Genetics Exam 2- Chapters 7-12

Sexual dimorphism (C7)

physical differences between males and females, specifically in anatomy, physiology, coloration, and behavior; relatively pervasive; can relate to gametes or any stage of development

Primary sex determinism (C7)

determines gamete size (big or small)

Secondary sex determinism (C7)

determines other sex related phenotypes

Isogamy (C7)

all gametes are the same size (no dimorphism); common especially in algae and ciliates

Anisogamy (C7)

when gametes exhibit size dimorphism (two different sized gametes); example is ovum and sperm; includes hermaphrodites

Hermaphrodites (C7)

produce eggs and sperm either simultaneously or at different times in the life cycle; doesn’t have to be two individuals

Sex chromosomes (C7)

sex is determined by the presence or absence of these; for mammals, typically an X and Y version of this exists, but there are other varieties for different organisms; chromosomes whose shape, number, and combination tends to be associated more with one biological sex than another in sexually dimorphic species and influence the development of primary and secondary sexual characteristics

Female sex chromosomes for humans (C7)

XX

Male sex chromosomes for humans (C7)

XY

Which chromosome is smaller, X or Y? (C7)

Y chromosome is smaller than X, fewer genes

Thomas Hunt and Lilian Vaughan Morgan (C7)

discovered the chromosomal basis of inheritance and genetics of sex through studying fruit flies; early 1900s

Autosomes (C7)

non sex chromosomes

Herterogametic sex (C7)

males have two different sex chromosomes; males will make gametes with either X or Y chromosomes; sex chromosomes different (general)

Homogametic sex (C7)

female has two similar sex chromosomes; all of her ova/gametes will have an X chromosome; sex chromosomes the same (general)

What other species shares the XY chromosomes for males of their species? (C7)

Drosophila melanogaster (fruit fly)

“Criss cross inheritance” (C7)

the trait goes from mother to son, showing inheritance of the X chromosome (x linked)

X linked (C7)

genes located on the x chromosome; because many genes map to the x chromosome and relatively few genes map to the y chromosomes, the terms of sex linked and x linked are used interchangeably

Y linked (C7)

(holandric) genes located on the y chromosome; relatively few genes map to the y chromosome; only in males

Hemizygous (C7)

a diploid in which only one copy of an allele is present at a locus, rather than two; XY males are hemizygous for x linked alleles, and individuals in which one copy of a gene has been deleted are hemizygous for the remaining allele; since there is no corresponding allele, a hemizygous allele exerts its effect on the phenotype without regard to dominance

Mutant phenotype (C7)

An individual having a phenotype that differs from the normal phenotype.

Gene product (C7)

protein made; The biochemical material, either RNA or protein, resulting from expression of a gene. The amount of gene product is used to measure how active a gene is

Homology (C7)

A condition denoting to the pair of chromosomes having corresponding genes for a particular trait or characteristic

Pseudoautosomal (C7)

similar or behaves like autosome, allowing meiosis in heterogametes (have one region in X and Y that synapse/connect to perform meiosis); inheritance pattern similar to autosomal genes in pedigrees, but the gene actually resides in both the x and y chromosomes

Examples of x linked traits and diseases (C7)

opsins (color blindness, more common in males but females can have it if they have it in both x chromosomes), dystrophin (muscle protein) leads to duchenne and becker muscle dystrophy, blood clotting factors VIII and IX (hemophilia)

Nondisjunction events (C7)

can also occur in sex chromosomes; process by which a pair of homologous chromosomes fails to separate from each other normally during one of the two meiotic divisions, resulting in gametes with too many or too few chromosomes

Aneuploidy (C7)

results in one meiotic product, the sperm or the egg, having an extra chromosome or missing a chromosome; nondisjunction event

Trisomies (C7)

an aneuploid diploid cell that has three copies of a chromosome, rather than two

Causes of nondisjunction during meiosis I (C7)

failure to crossover and chiasmata formation

Causes of nondisjunction during meiosis II (C7)

failure in sister chromatid cohesion (don’t stick together like they are supposed to)

