Exam 2 Chapter 4, 28, 3, and 6 Flashcards
What is epistasis?
masking or alternation of the expression of the alleles of one gene by the allelic combos of another gene
What occurs to the dihybrid ratio for epistasis?
normal dihybrid ratio is modified
What is Recessive Epistasis?
an individual must be homozygous for either recessive allele to mask a particular phenotype
-ccPP - white
-CCpp - white
- CcPp - purple
What is the dihybrid cross-phenotypic ratio for recessive epistasis?
9:3:4
What is the Gene Modifier Effect?
outcome in which the allele of one gene modifies the phenotype of the allele of another gene.
AA/Aa - agouti
aa- black
CC/Cc- color allowed
cc- albino
therefore - there are three possible phenotypes
What is dominant epistasis?
when the dominant allele of one gene hides the expression of all alleles of another gene.
What is the phenotypic dihybrid cross ratio of dominant epistasis?
12:3:1
A- white a- color B- yellow b - green
A-B- = white ——> 12/16
A- bb = white
aaB- = yellow ——–> 3/16
aabb = green ———> 1/16
What is complementation Epistasis?
when two mutant parents are crossed and all F1 are wild type and F2 show both mutant/wildtype phenotypes
What is the phenotypic ratio of complementation epistasis?
9:7
you need at least one dominant of both genes to get one phenotype. All other kinds of genotypes give one other phenotype.
A- blue a- no color B-red b- no color
A-B- = purple —> 9/16
A-bb = no color}
aaB- = no color}—>7/16
aabb = no color}
What is duplicate gene action?
Either gene can provide the wild type with a minimum contribution of only 1 dominant allele. Only a double recessive allele contribution from both genes will produce the mutant type
What is the phenotypic ratio of duplicate gene action?
15:1
What is suppression epistasis?
One gene fully suppresses the other gene.
What is the phenotypic ratio of suppression epistasis?
13:3
C- colored c -white
I = inhibition i = no inhibitor
C- I- = white = 13/16
ccI- = white
ccii = white
C-ii = colored 3/16
What is sex-limited inheritance?
expression of a specific phenotype is limited to only 1 sex
Example of sex-limited inheritance
Tail/neck plummage in fowl
H - hen feathering
h - cock feathering
female male
HH - hen hen
Hh - hen hen
hh- hen cock
only males experience cock feathering
What is sex-influenced inheritance?
The expression of a phenotype is influeced by the sex of the individual
Example of sex influenced inheritance
Pattern baldness in humans
B= bald
B’ = non bald
Female Male
BB bald bald
BB’ nonbald bald
B’B’ nonbald nonbald
The B’ gene is dominant in females and recessive in males
and B is dominant in males and recessive in females
Second Example of Sex Influenced Inheritance
Length of Index Finger
L = long finger L’ = short finger
L behaves dominantly in females and recessively in males
Heterozygous LL’ in males is short fingered and in females is long fingered.
in males the length of the index fingers is tried to exposure to testosterone in utero, higher test = shorter finger
also a measure of physical aggression only in males.
What is quantitative Genetics?
study of traits that can me described numerically
What are complex traits?
traits that are usually controlled by more than one gene and also affected by the environment.
(focus of quantitative genetics)
What is a continuous trait?
a trait that does not fall into discrete categories
ex. height or weight
What are meristic traits?
a type of trait that can be described by an integer (whole number only)
bristles on drosophila back
What is a discontinuous trait?
a trait that can fall into 2 or more distinct categories
white eyed or red eyed fruit flies
What statistical model describes quantitative traits?
Normal distribution
What is continuous variation?
Traits whose phenotypes are controlled by many different genes and environmental factors
aka human weight/skin tone, or fruit size in plants
What is polygenic Inheritance?
transmission of traits that are governed by two or more genes
What is the quantitative trait locus or QTL?
the location on a chromosome that affects the outcome of a quantitative trait
It identifies on the chromosome the gene/genes that affect the trait by highlight the area on the chromosome that corresponds to the trait
Who was the person that accidentally discovered continuous variation by breading a tall x dwarf plant and getting a broad variation in the F2 generation?
Joseph Gottlieb Kolreuter
Who was the geneticist that first demonstrated a link from continuous variation to polygenic inheritance by studying wheat in 1909?
Herman Nilsson-Ehle
What is implied by the multiple gene/ multiple factor hypothesis?
each gene adds together to create a net sum of the phenotype
In Hermans experiment for example
AABB- red
AABb - dark pink
AAbb - medium Pink
AaBB - dark pink
AaBb - medium pink
Aabb - light pink
aaBB - medium pink
aaBb - light pink
aabb - white
each of these dominant alleles quantitatively adds more redness to the phenotype
How to determine the level of environmental effect in quantitative traits?
Categories as seen on normal distributions blur together showing more phenotypic variation
How to calculate the ratio of F2 individuals expressing either extreme phenotype?
(1/4)^n
n = # of gene pairs involved
How to find the number of distinct F2 phenotypic classes?
2n + 1
n = # of gene pairs involved
What are the four main types of RNA?
mRNA, tRNA, rRNA, sRNA
What do you call the position of a gene on a chromosome?
locus
What do you a call a cell or organism with one complete set of chromosomes?
Haploid
What do you call a cell with two complete sets of chromosomes?
Diploid
What is a representation of all of the chromosomes of a cell?
Karyotype
What are chromosomes that have the same structures and loci called?
Homologous Chromosomes
What is a metacentric chromosome?
centromere directly in the middle
What is a submetacentric chromosome?
Slightly raised higher than in the middle
What is an acrocentric chromosome?
Centromere is very near the top
What is a telocentric chromosome?
Centromere is on the top.
What are the two purposes of cellular division?
Cell division allows unicellular organisms to create new individuals by asexual reproduction.
This also leads to multicellularity in many organisms.
What is binary fission?
The way that procaryotes procreate. They divide into the middle
What are the two parts of the cell cycle?
Interphase and mitosis
Interphase is divided into 3 main parts, what are they?
G1 = synthesis of of proteins and RNA,
S = synthesis of DNA
G2 = synthesis of proteins and RNA
What is the cell not doing during interphase?
Not actively dividing
In which interphase state does the most variation with respect to time occur?
G1
Why?
cell can follow 1 or 2:
1. - enter G0 to postpone division or never divide again
— this is called the restriction point
2. - finish cycle
At the end of the S phase the cell has [blank] as many chromatids as it did in G1.
twice
How does the definition of chromosome change throughout the cell cycle?
- in G1 (and late M phase) chromosome = 1 chromatid
- in G2 (and early M phase), chromosome = pair of sister chromatids
What is the shortage stage of the life/cell cycle?
mitosis
What are the two main parts of mitosis?
Karyokinesis : division of the nucleus
and
Cytokinesis: division of the cytoplasm
What are the 5 stages of Mitosis?
Prophase, Prometaphase, Metaphase, Anaphase, Telophase
What are the characteristics of Interphase (mitosis)?
- has chromatin fibers
- has 2 centrosomes with centriole pairs
- still has nuclear envelope
What are the characteristics of Prophase (mitosis)?
- chromosomes condense and pair up into sister chromatids
- Microtubules form the mitotic spindle
- nuclear envelope breaks down