Dihybrid Inheritance, Polygenic Inheritance & Allelic Interactions Flashcards
Define dihybrid
Individuals that are heterozygous for two characters being followed in a cross
ex. all F1 generations from two true breeding parents (YyRr)
How many gametes can a dihybrid produce?
4
ex. YR, Yr, yR, yr
Define dihybrid cross
A cross between organisms that are heterozygous for the same two traits
ex. YyRr x YyRr
What is the ratio that results from a dihybrid cross?
9:3:3:1
Describe Mendel’s Law of Independent Assortment and provide exceptions
each pair of alleles segregates separately of each other pair of alleles during gamete formation
What is the exception to Mendel’s law of independent assortment?
if the 2 genes are close together on the same chromosome, they will likely not separate or sort independently
What locational position is required for alleles to separate and sort independently?
they must either be on different chromosomes or very far apart on the same chromosome
Which stage of meiosis do genes on different chromosomes segregate independently of each other?
metaphase I of meiosis
each homologous pair lines up independently at the metaphase plate
Why do the maternal and paternal traits on different chromosomes have a reasonable chance of ending up in different gametes?
because when lined up at the metaphase plate, the mostly maternal and mostly paternal chromosomes in a pair have a 50% chance of being drawn to either pole
Define linked genes
genes on the same chromosome that tend to be inherited together
Do linked genes produce the 9:3:3:1 ratio?
no
How does crossing over increase the chances of far apart genes separating independently?
During prophase I of meiosis, crossing over exchanges maternal and paternal alleles among homologs
In Drosophilia melangaster, normal wings (N) is dominant to vestigial wings (n) and grey body (G) is dominant to ebony body (g).
Calculate the F1 genotypic and phenotypic ratios for the following cross:
NNGg x nngg
NG Ng
ng NnGg Nngg
ng NnGg Nngg
Genotypic: 1 NnGg: 1 Nngg
phenotypic: 1 normal-grey: 1 normal-ebony
In Drosophilia melangaster, normal wings (N) is dominant to vestigial wings (n) and grey body (G) is dominant to ebony body (g).
Calculate the F1 genotypic and phenotypic ratios for the following cross:
nnGG x Nngg
nG nG
Ng NnGg NnGg
ng nnGg nnGg
genotypic: 1 NnGg: 1 nnGg
phenotypic: 1 normal-grey: 1 vestigial-grey
Define incomplete dominance and describe the resulting phenotype of a heterozygous offspring
Occurs when alleles are not completely dominant or recessive
The phenotype is a COMPROMISE between the homozygous phenotypes
Does incomplete dominance result in heterozygous offspring displaying the same or different phenotypes than the homozygous organism?
Different
What is the genotypic and phenotypic ratio of the offspring of a monohybrid cross between a CRCW male x CRCW female?
CR = red CW = white CRCW = pink
is this codominance or incomplete dominance?
CR CW
CR CRCR CRCW
CW CRCW CWCW
Genotypic: 1 CRCR: 2 CRCW: 1 CWCW
Phenotypic: 1: red: 2 pink: 1 white
INCOMPLETE DOMINANCE because the heterozygous offspring display a compromise of the homozygous traits
How are the phenotypic or genotypic ratios of a cross with incomplete dominance reported? Give an example
Homozygous defined 1st: heterozygous: homozygous defined 2nd
ex. red: pink: white
T or F: with the incomplete dominance example of the red, pink, and white flowers, the pink flowers can only produce pink flowered offspring because the traits blended
FALSE. the traits did not blend, so the pink flower can still result in white and red flowered offspring because inheritance is still particulate
Define codominance and describe the phenotype of a heterozygous offspring.
Give an example
When two alleles each affect the phenotype in separate and distinguishable ways
heterozygotes display BOTH phenotypes, but not as an intermediate
ex.
CRCR = red flowers
CRCW = red and white flowers
CWCW = white flowers
Does codominance result in heterozygous offspring displaying the same or different phenotypes than the homozygous organism?
Different
Are human blood groups an example of incomplete dominance or codominance? Explain
Codominance
The A and B alleles are codominant = both the A and B molecule are being displayed, not an intermediate of the two
IAIA = red blood cells with only A molecules
IBIB = red blood cells with only B molecules
IAIB = red blood cells with both A and B molecules
Define multiple alleles and give an example
Most genes have more than 2 alleles
ex. ABO blood group in humans has 3 alleles = IA, IB, and i which results in 4 possible blood types/phenotypes
What are the 4 phenotypes the ABO human blood group alleles result in? Which is most popular?
A, B, AB, O
O is most popular; AB is rarest
If the genotype has 1 or 2 IA alleles, which carbohydrate molecule will be present on the red blood cells?
A
If the genotype has 1 or 2 IB alleles, which carbohydrate molecule will be present on the red blood cells?
B
If the genotype has 2 ii alleles, which carbohydrate molecule will be present on the red blood cells?
Neither A or B –> phenotype is O
O = ii
Which blood type is the best at donating blood, why?
O because they don’t have any carbohydrates on the blood cells
ii = neither A or B
Blood type A could have which 2 genotypes?
IAIA
IAi
Blood type B could have which 2 genotypes?
IBIB
IBi
Blood type AB could have which genotype?
