GENETICS THE BASICS 2 Genetics what is it

GENETICS THE BASICS

2 Genetics: what is it? • What is genetics? • “Genetics is the study of heredity, the process in which a parent passes certain genes onto their children. ” • What does that mean? • Children inherit their biological parents’ genes that express specific traits, such as some physical characteristics, natural talents, and genetic disorders.

Genetic Concepts • H 3 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.

Genetic Terms • allele: • genes: • dominant : • recessive: • homozygous: • heterozygous: • genotype: • phenotype: 4

Genetics Review • Alternative versions of genes account for variations in inherited characters • These alternative versions of a gene are now called alleles • Each gene resides at a specific locus on a specific chromosome Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Fig. 14 -4 Allele for purple flowers Locus for flower-color gene Allele for white flowers Homologous pair of chromosomes

• For each character an organism inherits two alleles, one from each parent • The two alleles at a locus on a chromosome may be identical • True breeding, homozygous • Alternatively, the two alleles at a locus may differ • Hybrids, heterozygous Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

• If the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance • Information from genetic experiments gives information about which alleles are dominant and recessive. • Gregor Mendel kept data about genetic crosses with pea plants Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Fig. 14 -3 -3 EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers F 1 Generation (hybrids) All plants had purple flowers F 2 Generation 705 purple-flowered 224 white-flowered plants

Table 14 -1

Fig. 14 -6 Phenotype 3 Genotype Purple PP (homozygous) Purple Pp (heterozygous) 1 2 1 Purple Pp (heterozygous) White pp (homozygous) Ratio 3: 1 Ratio 1: 2: 1 1

Write your own definition for • Genotype: • Phenotype:

Punnett Square Rules • Male is across the top • Female is across the left • Big letters always get written first • What letter? The first letter of the dominant phenotype