Molecular genetics exam 3 Flashcards
Mendel chose the garden pea as his model system because
obvious phenotypes, easy to control pollination, short generation time, and a lot of progeny
Name 5 characteristics that are important for a good model organism
easy to breed, easy to maintain, a lot of progeny, observable characteristics, and true breeding strains
name the 7 characteristics that Mendel observed
seed color, seed shape, seed coat color, pod color, pod shape, flower position, and stem length
Gene
an inherited factor(region of DNA) that helps determine a characteristic
Allele
One of two or more alternative forms of a gene
Locus
Specific place on a chromosome occupied by an allele
Genotype
Set of alleles possessed by an individual organism
Heterozygote
an individual organism possessing 2 different alleles at a locus
Homozygote
an individual organism possessing 2 of the same alleles at a locus
Phenotype of a trait
appearance or manifestation of a characteristic
characteristic or character
an attribute or feature possessed by an organism
Genotype is the listing
of alleles an individual carries for a specific gene
WW is
Homozygous dominant
Ww is
heterozygous
ww is
homozygous recessive
The molecular difference between alleles can be detected as a restriction length polymorphism (RFLP) using
the enzyme EcoRl and a probe that hybridizes at the site shown
P generation (P1 or P0) is
the initial cross
True breeding
have the same alleles for the gene
With true breeding strains, every time you self breed them you get
100% of the population as with the same phenotype as parent
If you breed 2 pure lines then the F1 is
heterozygous and displays the dominant phenotype
a cross of F1 plants forms the
f2 generation
2 heterozygotes crossed leads to what ratio of genotypes
1:2:1
1 YY, 1 Yy and 1 yy
2 heterozygotes crossed leads to what ratio of phenotypes
3:1
Results can be expressed as
homozygous or heterozygous
monohybrid crosses involve __ gene(s)
1
Monohybrid crosses reveal how
one trait is transmitted for generation to generation
Name of mendels 3 postulates
unit factors in pairs, dominance/recessiveness, and segregation
Describe the unit factors in pairs postulate
genetic characters are controlled by unit factors (genes) existing in pairs in individual organisms
Describe dominance/recessiveness postulate
In the pair of unit factors for a single characteristic in an individual, one unit factor is dominant and the other is recessive
Describe segregation postulate
the paired unit factors segregate (separate) independently during gamete formation
A way to determine whether an individual displaying the dominant phenotype is homozygous or heterozygous for the trait is to
test cross with a ww homozygous recessive because if it it is homozygous dominant, all of the progeny will be dominant because the dominant allele will hide it
what does not true breeding mean??
heterozygous for the trait
dihybrid cross involves
2 independent traits
what is mendels fourth postulate
independent assortment-traits assort independently during gamete formation and all possible combinations of gametes will form with equal frequency
the principle of segregation says that the alleles____ and the principle of independent assortment says that alleles ____
separate, separate independently of alleles at different loci
Trihybrid cross
involves 3 independent traits
chromatin fibers coil and condense to form __ during mitosis and meiosis
chromosomes
Chromosomes exist in __ in diploid organisms
homologous pairs
Somatic cells are aka
body cells
Humans have 46 chromosomes or 23__
pairs
how many autosome pairs are there?
22
how many pairs of sex chromosomes are there
1
Homologous chromosomes carry genes for
the same inherited characteristics but are not identical
what are alleles
different versions of the same genes
Genetic locus
the location of a particular gene on a chromosome
at each genetic locus, an individual has __ alleles, or one on each chromosome
2
are sex determining chromosomes homologous?
usually not homologous yet behave as homologous in meiosis
what does the letter before n mean ex. 2n
number of sets (2 sets)
n means
the number of unique chromosomes
chromatid is an
unreplicated chromosome
after replication there are 2 chromatids connected by a
centromere
what are the 2 chromatids connected by a centromere that are exactly the same?
sister chromatids
what are non sister chromatids?
a chromatid from each chromosome from a pair of homologous chromosomes
homologous chromosomes carry the same genes but can carry different __ of those genes
alleles
In males, how may of the 4 products of meiosis develop into functional sperm?
4
In females, how many of the 4 products of meiosis develop into an egg?
