Patterns of Inheritance By Clark and Garret

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

Question #1 What is the definition of “heredity”?

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

Question #2 Who established genetics and in what year?

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 What was Gregor Mendel’s theory?

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 What does the principle of segregation state?

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 What outcome could be predicted during the dihybrid cross?

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 What rule of heredity did Mendel propose and what did it state?

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 What is the definition of pleiotropy and what is one example of it?

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 Why are quantitative traits complicated to study?

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 If 2 traits happen to be on the same chromosome, what can happen?

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.

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

Question #18 JULIE, WILL YOU GO TO PROM WITH ME????