Complex Inheritance Patterns

Question 1

what is Mendel’s rules correct for? what don’t they work for?

Answer 1

correct for predicting genotype, but not for most phenotypes and traits

Question 2

define incomplete dominance

Answer 2

where neither allele completely dominates and you get a “blended” phenotype

Question 3

what does incomplete dominance reflect the importance of?

Answer 3

important of gene dosage in creating most phenotypes

Question 4

describe multiallelic genes

Answer 4

for most genes in diverse populations, there are almost always more than just two alleles

Question 5

example of multiallelic gene

Answer 5

tyrosinase- a tissue specific effector gene that encodes an enzyme required for melanin synthesis (there are 102 functional mutations - phenotypic alleles - of the mouse tyrosinase gene in exons and CREs

Question 6

describe pleiotropic genes, what rule does it defy?

Answer 6

mutations in a single gene affects many “traits”, defies the “one gene, one trait” rule

Question 7

describe continuous phenotypic variation

Answer 7

very few traits are “binary” like simple mendelian genetic diseases, most phenotypes fall on a broad spectrum

Question 8

potential causes of continuous phenotypic variation

Answer 8

1) CRE mutations that create partial LOF or GOF alleles with slight more/less expression
2) mulitgenic traits where several genes add together to give phenotype
3) environment contributes to variation

Question 9

example of “multigenic trait”

Answer 9

height- multiple intercellular signaling receptors/ligands, T.F.s and tissue specific effector genes work together to determine height

Question 10

the only “exception” to Mendel’s rules relating to genotype and alleles

Answer 10

genetic linkage, genes are not physically independent particles

Question 11

what does genetic linkage predict? who observed this?

Answer 11

predicts that certain phenotypes will tend to appear together, Thomas Hunt Morgan saw linkage using vinegar flies (probably because he looked at many more traits than Mendel)

Question 12

why does genetic linkage happen?

Answer 12

genes can be physically linked on chromosomes and as a result, alleles and phenotypes can co-segregate

Question 13

linkage in practical terms

Answer 13

phenotypes for body color, eye color, and wing shape would usually occur together and defy independent assortment ratios seen by Mendel

Question 14

why is linkage not usually complete?

Answer 14

because crossing over can “unlink” alleles & the further apart two genes are on a chromosome, the higher the odds of crossing over happening between them and then they behave more like “independently assorting” particles predicted by Mendel

Question 15

describe sex determination

Answer 15

whether germline cells differentiate into eggs, sperm, both or neither

Question 16

define anisogamous

Answer 16

meaning they have gametes of different sizes and morphology

Question 17

define isogamous

Answer 17

there is only one type of gamete

Question 18

define agamous

Answer 18

never go through meiosis, reproduce by budding or fragmentation

Question 19

how do different tissue-specific effector genes become activated in germline cells?

Answer 19

same way as usual development, different combos of T.F.s activate tissue-specific effector genes to differentiate eggs vs sperm

Question 20

examples of egg effector genes

Answer 20

yolk proteins, albumin proteins

Question 21

examples of sperm specific genes

Answer 21

flagellar proteins, intercellular signaling ligands/receptors

Question 22

what does the combo of transcription factors acquired by the germline depend on?

Answer 22

genetics and/or environmental factors, depending on the species

Question 23

describe environmental sex determination

Answer 23

environmental cues such as temperature, population density, nutrient availability, day/light cycle determine which gametes are produced; can also induce switching to asexual reproduction

Question 24

describe parthenogenesis

Answer 24

laying fertile eggs (budding or fragmentation)

Question 25

what sex determination mechanisms for vertebrates use?

Answer 25

wide variety of genetic and environmental factors

Question 26

sex determination in mammals and birds

Answer 26

is genetic

Question 27

sperm producer and egg producer in mammals

Answer 27

XY; XX

Question 28

sperm producer and egg producer in birds

Answer 28

ZZ; ZW

Question 29

in mammals, what T.F. controls sex determination

Answer 29

SRY gene on the Y chromosome

Question 30

in birds, what T.F. determines sex

Answer 30

DMRT-1 on the Z chromosome

Question 31

role of SRY

Answer 31

activates tissue specific effector genes for sperm production and inhibits those for egg production

Question 32

example of a true, completely dominant allele

Answer 32

SRY, “sperm production” is inherited according to simple Mendelian traits

Question 33

genes that happen to be on the X chromosome are called?

Answer 33

sex or X-linked genes

Question 34

consequence of the Y chromosome is missing lots of genes

Answer 34

disease-causing, recessive X-linked alleles ac dominant in gametic males