Unit 6 Study Guide (Condensed)

Homologous Chromosomes

Pairs of chromosomes carrying the same genes; one from each parent (23 pairs in humans).

Autosomes

Chromosomes 1–22; carry all traits except biological sex.

Sex Chromosomes

Chromosome pair 23; XX = female, XY = male.

Diploid (2n)

46 chromosomes; normal number in somatic (body) cells.

Haploid (n)

23 chromosomes; normal number in gametes (sperm and egg).

Gametes

Haploid sex cells produced by meiosis (sperm and ova).

Somatic Cells

Diploid body cells produced by mitosis.

Allele

Different form of a gene.

Locus

The specific location of a gene on a chromosome.

Meiosis

Type of cell division that produces four haploid gametes and reduces chromosome number by half.

Purpose of Meiosis

Produce gametes and maintain chromosome number after fertilization.

Where does meiosis occur?

Gonads (testes and ovaries).

Mitosis vs. Meiosis

Mitosis makes body cells; meiosis makes sex cells.

Homozygous

Two identical alleles (AA or aa).

Heterozygous

Two different alleles (Aa).

Dominant Allele

Masks the expression of a recessive allele; represented by a capital letter.

Recessive Allele

Expressed only when two recessive alleles are present; lowercase letter.

Genotype

Genetic makeup (AA, Aa, aa).

Phenotype

Physical expression of a trait.

Four Sources of Genetic Variation

Segregation, independent assortment, crossing over, random fertilization.

Segregation

Separation of homologous chromosomes during meiosis I.

Independent Assortment

Random distribution of chromosomes into gametes during meiosis.

Crossing Over

Exchange of DNA between homologous chromosomes during meiosis I.

Random Fertilization

Any sperm can fertilize any egg, increasing variation.

Punnett Square

Diagram used to predict offspring genotypes and phenotypes.

Monohybrid Cross

Cross involving one trait.

Aa × Aa Genotypic Ratio

1 AA : 2 Aa : 1 aa.

Aa × Aa Phenotypic Ratio

3 dominant : 1 recessive.

Dominant Inheritance

Only one dominant allele is needed for the trait to appear.

Recessive Inheritance

Requires two recessive alleles for the trait to appear.

Incomplete Dominance

Heterozygote shows an intermediate phenotype.

Codominance

Both alleles are fully expressed.

ABO Blood Type Alleles

IA, IB, i.

Type A Genotypes

IAIA or IAi.

Type B Genotypes

IBIB or IBi.

Type AB Genotype

IAIB.

Type O Genotype

ii.

Rh Positive

Dominant trait.

Rh Negative

Recessive trait.

Sex Determination

Father determines baby's sex by contributing either X or Y chromosome.

X-Linked Recessive Disorders

Hemophilia and red-green color blindness; more common in males.

Female Gonads

Ovaries.

Functions of Ovaries

Produce oocytes, estrogen, and progesterone.

Site of Fertilization

Ampulla of the uterine (fallopian) tube.

Fimbriae

Finger-like projections that sweep the oocyte into the uterine tube.

Functions of the Uterus

Receives, nourishes, and protects the developing embryo/fetus.

Endometrium

Inner uterine lining; implantation occurs here; shed during menstruation.

Myometrium

Thick smooth muscle layer responsible for labor contractions.

Perimetrium

Outermost serous layer of the uterus.

Cervix

Inferior opening of the uterus into the vagina.

Vagina

Birth canal, passage for menstrual flow, and copulatory organ.

Vulva

External female genitalia.

Bartholin's Glands

Produce mucus for lubrication.

GnRH

Released by the hypothalamus; stimulates FSH and LH release.

FSH (Female)

Stimulates follicle development and estrogen production.

LH (Female)

Triggers ovulation and corpus luteum formation.

Estrogen

Builds the endometrium and develops female secondary sex characteristics.

Progesterone

Prepares and maintains the uterus for pregnancy.

hCG

Produced by the placenta; maintains the corpus luteum and is detected by pregnancy tests.

Ovarian Cycle Phases

Follicular → Ovulation → Luteal.

Follicular Phase

Days 1–14; follicles develop and estrogen rises.

Ovulation

Occurs around Day 14; triggered by LH surge.

Luteal Phase

Days 14–28; corpus luteum secretes progesterone.

Menstrual Cycle Phases

Menstrual → Proliferative → Secretory.

Menstrual Phase

Days 1–5; shedding of the endometrium.

Proliferative Phase

Days 6–14; estrogen rebuilds the endometrium.

Secretory Phase

Days 15–28; progesterone prepares uterus for implantation.

Male Gonads

Testes.

Functions of Testes

Produce sperm and testosterone.

Seminiferous Tubules

Site of spermatogenesis.

Leydig Cells

Produce testosterone.

Sertoli (Sustentacular) Cells

Support developing sperm, form the blood-testis barrier, and secrete inhibin.

Blood-Testis Barrier

Protects developing sperm from the immune system.

Epididymis

Site where sperm mature and are stored.

Vas (Ductus) Deferens

Transports sperm from epididymis.

Ejaculatory Duct

Formed by vas deferens and seminal vesicle duct; empties into urethra.

Urethra (Male)

Passageway for urine and semen.

Seminal Vesicles

Produce about 70% of semen; rich in fructose.

Prostate Gland

Adds milky fluid that activates sperm.

Bulbourethral Glands

Produce lubricating mucus and neutralize acidic urine.

FSH (Male)

Acts on Sertoli cells to stimulate spermatogenesis.

LH (Male)

Acts on Leydig cells to stimulate testosterone production.

Testosterone

Promotes spermatogenesis and male secondary sex characteristics.

Inhibin

Inhibits FSH release.

Spermatogenesis

Production of sperm in seminiferous tubules; begins at puberty.

One Primary Spermatocyte Produces

4 sperm cells.

Spermiogenesis

Conversion of spermatids into mature sperm.

Structure of Sperm

Head (DNA/acrosome), midpiece (mitochondria), tail (flagellum).

Normal Semen Volume

Approximately 2–5 mL per ejaculation.

Normal Sperm Count

20–150 million sperm per mL.

Capacitation

Process that enables sperm to fertilize an egg.

Acrosome Reaction

Enzymes digest the zona pellucida so sperm can enter the oocyte.

Polyspermy

Fertilization by more than one sperm; prevented by fast and slow blocks.

Zygote

Single diploid cell formed after fertilization.

Order of Early Development

Zygote → Morula → Blastocyst → Implantation → Embryo → Fetus.

Morula

Solid ball of cells formed around days 3–4.

Blastocyst

Hollow ball of cells that implants into the uterus.

Implantation

Blastocyst embeds into the endometrium about 7 days after fertilization.

Embryo

Developing offspring from fertilization through week 8.

Fetus

Developing offspring from week 9 until birth.