ch.5 when inheritance doesn't follow Mendelian patterns

Question 1

What is complete dominance?

Answer 1

heterozygous phenotype same as homozygote for dominant allele (all phenotypes turn out the same exxcept 1; 3:1 ratio)

Question 2

What is incomplete dominance?

Answer 2

heterozygote phenotype is intermediate
- phenotype is somewhere between heterozygote and homozygote

Question 3

what is codominance?

Answer 3

heterozygote simultaneously expresses the phenotype of both homozygotes
-blood types

Question 4

What is penetrance?

Answer 4

• the extent to which a particular gene or set of genes is expressed in the phenotypes of individuals carrying it
  # of individuals expressing expected phenotype/ all individuals with particular genotype
• ex. human polydactyly

Question 5

What is variable expressivity?

Answer 5

the degree to which a gene is expressed is due to the environment or other genes from the genome

Question 6

What is a lethal allele?

Answer 6

-an allele that causes death at certain variations

Question 7

What is an allelic series?

Answer 7

multiple alleles for the same locus

Question 8

What is epistasis?

Answer 8

one gene at one locus masks the effect of another gene at another locus
- if genes are involved in the same biochemical pathway, a gene that affects an early step will be epistatic to a gene that affects a later step

Question 9

What is recessive epistasis and what is its ratio?

Answer 9

• 2 mutant alleles are necessary for gene to be epistatic to another
• ex. coat color in dogs
• 9:3:4

Question 10

What is dominant epistasis and its ratio?

Answer 10

• only one mutant allele necessary for gene to be epistatic to another
  -12:3:1
  ex. fruit color

Question 11

What is duplicate recessive epistasis and its ratio?

Answer 11

• When there is a recessive allele masking the expression of dominant alleles at two loci
• if you are double recessive for either or both of the genes then you will exhibit the phenotype
• ex. albinism in snails
• 9:7

Question 12

What are sex-influenced characteristics?

Answer 12

characteristics determined by autosomes can be expressed differently in males and females
-ex. bearded trait has higher penetrance in male goats than females

Question 13

What are sex-limited characteristics?

Answer 13

a trait determined by autosomal genes may only show up in one sex; in the other sex there is zero penetrance
- ex. tail feathers in chickens

Question 14

Where does cytoplasmic inheritance come from?

Answer 14

usually passes from mother to offspring but not all offspring will have the same chromosomes given to them
- means reciprocal crosses will not work the same way; all depends on the mom’s genome

Question 15

What is genetic maternal effect?

Answer 15

• genes are inherited from both parents but mother’s genotype determines offspring’s phenotype
  why? because what the mother puts in the egg determines the genotype

Question 16

What is genomic imprinting?

Answer 16

Genetic material can be differentially expressed based on which parent it came form
- ex. mammals = fetal growth
- ex. plants = endosperm
- ex in human disease = Prader-WIlli syndrome and Angelman syndrome

Question 17

What is heritability?

Answer 17

how much phenotypic variation in a population is due to genetic variation
-ex. high heritability - eye color
-ex. low heritability - personality traits

Question 18

What are discrete/discontinuous characteristics?

Answer 18

• usually characterized by presence/absence variation and follow mendelian inheritance patterns

Question 19

What are continuous/quantitative characteristics?

Answer 19

• have a continuous distribution of phenotypes
• most traits because they are effected by lots of genes and environment as well