Chapter 2

Humans are genetically very similar (99%). However each person is unique due to _____.

Gene variations called alleles.

When does conception occur?

When a sperm and an ovum join to form a zygote.

A zygote contains _____ genes stored on _____ chromosomes.

21,000 genes; 46 chromosomes (23 pairs).

How many chromosomes does a zygote have? How many pairs

46 chromosomes, 23 pairs.

What cells only have 23 chromosomes?

sperm and ova

True or False: Each reproductive cell gets one member of each chromosome pair, so which half it gets is random.

True.

• The parent has 46 chromosomes with 23 pairs. The reproductive cell only has 23 chromosomes. It takes one chromosome from each pair, therefore it has 23 total chromosomes.

How many unique combinations of chromosomes are there?

8 million ➡ 2²³.

• Ovum from mom w/ 23 chromosomes (from mom); Sperm from dad w/ 23 chromosomes (from dad).

Two parents can make how many different unique chromosome combinations for a child? Remember 8 mill for ovum and for sperm.

8 million (sperm) x 8 million (ovum) = 64 trillion possible zygotes.

Only 1 pair of the 23 chromosome pairs in a zygote determines the sex of the baby. What number is that pair? What are they called?

23rd pair (aka. the sex chromosomes). The rest are called autosomes.

Does a father or mother determine the sex of the zygote?

The father. The mother has XX, they contribute an X. The father has XY, meaning they can either give an X (girl) or a Y (boy).

What is the name of the gene contained in the Y chromosome of a male?

The SRY gene, which triggers male development around week 8 of gestation.

What happens after an egg is fertilized by a sperm?

It becomes a zygote.

What occurs after fertilization?

The zygote created is surrounded by a coating so no other sperm can enter.

What is a genome (gene)?

A genetic set of instructions for any living organisms.

Most of our genes are identical, so what makes us unique?

Small differences in genes (alleles) make us individual.

What are some examples of the differences alleles can create?

Eyebrow shape (minor) or tendency for heart attack or longevity (major).

What is the microbiome?

The trillions of microbes that live in and on our body, especially our guts.

What does our microbiome influence?

Weight, immunity, diseases, and mood.

Gut bacteria aid in…

Digesting food.

Clinics sometimes try to alter the _____ of patients to help with obesity or prediabetes.

Microbiome’s.

The microbiome’s impact can vary, depending on…

• Diet.

• Drugs.

• Exercise.

• Genes.

What is a genotype?

All inherited genes (the genetic blueprint).

What is a phenotype?

The observable traits, influenced by both genotype and the environment.

Give an example of the environment limiting a phenotype.

A child may have the genes to be 6 feet tall, but if they are malnourished they may only grow to 5 feet.

Genes are not fixed. Environmental factors such as food, toxins, and stress can alter gene expression. What is the name of the study of these changes?

Epigenetics.

Genes and environment interplay in education and gender. Give an example of this.

Early, only a few brave women pursued engineering, but with encouragement and role models, many of them now excel in STEM.

• Cognitive potential ➡ environment and social active factors can limit it.

True or False: Genetic diversity promotes health, creativity, and societal prosperity.

True

Why does inbreeding affect offspring?

There is less genetic variety.

What is additive heredity?

When multiple genes or alleles contribute to a physical trait by adding their effects together.

• Curliness.

• Skin color.

• Height.

What is it called when two or more genes work together to control a single physical trait?

Polygenic inheritance.

• ➡ children often differ in appearance from both parents b/c of this complex inheritance.

What is dominant-recessive heredity?

A pattern on inheritance where a dominant allele masks the expression of a recessive allele.

Recessive alleles are only expressed if…

Both copies are present.

Father is Bb for blue eyes; mother is bb. Using a punnet square predict whether their offspring will express the phenotype, carry it, or not have it at all.

50% expression; 50% carriers.

What are X-linked traits?

genetic characteristics that are determined by genes located on the X chromosome.

Let’s say a family has a baby boy (XY). The mother’s X chromosome has an x-linked recessive trait like red-green color blindness. Would the child have said trait?

Yes. There is no other X chromosome like in a girl, that can mask that recessive trait.

Why is color blindness in India 9x more common among boys?

Because of X-linked inheritance and the tendency to marry within close groups.

