Heredity

genetics

the study of heredity and hereditary variation

heredity

the transmission of traits from one generation to the next

genes

segment of DNA that codes for the basic units of heredity

asexual reproduction

Process by which a single parent reproduces by itself, creating offspring that are exact copies of the parent

sexual reproduction

A reproductive process that involves two parents that combine their genetic material to produce a new organism, which differs from both parents

homologous chromosomes

a pair of chromosomes (same size, length, centromere position) that carry the same genetic information. One is inherited from mom and one is inherited from dad

karyotype

A display of the chromosome pairs of a cell arranged by size and shape.

autosomes

chromosomes that do not determine the sex of an individual

sex chromosomes

The X and Y chromosomes that determine physical sex characteristics

trisomy 21

Carrying an extra copy of chromosome 21; also known as Down syndrome

Turner Syndrome

A chromosomal disorder in females in which an X chromosome is missing

Klinefelter syndrome

A chromosomal disorder in which males have an extra X chromosome, making them XXY instead of XY.

Nondisjunction

Error in meiosis in which homologous chromosomes fail to separate during Anaphase (I or II) resulting in chromosomal abnormalities in gametes (having too many or too few chromosomes)

somatic cells

Any cells in the body other than reproductive cells

Gametes (Gametic Cells)

sex cells (eggs and sperm)

Diploid

containing two complete sets of chromosomes, one from each parent, represented by 2n

Haploid

having a single set of unpaired chromosomes

life cycle

sequence of stages in the reproductive history of an organism from conception to its own reproduction

Fertilization

when a sperm cell fuses with an egg to form a zygote

Meiosis

a process that creates haploid gamete cells in sexually reproducing diploid organisms; results in 4 genetically unique haploid cells after 2 rounds of cellular division

mitosis

cellular division that creates 2, generically identical, diploid daughter cells

synapsis

process in which homologous chromosomes pair up to form a tetrad

crossing over

Process in which homologous chromosomes exchange portions of their chromatids during meiosis, results in recombinant chromosomes

chiasmata

X-shaped regions where crossing over occurred.

tetrad

structure containing 4 chromatids (homologous chromosomes in their pairs) that forms during meiosis

prophase I

The chromosomes condense, and the nuclear envelope breaks down. crossing-over occurs.

metaphase I

Pairs of homologous chromosomes (tetrads) move to the equator of the cell and line up at the metaphase plate

anaphase I

pairs of homologous chromosomes separate

telophase I and cytokinesis

Nuclei and cytoplasm divide. There is now a haploid set of chromosomes in each daughter cell

prophase II

new spindle forms around the chromosomes, no crossing over occurs

metaphase II

chromosomes line up single file on the metaphase plate

anaphase II

Sister chromatids separate and move towards opposite poles

Telophase II and Cytokinesis

A nuclear envelope forms around each set of chromosomes. the cytoplasm divides, resulting in 4 haploid cells

independent assortment of chromosomes

chromosomes are randomly oriented along the metaphase plate during Metaphase I; Each can orient with either the maternal or paternal chromosomes closer to a given pole

random fertilization

source of genetic variation caused by the unlimited number of possible sperm & egg combinations

Gregor Mendel

Austrian monk who experimented on pea plants and discovered the basic principles of heredity

alleles

alternative versions of a gene

true breeding

organisms that produce offspring of the same variety over many generations of self pollination because they only have type of allele

P generation

true-breeding parental generation

F1 generation

(first filial) hybrid offspring of P generation

F2 generation

(second filial) offspring of the F1 generation

dominant traits

always expressed if present and can mask recessive trait; use a capital letter

Recessive traits

only expressed if both inherited alleles are recessive; use a lower case letter

law of segregation

the two alleles for the same trait separate during gamete formation and end up in different gametes

monohybrid cross

a cross between the F1 hybrids that results in a 3:1 phenotypic ratio; Bb x Bb

punnett square

diagrams used to predict the allele combinations of offspring from a cross with known genetic compositions

Homozygous

An organism that has two identical alleles for a trait

Heterozygous

An organism that has two different alleles for a trait

Genotype

genetic makeup of an organism; an organism's combination of alleles

Phenotype

An organism's physical appearance, or visible traits.

test cross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

law of independent assortment

genes for one trait are not inherited with genes of another trait

dihybrid cross

a cross between F1 dihybrids: YyRr x YyRr

the multiplication rule

the probability that two or more independent events will occur together in some specific combination (both events will happen)

the additional rule

the probability that two or more mutually exclusive events will occur (this OR that will happen)