Unit test 2 (Ch. 16&17) Flashcards
Do genes segregate independently? This means are the combinations of alleles equally probable in the gametes?
It depends on where the genes controlling these traits are situated on an organism’s genome
How many autosomes and sex chromosomes does a fruit fly’s genome include?
3 pairs of autosomes
1 pair of sex chromosomes
What is the law of independent assortment?
any combination of alleles should have equal chance of being created (in gametes). Basically, the allele a gamete receives for 1 gene does not influence the allele received for another gene. In easiest terms, how different genes independently separate from 1 another in reproductive cells.
What happens if alleles occur on the same chromosome? what does it say about the law of independent assortment?
-if the genes (containing the alleles) on the same chromosome are far apart, they will segregate as though they were on sepearate chromosomes
-if the genes (containing the alleles) are close on the same chromosome, the less likely they will be able to segregate independently.
if the gene are really close together on a chromosome, what will the crossing over do?
the genes containg the alles will segregate together because the crossing over won’t split them up (rare)
if the gene are really close together on a chromosome, what will the crossing over do?
the genes containg the alles will segregate together because the crossing over won’t split them up (rare)
How do we know if the genes are close together on a chromosome?
-Punnett square will calculate the expected probabilities of offspring with both traits.
-if observed proportions match expected, genes assort independently
what does it mean when genes assort independently?
the genes are either on different chromosomes or far apart on the same chromosome
if observed proportions of offspring don’t match the expected in genetics…?
The genes are close and on the same chromosome
what is a dihybrid cross?
calculates probabilities of offspring with 2 traits. (i.e: shape and colour)
Do shape and colour genes assort independently?
if the observed ratios match the expected ratio –>this means they do assort independently (on the same chromosome but far or not on the same chromosome)
What does a dihybrid cross of true breeding parents result in? (i.e: black and short hair mom and brown and long hair dad)
The p-cross: BBSS x bbss will result in a heterozygous offspring for both parents traits BbSs
How would you do a dihybrid cross of the F1 generation of the offspring BbSs?
The gametes would be
BS, Bs, bS, bS, x BS, Bs, bS, bs and would result in a 9:3:3:1 ratio out of a total of 16 potential offspring.
** How do you find the number of possible gametes? Ex: AaBBccDd**EE?
ploidy #^# of heterozygous genes
so..
2^2=4
so the genotypes are…
ABcDE, aBcDE, ABcdE, aBcdE
How do you find out what fraction of the offspring of parents KkLlMm will be kkllmm?
-Calculate the punnett square for each individual allele:
Kk x Kk, Ll x Ll, Mm x Mm and calculate the genotype ratio
Does segregation of alleles takes place in human meiosis or in pea plants? Why?
They happen in both but it is harder to see the results in peas because of the vast offspring they produce.
what is a pedigree?
Diagram of family history summarizing ancesteral relationships
Can infer inheritance mechanisms of rare traits controlled by a single gene bc their inheritance mechanisms are much less complicated
what can you identify in a pedigree chart?
patterns of dominance and recessiveness can be seen
In a pedigree chart, what sign should you look for if it’s a dominat trait?
-The affected individuals will almost always be heterozygous (Aa)
-Usually, only 1 of the parents have the trait meaning to look for a mating that produces half of the offspring with the trait.
In a pedigree chart, what signs should you look for if the trait is recessive?
-Often skips a generation
-affected individuals must be homozygous (aa)
If a trait doesn’t skip a generation in a pedigree chart, what can you conclude from that?
The trait is either autosomal dominant or sex-linked dominant
how can you tell if the trait is sex linked or autosomal?
-if the affected father produces all daughters with trait
-if the affected mother produces all sons with trait
what are the inheritance mechanisms studied? (4)
-Law of segregation (dominant and recessive alleles)
-Law of independent assortment
-Penetrance & incomplete dominance
-Codominance & Multiple alleles
what is the law of segregation?
when the alleles show dominance. What everr the offspring’s phenotype will show the segregation of the dominant allele to the recessive allele
what is penetrance in inheritance mechanisms?
Complete= phenotype is present in all individuals
Incomplete= character is not present in individuals with the genotype
what is incomplete dominance?
p-cross produced offspring with a mix of both traits. Like hazel eyes, the parents who produced the offspring with hazel eyes either had a mom/dad with blue eyes and a mom/dad with green/or brown
what is the ratio of an incomplete dominance cross? (say the F1 generation is R^1R^2)
1:2:1 because the punnett square will give the 2 incomplete dominant trait (mix of both alleles)
What is codominance and multiple alleles in inheritance mechanisms?
Its when the heterozygous (Rr) present a mixture of both traits because the supossed ‘dominant trait’ is not completely dominant towards the ‘recessive trait’
what is an example of codominance and multiple alles in humans?
ABO blood group because it is controlled by a signle gene with multiple alleles
what blood type is codominant?
AB
both contain the alleles (I^A & I^B)
what are the genotypes of blood types?