CRISPR is a technique that can…

modify/edit genes at conception.

What are the two possible types of twins?

Monozygotic and dizygotic.

Monozygotic twins come from…

one (mono) zygote ➡ splits into 2+ embryos; identical.

True or False: Environmental factors can make identical twins differ.

True.

Dizygotic twins arise from…

two ova fertilized by two sperm; basically siblings.

Which is more common DZ or MZ twins?

DZ.

What are the three periods of prenatal development? When does each start?

Germinal (first 14 days).

Embryonic (3rd-8th week).

Fetal (9th week-birth).

What characterizes the germinal period of prenatal development?

• Begins with zygote formation.

• Duplicates and divides into a shell (placenta) and nucleus (embryo).

• 65% are lost during implantation.

What characterizes the embryonic period of prenatal development?

• Formation of the primitive streak [15] ➡ neural tube (future CNS) [22].

• Head and features start to form.

• Primitive hear beats.

• Basic organs and sexual development.

• 20% of embryo’s are lost due to chromosomal issues.

What causes sexual development in the embryonic period of prenatal development?

Influenced by hormones from chromosome pair 23.

What characterizes the fetal period of prenatal development?

• Rapid growth and brain maturation.

• *3 months, 3 inches, 3 ounces.

• Viability (potential to survive out of the womb) reached at 22 weeks.

• Third trimester: organs mature and reflexes develop.

• 27% of zygotes become living newborns.

What is viability? Why can’t a newborn under 22 weeks not survive outside of the womb?

Viability describes the potential of a preterm baby to survive outside of the womb.

Under 22 weeks, the brain cannot regulate vital functions ➡ infant death.

What % of zygotes are lost in the germinal period?

65%.

What % of offspring die in the embryonic period?

20%.

What % of offspring die in the fetal period?

5%.

True or False: Parents are to blame for a miscarriage.

False. Usually from chromosomal abnormality.

What role does cortisol play in prenatal development?

Helps prepare for labor.

What role does testosterone play in prenatal development?

Changes brain and skeleton development ➡ differences in hippocampus, amygdala, limb structures.

Male and female brain differences exist, but overlap is common. Most brains are a male/female _____.

Mosiac:

• Made up of both.

What hormone initiates birth?

A surge of oxytocin from the fetal brain.

How long is the labor period?

12 for first-time births, 7 for others.

True or False: Skull bones remain unfused to allow birth, and close soon after.

True.

How many weeks is considered a full-term birth?

38 weeks after conception.

What is the Apgar score?

A quick test to check a newborn’s physical condition and overall health after birth.

What does the Apgar score rate?

Color (Appearance), Pulse, Grimace (Cry), Activity (Muscle Tone), Respiration.

What Apgar score is healthy? Which are considered medical emergencies?

9-10 = healthy.

Less than 5 = medical emergency.

Preterm babies are MORE or LESS at risk for brain damage?

MORE

• Thin blood vessels / open fontanels.

True or False: After birth, newborns do not recognize their parents voices.

False.

Most newborns are healthy, a minority face life long impacts from…

• Inherited disorders.

• Chromosomal issues.

• Prenatal toxins.

• Poor nutrition.

• Complicated births.

What % of humans have a serious inherited condition?

8%

True or False: Serious inherited conditions are ONLY present at birth

False. Although some are present at birth, some are not apparent until later (dominant inherited conditions).

How many zygotes have more or fewer than 46 chromosomes? What does this cause?

Around half ➡ early miscarriage.

What is a trisomy?

When three copies of a chromosomes are present at one site instead of two.

What are some examples of trisomy’s?

• Trisomy 13 (Patau syndrome): around 1 in 10,000 births, fatal soon after birth.

• Trisomy 18 (Edwards syndrome): around 1 in 5,000, also usually fatal after birth.

• Trisomy 21 (Down syndrome): 1 in 700 births, survival rate much higher, distinct traits and lifelong impacts.

What are some traits of down syndrome?

• Round face.

• Slanted eyes.

• Unique hands/feet/fingerprints.

• Language delay.

• Atypical brain development.

What are some health challenges for people with down syndrome?

• Frequent heart and lung problems.

• Increased Alzheimer’s risk in middle age.

Why does down syndrome increase alzheimer’s risk?

