BIOL 1203 FINAL: Weeks 1-13

Gene

A sequence of DNA in a specific location in the genome that controls a particular character. E.g. hair color

Allele

Alternative form of a gene that codes for a trait. E.g. red hair

Genome

The total genetic content in an organism

Chromatin

A mixture made of DNA and proteins (histones) that packages DNA strands into a compact structure

Chromatid

One half of a duplicated chromosome

Sister chromatids

Two halves of a duplicated chromosome

What do chromatids condense into?

They condense into chromosomes

Central Dogma of Life

DNA →(transcription)→ RNA →(translation)→ proteins

Genetic code

A triplet of nucleotides that code for specific amino acids. E.g. AUA, GCU, GCC

How many chromosomes in somatic (body) cells

46 chromosomes → 23 pairs, with 23 chromosomes from mother and 23 from father

Autosome

Any chromosome that is not a sex chromosome

Sex chromosomes

Females → XX, Males → X Y

Karyotype

A complete profile of a person’s chromosomes. Matched using centromere location, size, and banding pattern

Meiosis

Cell division that creates four unique sex cells, reducing the chromosome number by 46 to 23

Mitosis

Cell division that creates two identical daughter cells

Diploid cell

A cell containing 2 sets of chromosomes (2n)

Haploid cell

A cell containing 1 set of chromosomes (n)

What holds together duplicated chromatids?

Centromeres hold them together

Zygote

The very first cell formed when a female egg and male sperm join during fertilization

4 phases of mitosis (PMAT)

Prophase → Metaphase → Anaphase → Telophase

Events of prophase (mitosis)

1. Chromatin condenses into chromosomes

2. A mitotic spindle forms

3. The nuclear envelope breaks down

Events of metaphase (mitosis)

The chromosomes align at the metaphase plate/middle

Events of anaphase (mitosis)

1. The centromeres split

2. Each member of a chromatid pair moves to opposite sides of the cell

Events of telophase (mitosis)

1. Chromosomes revert back to chromatin form

2. Nuclear envelope forms around each chromatin mass

3. Mitotic spindle breaks

4. Cytokinesis follows

Cytokinesis

Division of cytoplasm

Prophase I (meiosis)

Chromatin condenses, homologous chromosomes exhange DNA between non-sister chromatids

Metaphase I (meiosis)

The chromosomes line up in homologous pairs

Anaphase I (meiosis)

Homologous chromosomes come apart, so each cell gets one member of homologous pair

Telophase I (meiosis)

Cells split apart and two haploid cells form

Prophase II (meiosis)

New spindle forms in each of the two cells

Metaphase II (meiosis)

Chromosomes align on the metaphase plate

Anaphase II (meiosis)

Sister chromatids of each chromosome come apart, and move to opposite ends of cell as daughter chromosomes

Telophase II (meiosis)

Cells split apart, forming four unique haploid cells

Crossing over

Occurs during prophase I meiosis. Homologous chromosomes pair off, and non-sister chromatids exchange genes

Independent assortment

Occurs during metaphase I of meiosis. Homologous chromosomes independently line up on either side of the metaphase plate, causing “random shuffling”

Character

A heritable, observable feature (hair color, eye color)

Trait

A variant of a character (red hair, black eyes)

Dominant alleles

Allele that only requires one copy to express the trait. “A”

Recessive alleles

Allele that requires two copies to express the trait. May be masked by a dominant allele. “a”

Homozygous dominant

Two dominant alleles on homologous chromosomes. “AA”

Homozygous recessive

Two recessive alleles on homologous chromosomes. “aa”

Heterozygous

Different alleles on homologous chromosomes. “Aa”

Genotype

Genetic makeup of an individual

Phenotype

The observable physical characteristics of an individual, determined by genetics and environmental influences. Result of genotype + environment

Autosomal recessive inheritance

Pattern where a genetic trait or condition only appears when a child inherits two copies of a mutated gene

Sex-linked genes

Genes that are located on either sex chromosome

Point mutation

A single nucleotide base change. E.g. missense, nonsense, silent

Frameshift mutation

Insertion or deletion of a nucleotide, causing a shift

Albinism

Disorder caused by lack of melanin causing visual problems and sensitivity to UV radiation. Caused by inability of melanocytes to produce tyrosinase, which converts tyrosine to melanin

Phenylketonuria

Disorder caused by inability to make phenylalanine hydroxylase which converts phenylalanine to tyrosine. Leads to toxic buildup of phenylalanine and brain damage

Tay-Sachs disease

Disorder caused by ganglioside accumualtion in nerve cell membranes, causing abnormailities of mental development

Recessive lethal allele

Allele where if two copies (homozygous dominant) are inherited, it is embryonic lethal

Nondisjunction

Failure of homologous chromosomes or sister chromatids to separate properly during meiosis

Aneuploidy

When gametes produce an abnormal zygote following nondisjunction. Causes addition or deletion of chromosomes. E.g. down syndrome

Down syndrome

Syndrome caused by an additional chromosome 21. Causes mental delay. 47, XY, +21 or 47, XY, +21

Turner syndrome

Absence of one X chromosome. Causes lack of secondary sex characteristic development. 45, X

Klinefelter syndrome

Extra X chromosome (trisomy) in males. Causes long limbs and sterility. 47, XXY

Huntington’s disease

Autosomal dominant inherited neurodegenerative condition. Causes nerve cell breakdown in the brain

Main function of the male reproductive tract

To produce and introduce sperm into the female reproductive tract, where fertilization occurs

What do testes produce?

