Genetics Test 1 _ Ch2, 4, 6

Why did Mendel choose peas?

Why did Mendel choose peas?

He could control true breeding through self-pollination & he could make sure character traits would not change.

character

descriptor of trait

trait

descriptive qualitative visual

gene

section of dna

allele

different versions of genes

true breeding

AA

homozygous

AA or aa - same two alleles

heterozygous

Aa- two different alleles

genotype

combination of alleles (genetic make-up)

phenotype

observable traits

dominant

trait that will show when present

recessive

trait that will only show if no dominant traits is present

monohybrid

one trait is crossed(TTxtt)

dihybrid

two traits are crossed (TTpp x ttpp)

law of segregation

two copies of a gene segregate from each other during the process that gives rise to gametes

• discovered via monohybrid cross

• f1 generation = 3:1 phenotype ratio

law of independent assortment

two different genes will randomly assort their alleles during the process that gives rise to gametes

• discovered by dihybrid cross

• phenotypic ratio = 9:3:3:1

law of dominance

traits can be hidden behind dominant traits

chi square test

hypothesis testing - is the data consistent within Mendel’s laws?

null hypothesis

there is no difference between observed and expected values

chi square equation

degrees of freedom

n-1

simple mendelian inheritance

• dominant/recessive

• all individuals w at least one dominant allele express dominant phenotype

• 2 recessive alleles=recessive phenotype

incomplete penetrance

• despite dominant trait present, only some express phenotype

• expressing a percent penetrant

incomplete dominance

• a dominant allele cannot fully mask a recessive → intermediate phenotype

• recessive allele prevents full dominance

• neither alleles dominate

overdominance

heterozygous individual has a fitness advantage over homozygous

codominance

both alleles are expressed, no true dominance

x-linked

• gene is on a chromosome “x”

• females can compensate if affected, men more likely to show phenotype

sex-influenced

• gene on autosomes

• expression of phenotype differs in each sex (hair)

sex-limited

• gene on autosomes

• only expressed in one sex (lactation")

lethal alleles

two alleles = death

pleiotropy

expression differs in location/timing/tissues/development

epistasis

expression of one gene modified (masked) by the expression of one or more other genes

complementation

• to compliment = to make whole

• mutations in different gene lead to same phenotype

• two mutant parents can produce offspring with wild type phenotype

loss of function

at dna level, protein is changed and is non-functional

gain of function

at dna level, protein is changed and is more functional - common cause of cancer

hemophilia

“the royal disease” reduces clotting and can cause internal bleeding

what is linkage

two alleles for linked genes are typically inherited together because they are located on the same chromosome

how does linkage affect inheritance

certain phenotypes may not occur unless there is recombination - less phenotypic diversity

What are the characters that Mendel examined in the pea plants?

Height, color, position, seed color, seed shape, pod color, pod shape

Would it be possible to deduce the law of independent assortment from a single factor cross?

No, it is not possible to deduce the law of independent assortment from a single factor cross because this law requires two different genes to randomly assort themselves. This can only be achieved via a dihybrid cross.

What is the difference between cross-fertilization and self-fertilization?

Cross-fertilization is when the gametes needed to produce life come from another plant while in self-fertilization the gametes come from the same plant. Cross-fertilization creates a much higher level of diversity than self-fertilization.

An individual has a genotype Aa Bb Cc and makes an abnormal gamete with genotype AaBc. Does this gamete violate the law of independent assortment or the law of segregation?

law of segregation - This violates the law of segregation because the Aa alleles are still together after the cross has occurred, which directly violates the law of segregation. 

A true breeding tall pea plant was crossed with a true breeding dwarf plant. What is the probability that an F1 plant will be a true breeding plant? What is the probability that an F1 plant will be a true breeding tall plant?

None of the F1 generation will be a true breeding plant because all possible offspring with be heterozygous for both alleles. 

Identical twins are produced from the same sperm and egg (which splits after the first mitotic division), whereas fraternal twins are produced from separate eggs cells. If two parents with brown eyes (dominant trait) produce one twin boy with blue eyes.

 

What is the probability that if the twins are identical, the second twin will have blue eyes?