A, B, AB, O
A= I^A I^A
B= I^B I^B
AB= I^A I^B
O= ii
How do you write the genotypes of a heterozygous A-blood type and heterozygous B-blood type?
A= I^A i
B= I^B i
what is epistasis?
an inheritance mechanism
what does epistasis do?
**Refers to a situation where the expressivity of a trait is dependent on the presence of 1 or more genes. **
Presence of certain alleles of one gene that prevent or mask the expression of alleles of a different gene
what is an example of epistasis?
the coat of labradors because it involves 2 genes:
color for hair
color deposition
do the genes in epistasis act independently from eachother?
No, the genes all work together to affect a signle trait
what is expressivity in inheritance mechanisms?
individuals with the same genotype can show different degrees of the same phenotype.
Expressivity is the degree of how the trait expression differs among individuals
what is the difference between expressivity and penetrance?
expressivity describes the individual variability
Not the variability of a population of genotypes
What is an example of expressivity inheritance?
Marfan syndrome
Some people display differences in physical proprtions but others can experience life-threatening complications…It’s different for some
what is pleiotropy inheritance mechanism?
a single gene can have multiple effects on phenotype of individuals –> affecting different traits
what is an example of pleiotropy inheritance mechanism?
sickle cell anemia **because a gene product (defective protein) affects red blood cells –> affecting multiple symptoms **
In easy words what is pleiotropy?
a single gene undergoing pleiotropy causing multiple traits
what is polygenic inheritance? (what is it inverse to?)
many genes interacting to affect expression of 1 trait.
Basically the inverse of pleiotropy
What is an example of polygenic inheritance?
skin colour in humans because it’s controlled by at least 3 separate genes (multiple genes)
what is sex-linkage inheritance?
deals with characteristics inherited on sex Chromosomes
which chromosome does sex-liked inheritance mainly use?
the X chromosome
What do autosomes carry that are necessary for development?
genes
what do sex chromosomes carry/contain? (2)
-genes that determine the sex of the individuals
-genes for other characteristics
What do daughters receive from their mother and father? (in sex-linked inheritance)
Daughter receives X chromosomes from both parents
what does a son receive from his mother and his father? (in sex-linked inheritance)
Son receives an X chromosome from mother and Y chromosome from father
What are the characteristics controlled by in females? (in sex linked inheritance)
2 alleles
NN or Nn or nn
2 alleles=
1 N for 1 X chromosome
1 N for 1 X chromosome
what are the characteristics controlled by in males?
only 1 allele
Can an allele that is heterozygous be masked in diploid traits?
Yes, because heterozygous = Nn, Aa, Bb… so one of those alleles are dominant over an other making 1 of the alleles that is recessive masked.
What do we call a signle allele for an X-linked gene? (XY)
Hemizygous
What is dosage compensation in sex-linked inheritance?
a mechanism that makes the 2 doses females get (because they have 2 genes because they have 2 X chromosomes) equivalent to 1 dose.
what happens to 1 of the X chromosomes to achieve dosage compensation?
inactivation of 1 X chromosome called Barr body
What is an example of inactivation of 1 of the X chromosome?
calico Cat
Cat with black fur and orange patches
Is the x-inactivation uniform?
no its random
What does polyploidy mean when discussing the number of chromosomes?
multiple set of chromosomes
2n and above
what does aneuploidy mean when discussing number of chromosomes?
abnormalities caused by presence of an extra or absent chromosome
what is an example of aneuploidy?
disomy = normal # of chromosomes (if it’s 2…)
trisomy = an extra chromosome (then 3 chromosomes)
monosomy = an absent chromosome (then 1 chromosome)
what is aneuplodies caused by?
Nondisjunction event
what is a nondisjunction event in discussing chromosome numbers?
when a chromosome fails to separate
can nondisjunction events occur in sex chromosomes?
yes and autosomes
What is down syndrome or trisomy 21 caused by?
nondisjunction event where during meiosis, 1 of th chromosomes fails to separate causing an extra chromosome to be present in the cell.
What is klinefelter syndrome?
males = XXY
underdevelopped testes
what is Turner syndrome?
females = XO
undeveloped ovaries
(monosomy of X)
what if someone displays YO nondisjunction event?
This creates nonviable embryos because humans need at least 1 X
Is the phenotype of a trait determined by genes?
no
what is the phenotype of a trait determined by?
manifestation of genotype and environment
what is the rule for genes and the environment?
genes set the limits for the phenotype
environment molds the phenotype within it’s limits
what is an example of how the genes and environment affect the phenotype of a trait?
inheritance of height
For the inheritance of height, what sets the limits and what shapes the individual within those limits?
genes set the limits and the environment molds the person within the limits
what are some environmental conditions that affect the inheritance of height?
diet, sleep, health…
what is phenotypic plasticity?
allows organism’s to produce different phenotypes with changing environments which is an important factor of evolution since it allows populations to respond to natural selection pressures which can lead to new species over time.
basically phenotypic plasticity is…
a development for individuals in a population to increase/adapt their survival based on their environment.
