Modifications of Mendelian Genetics (Lec 3-7)

Question 1

Non-Mendelian mode of inheritance where the heterozygote condition is intermediate between the extreme phenotypes

Answer 1

Incomplete dominance (ex. flower color in snapdragons or raphanus shape and color)

Question 2

Heterozygote condition manifests both extremes of dominant and recessive phenotypes.

Answer 2

Co-Dominance (ex. Cattle coat color and MN Blood Group System)

Question 3

Differentiate incomplete dominance from codominance.

Answer 3

Incomplete dominance will be a mix of the two extremes of the trait.

Codominance will distinctly show the extremes of the trait

(Analogy: for incomplete dominance, red and white make pink. For codominance, red and white will appear at the same time)

Question 4

One gene pair, many effects. Different subsets of symptoms may superficially appear as if caused by different disorders

Answer 4

Pleiotropy (ex. Phenylketonuria)

Question 5

Caused by any mutation in the PAH gene (found on 12q23.2) that codes for the phenylalanine hydroxylase enzyme that converts phenylalanine (Phe) to tyrosine (Tyr)

Answer 5

Phenylketonuria

Question 6

Atleast three types of alleles for a particular trait, with two alleles in a single locus at a time.

Dominant hierarchy may be exhibited.

Answer 6

Multiple Alleles (ex. Coat color in rabbits: C>cch>ch>c or ABO Blood typing in Humans)

Question 7

Formula for # of genotypes for multiple alleles?

Answer 7

(n/2)(n+1) where n is the # of alleles in a series

Question 8

For the coat color of rabbits, C>cch>ch>c is the dominance hierarchy. How many genotypes can be made?

Answer 8

n = 4
Using (n/2)(n+1) = (2)(5)=10

=10 Genotypes.

Question 9

What is Bombay Phenotyping?

Answer 9

H-antigen is the base antigen in blood.

A- B- and O- genes will affect terminal sugar

O-gene will not add anything and retain that base antigen

B-Gene will use Galactosyl Transferase to turn H into a B antigen by adding Gal

A-Gene will use N-Acetylgalactosaminyl transferase to add GalNAc turning H into an A Antigen.

People are either hh, Ha_ or Hb_

Question 10

What is the general pattern of X-linked dominant inheritance?

Answer 10

Affected fathers will always have affected daughters

Question 11

What is the general pattern for x-linked recessive inheritance?

Answer 11

Affected mothers will always have affected sons

Question 12

For y-linked traits, what is the expected pattern of inheritance?

Answer 12

Father to son only

Question 13

What is Sex-linked inheritance

Answer 13

Traits are located on the sex chromosomes (X or Y).

Ex. RG Color blindness

Question 14

Why is sex-linked, inheritance more likely to affect males than females.

Answer 14

Males have only one X chromosome, so any recessive trait on that chromosome will be expressed.

Females have two X chromosomes, so a recessive trait needs to be present on both X chromosomes to be expressed.

Y chromosome linked traits are only passed from father to son

Question 15

What is sex-limited inheritance

Answer 15

Traits are located on autosomes but expression is limited to one sex.

Ex. Lactation

Question 16

What differentiates sex-limited from sex-linked.

Answer 16

For sex limited, traits can be present in both sexes but only activated in one due to hormonal or other regulatory factors.

Question 17

What is sex-influenced inheritance?

Answer 17

Traits are located on autosomes but their expression is influenced by sex hormones

Ex. Male Pattern Baldness

Question 18

What differentiates sex-influenced from sex-limited and sex-linked

Answer 18

Traits can be present in both and can still be exhibited despite regulatory and genetic factors but with different degrees.

Ex. Pattern baldness as alopecia in women.

Question 19

Gene interaction where some genes may mask or hide the effects of other genes?

Answer 19

Epistatic Genes

Ex. Rat Coat Color

Question 20

Term for genes that mask other genes

Answer 20

Epistatic Genes

Question 21

Term for genes that are masked

Answer 21

Hypostatic Genes

Question 22

Occurs when the phenotypic expression of an epistatic gene masks the effect of a hypostatic gene when the epistatic gene is in homozygous recessive form.

