenotype is expressed.

allels

alternative forms of a gene that can

appear at a particular site on a

chromosome.

What did Mendel discover about traits in offspring?

Some traits are dominant and appear more often in later generations, while others are recessive and less common.

dominant allel

a relatively powerful gene that is

expressed phenotypically and masks

the effect of a less powerful gene.

recesive allele

a less powerful gene that is not

expressed phenotypically when paired

with a dominant allele.

homozygous

having inherited two alleles for an

attribute that are identical in their

effects e.g. AA or aa

heterozygous

having inherited two alleles for an

attribute that have different effects e.g. Aa

carrier

a heterozygous individual who

displays no sign of a recessive allele

in his or her own phenotype but can

pass this gene to offspring.

How does dominant-recessive inheritance work in human vision?

The normal vision gene (N) is dominant over the nearsightedness gene (n), so individuals with either NN or Nn genotypes have normal vision.

Can two individuals with normal vision have a nearsighted child?

Yes, if both parents are heterozygous (Nn), there's a 1 in 4 chance their child will inherit the nn genotype and be nearsighted.

What is a Punnett Square?

A graphic representation of parents' alleles and their possible combinations to predict inherited traits in offspring.

What are the possible genotypes for vision, and what do they represent?

NN - Homozygous for normal vision (normal vision).

Nn - Heterozygous (normal vision, carrier of the recessive gene).

nn - Homozygous for nearsightedness (nearsighted).

dominant and recessive traits in humans

most of the

undesirable or maladaptive attributes are recessive

Huntington's disease

produced by a dominant gene; a condition that causes a gradual deterioration of the nervous system, leading to a progressive decline in physical and mental abilities and ultimately to death.

What is codominance?

A genetic pattern where both alleles are equally expressive, producing a phenotype that shows both traits without one dominating the other.

What is an example of codominance in humans?

Human blood types A and B are codominant. A person with one A allele and one B allele has blood type AB, showing both A and B antigens equally.

What is incomplete dominance?

A form of codominance where one allele is stronger than the other but does not completely mask its effects, resulting in a blended phenotype.

What is an example of incomplete dominance in humans?

The sickle cell trait, where a heterozygous person has some red blood cells with a sickle shape due to the presence of one sickle-cell allele.

What causes sickle-shaped red blood cells in sickle cell trait carriers?

The presence of one recessive sickle-cell allele causes some red blood cells to assume a sickle shape, especially under low-oxygen conditions

What are the symptoms of sickle cell trait?

Symptoms are rare but may include joint pain and fatigue during oxygen deprivation, such as at high altitudes or after intense physical exertion.

What happens if a person inherits two recessive sickle-cell genes?

They develop sickle-cell anemia, a severe blood disorder causing widespread sickling of red blood cells and poor oxygen distribution.

What are the health risks associated with sickle-cell anemia?

Risks include heart or kidney failure, respiratory diseases, and early death, often during childhood.

What factors can trigger symptoms in sickle cell trait carriers?

Oxygen deprivation, such as from physical exertion, high altitudes, or anesthesia, can trigger symptoms.

What are sex-linked characteristics?

Traits determined by genes located on the sex chromosomes, usually the X chromosome.

Who is more likely to inherit recessive X-linked traits, males or females?

Males, because they have only one X chromosome and no corresponding gene on the Y chromosome to counteract a recessive gene.

What is an example of a common sex-linked characteristic?

Red/green color blindness.

Why are males more likely to be color-blind?

If a male inherits an X chromosome with the color-blindness gene, he will be color-blind because the Y chromosome doesn't have a gene to counteract it.

Can females be color-blind?

Yes, but only if they inherit two X chromosomes with the recessive gene for color blindness.

What are some other sex-linked disorders besides color blindness?

Hemophilia, muscular dystrophy, degeneration of the optic nerve, certain forms of deafness, and night blindness.

Why are males more likely to suffer from X-linked disorders?

Because they have only one X chromosome, so a single recessive gene on that chromosome will express the disorder.

What are polygenic traits?

Traits influenced by many pairs of alleles rather than a single gene pair.

What are examples of polygenic traits?

Height, weight, intelligence, skin color, temperament, susceptibility to cancer, and more.

How does the number of genes influencing a trait affect genetic variation?

As the number of genes increases, the number of possible genotypes and phenotypes also increases, leading to greater variation.

How do observable traits for polygenic traits differ from single-gene traits?

They show continuous variation rather than either/or possibilities, following a bell-curve distribution with most individuals having intermediate traits.

What pattern do polygenic traits typically follow in populations?

A normal bell-curve distribution, with few people at the extremes and most in the middle.

How many genotypes and phenotypes are possible with one gene and two alleles?

Three genotypes and three phenotypes.

How many genotypes and phenotypes are possible with two genes and two alleles each?

Nine genotypes and five phenotypes.

How many genotypes and phenotypes are possible with three genes and two alleles each?

Twenty-seven genotypes and six phenotypes.

Why do polygenic traits show more complex patterns of inheritance?

Because they involve multiple genes that may also follow codominance, incomplete dominance, or sex-linked inheritance patterns.

What makes understanding the inheritance of behavioral traits complex?

Behavioral traits like intelligence and personality are influenced by many genes interacting with environmental factors, making inheritance patterns complex.