13. Mendelian Genetics

Dihybrid Crosses

Which protostome phyla successfully made the transition from water to land? Select True or False for each phylum.
T/F Mollusca
T/F Arthropoda
T/F Annelida
T/F Nematoda

No. Trees that produce big yellow apples could be AArr or Aarr. Trees that produce small red apples could be aaRR or aaRr. Because all the offspring are big, the big parent must be homozygous for A. Because half the apples are red and half are yellow, the red parent must be heterozygous for red. The conclusion is that the cross must be AArr &times; aaRr.

In this dihybrid cross, you need to work backward from the phenotypes of the offspring to predict the parental genotypes.

Assume that there is a gene in apples that determines fruit color and a second gene that determines fruit size. Let A represent the dominant allele for big apples and a represent the recessive allele for small apples. Similarly, let R represent the dominant allele for red apples and r represent the recessive allele for yellow apples. You have one tree that produces big yellow apples and another tree that produces small red apples. When the two are crossed, you find that half of the new trees produce big red apples and half produce big yellow apples. What are the genotypes of the parents?

Dihybrid Cross Explained

Animation: Crosses of Two Characters in "MendAliens"

In parakeets, two autosomal genes that are located on different chromosomes control the production of feather pigment. Gene B codes for an enzyme that is required for the synthesis of a blue pigment, and gene Y codes for an enzyme required for the synthesis of a yellow pigment. Green results from a mixture of yellow and blue pigments, and recessive mutations that prevent production of either pigment are known for both genes. Suppose that a breeder has two green parakeets and mates them. The offspring are green, blue, yellow, and albino (unpigmented). Based on this observation, what are the genotypes of the green parents? What genotypes produce each color in the offspring? What fraction of the progeny should exhibit each type of color?

A monohybrid cross involves a single parent, whereas a dihybrid cross involves two parents.

A dihybrid cross involves organisms that are heterozygous for two characters that are being studied, and a monohybrid cross involves organisms that are heterozygous for only one character being studied.

A monohybrid cross is performed for one generation, whereas a dihybrid cross is performed for two generations.

A monohybrid cross results in a 9:3:3:1 phenotypic ratio, whereas a dihybrid cross gives a phenotypic 3:1 ratio.

Which of the following statements is correct in describing the terms monohybrid cross and dihybrid cross?

Dihybrid Cross | Genetics

Dihybrid cross and the Law of Independent Assortment | High school biology | Khan Academy

Dihybrid Crosses & Punnett Squares

<div title="Page 16">In the dihybrid cross of AaBb x AaBb, what fraction of the offspring will be homozygous recessive for BOTH traits?</div><img src="https://static.studychannel-prd.pearsonprd.tech/courses/biology/thumbnails/images/524fc7a6" alt="" />

Use your understanding of insect evolution to predict two adaptations for terrestrial living that occurred in spiders.

Animation: A Simplified Cross of Two Characters in Humans

Animation: Mendel's Cross of Two Characters: Seed Shape and Seed Color

Dihybrid and Two-Trait Crosses

In maize (corn) plants, a dominant allele I inhibits kernel color, while the recessive allele i permits color when homozygous. At a different locus, the dominant allele P causes purple kernel color, while the homozygous recessive genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the offspring?

For any gene displaying complete dominance, heterozygous individuals exhibit the dominant phenotype.

Pure breeding plants, when mated with each other, produce completely homozygous offspring.

The phenotypic ratio produced from a F1 × F1 dihybrid cross is 9:3:3:1.

Smooth seed trait is dominant to wrinkled seed trait in peas.

Which of the following phenomena is a consequence of independent assortment?

DRAW IT Two pea plants heterozygous for the characters of pod color and pod shape are crossed. Draw a Punnett square to determine the phenotypic ratios of the offspring.

Black fur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails (t). What fraction of the progeny created by crossing BbTt × BBtt will be expected to have black fur and long tails?<img src="https://static.studychannel-prd.pearsonprd.tech/courses/biology/thumbnails/images/f6de577e" alt="" />

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Pedigrees

Genotype vs. Phenotype

Mendel's Laws

X-Inactivation

Incomplete Dominance vs. Codominance

Monohybrid Crosses

Test Crosses

Autosomal Inheritance

Non-Mendelian Genetics

Mendel's Experiments

Epistasis

Sex-Linked Inheritance

Introduction to Mendel's Experiments

Punnett Square Probability

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