Extensions to Mendel's Laws Flashcards by Emily Love

What is complete dominance?

The hybrid resembles one of the two parents

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What is incomplete dominance?

Hybrid is intermediate phenotype of both parents

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What is codominance?

Hybrid shows traits from both parents.

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What are the genotypic and phenotypic ratios of F2 progeny from F1 parents with incomplete dominance?

1:2:1

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What traits do F1 hybrids have in codominance?

Display traits of both parents

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What are the F2 progeny ratios in codominance?

1:2:1 for both phenotype and genotype

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What three alleles determine ABO blood types in humans?

I^A = A type sugar
I^B = B type sugar
i = no sugar

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When are successful blood transfusion made and why?

Only with matching blood types because antibodies are made against type A and type B sugars.

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Who are universal blood recipients?

Type AB

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Who are universal blood donors?

Type O

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What is an extreme example of multiple alleles?

Histocompatibility antigens

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What are histocompatibility antigens?

Cells surface molecules on all cells except for RBCs and sperm that facilitate proper immune response to foreign antigens.

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Why does everyone have a distinct histocompatibility phenotype?

Three major genes encode the antigens, each gene has 400-1200 codominant alleles

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What are mutations?

Chance alterations of genetic material that arise spontaneously

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When can mutations be transmitted to offspring?

If the occur in gamete-producing cells

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What is the frequency of gametes with mutations?

10^-4 to 10^-6

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How can mutations be used to follow gene transmission?

Mutations that result in phenotypic variants

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What is allele frequency?

Percentage of the total number of gene copies for one allele in a population

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What is the wild-type (+) allele

The most common allele in a population

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What is a mutant allele?

An allele that is rare in a population

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What does it mean for a gene to be monomorphic?

Gene has only one common wild-type allele

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What does it mean for a gene to be polymorphic?

Gene has more than one common allele

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What are common variants?

High-frequency alleles of polymorphic genes

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What is pleiotropy?

The phenomenon of a single gene determining several distinct and seemingly unrelated characteristics

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Give an example of pleiotropy

Many aboriginal Maori men have respiratory problems and are sterile. Defects due to mutations in a gene required for function of cilia and flagella

What does a 2:1 F1 ratio indicate?

A recessive lethal allele; synthetic lethality

What is epistasis?

An allele at one gene masks the effects of another gene

What is an epistatic gene? Hypostatic?

Epistatic = gene that does the masking Hypostatic = gene that is masked

Describe the two genes that determine coat colour in labs.

B alleles determine black and brown colour. ee of gene E is epistatic to B and determines yellow

What is an additive gene interaction?

Four distinct F2 phenotypes

What is the biochemical explanation for coat colour in labs?

Protein E helps generate eumelanin, protein B deposits it. B- deposits eumelanin densely (black) bb deposits eumelanin less densely (brown) ee animals cannot make eumelanin (yellow)

How does recessive epistasis lead to a rare blood type in humans?

Individual appears to have type O blood but can pass A or B to their children. Gene for substance H is epistatic to the ABO gene. Without H substance, there is nothing for A or B sugar to attach to. All type A, AB, B, O people are H- People with hh will appear to be type O

What are redundant genes?

Genes where only one dominant allele needs to be preset

What is the ratio of redundant genes?

15;1

What is the F2 phenotypic ratio for additive gene interactions?

9:3:3:1

What is the F2 phenotypic ratio of recessive epistasis?

9:3:4

What is the F2 phenotypic ratio of reciprocal recessive epistasis?

9 to 7

What is reciprocal recessive epistasis?

When homozygous, recessive allele of each gene masks the dominant allele of the other gene.

What is dominant epistasis I?

Dominant allele of one gene hinders effects of both alleles of the other gene

What is the ratio of dominant epistasis I?

12 to 3 to 1

What is dominant epistasis II?

Dominant allele of one gene hides effects of dominant allele of other gene

What is the F2 phenotypic ratio of dominant epistasis II?

13 to 3

What are heterogeneous traits?

Traits with the same phenotype but caused by different mutations in different genes.

What is an example of a heterogeneous trait in humans?

Deafness

What is complementation testing?

Used to determine if a particular phenotype arises from mutations in the same or separate genes.

What phenotypes can complementation testing be applied to?

Recessive

What can cause phenotypic variation (3)?

Effects of modifier genes Effects of environment Pure chance

What is pentrance?

The % of individuals with a particular genotype that show the expected phenotype

What is expressivity?

The degree or intensity with which a particular genotype is expressed in a phenotype.

What are modifier genes?

Genes that alter the phenotypes produced by alleles of other genes,

Describe an example of modifier genes.

T locus of mice Mutant T allele causes abnormally short tail Tails can be 75% of normal length or 10% Different inbred strains carry alternative alleles of a gene that modifies T phenotype.

How does temperature affect coat colour in siamese cats?

Extremities are darker than body because of a temperature sensitive allele.

How does temperature affect survivability of a Drosophila mutant?

Shibire mutants develop normally at <29C but are inviable at temperatures higher than that.

What are conditional lethal mutations?

Mutations that are lethal only under some conditions.

What is phenocopy?

Phenotype arising from an environmental agent that mimics the effect of a mutant gene.

Is phenocopy heritable?

Give examples of phenocopy in humans.

Thalidomide ingestion by pregnant women produced a phenocopy of phocomelia, a rare dominant trait. Children with heritable PKU can receive a protective diet. Genetic predisposition to cardiovascular disease can be influenced by diet and exercise. Genetic predisposition to lung cancer is strongly affected by cigarette smoking.

What are discontinuous traits?

Traits with either-or phenotypic differences between alternative alleles

How are discontinuous traits determined?

By segregating alleles of many genes that interact together and with the environment

What is a common feature of continuous traits? WHat does it mean?

Usually polygenic - controlled by multiple genes

What is another term for continuous traits?

Quantitative traits.

What are examples of continuous traits in humans?

Height and skin colour