BJU Press Biology Chapter 8--Basic Genetics

chromosomes

made up of condensed chromatids

chromatin

a cell’s genetic material

histones

proteins that chromatin coils around

genes

code for specific proteins to create certain characteristics in an organism

chromatid

each half of a duplicated chromosome

centromere

keeps the chromatids together and breaks them apart at the right times

sex chromosomes

determine whether an organism will be male or female

the two human sex chromosomes

X and Y

autosomes

chromosomes that don’t determine an organism’s gender/sex, contains most of the organism’s genes

humans have __ autosomes

44

humans have __ sets of autosomes

22

karyotype

an image of ordered chromosomes taken under a microscope

homologous

having the same proportions

diploid

organisms that have homologous pairs of chromosomes

haploid

organisms with just one set of chromosomes

diploid cell =

2n

haploid cell =

n

cell cycle

the process of cell growth

the three stages of the cell cycle

interphase, mitosis, and cytokinesis

interphase

phase where the cell spends most of its time. at the end of interphase, the tetraploid cell with its extra organelles, proteins, and chromosomes is ready for mitosis and cytokinesis

the four phases of mitosis

prophase, metaphase, anaphase, telophase

prophase

the centrosomes are carried to opposite ends of the cell by protein motors, then are assembled with fibers from the cytoskeleton into the mitotic spindle, chromatin coils into visible chromosomes in the nucleus, the nucleolus is disassembled, and the membrane around the nucleus breaks down to release the chromosomes

mitotic spindle

a structure formed during prophase that align and separates chromosomes in later phases

metaphase

begins when the mitotic spindle fibers attach to the proteins on the centromere of each chromosome, pull the chromosomes to align them along the equatorial plane

equatorial plane

an imaginary line that goes down the cell

anaphase

the centromeres send out signals to split the centromeres in half, the mitotic spindle pulls the chromatids towards the centromeres

telophase

the chromatids are now their own chromosomes, the nucleus begins to reform around them, nucleolus begins to reassemble and the chromosomes uncoil to become chromatin again, mitotic spindle in the cytoplasm assembles

cytokinesis

the cell divides the contents of its cytoplasm, forms a contractile ring between the two nuclei, pinches them into two separate cells, resulting in two genetically identical daughter cells

contractile ring

forms around the cell and splits it into two

meiosis

occurs during sexual reproduction, forms haploid gametes, doubles the chromosomes and cytoplasmic proteins and organelles

phases of meiosis

prophase I, metaphase I, anaphase I, telophase I, cytokinesis, prophase II, metaphase II, anaphase II, telophase II, cytokinesis

prophase I

membrane around the nucleus dissolves, chromosomes join to make tetrads, exchange genes in the process of crossing over, centromeres migrate and spindle forms

metaphase I

spindle fibers align tetrads on equatorial plane

anaphase I

spindles separate each tetrad and pulls whole chromosomes towards the centromeres instead of individual chromatids

telophase I and cytokinesis

nucleus reforms around each haploid chromosome set, cytoplasm is divided, cell is pinched into two

prophase II

immediately after cell division, spindle re-forms to begin meiosis II

metaphase II

spindle fibers align chromosomes on equatorial plane

anaphase II

chromosome centromeres split, spindles pulls chromatids towards centromeres

telophase II and cytokinesis

the nucleus re-forms around the haploid chromosome sets, resulting in four genetically different cells

Average human and mammal cells take about ______ to go through the cell cycle

24 hours

gametes

haploid cells that unite to form zygotes

zygotes

a diploid cell that is genetically different from either parent

asexual reproduction

a process that produces offspring that are genetically identical to their parents, used by many plants

sexual reproduction

a process that occurs when two haploid cells join to form a genetically different diploid zygote

heredity

the passing of traits from one generation to another

factor

contributed by both parent plants

dominant traits

expressed trait

recessive traits

the trait that isn’t expressed

alleles

the different forms a gene can have

homozygous

has the same alleles for a trait; purebred

heterozygous

has two different alleles for a gene; hybrid

genotype

an organism’s genetic makeup

phenotype

the physical expression of a trait

Punnett squares

squares drawn that show different ways alleles can segregate

monohybrid cross

a cross that only tests one set of alleles

dihybrid cross

the crossing of two sets of alleles

pedigree

a family history that charts a hereditary trait through past generations

incomplete dominance

the blending of alleles

codominance

when both alleles are expressed

example of multiple alleles

human blood type

polygenic inheritance

two or more genes working together to express a trait

sex-linked traits

traits determine by the sex chromosomes

most of an organism;s traits are determined by its _____

autosomes

carriers

organisms that carry an allele but don’t express it

gene expression

the process in which genetic information is activated to make a genetic product

promoters

little sequences of DNA that come before each gene and tell the RNA polymerase molecule where to bind to begin copying the gene into a strand of mRNA

TATA box

a promoter that binds to a group of transcription proteins that are attached to RNA polymerase

enhancers and silencers

attach to promoters in front of genes and act like switches

hormone-activated traits

when hormones bind with the DNA during transcription and activate genes that had not been activated before

transcription can be affected by:

light, temperature, hormones, chemicals

cell differentiation

the process in which zygotes are changed to perform more specialized tasks

totipotent

the cell has the potential to be any kind of cell

pluripotent

the cell is capable of producing many kinds of cells but not all

homeotic genes

a special set of genes in a baby’s cells that produce each kind of cell needed

stem cells

cells that have not differentiated into specialized cells

embryo

the early stage of an unborn young of a multicellular organism

somatic stem cells

“adult” stem cells