100%

Identical twins are produced from the same sperm and egg (which splits after the first mitotic division), whereas fraternal twins are produced from separate eggs cells. If two parents with brown eyes (dominant trait) produce one twin boy with blue eyes.

 

What is the probability that if the twins are fraternal, the second twin will have blue eyes?

25%

Genes that are not required for survival, but are likely to be beneficial to the organism, are called ________.

nonessential genes

For a certain trait, a heterozygous individual has a selective advantage as compared to a homozygous dominant or homozygous recessive individual. This is called ________.

overdominance

At the molecular level, which of the following best explain heterozygous advantage and overdominance?

• Infectious organisms may recognize only a specific functional protein

• A heterozygous individual can produce more varieties of homodimer proteins

• The alleles produce two different proteins with slightly different functions

• The proteins produced by the alleles may provide a broader range of environmental tolerance, such as temperature ranges

If an allele is dominant in one sex and recessive in another, it is an example of ________.

sex-influenced inheritance

Temperature-sensitive alleles that kill an organism only in a particular temperature range are examples of ________.

conditional lethal alleles

A paralog ________.

can explain the lack of phenotype for a gene knockout

A ________ allele is the most prevalent allele in a population and usually encodes a protein that is made in the proper amount and functions normally.

wild-type

If a combination of two or more genes is required to produce a specific trait, it is called a(n) ________.

gene interaction

T/F Incomplete dominance is an example of blending of phenotypes, not genotypes.

True

T/F Paralogs are often functionally redundant and can compensate for the loss of either of the paralogs in a set.

True

T/F In codominance, both alleles make functional gene products which are expressed simultaneously.

True

T/ F In sex influenced traits, both sexes can express the trait, depending on their genotype, but in sex limited inheritance a particular sex can only have one phenotype for the trait in question.

True

An individual with type A blood and an individual with type B blood mate and have offspring. What blood type is not possible in their offspring?

From this information given, all blood types are possible.

In a dihybrid cross of two heterozygous individuals, you expect a 9:3:3:1 phenotypic ratio in the offspring, but observe a ratio of 9:7. What is the most likely explanation?

epistatic interaction of the two genes

The multiple effects of a single gene on the phenotype of an organism is called ________.

pleiotropy

Which of the following defines the principle of linkage?

Both two or more genes that are physically connected on a chromosome and genes that are transmitted to the next generation as a group.

T/F A genetic linkage map indicates that precise distance between two genes of interest.

False

Crossing over is more likely to occur between genes that are ________ on a chromosome.

far apart

A testcross is always performed between the individual that is heterozygous for the genes to be mapped and an individual who is ________.

homozygous recessive for the genes

In a given mapping experiment, you expect that incidence of double crossovers is 3.5%, but you only observe 2.5%. This can be explained by ________.

interference

Another name for a chromosome is a ________, since it contains genes that are often inherited together.

linkage group

Two genes that are located on the same chromosome are said to be ________.

physically linked

T/F The rearrangement of alleles by the process of crossing over is called genetic linkage.

False

The first observational evidence that genes may be inherited together rather than by simple Mendelian inheritance was provided by ________.

Bateson and Punnett

T/F The percentage of recombination associated with independent assortment should approximate 50%.

True

In a chi-square test to determine if two genes are linked or assorting independently, what is the default (null) hypothesis that is tested?

The genes are assorting independently

While mapping two genes in Drosophila, you observe 30 recombinants among 200 total offspring. What is the distance between these genes?

15 Map units

Which of the following is not one of the principles of linkage that Morgan obtained from his experiments?

Genes that are on the same chromosome are always transmitted together as a unit.

T/F Following crossing-over, chromosomes with genetic combinations that resemble the parents' chromosomes are called nonrecombinant.

True

Assume that genes C and D are located on the same chromosome. On one chromosome, alleles C and D are found, while the homologue contains alleles c and d. Which of the following would be evidence of a recombination event?

Both alleles C and d together on one chromosome and alleles c and D together on one chromosome.

>50 units

assorts independently

frequency of recombination

number of recombinant offspring/ total progeny x 100

Map distance

number of recombinant offspring/ total progeny x 100

Coefficient of coincidence

observed number of double crossovers/ expected number of double crosses

expected double crosses

probability of cross 1 x probability of cross 2

interference

1-coc