Chapter 8 Outline

Guided Note Outline to Accompany Chapter 8 Patterns of Inheritance

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Concepts of Biology by Open Stax

8.1 Mendel’s Experiments

1. _________________ __________variation is the range of small differences we see among individuals in a characteristic like human height.
2. ___________________________ variation is the variation seen among individuals when each individual show one of two—or a very few—easily distinguishable traits, such as violet or white flowers.

1. ____________________________ involve mating two true-breeding individuals that have different traits.

1. Plants used in first-generation crosses were called _____, or parental generation, plants (Figure 8.3).
2. These offspring were called the ______, or the first filial (filial = daughter or son), generation.
3. Mendel then collected and grew the seeds from the F1 plants to produce the ____, or second filial, generation.

1. A _____________ is defined as a variation in the physical appearance of a heritable characteristic such as flower color, seed shape, height, and seed color.

1. _________________  ________________—a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross.
2. ___________________ traits are those inherited unchanged in a hybridization.
3. ___________________ traits become latent or disappear in a hybridization.

8.2 | Laws of Inheritance

1. The seven characteristics that Mendel evaluated in his pea plants were each expressed as one of two versions, or traits. Mendel deduced from his results that everyone had ______discrete copies of the characteristic that are passed individually to offspring. We now call those two copies ___________, which are carried on chromosomes.
2. Gene variants that arise by mutation and exist at the same relative locations on homologous chromosomes are called __________________.
3. Phenotypes and Genotypes

1. The observable traits expressed by an organism are referred to as its ________________.
2.  An organism’s underlying genetic makeup, consisting of both the physically visible and the non-expressed alleles, is called its ______________________.
3. Diploid organisms that are __________________for a gene have two identical alleles, one on each of their homologous chromosomes.
4. When P plants with contrasting traits were cross-fertilized, all of the offspring were ____________________________ for the contrasting trait, meaning their genotype had different alleles for the gene being examined.

1. Law of Dominance

1. Mendel’s _____________ ______ __________________ states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic (Figure 8.6),

1. Monohybrid Cross and the Punnett Square

1. When fertilization occurs between two true-breeding parents that differ by only the characteristic being studied, the process is called a _________________ cross, and the resulting offspring are called monohybrids. Mendel performed seven types of monohybrid crosses, each involving contrasting traits for different characteristics. Out of these crosses, all of the F1 offspring had the phenotype of one parent, and the F2 offspring had a ___: ____ phenotypic ratio.
2. A ____________  _________, devised by the British geneticist Reginald Punnett, is useful for determining probabilities because it is drawn to predict all possible outcomes of all possible random fertilization events and their expected frequencies Figure 8.9 

1. Law of Segregation

1. Observing that true-breeding pea plants with contrasting traits gave rise to F1 generations that all expressed the dominant trait and F2 generations that expressed the dominant and recessive traits in a 3:1 ratio, Mendel proposed the  _______ _____ _____________________. (Figure 8.7).

1. Test Cross

1. Mendel developed a way to determine whether an organism that expressed a dominant trait was a heterozygote or a homozygote, which is called the  _______________  _____________, Figure 8.8. This technique further validates Mendel’s postulate that pairs of unit factors segregate equally.

1. Law of Independent Assortment

1. Mendel’s _______  ________  ___________________  __________________ states that genes do not influence each other with regard to the sorting of alleles into gametes, and every possible combination of alleles for every gene is equally likely to occur.
2. Independent assortment of genes can be illustrated by the ____________ cross, a cross between two true-breeding parents that express different traits for two characteristics. (Figure 8.10).

8.3: Extensions of the Laws of Inheritance

1. Alternatives to Dominance and Recessiveness

1. Incomplete Dominance        

1. _________________ _____________________ is a  pattern of inheritance meaning that one of the alleles appears in the phenotype in the heterozygote, but not to the exclusion of the other, which can also be seen. The allele for red flowers is incompletely dominant over the allele for white flowers.

1. Codominance

1. A variation on incomplete dominance is __________________, in which both alleles for the same characteristic are simultaneously expressed in the heterozygote. An example of codominance occurs in the ABO blood groups of humans. (Figure 8.13).

1. Multiple Alleles

1. An example of multiple alleles is the _______________ blood-type system in humans.

3. Sex-Linked Traits

1. In humans, as well as in many other animals and some plants, the sex of the individual is determined by sex chromosomes—one pair of non-homologous chromosomes. When a gene being examined is present on the X, but not the Y, chromosome, it is  ____ - _______. An example of this is eye color in fruit flies.
2. In X-linked inheritance males are said to be _______________ meaning that they have only one allele for any X-linked characteristic.

1. What ratio of offspring would result from a cross between a white-eyed male and a female that is heterozygous for red eye color?

1. Other examples of X-linked inheritance for certain conditions (some color-blindness, hemophilia, and muscular dystrophy) are X-linked. Females who are heterozygous for these diseases are said to be ______________. These females will pass the disease to half of their sons and will pass carrier status to half of their daughters.

1. Linked Genes Violate the Law of Independent Assortment

1. ___________________occurs in which genes that are located physically close to each other on the same chromosome are more likely to be inherited as a pair.

1. This process  by which chromosome exchange equivalent portions with one another is called _____________________, or crossover.

1. Epistasis

1. Genes may also oppose each other, with one gene suppressing the expression of another. This antagonism is called  _________________.