genetics ch. 1-7 (exam 1)

what differentiates a eukaryotic cell from a prokaryotic cell?

eukaryotic cells have a nucleus where DNA is organized and packed into chromosomes, and membrane-bound organelles; prokaryotic cells do not have these, DNA is loose and spread throughout the cell

what is the typical structure of a chromosome?

a long strand of DNA coiled around histone proteins; centromere, telomeres, origin of replication

what are the phases of mitosis and what happens during each?

prophase (chromosomes condense and spindle forms), metaphase (chromosomes align at the cell's equator), anaphase (sister chromatids separate and move to opposite poles), telophase (nuclear membranes re-form around separated chromosomes), and cytokinesis (cytoplasm divides, resulting in two daughter cells)

how is meiosis I different from meiosis II?

meiosis I involves homologous chromosomes separating, resulting in two haploid cells, whereas meiosis II resembles mitosis where sister chromatids separate, leading to four haploid gametes

reduction division

a process during meiosis I where homologous chromosomes are separated, reducing the chromosome number by half and resulting in haploid cells (2 chromosomes, 4 DNA molecules)

equational division

a process during meiosis II where sister chromatids are separated, resulting in the formation of haploid cells that each contain a single set of chromosomes (2 chromosomes, 2 DNA molecules)

Mendel’s principle of segregation

during gamete formation, the two alleles for a trait separate so that each gamete carries only one allele

concept of dominance

when two different alleles are present in a genotype, only the trait encoded by one allele (dominant) is observed in the phenotype; the allele whose trait is not expressed is recessive

monohybrid cross

a genetic cross between parents that differ in a single trait

multiplication rule

the probability of two independent events occurring together is the product of their individual probabilities; use when the outcome of one event does not influence the other event, such as predicting the genetic ratio of offspring in a cross

addition rule

the probability of either of two mutually exclusive events occurring is the sum of their individual probabilities; use when determining the likelihood of different outcomes in a genetic cross

dihybrid cross

a genetic cross between parents that differ in two traits

independent assortment

the principle that alleles for different traits are distributed independently of one another during gamete formation, leading to genetic variation in offspring; occurs during metaphase I when homologous chromosomes randomly align

what does the chi-square goodness of fit test indicate?

the probability that the difference in observed vs. expected phenotypic ratios is due to chance

what are degrees of freedom?

the number of different expected phenotypes - 1

what does it mean if P > 0.05?

It indicates that the difference between observed and expected values is not statistically significant, suggesting that any variation is likely due to chance.

what does it mean if P < 0.05?

It indicates that the difference between observed and expected values is statistically significant, suggesting that the variation is unlikely due to chance.

what is the typical phenotypic ratio for a simple cross between two heterozygote parents (Aa x Aa)?

3:1, dominant:recessive

what is the typical phenotypic ratio for a simple cross between one heterozygote parent and one homozygous recessive parent (Aa x aa)?

1:1, dominant:recessive

what are the characteristics of the XX-XO system?

females are XX, males are XO, O = absence of a sex chromosome

what are the characteristics of the ZZ-ZW system?

females are ZW, males are ZZ,

haplodiploidy system

females are diploid, males are haploid; males develop from unfertilized eggs

genic sex-determining system

a system where sex is determined by specific genes rather than by sex chromosomes. In this system, a single gene can dictate the development of sexual characteristics.

environmental sex determination

a type of sex determination where environmental factors, such as temperature or social conditions, influence the sex of an organism during development.

Turner syndrome

a condition resulting from a missing or incomplete X chromosome in females (XO genotype), leading to various developmental and physical abnormalities.

Klinefelter syndrome

a genetic condition in males characterized by the presence of an extra X chromosome (XXY), leading to symptoms such as reduced testosterone levels, infertility, and physical abnormalities.

poly-x female

a genetic condition in females resulting from the presence of multiple X chromosomes (e.g., XXX), often associated with tall stature and potential learning difficulties, but many may be asymptomatic.

what happens if someone only has two Y chromosomes and no X?

This condition is typically lethal, as the presence of at least one X chromosome is essential for normal development.

what is the role of SRY?

The SRY gene, located on the Y chromosome, is responsible for initiating male sex determination by triggering the formation of testes, which produce male hormones.

androgen-insensitivity syndrom (AIS)

a genetic condition where individuals with XY chromosomes develop female physical traits due to the body's inability to respond to androgens (testosterone receptor), leading to female external genitalia but male internal structures.

how did the Y chromosome evolve?

The Y chromosome evolved from an ancestral pair of autosomes and has lost many of its genes over time, primarily retaining genes crucial for male sex determination and spermatogenesis.

what is dosage compensation?

Dosage compensation is a genetic mechanism that equalizes the expression of X-linked genes between males and females, ensuring that one of the two X chromosomes in females is effectively inactivated.

