Genetics and Inheritance Part 1 Human Biology Chapter 19 Genetics and Inheritance Part 1 Creature

Genetics Terminology Genes: DNA sequences that contain instructions for building proteins or RNA molecules with enzymatic functions Chromosomes: structures within the nucleus, composed of DNA and protein Humans: 23 pairs of chromosomes 22 pairs of homologous chromosomes, also known as autosomes 1 pair of sex chromosomes, which determine gender

More Terminology Homologous chromosomes One member of each pair is inherited from each parent Look alike (size, shape, banding pattern) Not identical: may have different alleles of particular genes Alleles: alternative forms of a gene Alleles arise from mutation

autosome carries the same genes at the locus Pair of autosomes. Each autosome carries the same genes at the locus Gene locus (plural loci). The location of a specific pair of genes A pair of genes. Normally both genes have the same structure and function Alleles. Alternative versions of the same gene pair Figure 19.1

http://biology.clc.uc.edu/fankhauser/Labs/Genetics/Drosophila_chromosomes/d.m._chromosome_images_index.html https://public.ornl.gov/site/gallery/gallery.cfm?topic=47&restsection=HGPArchive Both accessed January 29, 2012.

Traits can be inherited as Autosomal dominant Autosomal recessive Sex linked Codominant Incompletely dominant Polygenic Multiple alleles Epistatic Linked Maternal genes And more!

Genotype Is the Genetic Basis of Phenotype Genotype: an individual’s complete set of alleles Phenotype: observable physical and functional traits Examples Hair color, eye color, skin color, blood type, disease susceptibility Phenotype is determined by inherited alleles and environmental factors Punnett square analysis predicts patterns of inheritance

Gregor Mendel Developed Basic Rules of Inheritance Worked with pea plants in the 1850s in Austria Did multiple genetic experiments to develop basic rules of inheritance Law of segregation Gametes carry only one allele of each gene Law of independent assortment Genes for different traits are separated from each other independently during meiosis Applies for genes on different chromosomes

Dominant Alleles and Recessive Alleles Dominant allele (dominates) Masks or suppresses the expression of its complementary allele Always expressed, even if heterozygous Recessive allele (recedes) Will only be expressed if individual is homozygous for the recessive allele Dominant alleles are not always more common than recessive; sometimes they may be rare in a population

a) Mendel’s first cross yielded all yellow-pea plants Key: Y = yellow peas y = green peas Yellow pea Green pea a) Mendel’s first cross yielded all yellow-pea plants b) Mendel’s second cross between two of the offspring of his first cross yielded 75% yellow-pea and 25% green- pea plants Figure 19.3

Incomplete Dominance Heterozygous phenotype is intermediate between that of either homozygote Examples Hair Straight hair: HH Wavy hair: Hh Curly hair: hh Pink color in some flowers Familial hypercholesterolemia Dominant/recessive symbols used here. Alternatively use H1 , H2, since not actually dom/rec.

Codominance Codominance: products of both alleles are expressed Examples Genes for ABO blood types Sickle-cell gene Roan coloration in mammals

Genes A and B gene are codominant Genes A and B gene are codominant. Alternatively IA or I B or i symbols for alleles. An individual heterozygous for the A and B genes will be blood type AB, expressing both A and B antigens on red blood cells Type A Type B Type AB Type O Antigen A Antigen B Antigens A and B Neither A nor B antigens Red blood cells Possible genotypes AA AO BB BO AB OO Figure 19.10

Two different alleles of hemoglobin gene: Female Two different alleles of hemoglobin gene: HbA: encodes normal hemoglobin HbS encodes sickle cell hemoglobin Key: HbA = normal hemoglobin HbS = sickle-cell allele Sickle-cell trait Normal Male Sickle-cell anemia Sickle-cell anemia: HbS HbS (homozygous) Sickle-cell trait: HbA HbS (heterozygous) Affected individual makes both types of hemoglobin Figure 19.11