Mechanism of sex determination: XY/X0 systems (C7)

sex is determined by number of x chromosomes; the presence or absence of a Y chromosome does not influence sex; XX is females and X0 is males; examples include drosophilia (fruit flies), C. elegans, and many other invertebrates

What is SRY? (C7)

triggers the formation of testes in mammals; number of Ys matter since SRY is on the y chromosome; Y development of testes while just x is development of female reproductive organs; XXY showcases male sexual development while X0 is female sexual development; just the first step in a complex process (SRY interacts with several other genes in autosomes and on the x chromosome)

Aneuploidy of XXY (C7)

Kleinfelter syndrome; tolerable in humans; variable in phenotypes, typically delayed puberty and reduced fertility

Aneuploidy of X0 (C7)

turner syndrome; tolerable in humans; variable in phenotypes, typically delayed puberty and reduced fertility

Mosaicism (C7)

occurs when an an individual has cells with different genotypes;

Mosaicism and phenotypic variability example (C7)

(in notes and in textbook); fertilized XXY eggs go through a series of mitotic divisions; four cells in top row continue to divide by mitosis and the vertical column indicates mitotic descendants of that cell; XXY chromosomes that lose an X become XY (normal male karyotype); XXY cells that lose Y become XX (normal female karyotype); mitotic descendants retain that karyotype and two individuals can vary in proportion of XX and XY cells as well as which particular cell lineages are XX and XY

Mechanism of sex determinism: ZW/ZZ system (birds)(C7)

male birds are homogametic ZZ and females are heterogametic ZW; most similar to XX and XY system

Mechanism of sex determinism: no distinct sex chromosomes (C7)

do not have sex chromosomes but have particular mating

Mechanism of sex determinism: environmental determination (C7)

use environment signals to determine their sex; sex is not genetically inherited in these organisms; example is temperatures in which eggs incubate such as in reptiles (sea turtles); other signals include crowding or external food sources, pH

Haplodiploid species (C7)

examples are hymenoptera (ants, wasps, sawflies, bees); individuals are female is the egg producing parent (diploid) chooses to fertilize the egg and males develop from unfertilized (haploid) eggs; example: queen bee is diploid while worker bees are haploid and sterile

Sex determination (C7)

genetic, hormonal, environmental, negotiation within and across species

Dosage compensation (C7)

one of several distinct processes by which animals with different sex chromosomes regulate the level of x linked transcription, so that both sexes make similar amounts of x linked gene product; in mammals occurs by x chromosome inactivation

Dosage compensation in drosophila (fruit flies) (C7)

complex of proteins and RNA molecules called the dosage compensation complex (DCC) that increases x transcription in males; acts on one chromosome in XY

Dosage compensation in c elegans (C7)

complex of proteins and RNA molecules called the dosage compensation complex (DCC) that dampens transcription on both x chromosomes in XX producing lower levels of transcription for each z chromosome

Dosage compensation in mammals (C7)

complex of proteins and RNA molecules called the dosage compensation complex (DCC) that shuts down one of the x chromosomes on the XX completely (condenses it to no longer be available for transcription); only one x chromosome is expressed in any given cell and this differs from cell to cell

X chromosome inactivation (C7)

the process by which dosage compensation occurs in mammals; female embryos transcriptionally inactive one of their two chromosomes in each cell, so that males and females make equivalent amounts of products from x linked genes; either chromosome can be inactivated, but it remains inactive in subsequent mitotic division

Epigenetics (C7)

heritable change in gene activity and this the phenotype with no corresponding change in DNA sequence (example x chromosome inactivation and was discovered by Mary lyon)

Mendel’s Law of Independent Assortment (C8)

random during meiosis; traits on different chromosomes are inherited independently; alleles of two or more different genes get sorted into gametes independently of one another; increases variability; two or more different genes

Mendels’ Law of Segregation (C8)

only one of the two gene copies present in an organism is distributed to each gamete (egg or sperm cell) that it makes, and the allocation of the gene copies is random; increases variability; one single gene

Crossing two unlinked genes (C8)

predicting probability multiple the probabilities of each unlinked gene with each other