Answer 22

Recessive epistasis

Question 23

Give the modified phenotypic ratio for Recessive Epistasis. Let A be dominant to a, B be dominant to b, and bb recessively epistatic to A.

Answer 23

9:3:4:: A_B_ : aaB_ : __bb

Question 24

Occurs when the phenotypic expression of an epistatic gene masks the effect of a hypostatic gene as long as the epistatic gene has a dominant gene.

Answer 24

Dominant Epistasis

Question 25

Give the modified phenotypic ratio for Dominant Epistasis. Let A be dominant to a, B be dominant to b, and A_ be dominantly epistatic to B

Answer 25

12:3:1:: A_ _ _ :aaB_:aabb

Question 26

Occur when two genes produce the same phenotype when both the genes have a phenotype with dominant allele either in heterozygous or homozygous dominant condition. TL;DR: More dominant genes = More "complete" trait, similar to incomplete dominance but with two different loci

Answer 26

Duplicate Genes with cumulative effects

Question 27

What is the phenotypic ratio for Duplicate genes with cumulative effect? Let A be dominant to a, B be dominant to b

Answer 27

9:6:1::A_B_: A_bb+aaB_ :aabb

Question 28

Occurs when two loci code for the same trait where in only the homozygous recessive traits for both loci will show a different trait. Or, As long as there is one dominant gene, dominant trait is expressed

Answer 28

Duplicate dominant gene interaction

Question 29

Give the phenotypic ratio for Dominant Gene interaction. Let A be dominant to a, B be dominant to b

Answer 29

15:1::A_ _ _+ _ _ _ B : aabb

Question 30

Occurs when a homozygous recessive gene pair is present in either of the two loci that code for the same trait.

Answer 30

Duplicate Recessive Gene interaction

Question 31

Give the phenotypic ratio for Duplicate Recessive Gene Interaction

Answer 31

9:7::Dominant:Recessive

Question 32

Similar to dominant epistasis, occurs when certain genes have the ability to suppress the expression of a gene at a second locus.

Answer 32

Dominant and Recessive Gene interaction. (Dominant suppression epistasis in other literature)

Question 33

Give the phenotypic ratio of Dominant and Recessive Gene interaction.

Answer 33

13:3 Dominant: Recessive

Question 34

Genes with effects drastic enough to cause death of the individual at the embryonic stage

Answer 34

Lethal Genes

Question 35

Genes that shorten the normal life expectancy of an individual.

Answer 35

Sublethal genes

Question 36

Example for Lethal Genes in the Lecture, and give the phenotypic ratio. (Either of the two, for mouse or for humans)

Answer 36

**Coat color in mice** * Yellow fur color heterozygous (A^Y A) * Hybrids yield phenotypic ratio of 2/3 yellow and 1/3 agouti * Hybrids associated with obesity, diabetes, and tumors * AYAY genotypes result in preimplantation embryonic lethality * AY mutation disrupts structure & expression of Merc gene (renamed Raly) that codes for an RNA-binding protein expressed throughout development **Achondroplasia in Humans** * homozygote dominants are usually lethal

Question 37

Condition defined by multiple basal cell carcinomas (basaliomas) and other skin malignancies occuring at a young age. This is an example of?

Answer 37

Xeroderma pigmentosum; Sublethal genes.

Question 38

Occurs when a single phenotypic character is affected by two or more genes

Answer 38

Polygenic Inheritance

Question 39

Extrachromosomal or Extranuclear Inheritance involving DNA in chloroplasts and mitochondria

Answer 39

Organelle Heredity

Question 40

How is organelle heredity transmitted?

Answer 40

Transmission occurs form maternal parent through the ooplasm

Question 41

Where is DNA found in chloroplasts?

Answer 41

In the Stroma

Question 42

Chloroplast DNA (cpDNA) is commonly how large in size?

Answer 42

100-225 kbp

Question 43

T/F Chloroplast contains circular DNA and a complete gene expression system

Answer 43

True

Question 44

T/F Mitochondrial DNA is commonly circular, and sometimes normal.

Answer 44

True

Question 45

Mitochondrial DNA is usually how large

Answer 45

10-81 kb, average 16 kb in animals

Question 46

How large is the Human Mitochondrial DNA?

