General Genetics Practical Session BIO 221 Lecturer Alshehri

General Genetics (Practical Session) BIO 221 Lecturer Alshehri, Dokhnah Saeed

First lab Introduction to Genetics and MENDEL’S FIRST LAW

Outlines: �Introduction to Genetics. �Mendelian Inheritance. �Basic Genetic Concepts & Terms. �Class Activities. �Some practical Exercises.

Introduction to Genetics � Genetics is a branch of biology which deals with transmission of characters from one generation to the next. � Recent advances in cytological studies demonstrated that hereditary characters are determined by certain factors, traits, or genes located on the chromosome. � Each gene is found in a fixed position on a particular chromosome.

Mendelian Inheritance Each person has 2 copies of every gene—one copy from mom and a second copy from dad. These copies may come in different variations, known as alleles, that express different traits. For example, 2 alleles in the gene for freckles are inherited from mom and dad: – allele – child allele from mom = has freckles (F) from dad = no freckles (f) has the inherited gene pair of alleles, Ff (F from mom and f allele from dad). 5

Gregor Mendel � The basic laws of heredity were first formed during the mid -1800’s by Gregor Mendel. Because his work laid the foundation to the study of heredity, Mendel is referred to as “The Father of Genetics. ”

Essential Terms � The term genotype the genes present in the DNA of an organism. We will use a pair of letters (ex: Tt or YY or ss, etc. ) to represent genotypes for one particular trait. There always two letters in the genotype because (as a result of sexual reproduction) one code for the trait comes from mama organism & the other comes from papa organism, so every offspring gets two codes (two letters).

�When we have two capital or two lowercase letters in the GENOTYPE (ex: TT or tt) it's called HOMOZYGOUS ("homo" means "the same"). Sometimes the term "PURE" is used instead of homozygous. �When the GENOTYPE is made up of one capital letter & one lowercase letter (ex: Tt) it's called HETEROZYGOUS ("hetero" means "other"). Just to confuse you, a heterozygous genotype can also be referred to as HYBRID. OK?

� Let's Summarize: � Genotype = genes present in an organism (usually abbreviated as two letters) � TT = homozygous = pure � Tt = heterozygous = hybrid � tt = homozygous = pure

� The term phenotype refers to the final expression of all inherited information in the individual, or its total characteristic features. In other wards, how the trait physically shows-up in the organism. If you wanted to know the simplest way to determine an organism's phenotype ? Look at it. Examples of phenotypes: blue eyes, brown fur, striped fruit, yellow flowers.

In each organism, paired or homologous chromosomes are present, there are 2 genes for every character; one gene on each chromosome. The cells of the organism divided by reduction division to give the gametes. In each gamete there is a single gene for every character. When these gametes unite together to form zygotes, each zygote will again have diploid number of chromosomes. The two genes located in two corresponding location on 2 chromosomes are called allels.

Vocabulary Review Questions � 1. Which of the following is a possible abbreviation for a genotype? � A. BC B. Pp C. Ty D. fg

� 2 -Which of the following pairs is not correct? A. kk = hybrid B. hybrid = heterozygous C. heterozygous = Hh D. homozygous = RR

� 3 - The genes present in an organism represent the organism's _____. � A. genotype B. phenotype C. physical traits

Word Match Activity Match the genetic terms to their corresponding parts of the illustration. • base pair • cell • chromosome • DNA • double helix* • genes • nucleus Illustration Source: Talking Glossary of Genetic Terms http: //www. genome. gov/glossary. cfm? key=chromoso me

nucleus chromosome cell base pair DNA genes

Genetic Concepts �H describes how some traits are passed from parents to their children. � The traits are expressed by g , which are small sections of DNA that are coded for specific traits. � Genes are found on ch ___. � Humans have two sets of _ (hint: a number) chromosomes—one set from each parent. 20

Genetic Concepts � Heredity describes how some traits are passed from parents to their children. � The traits are expressed by genes, which are small sections of DNA that are coded for specific traits. � Genes are found on chromosomes. � Humans have two sets of 23 chromosomes— one set from each parent. 21

�Dominant and Recessive Genes: � Alleles that mask or hide other alleles, such as the “tall” allele, are said to be dominant. � A recessive allele, such as the short allele, is masked, or covered up, whenever the dominant allele is present.

Exercise 1 �Mendel crossed red pea plants with white ones. The F 1 plants were all red. Give the genotypes and phenotypes of the F 1 and F 2 generation produced.

Exercise 2 �A brown-eyed man marries a blue -eyed woman, and they have eight children , all brown-eyed. What are the genotypes of all the individuals in the family?

Excercise 3 �A blue-eyed man, both of whose parents were brown-eyed, marries a brown-eyed woman. They have one child, who is blue-eyed. What are the genotypes of all the individuals mentioned?