AP Bio Unit 5

heredity

transmission of traits from one generation to the next

genes

hereditary units containing coded information that account for resemblances

gametes

reproductive cells, have only half the number of chromosomes as body cells

somatic cells

body cells with 46 chromosomes

locus

a gene's specific location along the length of a chromosome

asexual reproduction

a single individual is the sole parent and passes copies of all its genes to its offspring without the fusion of gametes

sexual reproduction

two parents give rise to offspring that have unique combinations of genes inherited from the two parents

homologous chromosomes

chromosomes with the same length, centromere position and staining position

autosomes

Chromosomes that do not determine the sex of an individual

diploid cell

cell with two sets of chromosomes (2n)

haploid cell

single set of chromosomes (n)

zygote

a fertilized egg, diploid cell

meiosis

a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.

crossing over

genetic rearrangement between non-sister chromatids involving the exchange of corresponding segments of DNA molecules

chiasmata

point where a crossover has occurred, and appears as a cross because the original sister chromatids are still held together

metaphase I

chromosomes line up by homologous pairs

anaphase I

each pair of homologous chromosomes separates but the sister chromatids are still attached

telophase I and cytokinesis

two haploid cells form; each chromosome consists of two sister chromatids

prophase II

spindle apparatus forms, chromosomes move to metaphase II plate

metaphase II

kinetochores of sister chromatids separate and move toward opposite poles as individual chromosomes

telophase II and cytokinesis

four genetically distant haploid cells form

trait

each variant for a characteristic (ex: purple/white)

true-breeding

produce only the same variety as the parent plant

hybridization

mating of two true-breeding varieties

alleles

alternative versions of genes that account for variations in inherited characters (DNA sequence variations)

law of segregation

two alleles for a heritable character segregate during gamete formation and end up in different gametes (the egg/sperm only gets one of two alleles)

punnett square

A chart that shows all the possible combinations of alleles that can result from a genetic cross

homozygous

having a pair of identical alleles for a gene

heterozygous

having two different alleles for a gene

phenotype

appearance/observable traits

genotype

genetic makeup

testcross

breeding an organism of unknown genotype with a recessive homozygote to reveal genotype

monohybrid cross

cross between two heterozygotes for one trait

dihybrid cross

heterozygous for two traits being followed in a cross

law of independent assortment

each pair of alleles segregates independently of each other pair of alleles during gamete formation

multiplication rule

to determine probability, multiply the probabilities of two events

addition rule

the probability that any one of two mutually exclusive events will occur is calculated by adding their individual probabilities

complete dominance

phenotypes of the heterozygote and the dominant homozygote are indistinguishable

incomplete dominance

neither allele is completely dominant and the phenotype is somewhere between those of the two parental varieties

codominance

two alleles affect a phenotype in separate, distinguishable ways

pleiotropy

genes have multiple phenotypic effects

epistasis

phenotypic expression of a gene at one locus alters that of a gene at a second locus

ex: one gene in labs dictates brown/black color, another gene designates pigment deposition

polygenic inheritance

additive effect of two or more genes on a single phenotypic character

pedigree

family tree describing the traits of parents and children across generations

cystic fibrosis

-recessive

-caused by defective or absent chloride transport channels in the membrane and leads to a buildup of mucus in organs

sickle-cell disease

-recessive

-caused by a substitution of amino acid in a hemoglobin protein of red blood cells so the cells become sickle-shaped and can block blood vessels

-heterozygotes may show some symptoms (organismal), at the molecular level, the alleles are codominant

-evolutionarily advantageous to be heterozygous bc it prevents malaria

Thomas Hunt Morgan

showed that a specific gene is carried on a specific chromosome and that genes located on a sex chromosome exhibit unique inheritance patterns through his experiments with fruit flies

sex-linked gene

A gene located on either sex chromosome. Most sex-linked genes are on the X chromosome and show distinctive patterns of inheritance; there are very few genes on the Y chromosome.

X-linked genes

fathers pass x-linked genes only to daughters, and females will express a recessive allele only if she is homozygous recessive

ex: Duchenne Muscular Dystrophy, hemophilia

hemizygous

any male receiving a recessive allele from his mother will display the recessive phenotype

Barr body

inactive X in each female cell condenses and is reactivated in cells that give rise to eggs

-if a female is heterozygous for a sex-linked trait, half her cells will express one allele while the others will express the alternate allele because the selection of the inactive chromosome is random

linked genes

genes located near each other on the same chromosome tend to inherited together in genetic crosses

genetic recombination

production of offspring with combinations of traits that differ from those found in the parents

recombinant chromosomes

A chromosome created when crossing over combines the DNA from two parents into a single chromosome.

apoptosis

process of programmed cell death

aneuploidy

having an abnormal number of a particular chromosome

monosomic

2n-1 chromosomes

trisomic

2n+1 chromosomes

polyploidy

more than two complete chromosomes in all somatic cells

sex chromosomes

X and Y chromosomes.

wild-type allele

most common allele in a population

Anaphase II

The centromere divides. The chromatids seperate and move to opposite ends of the cell. Each chromatid is now an individual chromosome.