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The scientist Jean Baptiste Lamarck proposed that if an individual acquired a particular characteristic—such as strength from lifting weights—this characteristic would be inherited by the organism's offspring. This same idea is also part of a more ancient idea, the idea of

unchanging (immutable), heritable factors that were contributed by each parent and never mixed

particles that travel throughout the body, capturing particular characteristics, before the particles ultimately come to reside in sperm and egg for transmission to the next generation

F2 generation

Two mice are crossed. Matings are carried out between the offspring of these mice to produce "grandchildren" of the original mated pair. In the standard terminology of genetics, the "grandchildren" are the

Observe the trait expressed by the F1 plants.

True-breeding individuals differing in a single character, say a pea plant bearing green seeds and another bearing yellow seeds, are crossed. Assuming that this trait is determined by a single gene that is present in two forms (yellow and green, in this case), how can you tell which allele is dominant and which is recessive?


Mendel was a meticulous experimentalist. One set of crosses he performed to test his idea that a pair of hereditary determinants segregated into gametes was to allow self-fertilization of F2 individuals to produce F3 offspring. What proportion of the purple-flowered F2 individuals did Mendel predict to be true-breeding?


An insect that has the genotype EeGGcc will have the same phenotype as an insect with the genotype

One allele is on one chromosome, and the other is in the same position (locus) on the homologous chromosome.

In an individual of genotype Aa, where are the A and a alleles physically located

independent assortment of alleles of one gene relative to the alleles of any other gene

Mendel's principle of independent assortment applies to the


Assume that in cattle a spotted coat is dominant to an even coat, short horns are dominant to long horns, and the traits for coat type and horn length assort independently. In a cross between cattle that are each heterozygous for both traits, what proportion of their offspring are expected to have long horns?

LLss and llSs

You cross two fruit trees. One tree produces lemons with spiky leaves, the other produces limes with smooth leaves. Your F1 generation produces lemons with smooth leaves and spiky leaves. What are the genotypes of the parents? L = lemons; l = limes; S = smooth leaf; s = spiky leaf.

Cross the long-finned fish with short-finned fish; if the offspring are all long-finned, the long-finned parent is homozygous.

Imagine that long fins in zebrafish is a dominant trait. A breeder wants to set up a breeding program beginning with homozygous dominant long-finned fish. If she obtains a handful of the rare long-finned fish, how can she tell which if any of these are homozygous for the trait?


In Labrador dogs, black coat is dominant to chocolate, normal vision is dominant to progressive retinal atrophy (PRA), and normal hip joint is dominant to hip dysplasia. All these genes assort independently. Two dogs that are heterozygous for alleles of all three genes are crossed. Using rules of probability (not a Punnett square), what is the chance that the first pup born to these dogs will be chocolate, have normal vision, and have normal hip joints

Either one of her parents or both of her parents were heterozygous for the trait.

Two normal parents have three normal children: one son and two daughters. Their son and one of their daughters marry and also have normal children. Their second daughter, Mary, marries a man with a rare, recessive blood disorder. They have two children, and both children develop the blood disorder. What were the genotypes of Mary's parents?

are most often recessive

Human genetic disorders

Lethal dominant alleles are harmful whether they are carried in homozygous or heterozygous form, so there is always strong selection against these alleles

Why are lethal dominant alleles so much more rare than lethal recessive alleles

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