slides/ap videos 5.1-5.6

genotype

genotype

the organisms underlying genetic makeup

chloroplast inheritance

mutated alleles in chloroplast DNA

meiosis 1 (reductional division)

where homologs pair up and separate, resulting in two haploid daughter cells with replicated chromosomes

preceded by interphase (when the chromosomes are duplicated to form sister chromatids)

meiosis 2 (equational division)

sister chromatids separate resulting in 4 haploid daughter cells with unreplicated chromosomes (similar to mitosis)

zygote

a fertilized egg (has a set of chromosomes from each parent)

→ produces somatic cells via mitosis and develops into an adult

ovum

unfertilized egg

sister chromatids

the identical copies (chromatids) formed by DNA synthesis, with both copies joined by a common centromere (half of a duplicated chromosome)

each replicated chromosome consists of two identical ___ ____

Genes

Units of heredity made up of DNA segments, located on chromosomes

Heredity

Transmission of traits from one generation to the next

Gametes

Reproductive cells (sperm and eggs) that pass genes to the next generation

locus

the physical location of a specific gene on a chromosome

Chromosomes

DNA packaged structures where genes are located

Asexual Reproduction

Passing genes to offspring without gamete fusion

Clone

Group of genetically identical individuals from the same parent

Sexual Reproduction

Two parents give rise to offspring with unique gene combinations

this requires fertilization (the fusion of egg and sperm)

somatic cells

any cell other than a gamete

human ___ ___ have 23 pairs of chromosomes

Diploid Cell

Cell with two sets of chromosomes (2n)

• chromosome pairs differ in sizes, shape, genetic info, centromere location

• cells contain one set from each parent

• ex: body cells (skin cells, leaf cells, hypha cell)

there are 46 chromosomes in a human somatic cell (23 ×2 → one from egg and the other from sperm)

humans → 2n = 46

Haploid Cell

Cell with one set of chromosomes (n)

ex: gametes, sex cells (e.g. pollen, egg)

(two ____ gamete cells come together in sexual reproduction to produce a diploid cell)

humans → n = 23

Karyotype

an ordered display of chromosome pairs from a cell

an image of a cell’s ordered metaphase chromosomes

Homologous Chromosomes (homologs)

Chromosome pairs with the same genes, one from each parent

homologous pair

chromosomes in a ______ ___ are the same length and shape, and carry genes controlling the same inherited characters

hemizygous

a non-homologous pair

Sex Chromosomes

Determine an individual's sex (X and Y in humans, X and W in birds)

Autosomes

Non-sex chromosomes in humans

Fertilization

Fusion of sperm and egg to form a zygote

Mitosis

Cell division producing genetically identical daughter cells

Meiosis

Process that transmits chromosomes and reduces the chromosome number in gametes

results in one set of chromosomes in each gamete (half the number of chromosomes as the parent cell)

• the diploid parent cells produce 4 haploid daughter cells

takes place in two sets of cell divisions

tetrad

foursome during meiosis made by two homologous chromosomes that have already replicated into a pair of sister chromatids

synapsis

the fusion of chromosome pairs at the start of meiosis

prophase 1

(meiosis 1)

• chromosomes begin to condense

  • DNA coils into visible duplicated chromosomes made up of sister chromatids

• in synapsis, homologous chromosomes loosely pair up, aligned gene by gene, forming a tetrad

• nuclear envelope begins to disappear

• fibers begin to form

*while closely aligned crossing over may occur

chiasmata

point of contact between non-sister chromatids of homologous chromosomes where crossing over and exchange of genetic material occurs

(x-shaped regions where crossing over occurred - each tetrad usually has one or more)

kinetochores

proteins associated with the centromere of chromatids

metaphase 1

(meiosis 1)

• tetrads line up at the ___ plate, with one chromosome facing each pole

  • double chromosomes remain in pairs

  • fibers align across the center of the cell

• microtubules from one pole are attached to the kinetochores of one chromosome of each tetrad (same for other side)

anaphase 1

(meiosis 1)

• pairs of homologous chromosomes separate (via fibers)

• one chromosome moves toward each pole, guided by the spindle apparatus

  • each double chromosome, from the pair, migrates to opposite sides of the cell

• sister chromatids remain attached at the centromere and move as one unit toward the pole

telophase 1 and cytokinesis

(meiosis 1)

• each half of the cell has a haploid set of chromosomes (each chromosome still consists of sister chromatids)

• _____ usually occurs simultaneously, forming two haploid daughter cells

• nuclear envelope reappears and establishes two separate nuclei

  • each containing half of the total info the parent nucleus contained

prophase 2

(meiosis 2)

• spindle forms and chromosomes migrate toward the center

• nuclear envelope begins to disappear

metaphase 2

(meiosis 2)

• genetically distinct sister chromatids align on the ____ plate, a spindle attaches to each sister chromatid

anaphase 2

(meiosis 2)

• sister chromatids separate (becoming single chromosomes) and migrate toward opposite poles as spindle fibers shorten

telophase 2 and cytokinesis

(meiosis 2)

• (genetically unique) new haploid nuclei form as chromosomes decondense

Crossing Over

occurs wherein nonsister chromatids exchange DNA segments, producing recombinant chromosomes

begins early in prophase 1

Independent Assortment

Random alignment of chromosomes in meiosis I contributing to genetic diversity (alleles on different chromosomes are inherited independently from one another)

Genes for different traits sorting into gametes independently, not linked.

