Biology Unit 2

somatic cells

the body cells that continue to undergo cell division even as an adult

cell division

enables a single-celled fertilized egg grow into an organism with trillions of cells

apoptosis

programmed cell death, cell passes through typical series of events that brings about cell destruction

cell cycle

the order sequence of stages that occurs between the time a cell divides and the time the resulting daughter cells also divide

interphase

divided into three stages G1, S, and G2

G1

stage before DNA synthesis, cell doubles its organelles and accumulates material for DNA synthesis

G0

occurs in some cells: pause and carry out normal functions but don’t prepare to divide

S

DNA synthesis, DNA replication occurs

G2

stage after DNA synthesis, the cell synthesizes proteins for cell division

Mitotic stage

Mitosis and cytokinesis

Mitosis

division of the nucleus, the sister chromatids separate into daughter chromosomes

Cytokinesis

division of the cytoplasm, two daughter cells that are identical to the mother cell are the result

chromatid

chromosome with one DNA molecule

sister chromatids

two DNA molecules

eukaryotic cells

have a complex system for regulating the cell cycle

internal signals

what the cell cycle is controlled by; helps control timing of events

cyclin

a protein that acts as an internal timekeeper for the cell

external signals

tell the cell whether or not to divide

checkpoints

G1, G2, and M; critical for preventing cancer development

G1

checks if the DNA is damaged

G2

checks if the DNA replication is complete

M

checks to see if the chromosomes are going to be properly distributed

mammalian cells

enter the cell cycle only when stimulated by an external factor

growth factors

signals that set into motion the events associated with entering the cell cycle

proto-oncogenes

encode proteins that promote the cell cycle and prevent apoptosis; mutate to become oncogenes

oncogenes

cancer-causing genes

tumor-suppressor genes

encode proteins that stop the cell cycle and promote apoptosis; gene products no longer inhibit cell cycle

chromatin

what eukaryotic chromosomes are composed of; a combination of DNA and protein mostly histones

histones

play a role in coiling DNA tightly

diploid (2n)

cells have two (a pair) of each type of chromosome (human body cells = 46 in 23 pairs)

haploid (1n)

cells have only one of each type of chromosome (half the diploid #) (human eggs or sperm = 23 or 1 member of each pair)

centromere

holds together sister chromatids

meristematic tissues

where mitosis occurs in plant cells

cleavage furrow

forms between daughter nucleus and then two ends pull apart

meiosis

occurs in the life cycle of sexually reproducing organisms; reduces the chromosome number in half; provides offspring with a different combination of traits from that of either parent

fertilization

daughter cells of meiosis mature into gametes; gametes fuse together; restores the diploid number (n+n =2n); creates a cell that will develop into a new individual

gametes

sperm and eggs (sex cells)

genetic variation

produces cells no longer identical to parental cell; occurs in two ways, crossing-over and independent assortment; main advantage of sexual reproduction

crossing-over

between non sister chromatids

independent assortment

sorts chromosomes during anaphase I

DNA replication

occurs only once prior to either meiosis or mitosis

zygote

result of fertilization; has a diploid (2n) number of chromosomes

spermatogenesis

produces sperm: meiosis in the testes of males

oogenesis

produces eggs; meiosis in the ovaries of females; begins in the ovaries as a fetus and resumes at puberty

genetics

explains the process of inheritance and why there are variations between offspring from one generation to the next

Gregor Mendel

our understanding of genetics is based on his work; investigated inheritance in plants in the 1860s; concluded that plats transmit distinct factors to offspring

homologous chromosomes

chromosomes that come in pairs

alleles

alternate forms of a gene for a trait

locus

where alleles for a particular gene are found

law of segregation

factors segregate during the formation of gametes; each gamete contains only one factor from each pair of factors; fertilization gives each new individual two factors for each trait

phenotype

an individuals actual appearance; may include physical characteristics to microscopic and metabolic characteristics

genotype

alleles carried by the chromosomes that are responsible for a given trait

diploid organisms

a pair of homologous chromosomes that contain two alleles for each trait; one allele is on each member of the homologous pair

dominant allele

symbolized by a capital letter; refers to the allele that will mask the expression of the alternate (recessive) allele when both are present in a given organism

recessive allele

symbolized by a lowercase letter

homozygous

the two alleles are the same

heterozygous

the two alleles are different

monohybrid

considering one trait at a time instead of two three or more simultaneously

law of independent assortment

each pair of factors assorts independently; all possible combinations of factors can occur in the gametes

pedigree

a chart of family history with regard to a particular genetic trait

tay sachs disease

autosomal recessive disorder

cystic fibrosis

autosomal recessive disorder

phenylketonuria

autosomal recessive disorder

sickle cell disease

autosomal recessive disorder

marfan syndrom

autosomal dominant disorder

huntingtons disease

autosomal dominant disorder

osteogenesis imperfecta

autosomal dominant disorder

autosomal dominant disorders

the child is unaffected but the parents are both affected; possible if the condition is autosomal dominant and the parents are heterozygotes

autosomal recessive disorder

the child is affected but neither parent is; the parents are carriers because they are unaffected but are capable of having a child with the genetic disorder

incomplete dominance

occurs when the heterozygote has an intermediate phenotype between the two homozygotes

multiple alleles

the gene exists in several allelic forms

polygenic inheritance

occurs when a trait is governed by two or more genes

environmental influences

nutrition or temperature can influence the expression of genetic traits

gene linkage

a single chromosome contains many alleles in a definite fixed order

sex linked traits

controlled by genes on the sex chromosome

x-linked genes

found on the x chromosome

y-linked genes

found on the y chromosome

color blindness

x-linked recessive disorder

Duchenne muscular dystrophy

x-linked recessive disorder

fragile x syndrome

x-linked recessive disorder

hemophilia

x-linked recessive disorder

karyotype

chromosomes arranged by pairs according to their size and general appearance

nondisjunction

failure of chromosomes or sister chromatids to separate during meiosis

trisomy

a chromosome is present in three copies

monosomy

a chromosome is present in one copy

down syndrome

trisomy 21

barr body

one of the X chromosomes in females that is inactivated and becomes a darkly stained mass

turner syndrome

changes in sex chromosome number

klinefelter syndrome

changes in sex chromosome number

poly-x females

changes in sex chromosome number

jacobs syndrome

changes in sex chromosome number

chromosomal mutations

occur when chromosomes break; environmental agents

deletion

occurs when a single break causes a chromosome to lose an end piece or when two simultaneous breaks lead to the loss of an internal chromosomal segment

duplication

a chromosomal segment occurs more than once in the same chromsome

translocation

the movement of a chromosome segment from one chromosome to another nonhomologous chromosome

inversions

a segment of a chromosome turned 180 degrees

DNA

deoxyribonucleic acid; genetic material; chain of nucleotides

James Watson and Francis H C Crick

determined the structure of DNA in 1953

nucleotide

a complex of three units: phosphoric acid, a pentose sugar, and a nitrogen-containing base

dna replication

the process of copying one DNA double helix into two identical double helices; semiconservative