Genetics Exam Two

What did Morgan’s experiments (1910) show?

Gene for eye color located on chromosome X in Drosophilia

If you cross a white eye male and wildtype red eye female what color eyes do F1 have?

all red eye so red is dominant

What was the F2 ratio in Morgan’s experiments?

4\.4:1

Why was the F2 ratio 4.4:1 in Morgan’s Experiment?

1) pleiotropy, 2) too few white-eyed mutants survived, 3) mutant inviability

What pattern did Morgan see among the white-eyed mutants that lived?

they were all male

Hemizygous

only one allele of a gene, males

What does the punnet square of the F2 look like?

1) all females are red-eyed (W+w), 2) half of the males are white-eyed (wY), 3) half of the males are red-eyed (w+Y)

What was Morgan’s reciprocal cross?

Red eye male (W+Y) and white eye female (ww)

What did the F1 generation look like in Morgan’s reciprocal cross?

1) all females were red (W+w), 2) all males were white (wY)

What did the F2 generation look like in Morgan’s reciprocal cross?

1) half of males were white (wY), 2) half of females were white (ww), 3) other half of progeny (both male and female) are red

What is the outcome of a reciprocal cross for an X linked trait?

The X linked trait will have a different outcome in the reciprocal cross than the original when in Mendel’s it didn’t matter

What is Bridge’s hypothesis about Drosophila eye color?

Sex chromosomes failed to separate in Meiosis 1 or 2 as a result of a nondisjunction mutation

What does nondisjunction look like in females crossed with wild-type male?

1) the progeny that is W+- would die, 2) wwy would be male and white eye

What is the result of researching Bridge’s hypothesis?

gene segregation and chromosome segregation are parallel

What are the 2 mechanisms of sex determination?

1) genotypic sex determination, 2) environmental sex determination

Y chromosome genotypic sex determination

1) humans, 2) y is active in determining maleness, 3) intersex

Intersex

expression falls between standard male or female

How common is intersex?

1 in 100 are classified as intersex

What are examples of Y chromosome genotypic sex determination?

1) turner syndrome where X- is female, 2) Klinefelter syndrome where XXY or XXXY is male

X chromosomal-autosomal balance system (genotypic)

1) flies, 2) ratio of number of X chromosomes to number of set of chromosomes determines sex

In the X chromosomal-autosomal balance system, how can you classify a male?

ratio is between X chromosomes to number of sets in less than or equal to 0.5

In the X chromosomal-autosomal balance system, how can you classify a female?

ratio is between X chromosomes to number of sets in greater than or equal to 1

In the X chromosomal-autosomal balance system, what is classified as intersex?

ratio is between X chromosomes to number of sets is equal to 0.75 (XXXY: AAAA)

Bird and Lepidoptera genotypic sex determination

1) females are heterogametic (ZW), where W determines femaleness

What is an example of the bird and lepidoptera genotypic sex determination?

1) platypus, 2) hymenopteran males are haploid in bees, 3) female bees are diploid

What are some examples of envrironmental sex determination?

1) marine worn bonelia, 2) turtles, 3) clownfish

How are Marine worn Bonelia sexually determined by the environment?

1) start undifferentiated as larvae, 2) if they settle down and avoid others they are female, 3) if they settle down near or on a female they are male

How are turtles sexually determined by the environment?

1) if the temperature is greater than 32 degrees C they are female, 2) if they temp is less than 28 degrees C they are male\`

How are clownfish sexually determined by the envrionment?

1) developmentally determined sex, 2) when developing or small they are male, 3) when mature they are female

Characteristics of an X linked recessive pedigree

1) female must be homozygous to be recessive, 2) affected males transmit to all daughters, 3) many more males affected, 4) all sons of affected mom are affected, 5) 1:1 in sons of carriers, 6) half of daughters will be carriers

If you an unable to determine the genotype of one outside of family what can you assume?

You can assume wildtype because it is the most frequent allele

What are the characteristics of a X linked dominant pedigree?

1) more rare, easy to eliminate, 2) heterozygous females affected, 3) more females affected than males, 4) affected males pass to all daughters but not sons

What are the characteristics of a Y linked trait?

1) every son affected from affected male, 2) no females affected, 3) non dominant v. recessive

complete dominance

phenotype of heterozygous is homozygous dominant phenotype

Incomplete Dominance

phenotype of heterozygous is intermediate

Codominance

heterozygous exhibit phenotypes of both homozygotes

Complete recessivity

recessive allele masked in heterozygote

lethal allele

occur at genes necessary for survival

Describe dominant lethal alleles in coat color in mice with 2 heterozygote parents for yellow and agouti, where yellow is dominant

1) YY is dead, 2) Y+ is yellow, 3) ++ is agouti, 4) phenotype is 2:1 with 2/3 yellow and 1 wildtype

Pleiotropy

one gene has multiple phenotypic effects

What is an example of a dominant allele?

huntington’s disease and death occurs after reproduction

Epistasis

interaction between two or more genes that control a single phenotype (unlinked or linked)

Why are recessive lethal alleles upheld in natural selection?

recessive phenotype is rare but in carriers

Why are dominant lethal alleles not upheld in natural selection?

occur in every generation and can be weeded out via death before reproduction

What is the fruit shape in summer squash in epistasis?

It is a special case of epistasis with an f2 ratio of 9:6:1 where 9 is the heterozygous intermediate, 6 is spheres that occur with an kind of homozygous recessive, and 1 is when non dominant alleles are present so other genes give phenotype

What is the outcome of recessive epistasis?

9:3:4 phenotypic ratio

What is an example of recessive epistasis?

coat color in labs

Recessive epistasis

Homozygous recessive allele of one gene blocks expression of 2nd genes, recessive homozygous stops regular pathway

What is the pathway for coat color in labs?