Random Fertilization

Fusion of any sperm with any ovum (egg) increasing genetic variation - any gamete can contribute to the diploid nature of the genomes in offspring

Mendel

Conducted breeding experiments on garden peas, established principles of inheritance

Allele

Different versions of a gene, represented by uppercase/lowercase letters

→ diploid organisms have 2 ____ for a trait at a particular locus on a homologous pair

Phenotype

Organism's appearance due to its genetic composition (genotype)

Homozygous

Genotype with two identical alleles

Heterozygous

Genotype with two different alleles

Law of Segregation

Alleles segregate during gamete formation, leading to varied combinations

Law of Independent Assortment

gregor mendel’s law stating that alleles of different genes segregate independently during gamete formation

p generation

the true-breeding parents

F1 generation

the hybrid offspring of the p gen

F2 generation

produced when individuals self-pollinate or cross-pollinate with other F1 hybrids

true-breeding

plants that produce offspring of the same variety when they self-pollinate

Dihybrid Cross

the mating or coming together of two organisms having contrasting traits for two characteristics (the visual reputation of genotype frequencies)

Testcross

a cross performed to determine the genotype of an organism showing the dominant trait

to do a ____, cross the phenotypically dominant organism and an unknown genotype with a recessive organism to determine the genotype of the dominant organism

Multiplication Rule

Probability of independent events occurring together is the product of their individual probabilities.

Addition Rule

Probability of exclusive events occurring is the sum of their individual probabilities.

Pedigree Chart

Family tree showing inheritance patterns of traits across generations

→ shading indicates the individual is “affected”

→ an individual who possesses a mutated allele but is not affected is a carrier

Autosomal Recessive

Traits on autosomes needing two mutated alleles to appear.

X-Linked Recessive

Traits on the X chromosome needing two mutated X chromosomes in females or one in males to appear.

Y-linkage

an allele on the Y chromosome

Mitochondrial Inheritance

Traits inherited through mutated alleles in mitochondrial DNA → maternal

Linked Genes

Genes close on the same chromosome, inherited together, less likely to separate during crossing over (exception to mendelian genetics)

Phenotypic Plasticity

Ability of genotypes to produce different phenotypes under varying environmental conditions.

common ancestry

• all organisms use nucleic acids to store and transmit genetic info

• all cells use ribosomes for protein synthesis

• some genes widely conserved

  • active-transport proteins

  • the small ribosomal subunit

  • glycolysis

incomplete dominance

when the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

codominance

when two dominant alleles affect the phenotype in separate, distinguishable ways

multiple alleles

traits that have more than two allelic forms

ex: human blood type

polygenic inheritance

an additive effect of two or more genes on a single phenotype (usually indicated by quantitative variation)

→ where multiple independent genes have an additive or similar effect on a single quantitative trait

ex: skin color

autosomal dominant

Traits on autosomes needing one mutated allele to appear.

X-linked dominant

Traits on the X chromosome needing one mutated X chromosome in females/males

thomas hunt morgan

experimented with fruit flies; breaded wild type red eyes and mutant white eyes, got a 3:1 ratio, and this evidence supported sex-linked genes

he also found evidence for linked genes

recombinant chromosomes

the rearrangement of DNA sequences by the breakage and rejoining of chromosomes or chromosome segments

gene mapping

linked genes have a recombination frequency of less than 50%

a linkage map is a genetic map of a chromosome based on recombination frequencies

distances between genes can be expressed as map units; one map unit, or centimorgan, represents a 1% recombination frequency

map units indicate relative distance and order, not precise locations of genes

ex) if a pair of linked genes has a a recombination frequency of 30%, they are considered 30 map units apart

phenotype plasticity

the ability of individual genotypes to produce different phenotypes when exposed to different environmental conditions

chromosomal inheritance

a source of genetic variance (i.e. segregation, independent assortment, random fertilization → create new combinations of alleles)

ex)provides an understanding for gene transmission

• certain genetic disorders can be caused by a single mutated allele or a specific chromosomal change that is passed from parents to offspring

• parent to offspring inheritance can be analyzed to determine patterns of gene transmission

• mutations or mis-formations in gametes can result in disorders being present in offspring that were not present in parents

nondisjunction

the failure of homologous chromosomes to separate during meiosis 1 or failure of sister chromatids to separate during meiosis 2