Testosterone and sperm (65-75 days, 300 million sperm cells produced daily)

Why is the scrotum outside of the body cavity?

Because a lower temperature is needed for sperm survival

Pathway of sperm

Epididymis → vas deferens → ejaculatory duct → urethra

Epididymis

Organ located posteriorly to the testes, where sperm matures and is stored for up to 4 weeks

Vas deferens

Transports sperm to the ejaculatory duct. May also store sperm for several months

Ejaculatory duct

Site where contents from the seminal vesicles and vas deferens merge

Urethra

Final duct that carries semen (and urine) out of the penis. Contains three regions: Prostatic, intermediate, spongy

Seminal vesicles

Secretes an alkaline and viscous fluid that neutralizes the acidic female environment. High in fructose, to supply sperm with ATP

Prostate gland

Chestnut-sized gland that produces a milky, acidic substance. Contains citric acid (for ATP), and enzymes and prostaglandins that help sperm mobility and viability

Bulbourethral (Cowper’s) gland

Secretes alkaline (neutralizes acidic urine in urethra and vagina) mucous for lubrication

What does the parasympathetic reflex in the penis cause?

Erection through dilation of arterioles in erectile tissue

What does the sympathetic reflex in the penis cause?

Ejaculation, through propulsion of semen by peristalsis and contraction of urethral and penile muscles

What do the ovaries produce?

Ova (eggs), estrogen, and progesterone

Uterine/fallopian tubes

Site of fertilization and transport of ovum/zygote to uterus

What happens when a fertilized egg implants outside the uterus?

An ectopic (non-viable) pregnancy occurs

Three layers of the uterine wall (innermost to outermost)

Endometrium → myometrium → perimetrium

Endometrium

Mucosal lining of the uterine cavity, sheds during menstruation

Layers of endometrium

Stratum functionalis (sheds at menstruation) and stratum basalis (always stays)

Myometrium

Middle layer of uterine wall, contains layers of smooth muscle

Perimetrium

Outermost serous layer of visceral peritoneum (uterine wall)

Function of Bartholin’s (side of vaginal orfice) and Skene’s (side of urethral orfice) glands

Has a mucous secretion that acts as lubricant

Approximately how long does each female reproductive cycle last?

About 28 days

How many primary follicles in each ovary?

About 200k promary follicles

How often and how many eggs mature and are released in the ovarian cycle?

One mature egg is released approximately every 28 days

What hormones regulate the ovarian cycle?

GnRH, FSH, LH, estrogen, and progesterone

Ovarian cycle (day 1-13) hormonal action

Hypothalamus secretes GnRH, a. pituitary secretes FSH and LH. Then, estrogen produced by a follicle acts on hypothalamus to stop FSH and LH secretion.

Ovarian cycle (day 1-13) follicle action

4-5 primary follicles begin development → all primary follicles except for one degenerate → the remaining follicle becomes a secondary follicle

What occurs at around day 6 of ovulation to the secondary follicle?

A single tertiary follicle grows and the fluid inside increases

Graafian follicle

Mature follicle found in the ovaries

When does ovulation occur (approximately)?

Day 14

Ovarian cycle: day 14 ovulation hormonal events

Estrogen levels peak → positive feedback on hypothalamus → increased LH → LH peaks → ovulation occurs

How is the egg released during ovulation?

The follicle bursts, and the ovum is released into the fallopian tube

What does LH transform the ruptured follicle into?

LH transforms the ruptured follicle into a corpus luteum. It produces progesterone and estrogen

What hormone is measured with pregnancy tests?

hCG (human chorionic gonadotropin) is measured, produced by developing placenta

When does the corpus luteum degenerate and the placenta takes over estrogen and progesterone production?

At around 4 months, when the placenta becomes well-developed

Which hormone maintains the corpus luteum?

hCG, produced by developing placenta

What occurs during the Luteal phase that leads to inhibition of GnRH (FSH and LH)?

High levels of progesterone and decreasing levels of estrogen leads to inhibition of GnRH (and thus FSH and LH)

If the egg is not fertilized, what happens to the corpus luteum?

The corpus luteum degrades and becomes the corpus albicans. Progesterone is no longer produced

What is the menstrual (uterine) cycle?

It is a series of changes the uterine endometrium undergoes each month in response to ovarian hormones in the blood

Phases of the menstrual (uterine) cycle

Menstrual (days 1-5) → proliferative (days 6-14) → secretory (days 15-28)

Menstrual (menses) phase of menstrual cycle

The uterus sheds stratum functionalis (in absence of fertilized egg); low levels of estrogen and progesterone. Happens in days 1-5