Chapter 2 - Kaplan MCAT Biology Review

2025-2026

haploid

-n

-one copy of each chromosome

germ cells are (haploid/diploid)

haploid

diploid

-2n

-2 copies of each chromosome

autosomal cells are (haploid/diploid)

diploid

cell cycle

G0, G1, S, G2, M

G0 stage

cell performs its functions without dividing

interphase

-G1, S, G2

-actively diving cells spend 90% of time here

G1 stage

-presynthetic gap

-cells create organelles for energy and protein production & increase their size

first restriction point in cell cycle

quality checkpoint at G1/S

S stage

-synthesis

-DNA is replicated

-chromatids held together at centromere

G2 stage

-postsynthetic gap

-further cell growth and replication of organelles

second restriction point in cell cycle

quality checkpoint at G2/M

M stage

-mitosis

-mitosis and cytokinesis occur

restriction points in cell cycle

quality checkpoint

restriction points are controlled by

protein p53

molecules responsible for cell cycle are

cyclins and cyclin-dependent kinases (CDK)

when cyclins bind to CDKs

they phosphorylate and activate transcription factors for next stage of cell cycle

cyclins and CDKs rise and fall during

cell cycle

common mutation to cause cancer

P53 —> TP53

cancer occurs when cell cycle control becomes irregular, allowing

damages cells to undergo mitosis

cancer cells can undergo ______, causing tumors

rapid cell division

metastasize

when cancer cells spread through blood/lymphatic system

mitosis phases

-prophase

-metaphase

-anaphase

-telophase, cytokinesis

prophase

-chromosomes condense

-nuclear membrane dissolves

-nucleoli disappear

-centrioles migrate to opposite sides of cell

-spindle apparatus begins to form

spindle apparatus also called

kinetochore fibers

kinetochores

protein structures located on centromeres, attachment points for fibers of spindle apparatus

metaphase

chromosomes line up along metaphase plate

equatorial plate

metaphase plate

anaphase

sister chromatids are separated and pulled to opposite poles

telophase

-nuclear membrane re-forms

-spindle apparatus disappears

-cytosol + organelles split between 2 daughter cells

cytokinesis

-end of telophase

-separation of cytoplasm and organelles

meiosis occurs in

gametocytes (germ cells)

meiosis produces up to _ non-identical haploid sex cells (gametes)

4

meiosis phases

-Meiosis I

• prophase I

• metaphase I

• anaphase I

• telophase I

-Meiosis II

• prophase II

• metaphase II

• anaphase II

• telophase II

meiosis has __ round(s) of replication and _ round(s) of division

1, 2

Meiosis I

homologous parts of chromosomes (homologues) are separated

homologues

chromosomes given same number but are of opposite parental origin

prophase I

same as prophase but homologues come together and intertwine

synapsis

when homologues come together and intertwine

tetras

the 4 chromatids of prophase 1

crossing over

the exchange of genetic material between one chromatid and material from a chromatid in the homologous chromosome

crossing over explains

mendels second law (of independent assortment)

mendels second law

the inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes

metaphase 1

homologous chromosomes line up on opposite sides of the metaphase plate

anaphase 1

homologous chromosomes are pulled to opposite poles of the cell (disjunction)

disjunction

the process of homologous chromosomes being pulled to opposite poles of the cell

anaphase 1 accounts for

mendels first law (of segregation)

mendels first law

during the formation of gametes, each organism’s 2 copies of a particular gene separate in gamete formation and only one copy is passed to offspring

telophase 1

the chromosomes may or may not fully decondense and the cell may enter interkinesis after cytokinesis

interkinesis

rest period

meiosis II

sister chromatids are separated from each other in a process functionally identical to mitosis

sister chromatids

copies of the same DNA held together at centromere

prophase 2

-nuclear envelope dissolves

-nucleoli disappear

-centrioles migrate to opposite poles

-spindle apparatus begins to form

sex is determines by the ___ chromosome pair

23rd

XX

female

XY

male

x chromosome

carries lots of genetic info

mutations of x-linked genes can cause ____ (even if only one recessive disease carrying allele)

sex-linked disorders

females with one copy of mutated X-linked gene are

carriers

y chromosome

-carries little genetic info

-contains SRY

SRY

-sex-determining region Y

-causes gonads to differentiate into testes

sperm develop in the

seminiferous tubules

seminiferous tubules are in the

testes

sperm is nourished by

sertoli cells

interstitial cells of leydig

-in testes

-secrete testosterone and androgens

testes are located in

scrotum

scrotum location

outside abdominal cavity

scrotum has a ___ temp that rest of body

lower

once formed, sperm gain motility in the

epidymis

sperm is stored in ____ until ejaculation

epidymis

during ejaculation, sperm travels through the ____ to the ____ to the ____ and out through the penis

-vas deferens

-ejaculatory duct

-urethra

seminal vesicles

contribute fructose to nourish sperm and produce alkaline fluid

prostate gland

produces alkaline fluid

bulbourethral glands

produces clear viscous fluid that cleans out any urine and lubricates urethra

semen is composed of

sperm and seminal fluid

spermatogenesis

4 haploid sperm are produced from a spermatogonium (meiosis)

after S stage, germ cells are called

primary spermatocytes

after meiosis 1, germ cells are called

secondary spermatocytes

after meiosis 2, germ cells are called

spermatids

after maturation, germ cells are called

spermatozoa

sperm physically contains

-head

-midpiece

-flagellum

sperm head

contains the genetic material and is covered w an acrosome

acrosome

-modified golgi apparatus

-contains enzymes that help the sperm fuse with and penetrate the ovum

sperm midpiece

-generates ATP from fructose

-contains many mitochondria

sperm flagellum

promotes motility

ova

eggs

ova are produced in

follicles in the ovaries

once each month, an egg is ___

ovulated

eggs are ovulated into the

peritoneal sac

from the peritoneal sac, eggs are drawn to the ____ or ___

fallopian tube or oviduct

fallopian tubes are connected to the

uterus

lower end of uterus is

cervix

vaginal canal lies below the

cervix

vaginal canal

-where sperm are deposited during intercourse

-site of childbirth

external parts of female genital organs are collectively known as the

vulva

oogenesis

one haploid ovum and a number of polar bodies are formed from an oogonium (meiosis)

at birth, all oogonia have already undergone

replication

at birth all oogonia are considered

primary oocytes

primary oocytes are arrested in

prophase 1

ovulated egg each month is a

secondary oocyte