Genetics & Inheritance Part 1 Earth Day Creature!
Genetics Terminology Genes are DNA sequences that contain instructions for building proteins or RNA molecules with enzymatic functions. Chromosomes are structures within the nucleus composed of DNA and protein. Human cells usually have 23 pairs of chromosomes. 22 pairs of homologous chromosomes, also known as autosomes 1 pair of sex chromosomes, paired as autosomes, 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 are alternative forms of a gene Alleles arise from mutation
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 are 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 refers to an individual s complete set of alleles. Phenotype refers to observable physical and functional traits. Phenotype is determined by inherited alleles and environmental factors. Examples are hair color, eye color, skin color, blood type, disease susceptibility. 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 Developed laws Law of Segregation Law of Independent Assortment
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) o 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.
Key: Y = yellow peas y = green peas Mendel s Work 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% greenpea plants. Figure 19.3
Key: W = widow s peak w = straight hairline Female Widow s peak Male Straight hairline Figure 19.4
Maternal Inheritance Mitochondria contain a small amount of DNA. Fathers do not usually pass these disorders to their children (Mitochondria mostly used for propulsion; tail of sperm remains outside of egg.) Only females usually pass on mitochondrial mutations to their children. This inheritance can affect both males and females. Since the mitochondria are responsible for processing oxygen and converting substances from the foods we eat into energy for essential cellular functions, problems with the mitochondria can lead to many defects for adults such as Stroke-like symptoms Cancer Parkinson s disease
Two- Trait Crosses Exhibit Independent Assortment Outcome of two-trait crosses can be predicted by Punnett square analysis Law of Segregation States gametes carry only one allele of each gene. During meiosis shuffling one of each pair of chromosomes goes into the gamete Is what we are illustrating with Punnett square. Mendel used quadratic equations. Law of Independent Assortment The alleles of different genes are distributed to gametes independently during meiosis. This law applies only if the two genes in question are on different chromosomes.
Key: E = free earlobes e = attached earlobes W = widow s peak w = straight hairline Widow s peak Free earlobes Female Straight hairline Attached earlobes Male a) A mating between a homozygous person with a widow s peak and free earlobes (EEWW) and a homozygous person with a straight hairline and attached earlobes (eeww). All of the offpsring will have the dominant widow s peak and free earlobes phenotypes. Figure 19.7a
Key: Hb A = normal hemoglobin Hb S = sickle-cell allele Normal Female Sickle-cell trait Two different alleles of hemoglobin gene: Hb A : encodes normal hemoglobin Hb S encodes sickle cell hemoglobin Male Sickle-cell anemia Sickle-cell anemia: Hb S Hb S (homozygous) Sickle-cell trait: Hb A Hb S (heterozygous) Affected individual makes both types of hemoglobin Figure 19.11