Dihybrid Inheritance, Polygenic Inheritance & Allelic Interactions Flashcards by Heidi Sawyer

Define dihybrid

Individuals that are heterozygous for two characters being followed in a cross

ex. all F1 generations from two true breeding parents (YyRr)

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How many gametes can a dihybrid produce?

ex. YR, Yr, yR, yr

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Define dihybrid cross

A cross between organisms that are heterozygous for the same two traits

ex. YyRr x YyRr

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What is the ratio that results from a dihybrid cross?

9:3:3:1

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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

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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

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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

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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

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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

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Define linked genes

genes on the same chromosome that tend to be inherited together

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Do linked genes produce the 9:3:3:1 ratio?

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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

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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

Genotypic: 1 NnGg: 1 Nngg

phenotypic: 1 normal-grey: 1 normal-ebony

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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

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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

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Does incomplete dominance result in heterozygous offspring displaying the same or different phenotypes than the homozygous organism?

Different

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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

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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

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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

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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

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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?

If the genotype has 1 or 2 IB alleles, which carbohydrate molecule will be present on the red blood cells?

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?

Which blood type allele is recessive?

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