1
the egg producing spore in higher plants is the
megaspore
the sperm producing spore in higher plants is the
microspore
in higher plants, the diploid spore producing generation (___) is conspicuois
sporophyte
in higher p-lants, the gamete producing (___) generation is microscopic
gametophyte
meiosis creates __ and mitosis creates the __
gametes, organism
what is meiosis
specialize form of cell division that makes sexual reproduction possible and produces gametes or sex cells
why does meiosis reduce the genetic info passed down to the daughter by half?
sperm and egg come together to make 2n a diploid organism
why do males create 4 sperm to a females 1 egg?
the egg provides every component of the cell and thus there is an unequal division of the cytoplasmic material and sperm only contributes DNA
in mitosis the daughter cells are _n
2
in meiosis the daughter cells are _n
1
when does crossing over occur?
In prophase 1
when do homologous pairs of chromosomes allign on the metaphase plate?
metaphase 1
when do pairs of chromosomes separate?
anaphase 1
when do individual chromosomes allign on the metaphase plate?
metaphase 2
when do chromatids separate?
anaphase 2
meiosis 1
reduces the number of chromosomes by separating homologous pairs
meiosis 2
separates sister chromatids into 2 different daughter cells
which part of meiosis looks exactly like mitosis?
meiosis 2
what happens in prophase 1?
homologous chromosomes pair and crossing over between non sister chromatids
why is chromosome pairing important?
so that the number of chromosomes can be reduced
what is crossing over?
an equal exchange of genetic material such that nothing is lost. It is a rearrangement such that alleles will be inherited will alleles of different genes
what happens in metaphase?
paired homologas chromosomes line up together on the metaphase plate and independent assortment
what is independent assortment
orientation of pairs to poles is random. this leaves some paternal and some maternal on the left and right
what happens in anaphase 1
homologous chromosomes separate and move toward poles
what happens in telophase 1?
each pole now has a haploid set of chromosomes
the 2 cells at the end of meiosis 1 now have a compliment of
n
meiosis 2 starts as __ and ends as __
haploid, haploid
meiosis 1 starts as __ and ends as __
diploid, haploid
what is the product law?
when 2 independent events occur simultaneously, the probability of the two outcomes occurring incolmbineation is equal to the product of their individual probabilities
what does a pedigree analysis do?
demonstrates a family tree with respect to a given trait and reveals a pattern of inheritance
the sex of the progeny after fertilization is determined by the
sex chromosome contained in the sperm
the result of meiosis is _ type(s) of egg and __ type(s) of sperm
1, 2
heteromorphic chromosomes (___) characterize ___
(dissimilar) one sex or the other
what is another word for heteromorphic chromosomes
sex chromosomes
what serves as the underlying basis of sex determination?
genes, not chromosomes
life cycles depend on
sexual differentiation
in multicellular organisms it is important to distinguish between __ and __
primary sexual differentiation and secondary sexual differentiation
what is primary sexual differentiation?
involves only the gonads where gametes are produced
what is secondary sexual differentiation ?
involves the overall appearance of the organism
what is unisexual?
individuals that contain only male or female reproductive organs
what are 2 other names for unisexual?
dioecious or gonochoric
what is bisexual?
individuals that contain both male and female reproductive organs and can produce both male and female gametes
2 other names for bisexual
monoecious and hermaphroditic
for c elegans XX is
hemaphrodite
for c elegans X or X0 is
male
for c elegans, when males are crossed with a hermaphrodite, the progeny will be
50% hermaphrodite and 50% male
Female gametes have _ chromosome(s)
x
Male gametes have _ chromsome(s)
either an x or y
in chromosomal sex determination, each son gets his X chromosome from his _ and y from his _
mother, father
two X chromosomes (_) result in _ offspring
homogametous, female
one x and one Y chromosome (_) result in _ offspring
heterogametous. male
pseudoautosomal regions present where?
on Both ends of the y chromosome
pseudoautosomal regions share homology with regions on the _ chromosome
x
Y chromosomes have at least _ genes
75
which chromosome has pseudoautosomal regions?
y chromosomes
SRY is the
sex determining region on a y chromosome
when do SRY genes become active in XY embryos
6-8 weeks of development
what is the testis determining factor (TDF)?
a protein encoded by a gene in the SRY that triggers testes formation
what is nondisjunction?
when the chromosomes do not properly segregate during meiosis
what happens if nondisjunction occurs?
if this happens to the X chromosome, the result is 1 egg with 2xs and one with none. When it joins the sperm it can result in a number of disorders. it can also happen in sperm
homozygous traits, if parents are unaffected Both parents must be
heterozygous
sex determination in drosphilia
Y does not determine sex. Sex is determined by the ration of X chromosomes to autosomes
what controls sex determination in reptiles?
temperature
For all crocodiles, most turtles, and some lizards, sex determination is achieved according to the
incubation temperature of eggs during a critical period of embryonic development
what is the genie sex determining system?