IAIB
Blood type O could have which genotype?
ii
Which blood type allele is recessive?
i
T or F: genes with multiple alleles can have a variety of dominance patterns between the alleles
True
Give an example of a variety of dominance patterns between alleles of genes with multiple alleles
rabbit coat colour
Order of dominance:
C (full colour) > cch (chincilla) > ch (himalayan) > c (albino)
full colour can hide all the other colours, whereas himalayan could only hide albino and albino couldn’t hide any
T or F: dominant alleles are always the most common allele
FALSE
What does phenotype depend on?
dominance and gene frequency
Define polygenic inheritance
When two or more sequences of nucleotides are impacting a single phenotype
Characters that vary in ____ are caused by polygenic inheritance
gradations
What are examples of characters caused by polygenic inheritance?
traits that have continuums such as human skin pigmentation, eye colour, height
If alleles A, B and C each contribute to the deposition of skin pigments and the dominant alleles are darker, would this person have dark or light skin?
C^AC^AC^BC^BC^CC^C
Very dark because they possess only dominant alleles
If alleles A, B and C each contribute to the deposition of skin pigments and the dominant alleles are darker, would this person have dark or light skin?
C^aC^aC^bC^bC^cC^c
Very light because they possess only recessive alleles
There are 3 cat colour phenotypes produced by 3 different alleles of one gene. For this gene black > chocolate > cinnamon (B > bc > bn)
is this an example of multiple allelism or polygenic inheritance?
multiple allelism –> “3 different alleles for one gene”
There are 3 cat colour phenotypes produced by 3 different alleles of one gene. For this gene black > chocolate > cinnamon (B > bc > bn).
How many genotypes are possible for a black cat?
BB, Bbc, Bbn
3 possible genotypes for a black cat
There are 3 cat colour phenotypes produced by 3 different alleles of one gene. For this gene black > chocolate > cinnamon (B > bc > bn).
Suppose a black cat that had a cinnamon father is mated to a chocolate cat that had a cinnamon mother. Determine the expected genotypic and phenotypic ratios of their offspring
black cat with cinnamon father = Bbc
chocolate cat with cinnamon mother = bcbn
Bbc x bcbn:
B bn
bc Bbc bcbn
bn Bbn bnbn
Genotypic: 1 Bbc: 1 BBn: 1 bcbn: 1 bnbn
phenotypic: 2 black: 1 chocolate: 1 cinnamon
In a paternity case, a woman of blood group AB presented a baby of group O which she claimed as her baby. What bearing might the blood-type information have on her case?
Woman’s genotype: IAIB x man =
baby’s genotype: ii
No matter what the genotype of the male was, the woman cannot be the biological mother because she can only have given either a IA or IB allele, not i
In certain cattle, hair colour can be red (CRCR), white (CWCW), or roan (light red, CRCW). If 2 roan cattle are mated, what is the expected genotypic and phenotypic ratios of their offspring? Is this incomplete dominance or codominance?
Incomplete dominance because roan is light red = an intermediate between red and white alleles
CRCW x CRCW
CR CW
CR CRCR CRCW
CW CRCW CWCW
genotypic: 1 CRCR: 2 CRCW: 1 CWCW
phenotypic: 1 red: 2 roan: 1 white
One type of hostas displays yellow blotches (BYBY), white blotches (BWBW, or both yellow and white blotches (BYBW). What genotypic and phenotypic ratios are expected from a BYBY x BWBW? Is this incomplete dominance or codominance?
Codominance because both the yellow and white blotches are displayed in the heterozygotes (not an intermediate)
BY BY
BW BYBW BYBW
BW BYBW BYBW
Genotypic: 1 BYBW
Phenotypic: 1 yellow-white blotches
Feather patterns in ducks can either be restricted (MR), mallard (M), or dusky (md). This allelic series can be written as:
MR > M > md
A restricted female duck that had a homozygous mallard mother is crossed to a dusky male
What are the genotypes of the 2 ducks being crossed?
Is this multiple allelism or polygenic inheritance?
Multiple allelism –> MR > M > md
female: MRM
Male: mdmd
Feather patterns in ducks can either be restricted (MR), mallard (M), or dusky (md). This allelic series can be written as:
MR > M > md
A restricted female duck that had a homozygous mallard mother is crossed to a dusky male
predict the genotypic and phenotypic ratios of their offspring
md md
MR MRmd MRmd
M Mmd Mmd
Genotypic: 1 Mrmd: 1 Mmd
phenotypic: 1 restricted: 1 mallard
Using the rabbit coat colour symbols: C (full colour) > cch (chincilla) > ch (himalayan) > c (albino)
what are the genotypic and phenotypic ratios expected from crossing a true breeding chinchilla with a himalayan rabbit?
Is this multiple allelism or polygenic inheritance?
Multiple allelism
true breeding chinchilla: cchcch
true breeding himalayan: chch
cch
ch cchch
Genotypic: 1 cchch
Phenotypic: 1 chinchilla
What advice would a practicing counsellor on genetics offer to a woman who, while having no hemophilic symptoms, informed him that her father was a hemophiliac? She is married to an unaffected man but is concerned about the prospects of this affliction being passed onto her children
Is this a chromosomal or sex linked issue?
Sex linked
Hemophilia is recessive
XH = normal clotting Xh = abnormal clotting/hemophilia
Female’s father: XhY
female: XHXh (carrier)
male: XHY (unaffected)
XH Y
XH XHXH XHY
Xh XHXh XhY
female genotype: 1 XHXH: 1 XHXh
–> half her daughters will be carriers of hemophilia but none will present it
male genotype: 1 XHY: 1 XhY
–> half her sons will be hemophilic