Mendelian inheritance is what? (C8)

one gene, two alleles

Why do many traits not follow the simple model of mendelian inheritance? (C8)

relationship between genotype and phenotype is rarely as simple as the pea plant example; many heritable characters are not determined by only one gene with two alleles; however the basic principles of segregation and independent assortment apply even more to complex patterns of inheritance

When may the inheritance of a single gene deviate from the mendelian pattern? (C8)

when alleles are not completely dominant or recessive, when gene produces multiple phenotypes, when a gene has more than two alleles, lethal homozygotes

Complex trait (C8)

traits that show some tendency to be inherited, but whose inheritance pattern cannot be described by the behavior of one or a few genes; phenotypes are affected by variation in both genes and the environment; influenced by many genetic loci and the environment (most diseases); vary continuously

Complete dominance (C8)

occurs when phenotypes of the heterozygote and dominant homozygote are identical

Incomplete dominance (C8)

the phenotype of the F1 hybrids is somewhere between the phenotypes of the two parental varieties (combos of colors) (example is white and black dog producing gray offspring)

Codominance (C8)

two dominant alleles affect the phenotype in separate, distinguishable ways (example is patches) (example is the ABO blood group)

Relation between dominance and phenotype (C8)

dominant allele does not subdue the recessive allele, alleles don't interact that way; alleles are simply variations in a gene’s nucleotide sequence; for any character the dominance relationships of alleles depend on the level at which we examine the phenotype

Can dominance be different at different levels of the organism, biochemical, and molecular level? (C8)

yes it can be different at each of these three levels

Taysachs disease (C8)

fatal; a dysfunctional enzyme causes an accumulation of lipids in the brain; inherited

Dominance in taysachs disease (C8)

organismal level allele is recessive; biochemical level phenotype is incompletely dominant; molecular level alleles are codominant

Misconceptions of dominant alleles (C8)

dominant alleles are not necessarily more common in populations that recessive alleles (one baby out of 400 in the US is born with extra fingers or toes; rare but its dominant; recessive allele is much more prominent that the dominant allele)

When (what situations) may inheritance characters of a single gene deviate from mendelian patterns? (C8)

when alleles are not completely dominant or recessive; when a gene produces multiple phenotypes (pleiotropy, reduced penetrance/environmental effects); when a gene has more than two alleles

Pleiotropy (C8)

most genes have multiple phenotypic effects; for example pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle cell disease; multiple different phenotypic effects that occur together as a result of a single mutation

Alleles with reduced penetrance (C8)

not every individual with the mutant genotype displays a mutant phenotype; could be caused by environmental and developmental instances and switches; example is the recessive mutation in bli

Penetrance percent (C8)

percent penetrance= percent that have that mutation in the population; example 72% of worms have blisters (mutation) so there is 72% penetrance

Variable expressivity (C8)

individuals who share the same genotype for an allele differ in the severity or strength of the associated phenotype; have traits at different degrees; example is human diseases; dependent on developmental and environmental factors

Phenotypic plasticity (C8)

individuals may express different phenotypes in different environments; example is hydrangeas and how they are purple or blue depending on soil acidity

Polymorphic (C8)

there is more than one common allele or variant for a gene

Carriers (C8)

recessive lethal alleles that are maintained in the population at low levels in heterozygotes

Agouti coloration example (C8)

agouti locus produces molecule that regulates the synthesis of the black pigment eumelanin; different alleles at the agouti locus modify this pattern of bands on a hair shaft in various ways; for example ay is dominant to other alleles since it produces eumelanin (4 total different alleles); look at notes

Mendelian ratios with lethal alleles (C8)

some lethal alleles are recessive; when two heterozygotes for a lethal allele are mated, one fourth of their offspring will die. Therefore phenotypes and genotypes are based on the surviving offspring (thirds); example is curling wings in flies that is lethal when homozygous dominant

Epistasis (C8)

a gene at one locus alters the phenotypic expression of a gene at a second locus (one trait multiple genes) (one gene influencing another) (example in notes the phenotype was dependent on the action of both genes; in second example only one working copy is needed since the two genes do the same job)

Epistasis in labrador retrievers (C8)

coat color depends on two genes (true for many mammals as well); one gene determines pigment color (B is black b brown) and the other gene (E for color and e for no color) determines if the pigment will be deposited in the hair; ee _ _ = blonde E_ B_ = black E_ bb= brown (9:3:4 phenotypic ratio)