Barr body

A condensed, inactivated X chromosome found in female mammals that ensures dosage compensation between males (XY) and females (XX) by preventing the overexpression of X-linked genes.

what does it mean that females are mosaic?

some cells express genes from one X chromosome, while some cells express genes from the other X chromosome; random x-inactivation

incomplete dominance

the phenotype of offspring falls between the parents’ phenotypes; neither allele is completely dominant

co-dominance

the phenotype of offspring displays characteristics of both parents equally; both alleles are expressed distinctly.

penetrance

the proportion of individuals with a specific genotype that display the associated phenotype; reflects the extent to which a gene manifests itself.

incomplete penetrance

the situation where not all individuals with a particular genotype express the expected phenotype; some may show the trait while others do not.

expressivity

the degree to which a genotype is expressed in an individual's phenotype; it varies among individuals.

lethal allele

an allele that, when homozygous, leads to the death of an organism; this can affect the expression of phenotypes in a population.

multiple alleles

the existence of more than two alleles for a particular gene locus in a population; individuals can inherit any combination of these alleles (ex: ABO blood types)

gene interaction

the process by which different genes influence each other's effects on a phenotype, often resulting in a combined phenotypic effect that differs from what would be expected from the individual genes alone.

epistasis

a type of gene interaction where the presence of a particular allele at one gene locus can mask or modify the effects of alleles at another locus, affecting the phenotype.

epistatic gene

A gene that can mask or modify the expression of another gene's alleles, influencing the overall phenotype.

hypostatic gene

A gene whose expression is masked or modified by another gene's alleles, often resulting in altered phenotypic outcomes.

recessive epistasis

A form of epistasis where an epistatic gene's recessive alleles can mask the effects of a hypostatic gene, leading to a specific phenotypic expression; phenotypic ratio = 9:3:4 in a dihybrid cross.

dominant epistasis

A form of epistasis where a dominant allele of an epistatic gene masks the expression of a hypostatic gene, altering the resulting phenotype; phenotypic ratio = 12:3:1 in a dihybrid cross.

duplicate recessive epistasis

A form of epistasis where two recessive alleles of different genes can mask the expression of a hypostatic gene, leading to a specific phenotypic outcome; phenotypic ratio = 9:7 in a dihybrid cross.

sex-influenced traits

traits are determined by autosomal genes which are inherited normally but are expressed differently in males and females; higher penetrance in one sex, but still present in other sex

sex-limited traits

Traits that are determined by autosomal genes but are expressed only in one sex, often due to hormonal influences; they do not manifest in the other sex; both males and females can transmit the trait, but only one sex can express it

cytoplasmic inheritance

A type of inheritance where genes located in the mitochondria or plastids are passed from one generation to another, primarily through the maternal line; this often leads to traits that are strictly inherited from the mother.

genetic maternal effect

A phenomenon where the genotype of the mother directly influences the phenotype of her offspring, regardless of the offspring's own genotype; genes are still inherited from both parents

pedigrees for autosomal recessive traits

usually appear equally in males and females, tend to skip generations, more likely to appear among progeny of related parents

pedigrees for autosomal dominant traits

usually appear in every generation, affect males and females equally, and are typically present in at least one parent of an affected offspring

pedigrees for x-linked recessive traits

usually appear more frequently in males than in females, tend to skip generations, are often transmitted from carrier mothers to affected sons, affected males cannot pass trait to sons but can pass to a daughter (typically a carrier)

pedigrees for x-linked dominant traits

usually appear in every generation, affect males and females but often more severe in males, affected males pass the trait to all daughters but not to sons, affected females (heterozygous) pass trait to half of their sons and half of their daughters

pedigrees for y-linked traits

usually appear only in males, are passed directly from father to son, and do not skip generations.

recombination

the exchange of genetic material between homologous chromosomes during meiosis, leading to new allele combinations.

recombinant gametes

gametes that contain combinations of alleles that differ from those in the parents, resulting from recombination during meiosis.

non-recombinant gametes

gametes that retain the original combination of alleles from the parents and do not undergo recombination.

linked genes

genes that are located close to each other on the same chromosome and tend to be inherited together during meiosis.

independent assortment vs. linked genes

Independent assortment refers to the principle that alleles of different genes segregate independently of one another during gamete formation, while linked genes tend to be inherited together due to their proximity on the same chromosome.

complete linkage

occurs when two genes are located very close together on the same chromosome, resulting in no crossing over/recombination between them during meiosis.

unlinked genes

genes that are located on different chromosomes or are far apart on the same chromosome, leading to independent assortment during gamete formation; half recombinant progeny and half non-recombinant progeny

incomplete linked genes

genes that are located close together on the same chromosome but are not completely linked; allows for some crossing over during meiosis, resulting in a mix of parental and recombinant types; this leads to a higher proportion of non-recombinant offspring compared to recombinant offspring (frequency of recombinant gametes = half the frequency of crossing over)

recombination frequency

the proportion of recombinant offspring produced in a cross, indicating the distance between two genes on a chromosome; it is used to estimate gene mapping and is measured as a percentage; = (number of recombinant offspring / total offspring) x 100%

coupling (cis configuration)

one chromosome contains both wild-type alleles, one chromosome contains both mutant alleles (ex: p+ b/ p b+)

repulsion (trans configuration)

one chromosome contains a wild-type allele and a mutant allele, while the other chromosome contains the opposite alleles (ex: p+ b/ p b+)

gene mapping

the process of determining the relative positions of genes on a chromosome and the distances between them, often using recombination frequencies to predict inheritance patterns; smaller recombination frequency = shorter distance; the further apart the genes, the more crossovers can occur