Figare 11.1. When these F 1 offspring self-pollinated, the next generation ( F 2 ) showed both traits in a 3.1 ratio. The trait shown in the F 1 was always the more commen trait in the F 2 , with 3 out of every 4 offspring expressing it. See Figure 11.2 . Figure 11.2. Essentially, Mendel's explanation for what he saw was: 1. Traits are controlled by what he called "factors" and which we now call genes. 2. An organism has a pair of genes for each trait. We now know that cach gene is located on one of two similar (homologous) chromosomes. 3. An organism mandomly inherits one gene from each of its parents' pair of genes. Thus, its own pair consists of one gene that is puternal and one gene that is maternal. 4. The pairs of genes can be identical, or they can be different. If they are the same, the organism is said to be homoxygous; if different, the organism is said to be heterozygous. Different versions of genes are called alleles. Thus, an organism with two different alleles is heterozygous and one with identical alleles is homozygous. 5. Contrasting alleles can vary in their effect. Since his F 1 generation resembled only one of the parents, while both of the traits present in the parents reappeared in the F 2 generation, he concluded that the factons do not blend or disappear. He defined a rule of dominance to explain this: The allele that determines the appearance of a heterozygote is called the dominant allele. The one that is hidden is the recessive allele. The visible outcome of the genes is the phenotype, while the actual genetic outcome is the genotype. The 3 : 1 ratio in the F 2 generation refers specifically to 3 dominant traits being expressed for every one recessive. Today you will examine several traits that illustrate Mendel's basic explanations for patterns of inheritance. You will also see some ways in which these basic explanations can be used to study human genetics and to understand how to do pedigree analysis. EXERCISE 1. REVIEW OF BASIC GENETICS TERMS PROCEDURE Using your lecture materials and textbook as a reference, review the following genetic situation and answer the questions that follow. When a true-breeding brown mink is crossed with a true-breeding silver-blue mink they produce offspring all with the same phenotype: brown. When these F 1 mink were crossed amongst themselves, they produced 47 brown animals and 15 silver-blue animals ( F 2 generation). 1. What does the gene being discussed code for? 2. What allelles for this gene are being discussed? 3. Which one of these alleles is dominant and how do you know it is dominant? 4. Which one of the alleles is recessive and how do you know it is recessive? 5. What does F 1 stand for? Explain what the F 1 generation is. F = childien 1 = Grotaeneration 6. What is the meaning of the word phenotype? In this particular case, what was the phenotype of the F 1 ? 7. If you were studying genotypes, what would you be looking at? In general, what different genotypes can you find i.

1. Figare 11.1. When these F 1 offspring self-pollinated, the next generation ( F 2 ) showed both
traits in a 3.1 ratio. The trait shown in the F 1 was always the more commen trait in the F 2 , with
3 out of every 4 offspring expressing it. See Figure 11.2 . Figure 11.2. Essentially, Mendel's
explanation for what he saw was: 1. Traits are controlled by what he called "factors" and which
we now call genes. 2. An organism has a pair of genes for each trait. We now know that cach
gene is located on one of two similar (homologous) chromosomes. 3. An organism mandomly
inherits one gene from each of its parents' pair of genes. Thus, its own pair consists of one gene
that is puternal and one gene that is maternal. 4. The pairs of genes can be identical, or they can
be different. If they are the same, the organism is said to be homoxygous; if different, the
organism is said to be heterozygous. Different versions of genes are called alleles. Thus, an
organism with two different alleles is heterozygous and one with identical alleles is homozygous.
5. Contrasting alleles can vary in their effect. Since his F 1 generation resembled only one of the
parents, while both of the traits present in the parents reappeared in the F 2 generation, he
concluded that the factons do not blend or disappear. He defined a rule of dominance to explain
this: The allele that determines the appearance of a heterozygote is called the dominant allele.
The one that is hidden is the recessive allele. The visible outcome of the genes is the phenotype,
while the actual genetic outcome is the genotype. The 3 : 1 ratio in the F 2 generation refers
specifically to 3 dominant traits being expressed for every one recessive. Today you will
examine several traits that illustrate Mendel's basic explanations for patterns of inheritance. You
will also see some ways in which these basic explanations can be used to study human genetics
and to understand how to do pedigree analysis. EXERCISE 1. REVIEW OF BASIC GENETICS
TERMS PROCEDURE Using your lecture materials and textbook as a reference, review the
following genetic situation and answer the questions that follow. When a true-breeding brown
mink is crossed with a true-breeding silver-blue mink they produce offspring all with the same
phenotype: brown. When these F 1 mink were crossed amongst themselves, they produced 47
brown animals and 15 silver-blue animals ( F 2 generation). 1. What does the gene being
discussed code for? 2. What allelles for this gene are being discussed? 3. Which one of these
alleles is dominant and how do you know it is dominant? 4. Which one of the alleles is recessive
and how do you know it is recessive? 5. What does F 1 stand for? Explain what the F 1
generation is. F = childien 1 = Grotaeneration 6. What is the meaning of the word phenotype? In
this particular case, what was the phenotype of the F 1 ? 7. If you were studying genotypes, what
would you be looking at? In general, what different genotypes can you find in organisms? 8. If
you were a mink breeder, you would most likely be using the terms "true breeding" and "hybrid."
What are the geneticists' equivalent terms to true breeding and hybrid in terms of generation?