Complementation test (C8)

functional test to determine if two recessive mutations are different alleles of the same gene or if they are alleles of two different genes (REVIEW EXAMPLES IN NOTES); can also test using plasmids

Quantitative characters in polygenic inheritance (C8)

those that vary in the population along a continuum (height, skin color, etc); usually indicated polygenic inheritance

Polygenic inheritance (C8)

additive effect of two or more genes on a single phenotype; influence by many genetic loci (interaction between alleles; epistasis)

Quantitative genetics (C8)

study of the genetic mechanisms of continuous phenotypic traits

Variance of complex traits (C8)

a measure of how widely dispersed trait values are from the mean (standard deviation ?)

Why would we want to know the location of genes? What can we learn? (C9)

help with gene therapies; gene modifications

Linked genes (C9)

alleles of gene located on same chromosome will NOT be inherited independently

Unlinked genes (C9)

alleles of genes on different chromosomes that are inherited independently

Linkage talks about what (C9)

talkies about location on chromosome(s)

Why are genes located on the same chromosome inherited together while those on different chromosomes inherited independently? (C9)

meiosis and independent assortment

Recombination (C9)

any of several processes by which the genetic information in one generation is combined in new combinations in succeeding generations; includes fertilization, independent assortment, horizontal gene transfer, crossing over during meiosis, but often used to refer to crossing over

Genetic maps (C9)

a record of the locations of the genes on the chromosomes of species; distances between the genes reflect the frequency of recombination that occurs between the genes; a map based on the recombination distances (cM); population specific; aka linkage map

If we know the location of some genes in a genome, how can we use that information to determine the location of genes that cause specific traits of interest? (C9)

two factor test cross is one method

Test crosses (C9)

a mating to an individual or a strain that is homozygous recessive for all alleles being investigated; since the homozygous recessive parent has no dominant alleles, all of the alleles in the other parent are revealed by the phenotypes of the offspring

Parentals (C9)

gametes that have the same combination of alleles as the original homozygous parents

Recombinants (C9)

gametes that have different combination of alleles as the original homozygous parents; in unlinked genes arise from the shuffling of parental chromosomes during meiosis in F1

Two factor test cross with unlinked genes (C9)

LOOK AT THE EXAMPLES IN THE NOTES; four gametes made by the F1 heterozygote are equally frequent; four phenotypes from the test cross are equally frequent

Two factor test cross with linked genes (C9)

LOOK AT THE EXAMPLES IN THE NOTES; four phenotypes arising from the test cross are NOT equally frequent so __ and ___ must be linked; traits do not segregate independently so genes must be linked; genotypes of the parentals will always be the most common

T/F crossing over must occur at least once in meiosis (C9)

true

What does the number of recombinants tell you? (C9)

tells us about how far apart the genes are (less frequent)

Map units (C9)

measure the distance between genes; given in centimorgans of cMs; 1cM = 1% recombination rate between to genes; more than 50 map units or 50% means they are unlinked so not on the same chromosome; larger values= more crossing over= more distance between the genes

The closer two genes are ______(C9)

the less likely they are to crossover

Are recombinants more or less frequent than parentals? (C9)

always less frequent because only two of the four chromatids are involved in crossover and crossovers that occur elsewhere on the chromosome produce only parental gametes

Balanced heterozygote (C9)

an organism or strain that remains as a heterozygote for several linked alleles or polymorphisms over many generations

Balancer chromosomes (C9)

a genetically altered chromosome that cannot recombine with its normal homologous chromosome; any recessive mutations on the normal homologous chromosome will be inherited together if they are maintained as a heterozygote with a balancer chromosome; suppressed recombination across entire link (taken advantage of recombination); reduce crossing over in the region of interest; individuals homozygous for the balancer must be distinguishable from heterozygotes which also must be distinguishable from individuals homozygous for the non balancer (lethal or glowing)

Genetic crosses tell and can be used for what? (C9)

can be used to determine if two traits are linked and if there are known markers, can be used to map the location of genes of interest

What applications can genetic maps be used for? (C9)

human health and agriculture