BIOL 142 Lecture Notes - Lecture 6: Reciprocal Cross, Genetic Linkage, Meiosis

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Thursday, February 8, 2018

BIOL 142

•Incomplete dominance: heterozygotes display a phenotype that is intermediate of

the 2 homozygous parents"

•Co-dominance: simultaneous expression of the phenotype associated with both

alleles in a heterozygote"

•Most traits are inherited in ways that are more complex than simple mendelian

inheritance"

•Incomplete dominance/co-dominance"

•Epistasis"

•Polygenic inheritance"

•Mendel’s experiments tested two contrasting hypotheses"

•Independent assortment - alleles of diﬀerent genes are transmitted independently

of each other"

•Dependent assortment - the transmission of one allele depends on the

transmission of another"

•Dihybrid cross - matings between parents that are heterozygous for both traits"

•Dihybrid cross - should be 9 diﬀerent oﬀspring genotypes and 4 phenotypes, four

possible phenotypes should be present in 9:3:3:1 ratio"

•In a test cross - a parent that is homozygous recessive for a particular trait is mated

with a parent that has the dominant phenotype but an unknown genotype"

•Because the genetic contribution of the homozygous recessive parent is known - the

genotype of the other parent can be inferred from the results"

•Linked genes - genes on the same chromosome cannot segregate independently"

•Fruit ﬂies as a model organism for genetic research"

•Wild type - the most common phenotype for each trait"

•Y chromosome is smaller than X chromosome - sex-linked traits are generally found

on X chromosome"

•X-linked - uneven distribution between males and females"

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Related Questions

What is the difference between incomplete dominance and codominance?

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What is the difference between incomplete dominance and codominance?

1. In incomplete dominance, the dominant phenotype is expressed in heterozygotes. In codominance, both phenotypes are expressed in heterozygotes.

2. The phenotype reveals the genotype only in codominance.

3. In both types of inheritance, the heterozygotes express the phenotypes dictated by both alleles.

4. In codominance, both phenotypes are expressed in heterozygotes. In incomplete dominance, the heterozygote shows a phenotype that is intermediate between the two homozygotes.

These all relate to exceptions to the inheritance patterns encountered by Mendel.â

Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?

Select the four correct statements.

-When an essential gene is mutated, it can result in a lethal phenotype. There are no classic Mendelian monohybrid and dihybrid ratios.

-In the case of codominance, heterozygotes produce gene products from both alleles of a gene. Classic Mendelian monohybrid and dihybrid ratios are modified by codominance.

-In the case of incomplete dominance, the phenotype of the heterozygote is distinct from and often intermediate to the phenotypes of homozygous individuals. Classic Mendelian monohybrid and dihybrid ratios are modified by incomplete dominance.

-Genes exist in a large number of allelic versions and a diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios.

-When an essential gene is mutated, it can result in a lethal phenotype. This results in a modification of classic Mendelian ratios.

-The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The joint expression of both alleles in a heterozygote is called codominance. There are no classic Mendelian monohybrid and dihybrid ratios.

-Genes exist in a large number of allelic versions, but in a diploid organism, only one allele of the gene can occupy one homologous gene loci. Classic Mendelian inheritance cannot explain this phenomenon.

-Each gene produces a unique gene product. The effect of one allele in a heterozygote completely masks the effect of the other. Classic Mendelian genetics cannot explain this phenomenon.

QUESTION 1

Jim is blood type A, his brother John is type O and his sister Jane is type AB. What are the genotypes of their parents?

Which of the following is true for alleles that show incomplete dominance?

Heterozygotes have a genotype like the dominant allele.

Homozygotes have a genotype like the recessive allele.

Heterozygotes have a phenotype intermediate between the dominant and recessive alleles.

Homozygotes have the same phenotype as the heterozygotes.

QUESTION 3

Which principle of inheritance concluded that when games are formed in meiosis, the two alleles of each gene separate from one another, and each gamete receives only one allele?

independent assortment

Which term best describes a condition in which alleles at one locus can alter the expression of alleles at another locus?

polygenic inheritance

A single unit of genetic information located on a chromosome defines:

The physical expression (appearance or function) of an organism's genes defines:

genotype

a single characteristic

Palomino horses (golden color with a blond mane) are an incompletely dominant trait produced by the combination of the chestnut color allele and the cream color allele. If you wanted to produce as many palominos as possible, which mating strategy below would be the best choice?

Which term best describes the effect of a single gene on multiple aspects of the phenotype?

polygenic inheritance

QUESTION 9

Which term best describes the separate expression of both alleles for a single trait in the same cell?

polygenic inheritance

QUESTION 10

One form of a gene found on a single chromosome defines:

A chocolate lab (whose mother was a yellow lab) is mated with a black lab whose genotype is BbEe. What fraction of the offspring would be expected to be yellow labs?

What type of allele is always expressed regardless of whether the individual is homozygous or heterozygous for it?

Both the dominant and recessive alleles

Given the parents AABBGgHhrr Ã AabbGgHhRr, assume simple dominance and independent assortment. What proportion of the progeny will be expected to have the genotype AaBbggHHrr?

___________________ is defined as having two of the same type of allele for a particular trait.

The physical position of an allele on a single chromosome defines:

Which term best describes two or more genes affecting the phenotype in an additive fashion?

codominance

polygenic inheritance

BIOL 142 Lecture Notes - Lecture 6: Reciprocal Cross, Genetic Linkage, Meiosis

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