AP Bio Unit 5

Locus

The location of a gene on a chromosome

Somatic cells

Body cells

Hereditary

How traits are passed down from parents to offspring

Genes

Segments of DNA that encode proteins that affect how traits are expressed

Alleles

Versions of a gene

Homologous Chromosomes

Pairs of chromosomes that carry the same genes at the same locus but with different alleles, one is inherited from each parent

Karyotype

A picture of an organisms chromosomes, can be used to detect genetic disorders in fetuses

Autosomes

The 22 chromosomes that do not determine sex

Gametes

Sperm and ova/eggs, haploids

Haploids

Only have one chromosome from each homologous pair, gametes

Fertilization

The combination of a sperm and an egg cell

Zygote

A fertilized egg, diploid

Meiosis

Specialized cell division that results in four genetically different haploid gametes

Synapsis

The joining of homologous chromosomes during prophase forming a tetrad

Crossing over

DNA of homologous chromosomes cross over on the medial chromosome’s legs creating more genetic diversity

Recombinant chromosomes

The result of crossing over, not genetically identical to either parent’s chromosome

Parental Chromosomes

Chromosomes that do not cross over

Meiosis 1

First cellular division and results in two haploids that have two sister chromatids

Prophase 1

• chromosomes condense and sister chromatids attach at the centromere

• Homologous pairs then join and cross over

• Nuclear envelope disintegrates, spindle poles move away from each other, spindle fibers attach to the kinetochores of the chromosomes

Chiasmata

The region where crossing over happens, holds the homologs together until they separate in anaphase

Phenotype

The physical expression of one or many genes

Nondisjunction

When chromosomes or sister chromatids dont separate during anaphase, causes genetic defects

Metaphase 1

• homologous chromosomes line up at the metaphase plate

• Each pair sorts randomly

Independent assortment 1

Maternal and paternal chromosomes line up independently of each other which increases genetic diversity 1

Anaphase 1

• homologous pairs separate towards opposite sides of the cell

• Spindle fibers shorten at the kinetochore end

• Sister chromatids are still together

Telophase 1 and Cytokinesis

• the cleavage furrow forms

• Cytoplasm splits creating two haploids cells

Primary oocyte

oogenesis only creates one oocyte with enough cytoplasm to function as an egg

Polar body

All of the products of oogenesis that are not the primary oocyte, usually dont have enough cytoplasm

Meiosis 2

• second division in meiosis

• Starts with 2 haploids and ends with 4 haploids

• Only happens in oogenesis after fertilization

Prophase 2

• spindle apparatus forms

• Sister chromatids are still together

Metaphase 2

• sister chromatids line up at the metaphase plate

• Spindle fibers are attached to each kinetochore

Anaphase 2

• sister chromatids are pulled apart

• Spindle fibers shorten at the kinetochore ends

Telophase 2 and cytokinesis

• nuclei reappears and cytoplasm is spilt

• 4 genetically different haploid cells are created

Random fertilization

Each egg and sperm is different, so there are many different possible outcomes of fertilization which increases genetic diversity

True-breading plants

Plants that self pollinate and produce progeny with the same traits

Parental generation

Made up of true-breeding plants

F1 generation

First filial generation, offspring of the parent generation

F2 generation

Second filial generation, offspring of the F1 generation, 3:1 ratio

Mendel’s law of segregation

The two alleles from a parent separate during the forming of gametes so each gamete only gets one

Mendel’s law of independent assortment

Maternal and paternal chromosomes sort independently of each other, so the gamete can get any mix of them

Dominant alleles

Mask the phenotypic expression of recessive alleles

Homozygous

Two of the same alleles for a trait, can be dominant or ressesive

Heterozygous

Two different alleles, will express the dominant phenotype unless there is co-dominance or incomplete dominance

Phenotype

An organism’s expression of physical traits

Genotype

An organisms genetic makeup

Testcross

• Done to determine if an individual is homozygous dominant or heterozygous

• Bread with homozygous recessive

Rule of multiplication

When calculating the probability that two or more independent events will occur multiple them (Ex. The probability that offspring will have green eyes and brown hair)

Rule of addition

When calculating the probability that any two or more mutually exclusive events will happen add them (Ex. The probability that offspring will produce the dominant phenotype)

Complete dominance

Heterozygous and homozygous dominant produce an indistinguishable phenotype

Incomplete dominance

Heterozygous genotype will produce a phenotype between the two parents (Ex. Red x White = Pink)

Codominance

When two alleles are dominant and affect the phenotype indifferent but equal ways (Ex. AB blood)

Polygenic inheritance

Two or more genes have an additive effect on a single character in the phenotype (Ex. Height and skin color)

Phenotypic plasticity

When a phenotype is affected by the environment of an organism, identical genotypes have different phenotypes (Ex. Colder temps cause an enzyme to fold incorrectly and not produce pigment)

Pedigree

A family tree that shows the frequency of a specific trait, affected individuals are shaded in

Autosomal dominant

• trait appears in every generation

• Both males and females are equally likely to express the trait

• Affected individuals have at least one affected parent

• Unaffected individuals do not pass the trait on to their offspring

Autosomal Recessive

• the trait can skip a generation

• Both males and females are equally affected

• Affected individuals can have unaffected parents (carriers)

X-Linked Dominant

• trait does not skip generations

• Affected males pass the trait to their daughters but not sons

• Affected females can pass the trait to sons and daughters

X-linked Recessive

• more males are affected than females

• Affected males often have unaffected carrier mothers

• The trait can skip generations

• Sons of affected males are not affected and daughters are carriers

Y-linked

• only males are affected

• The trait is passed from affected father to all of their sons

• Does nit skip generations

X inactivation

Occurs in females when one x chromosome is randomly inactivated during early development, causes different cells to express different alleles like in calico cats

Mosaicism

When different cells express different alleles depending on which X chromosome is inactivated

X linked disorders

• Duchenne muscular dystrophy: progressive weakening muscles and loss of coordination

• Hemophilia: inability to clot blood

Linked genes

Genes located on the same chromosome that are therefore more likely to be inherited together

Genetic recombination

• the percentage of offspring with new combinations of genes

• Used to measure the distance between genes on chromosomes

• If the rate of recombination is below 50% it is likely that the genes are linked

Linkage maps

• A picture of where genes are on a chromosome

• created using recombination frequencies

• 1% of recombination is 1 centimogran

Nondisjunction disorders

• down syndrome: caused by an extra chromosome 21

• Klinefelter syndrome: when a male has an extra chromosome causing infertility (both x chromosomes are active)

• Turner syndrome: when a female only has 1 d chromosome causing them to be sterile

Mitochondrial and Chloroplast DNA

Only passed down maternally

Recessively inherited disorders

• cystic fibrosis: thicker and stickier mucus causes organ malfunctions and recurrent bacterial infections

• Tay-Sachs disease: lipids are not broken down and build up in the brain causing death

• Sickle cell anemia: small blood vessels are clogged by abnormally shaped red blood cells

Dominantly inherited disorders

• Huntington’s disease: causes degeneration of the nervous system starting around 40

• Achondroplasia: a form of dwarfism

Core metabolic pathways

• fundamental processes and features that support the concept of common ancestry for all organisms

• Ex. Cellular respiration, glycolysis

• Inserting genetic DNA from one organism to another will allow it to carry out the same function