No sex chromosomes, only sex determining genes. Found in some plants fungi, protozoans and fish
sex linked characteristics
gene located on the sex chromosome
dosage compensation of x linked genes
prevents excessive expression of x linked genes in humans other than mammals and balances the dose of X chromosome gene expression in females and males
a calico cat is female and the coloring pattern is due to
dosage compensation
describe dosage compensation in cats
fur color is on the X chromosome so when some cells deactivate the x for black and some cells deactivate the x for orange, both will be expressed.
what is dominant and recessive inheritance?
when it deals with recessive and dominant inheritance
what is incomplete dominance?
The resulting offspring have a phenotype that is a blending of the parental traits.
in incomplete dominance and codominance how do the phenotypic and genotypic ratio compare? Why?
they are the same. because heterozygotes have their own phenotype
what is codominance?
two alleles at a locus produce different and detectable gene products in heterozygote. A condition in which both alleles for a gene are fully expressed
what occurs due to codominance?
No dominance or recessiveness, no blended phenotype
multiple alleles
three or more alleles of a gene that code for a single trait
Blood type a or Ia allele is responsible for
an enzyme that can add the terminal sugar n-acetylflactosamine to the H substance
Blood type B or Ib is responsible for
a modified enzyme that can add a terminal galactose
Blood type or or the o phenotype results
from an absence of either terminal sugar
Ia and Ib alleles
are dominant over I
Ia and Ib alleles are
codominant
Type 0 blood type has what kind of antigens? antibodies?
none, anti a and anti b
type a has what kind of antigens?antibodies?
a, anti b
type b has what kind of antigens? antibodies?
b, anti a
type ab has what kind of antigens? antibodies?
a and b, none
what is an example of multiple alleles?
colors of rabbits
what is pleiotropy?
when the expression of a single gene has multiple phenotypic effects
give an example of pleiotropy
marfan syndrome-the autosomal dominant mutation in the gene encoding the connective tissue protein fibrillar
what all does Marfan syndrome cause?
Many tissues including eye lens dislocation, increased risk or aortic aneurysm and lengthened bones in limbs
Gene interaction
the cellular function of numerous gene oviducts contributes to the development of a common phenotype
what is epigenesis?
development concept whereby each step of development increases the complexity of the sensory organ and is under the control and influence of one or more genes
sex limited
Autosomal genes whose expression is limited to one sex
example of sex limited traits
feather plumage in chickens
Sex influenced
Genes on an autosome that are more readily expressed in one sexF
example of sex influenced traits
pattern baldnesss in humans. Allele B for baldness acts as dominant in males and recessive in females and appears to be related to the levels of the male sex hormones
what are temperature sensitive mutations?
expression is affected by the temperature
what is organelle heredity?
DNA contained in the mitochondria or chloroplasts determine certain phenotypic characteristics of offspring
what is the maternal effect?
nuclear gene products are stored in the egg and transmitted through the ooplasm to the offspring effecting the genotype
two forms of extranuclear inheritance
organelle heredity and maternal effect
what makes the analysis fo inheritance patterns resulting from mutant alleles in chloroplast and mitochondria difficult?
function fo these organelles is dependent on the gene products from the nucleus and the organelle DNA making the origin of mutations affecting the organelle function difficult
what are the 4 characteristics of cytoplasmic inherited traits?
1-present in male and females,
2-usually inherited from 1 parent, typically the maternal parent.
3-reciprocal crosses give different results
4-exhibit extensive phenotypic variations, even within a single family
describe how genes are related to chloroplast
genes carried on the DNA encode products involved in photosynthesis and translation and mutation in these genes may inactivate photosynthesis
products of the maternal genes are
synthesized in the developing egg
stored in the oocyte prior to fertilization
following fertilization, they specify molecular gradients that determine spatial organization within the zygote
genetic maternal effects
nuclear genotype of the maternal parent
cytoplasmic inheritance
cytoplasmic genes, which are usually inherited entirely from one parent
genomic imprinting
genes whose expression is affected by the sex of the transmitting parent
Dominant
an allele that is always expressed
recessive
an allele that is masked when the dominant allele is present
epistasis
A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.
complementary gene interaction
Must have at least one dominant allele at each locus (A-B-) to have the phenotype
