Biology 317 Chapter 9: Patterns of Inheritance

Two influences which have made you what you are: 1. Heredity: the passing on of traits from parents to offspring. 2. Environment: all the outside forces that act on an organism There are two types of inherited traits: Species traits Individual traits common to all humans traits that make you different from ex. two legs others ex. eye color

9.2 Gregor Mendel (genetics started in an abbey garden) - Austrian monk who experimented w/ heredity in plants. - Findings are basis of modern genetics - he stopped self-fertilization, was able to cross pollinate to make sure the flowers were true-breeding - he created hybrids – the offspring of two different varieties. - Through pollination he crossed plants that had a particular strain (pure for a specific trait) ex. tall X short OR yellow seed X green seed - He described the offspring as follows: P1 = true breeding parental plants F1 = hybrid offspring (f=filial, latin for son) F2 = offspring of F1 plants - Mendel found inherited traits are controlled by factors (genes) which occur in pairs.

- A gene is a segment of DNA on a chromosome that controls a particular heredity trait. - Genes occur in pairs (as do chromosomes) Each contrasting form of a gene are called alleles - this is what Mendel called ‘factors’

9.3 Mendel’s law of segregation describes the inheritance of a single characteristic - Mendel developed four hypotheses: 1. There are alternative forms of a genes that account for variations in inherited characteristics. - alternate versions of genes now called alleles 2. For each characteristic, an organism inheritis two alleles, one from each parent. These alleles may be the same or different. - same alleles called homozygous - different alleles called heterozygous 3. If the two alleles of an inherited pair differ, then one determines the organism’s appearance and is called the dominant allele; the other has no noticeable effect on the organism’s appearance and is called the recessive allele. - “One gene in a pair masks the other” - dominant showm by capitol letters 4. A sperm or egg carries only one allele for each inherited trait because the allele pairs separate (segregate) from each other during the productionof gametes. - this statement now known as Law of Segregation - when egg & sperm unite – each contributes an allele, restoring the paired condition of the offspring.

- Punnett squares are used to show the possible combinations of a cross. - the expressed, physical traits are called phenotype - ex. Purple or white flowers - the genetic make-u is called genotype - ex. PP, Pp or pp Mendel formulated what is now known as Mendel's law of segregation. This law states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization. There are four main concepts involved in this idea. They are: 1. There are alternative forms for genes. 2. For each characteristic or trait organisms inherit two alternative forms of that gene, one from each parent. These alternative forms of a gene are called alleles. 3. When gametes (sex cells) are produced, allele pairs separate or segregate leaving them with a single allele for each trait. 4. When the two alleles of a pair are different, one is dominant and the other is recessive. 9.4 Homologous chromosomes bear the two alleles for each other

9.5 Law of independent assortment can be revealed by tracking two characteristics - Each pair of alleles segregates independently of the other pairs of alleles during gamete formation - From these experiments Mendel formulated what is now known as Mendel's law of independent assortment. This law states that allele pairs separate independently during the formation of gametes. Therefore, traits are transmitted to offspring independently of one another. - Law of Segregation – single trait- monohybrid - Law of Independent Assortment – two traits – dihybrid

Law of Independent assortment shown in metaphase 1 Law of Segregation shown by separation of homologues in anaphase 1

9.6 Testcross used to determine unknown genetype

9.7 Mendel’s law reflects the rules of probability Probability - probability is the likelihood that a specific event will occur. Probability = # of one kind of event # of all events - can be shown as a fraction, decimal or % ex. 6,022 / 8,023 OR 0.75 OR 75% - if two coins tossed simultaneously, the outcome is independent. What is chance of both heads up?

- the probability of compound events is the product of separate probabilities of the ind. events. This is called rule of multiplication and it hold true for genetics. Ex. ½ x ½ = ¼ or prob. of bb ½ x ½ = ¼ - the probability that an event ca occur in two or more ways is the sum of the separate possibilities – this is known as the rule of addition Ex. ¼ + ¼ = ½ Golden rule: homo = ¼ & hetero = ½ 9.8 Genetics traits in humans can be tracked though family pedigrees.

9.9 Many inherited disorders in humans are controlled by a single gene - albinism, cystic fibrosis, sickle cell, Huntington’s achondroplasia (dwarfism) 9.10 New technol. can provide insight into one’s genetic legacy - fetal testing - amniocentesis - CVS – chorionic villus sampling - fetal imaging - ultrasound 9.12 Incomplete Dominance

9.13 Many genes have more than two alleles in a population - abo blood group 9.14 A single gene may affect many phenotypic characterisitcs - called pleiotrophy ex. sicke cell

9.15 A single characteristic can be influenced by many genes - polygenic inheritance – the additive effects of two or more genes on a single phenotypic characteristic - ex. human skin color and height - this is the opposite of pleiotrophy where single gene affects several characterisitcs

9.22 Chromosomes determine sex in many species