1) yellow → (E enzyme) 2) brown →( B enzyme) 3) black

If the Parental generation in recessive epistasis is BBEE (black) x bbee (yellow) , what does F1 look like?

BbEe (black) because black is dominant

If the Parental generation in recessive epistasis is BBEE (black) x bbee (yellow) , what does F2 look like?

9 B-E- (black) : 3 bbE- (brown) : 4 --ee (yellow)

Dominant epistasis

presence of dominant allele of one gene masks expression of 2nd gene, dominance stops regular pathway

What is the outcome of dominant epistasis?

12:3:1 phenotypic ratios

What is an example of dominant epistasis?

squash fruit color when yellow is dominant to green

If the F1 in dominant epistasis is WwYy (white)x WwYy (white), what is the f2 ==generation==?

12 W--- (white) : 3 wwY- (yellow) : 1 wwyy (green)

What is the genetic pathway of dominant epistasis?

white → (w gene) → green → (y gene) → yellow, where w needs to produce recessive homozygous to continue pathway

Penetrance

frequency in which a genotype is manifested in phenotypes of population

What is an example of 100% penetrance?

ABO blood system

Incomplete penetrance

Individuals with particular genotype do not necessarily show corresponding phenotype

What is an example of incomplete penetrance?

polydactyl where you can have allele just not show phenotype

Expressivity

degree to which a penetrant gene is phenotypically expressed

What is an example of expressivity?

osteogenesis imperfecta has 100 % penetrance but varies in severity of symptoms

What are some environmental affects on how genes present phenotypically?

1) internal environmental affects, 2) external environmental affects

What are some examples of internal environmental affects?

1) age, 2) sex

What are some examples of external environmental factors?

1) temperature (Himalayan coat color), 2) chemicals (PKU)

What are the requirements for genetic material?

1) store information, 2) replicate accurately, 3) must be variable or capable of change

What was the belief in 1900s?

1) chromosomes as carriers of heredity, 2) proteins in chromosomes were more variable and thus more capable of carrying genetic information

What two experiments showed that DNA not proteins were responsible for heredity/

1) Griffith’s transformation experiments (1928), 2) Avery’s Transformation Experiments (1944)

Transformation

when environmental DNA is taken up by cell

Griffith’s Experiment

isolated several strains of streptococcus pneumonia

What were Griffith’s two strains and their differences?

1) had smooth which has a polysaccharide coating and is virulent and sometimes mutated to rough, 2) rough did not contain coat and is nonvirulent

What did Griffith discover about smooth bacteria?

If it was heat shocked it became nonvirulent

What did Griffith discover about combining rough and smooth?

If he combined heat shocked smooth with rough it became virulent

What was Griffith’s conclusion?

something ( in coat) passed from dead bacteria to living bacteria that allowed it to be virulent aka the transforming principle

Avery’s Transformation Experiments

collected Griffith’s heat shocked strain and released cell content then centrifuged it where it separated into debris and extract, incubated cellular extract with rough nonvirulent bacteria

What was produced when Avery incubated cellular extract from heat shocked smooth strain with rough strain?

Smooth transformed deadly bacteria were formed

What does the extract contain?

1) polysaccharides, 2) proteins, 3) RNA, 4) DNA

Once Avery knew that cellular extract contained the transforming principle what did he do next?

In order to narrow it down into what specifically in cellular extract was the transforming principle he tried each component singly

What was Avery’s conclusion?

DNA was the transforming principle, because every time DNA was taken out the transformation did not happen

“bacteriophage” Experiments (1953)

grew DNA only phage and protein only phage with radioactivity to track

What is special about the bacteriopahges?

they only have DNA and protein

How do bacteriophages work?

1) moon lander looking phage that lands on bacteria cells and injects with DNA, 2)lysis cell and phages are released to find another host cell

What was the result of the bacteriophage experiments?

DNA phage progeny had radioactivity while protein phages did not

Linkage

2 or more genes are linked if they occur on the same chromosome

test cross

the F1 generation crossed with homozygous recessive

What are Mendel’s expected ratio for a dihybrid test cross?

1:1:1:1 with all 4 possible genotypes/ phenotypes

In a test cross between a heterozygote and a homozygous recessive, what are the phenotypic ratios of F2 if linked?

1:1 if completely linked with only phenotypes or parents present

When Mendel test crossed with linked genes what was the outcome?

1) a lot of progeny had parental phenotypes, 2) few had other phenotypes

How do you know what phenotypes are parental?

The most common phenotypes are parental phenotypes

What are recombinants a result of?

crossing over event occurred between the two genes on the chromosome

synaptonemal complex

protein structure that holds together homologous chromosomes early during prophase 1

Chiasma cross

Connections resulting from the breakage of chromosomes

cis configuration

when the wildtype alleles of two linked genes are linked together on the same chromosomes or the mutant alleles are linked

Trans configuration

when one mutant allele and one wildtype allele of two linked genes are linked on the same chromosome

What happens when 2 genes are far apart on Chromosomes?

1) The possibility of a cross over event occuring between them is greater with more distance, 2) higher the number of recombinants

Centimorgans

measure of closeness of genes on a chromosome

How do you calculate the frequency of recombinants?

% recombinants = (# of recombinants)/( total # of progeny), were 1 % recombinant = I map unit or centimorgan

Why is the maximum 50% recombinant?

After 50% the genes are sorting independently

What can be determined in 3 point mapping?

1) distance, 2) orientation

What are the steps to map a 3 point linkage?

1) is it cis or trans?, 2) determine genotypes of gametes, 3) determine parentals, 4) determine double cross over recombinants, 5) using double cross over determine which gene is in the middle, 6) calculate map distance