SC.912.L.16.1 Genetics

1. SC.912.L.16.1Genetics By: Jonathan Barredo

2. Mendel’s Laws of Segregation • 4 main concepts to this principle: • A gene can exist in more than one form. • Organisms inherit two alleles for each trait. • When gametes are produced (through meiosis), allele pairs separate leaving each cell with a single allele for each trait. • When the two alleles of a pair are different, one is dominant and the other is recessive. • Basic definition: • The principles that govern heredity were discovered by a monk named Gregor Mendel in the 1860's. One of these principles, now called Mendel’s laws of segregation, says that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization.

3. Mendel’s Laws of Independent Assortment • Mendel performed dihybrid crosses in plants that were true-breeding for two traits. • For example, a plant that had green pod color and yellow seed color was cross-pollinated with a plant that had yellow pod color and green seeds.  • Green pod color traits (GG) and yellow pod color traits. (YY) are dominant.(gg) and (yy) are recessive. Offspring = (GgYy) • Basic Definition: • This principle states that the alleles for a trait separate when gametes are formed. • Mendel formulated this principle after discovering the Laws of Segregation.

4. Inheritance Patterns • He performed his work with pea plants, studying seven traits. • Pod shape plant height, pod color, seed shape, flower color, seed color, and flower location. • Definition: • The transmission of a gene from parent to child. The pattern of inheritance is the way in which a gene is transmitted. • Mendel was the first scientist to develop a method for predicting the outcome of inheritance patterns.

5. Dominant Traits • X-linked dominant inheritance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome. • Basic Definition: • An inherited trait that results from the expression of the dominant allele over the recessive allele. • Examples: • Brown eyes • Farsightedness • Dark Hair • Dimples

6. Recessive Traits • Autosomal recessive • Two mutated copies of the gene are present in each cell when a person has an autosomal recessive disorder. An affected person usually has unaffected parents who each carry a single copy of the mutated gene (and are referred to as carriers). • Basic definition: • A trait that must be contributed by both parents in order to appear in the offspring. Recessive traits can be carried in a person’s genes without appearing in that person. • An autosomal disease can be transmitted from parent to child through a recessive (hidden) trait. • For Example: • There is (50%) chance the offspring will inherit one copy of the disease allele and will be a carrier.

7. Dihybrid crosses • A dihybrid cross involves a study of inheritance patterns for organisms differing in two traits. • Mendel invented the dihybrid cross to determine if different traits of pea plants, such as flower color and seed shape, were inherited independently.

8. Codominance • In codominant inheritance, two different alleles of a gene can be expressed, and each allele makes a slightly different protein. •  For Example: • In this picture blood type AB is inherited through codominance. Based on their offspring you can see the different types of blood given to the kids. Only one of the children receive a codominance of both AB blood type, very rare in most humans.

9. Incomplete dominance • For Example: • The two red and white flowers all share that same allele that is not completely dominant over the other making the flowers the color pink a mixture of both red and white. • Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele. • This incomplete dominance is what can cause mutations in species.

10. Multiple Alleles As shown in the picture below not all four figures share the same traits but the third figure possesses all three genes making the figure have multiple alleles. • Multiple alleles : • When there are three or more forms of a gene for a trait. • This doesn't have to mean that a person can have all three of them. The person still only gets two, it's just that there are three or more of the alleles in the same gene pool that are available.

11. Sex linkage • As a result, the genes located on the X chromosome, portray a pattern of inheritance referred to as sex- linkage. • In many organisms, their sex is determined by a pair of chromosomes and genetic traits. • The X chromosome carries hundreds of genes, and many of these are not connected with the determination of sex. The smaller Y chromosome contains a number of genes responsible for the initiation of maleness, but it needs copies of most of the genes that are found on the X chromosome.

12. Polygenic inheritance • For example: • Parents that have black hair and tan skin can have an offspring that possesses lighter skin and blond hair. • This is due to polygenic inheritance. • Polygenic inheritance is when a single trait is controlled by 2 or more sets of alleles. Most human traits are polygenically inherited. • This can explain how parents can have children with different eye color and skin color than what the parents have.