Answer 46

16.6 kb

Question 47

Where is mitochondrial DNA found?

Answer 47

In the mitochondrial matrix within the inner membrane

Question 48

Describe the organization of Mitochondrial DNA

Answer 48

Double stranded, circular, and small, free of proteins. 5-10 copies/organelle in vertebrates, 20-40 in plants

Question 49

Genetic code in mtDNA is similar to nuclear genetic code. How is it different?

Answer 49

trp is the stop codon in mtDNA, not UGA AUA is methionine, in mtDNA, isoleucine in nuclear genetic code

Question 50

Theory proposed by Lynn Margulis to explain presence of DNA in organelles. What does it discuss?

Answer 50

Endosymbiont Theory Primitive eukaryotes engulfed other prokaryotes as endosymbionts

Question 51

What are the traits in Chloroplast Mutations in Chlamydomonas reinhardi

Answer 51

unicellular haploid single large chloroplast 75-80 copies of circular double-stranded DNA molecule, 195 kb in size two mating types: mt+ and mt- Streptomycin resistance or sensitivity come from mt+ parent

Question 52

What are the traits in Mitochondrial Mutations of poky in Neurospora

Answer 52

* slow-growing mutants; loss of several cytochromes * cytoplasmic/maternal inheritance – maternal poky x paternal wt→ all poky – maternal wt x paternal poky→ all wt * hyphae fusions between poky and wt produce heterokaryons (two nuclei) with mitochondria from both parental cells – begins with normal phenotype – become progressively more abnormal (poky) – poky is a suppressive mutation

Question 53

Saccharomyces petite Mutations are defined by?

Answer 53

petite mutations giving rise to small colonies due to blocked aerobic respiration.

Question 54

What are the two types of petites in Saccharomyces petite mutations?

Answer 54

Segregational petites: encoded by nuclear genes showing Mendelian inheritance Cytoplasmic transmission pattern petites

Question 55

Cytoplasmic transmission pattern petites have two types, what are they?

Answer 55

Neutral: give all wt offspring when crossed to wt suppressive petites: Will mask any other trait making them all petite

Question 56

Variable mixture of genetically distinct mitochondria/mtDNAs is called?

Answer 56

Heteroplasmy

Question 57

What are the 3 properties of mtDNA-encoded traits

Answer 57

– Maternal inheritance pattern – Deficiency in bioenergetic function of organelle – Specific mutation in one or more mtDNA genes

Question 58

Human mtDNA consists of how many base pairs?

Answer 58

16,569 bps or 16.6 kbp

Question 59

The human mtDNA is composed of how many rRNAs, tRNAs, and polypeptides?

Answer 59

2rRNAs 22tRNAs 13 polypeptides

Question 60

Human mtDNA Disorder characterized by Ataxia, deafness, dementia, epileptic seizures, and presence of fibers from proliferation of aberrant mitochondria

Answer 60

Myoclonic epilepsy and ragged red fiber disease (MERRF) Caused by A-to-G mutation in mtDNA tRNALys gene

Question 61

Human mtDNA disorder characterized by Sudden bilateral blindness (average age 27 yrs) Most mutations in NADH dehydrogenase gene Maternal transmission to all offspring

Answer 61

Leber’s hereditary optic neuropathy (LHON)

Question 62

What are the two methods of Mitochondrial Replacement Therapy?

Answer 62

Maternal Spindle Transfer Technique Pronuclear Transfer Technique

Question 63

Transmission characterized by cytoplasmically transmitted phenotypes in eukaryotes due to an invading microorganism or particle (e.g. virus)

Answer 63

Infectious Heredity

Question 64

T/F in infectious heredity, the invader coexists in a symbiotic relationship with the host.

Answer 64

True

Question 65

T/F The invader is never passed through the maternal ooplasm to progeny cells or organism.

Answer 65

False, Usually passed through maternal ooplasm

Question 66

For Kappa in Paramecium, Certain strains of P. aurelia are called killers because _________/

Answer 66

They release Paramecin, a substance toxic to sensitive strains.

Question 67

Offspring’s phenotype under control of nuclear gene product present in the egg. (Ex. Right handed or left handed snail shell coiling in Limnaea peregra)

Answer 67

Maternal effect/Maternal Influence