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)
