Extensions to Mendel's Rules II - Lecture 7

Question 1

Sex-influenced characters

Answer 1

Determined by autosomal genes
Inherited according to Mendels principles
Characters expressed differently in males and females
Ex. beards in goats

Question 2

Sex-limited characters

Answer 2

Located on autosomes but are expressed in only one sex
Zero penetrance in opposite sex.
Ex. cock feathering is autosomal recessive that is sex-limited to male chickens

Question 3

Cytoplasmic inheritance

Answer 3

Mitochondrial (and chloroplast) genes
Some characteristics are encoded by genes located in the cytoplasm.
Phenotype is determined by cytoplasmic genes
Frequently exhibit extensive phenotypic variation
Usually maternal

Question 4

Genetic Maternal Effect

Answer 4

The phenotype of offspring is determined by genotype of mother.
Genes are inherited from both parents but the offspring’s phenotype is determined not by it’s own genotype.
Ex. Shell coiling in snails

Question 5

Genomic Imprinting

Answer 5

Differential expression depending on whether it is inherited from the male or female parent
DNA methylation is essential. In mammals methylation is erased in the germ cells of each generation and then reestablished in the course of gamete formation with sperm and eggs undergoing different levels of methylation, resulting in the differential expression of male and female alleles in the offspring.

Question 6

Prader-Willi

Answer 6

Missing small region on long arm of chromosome 15, inherited from the father.
If this deletion is inherited from mother it produces different set of syndromes called Angelman syndrome

Question 7

Angelman Syndrome

Answer 7

Deletion chromosome 15 inherited from mother

Exhibit frequent laughter, uncontrolled muscle movement, large mouth, unusual seizures

Question 8

Anticipation

Answer 8

The stronger or earlier expression of a genetic trait through succeeding generations, caused by an unstable region of DNA that increases or decreases in size.
Ex. myotonic dystrophy

Question 9

Environmental effects on gene expression

Answer 9

The phenotypic expression of some genotypes critically depends on the presence of a specific environment.
Ex. Himalayan allele in rabbits have dark fur in extremities when temp is below 25 C. An enzyme necessary for the production of dark pigment is inactivated at higher temperatures.

Question 10

Temperature-sensitive allele

Answer 10

An allele whose product is functional only at certain temps

Question 11

Discontinuous Characteristics

Answer 11

Have few easily distinguished phenotypes.

Ex. smooth or wrinkled seed, yellow or green or blood types

Question 12

Continuous Characteristics

Answer 12

Often called quantitative characteristics

Because they often have many possible phenotypes and must be described in quantitative terms. Ex. Human height.

Question 13

Polygeny

Answer 13

Characteristics encoded by genes at many loci are polygenic characteristics.
The number of genotypes encoding a characteristic is 3^n, where n is the number of loci, each with two alleles, that influence the characteristic.

Question 14

Pleiotropy

Answer 14

One gene affects multiple characteristics.
Opposite of polygeny
Ex. PKU results from a recessive allele and people who are homozygous for it, if untreated, exhibit MR, blue eyes and light skin color

Question 15

Genetic-conflict hypothesis

Answer 15

There are different and conflicting evolutionary pressures acting on maternal and paternal alleles for genes that affect fetal growth

Question 16

Epigenetics

Answer 16

Some traits are caused by alterations to the DNA that affect the way in which the DNA sequences are expressed. They are stable and heritable, passed from one cell to another.

Question 17

Anticipation

Answer 17

A genetic trait becomes more strongly expressed or is expressed at an earlier age as it is passed from generation to generation.

Question 18

Phenocopy

Answer 18

Environmental factors alone can produce a phenotype that is the same as the phenotype produced by the genotype

Question 19

Multifactorial characteristics

Answer 19

Continuous characteristics that are both polygenic and influenced by enviro factors. Many factors help determine the phenotype.

Question 20

How do sex-influenced and sex-limited differ from sex-linked traits?

Answer 20

Both sex-influenced and sex-limited traits are encoded by autosomal genes whose expression is affected by the sex of the individual organism possessing the gene. Sex-linked traits are encoded by genes on the sex chromosome.

Question 21

How might you determine if trait is due to cytoplasmic inheritance or to genetic maternal effect?

Answer 21

Cytoplasmically inherited traits are encoded by genes in the cytoplasm, which is usually inherited from the female parent. So a trait due to cytoplasmic will always be passed through females. Traits due to genetic maternal effect are encoded by autosomal genes and can therefore be passed through males, although any individual organism’s trait is determined by the genotype of the maternal parent.

Question 22

What type of epigenetic mark is responsible for genomic imprinting?

Answer 22

Methylation of DNA