• Definition- The transmission of traits from one generation to the next.

Question #1

• Definition- The scientific study of heredity.
• Genetics was established in
1860 by Gregor Mendel.

Question #2
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History of Heredity
• The basis of heredity is genes and these genes of each parent combine together to form different characteristics for the parents offspring.

Question #3
• What is the basis of heredity?

Gregor Mendel
• He was an Augustinian monk who studied physics, mathematics, and chemistry.
• In 1866, he correctly argued that parents pass on heritable factors to their offspring.
• He did a test to prove his theory by using pea plants because they self-fertilize and could easily be cross-fertilized.
• Mendel worked with these plants until he had gotten all pure breeding.
• He also discovered monohybrids and hybrids.

Question #4
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Phenotype and Genotype
• Genotype- The actual genetic makeup.
• Phenotype- The physical makeup.
• If a gene has identical alleles at a locus the condition is called homozygous and if the gene is the dominant form then it is homozygous dominant.
• If a locus has different alleles at a locus the conditions is called heterozygous and if those alleles are in the recessive form then it is heterozygous recessive.

Question #5
• What is the difference between a phenotype and a genotype?

Phenotype and Genotype (continued)
• The mechanism underlying the pattern of inheritance is stated by the principle of segregation. This states that pairs of genes separate during gamete formation.
• A test cross can allow you to determine the genotype of the organism. In a test cross an individual organism of unknown genotype is crossed with a plant whose genotype is homozygous recessive for the trait.

Question #6
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Recessive and Dominant Alleles
• When the 2 genes of a pair are different alleles, one is fully expressed and the other has no noticeable effect on the organism’s appearance.
• There are a number of human traits that are thought to be determined by simple dominant-recessive inheritance.

Question #7
• What happens when 2 genes of a pair are different alleles?

Recessive and Dominant Alleles
(continued)
• Incomplete dominance is a condition whereby neither allele in a heterozygote is dominant, instead, both alleles contribute to the phenotype.
• Codominant means that both alleles are expressed in heterozygous individuals who have type AB blood.
• For some traits, the F1 hybrids have an appearance somewhat in between the phenotypes of the 2 parental varieties.

Question #8
• What is incomplete dominance?

The Dihybrid Cross
• The dihybrid cross is a mating between parents that differ with respect to 2 traits.
• The outcome of the dihybrid cross could be predicted by assuming that 2 gene pairs assort independently during the formation of gametes.

Question #9
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The Dihybrid Cross (continued)
• Mendel then proposed the second rule of heredity called the principle of independent assortment. This states that different traits separate independently of each other during the formation of the gametes.
• The chromosomal theory of inheritance states that genes are located on chromosomes and that the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns.

Question #10
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Pleiotropy
• In many cases one gene can influence several traits.
• The impact of a single gene on 2 or more traits is called pleiotropy.
• An example of pleiotropy in humans is called sickle-cell anemia.

Question #11
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Traits Controlled by Many Genes
• Quantitative traits are traits that are not qualitatively distinct, but vary quantitatively over a range of values.
• These traits are somewhat complicated to study because they are controlled by several interacting genes, rather than by a pair of alleles at a single locus. This phenomenon is referred to as polygenic inheritance. A case in point of polygenic inheritance is skin pigmentation in humans.

Question #12
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Linkage
• Linkage is defined as the presence of 2 or more traits on the same chromosome.
• If 2 traits happen to be on the same chromosome then the inheritance patterns can be changed. This is why linkage is very important to inheritance patterns.

Question #13
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Crossing-Over and Mapping Genes
• Crossing-over data can be very useful in mapping the relative position of gene loci on chromosomes. This process was discovered by
Sturtevant.
• Assuming that the chance of crossing-over is approximately equal at all points on a chromosome, Sturtevant hypothesized that the further apart 2 genes are on a chromosome, the higher the probability that a cross-over would occur between them.

Question #14
• What did Sturtevant hypothesize?

Sex-Linked Inheritance
• Chromosome pairs, with 2 identical members in both males and females are called the autosomes. Humans have 44 autosomes with 2 sex chromosomes.
• Chromosomes that may have dissimilar members in the sexes are called sex chromosomes.
• In humans, females have 2 identical sex chromosomes called X chromosomes. Males have only one X chromosome, and a smaller unpaired chromosome called the Y chromosome.

Question #15
• How many and what kind of chromosomes do females have?
How many and what kind of chromosomes do males have?

Sex-Linked Inheritance (continued)
• As a result of chromosome segregation during meiosis, each gamete (sex cell) contains a sex chromosome and a haploid of autosomes.
• All eggs have one X chromosome and each sperm has either an X or Y chromosome.
Offspring sex depends on which sperm fertilizes the egg.
• Sex chromosomes determine things other than just the sex of the baby.

Question #16
• What chromosome do all eggs have and what chromosomes do all sperm cells have?

Sex-Linked Inheritance (continued)
• Any gene on a sex chromosome is a sex-linked gene and most are found on the X chromosome.
• Red green color blindness is a sex-linked disorder caused by a malfunction of light sensitive cells in the eyes.

• What is red green color blindness caused from?
Question #17

Question #18