Chromosome 21 carries a gene related to amyloid plaque.

What are some positive aspects about down syndrome?

Less depression or crying and reports of enjoying life (socializing, exercising, and learning).

True or False: Some people only have one X chromosome.

True. (XO).

• Some have extra too ➡ XXX, XXY, XYY

What do differing X chromosomes cause? What are some conditions?

Affects cognition, fertility, sexual maturation, and may shorten life span.

• Turner Syndrome (XO).

• Extra sex chromosomes (e.g., XXX, XXY).

What are some characteristics of Turner syndrome?

Wide neck, low hairline, short, absent puberty/secondary sexual characteristics; learning disabilities in math/spatial skills and sometimes recognizing emotions.

What are characteristics of extra sex chromosomes?

Often not diagnosed until fertility or puberty issues arise; cognitive impacts possible.

What are some characteristics of dominant gene disorders?

• Mild, severe ones tend to result in early death.

• Some persist b/c symptoms appear in adulthood after reproduction.

  • Huntington’s disease.

  • Marfan syndrome.

  • Early-onset alzheimer’s.

What are some characteristics of recessive disorders?

• More numerous; carriers are unaware they have the gene unless matched w/ another carrier.

• X-linked reccesive disorders:

  • Hemophilia.

  • Duchenne muscular dystrophy.

  • Fragile X syndrome (most common).

Is sickle-cell disease recessive or dominant? Why did it become so prevalent in Africa?

Recessive.

• Carriers are protected against malaria; those who express the phenotype/disaese have a double recessive.

Why do so many harmful genes remain in some populations?

They provided advantages in certain environments, think of sickle-cell disease.

Anxiety! both beneficial (awareness) and risky (disorders).

What is a teratogen?

Anything that increases prenatal risk such as drugs, viruses, pollutants, stress, and malnutrition.

Drinking alcohol during pregnancy can result in fetal alcohol syndrome or fetal alcohol effects. Explain their differences.

FAS: large amounts of alcohol early in development (change face shape).

FAE: large amounts of alcohol later in development (behavior/cognitive issues).

What is LBW? VLBW? ELBW?

Low Birth Weight: under 2,500g (5.5lbs).

Very Low Birth Weight = under 1,500g.

Extremely Low Birth Weight = under 1,000g.

What are causes of low birth weight?

• Preterm births (before 37 weeks) as there is less time to gain weight.

• Slow uterine growth (SGA: small for gestational age).

  • maternal malnutrition/illness/drug use, lack of care, pollution.

Why is LBW rising in the US?

Older maternal age, obesity, diabetes, cultural preferences, stress, etc.

What are the consequences of LBW?

Delayed milestones (walking, talking), cognitive behavioral problems.

Later in life ➡ higher rates of obesity, hypertension, kidney disease.

True or False: ELBW infants have lifelong neurological problems.

True.

True or False: In the US, immigrant mothers’ babies tend to have worse birth weight outcomes, possibly due to worse support from families/communities.

False ➡ better support from families/communities.

True or False: in poorer nations, many births occur at home.

True

Death rates are higher for home births, however if a trained attendant is present, they can actually be safer than giving birth at a hospital. Why is that?

Some hospitals are understaffed.

Why do people choose to have home births?

To allow more loved ones present and to reduce medical interventions ➡ reduces stress for the mother.

• Must be balanced, they must ensure trained attendant’s are present.

In the mid-20th century, high-income nations switched to isolated births rather than having loved ones present. What was the effect of this?

Mothers became more stressed and the need for medical interventions became greater.

Studies reveal that labor outcomes improve when a trusted person is present. What are some of those improvements?

Shorter labor, fewer complications, and happier parents.

What is a Doula?

Non-medical professionals who are trained to emotionally and physically support birthing parents, especially for vulnerable populations.

During Covid many hospitals excluded support people from being present during births, what did this cause?

• Surge in home births.

• Increased isolation.

C-sections are needed for about 10-15% of births, but rates in some nations can get range from 30-50%. Why is this bad?

People who don’t need c-sections get them ➡ unnecessary surgical risk.

Why do people decide to get c-sections without needing them?

Prior experiences, political values, culture, insurance type, etc.

What is postpartum depression?

Depression after birth that is triggered by hormonal changes and situational stress (finances, birth difficulties).