Heredity Patterns Unit 5, Lesson 4

Trait Inventory

Heredity The passing of genetic material from parent to offspring

Gregor Mendel An Austrian Monk who used pea plants to study patterns of inheritance Looked at specific characteristics that all had only TWO different forms plant height, flower and pod position, seed shape, seed color, pod shape, pod color and flower color

What did Mendel do with Pea Plants? Mendel crossed pea-plants with known characteristics (a feature that has different forms in a population) He studied each pea plant characteristic separately, always starting with plants that were true-breeding for that characteristic. True-breeding- will always have an offspring with a certain trait (e.g. green pea pod true-breeding plants produce offspring with green pea pods) Each characteristics only had two different forms After counting how many plants had each characteristics from the first generation, Mendel then crossed the offspring to produce a second generation and recounted the characteristics

Gene Segments of DNA found in chromosomes that give instructions for producing a certain characteristic Genes are inherited from parents, so all organisms that reproduce sexually have two sets of the same gene for each characteristic (one from each parent) Traits Different forms of a characteristic Alleles Different versions of the same gene

Genotype vs. Phenotype Genotype Phenotype The entire genetic makeup of an organism; the combination of genes for one or more specific traits The combination of alleles inherited from parents The actual GENES Ex) GG (one “G” from each parent) = green pea pod An organism’s appearance or other detectable appearance Observable traits PHYSICAL appearance Ex) GG = Green pea pod (observable trait; based on genotype)

Types of Alleles Dominant Recessive Shown with a capital letter The allele that is fully expressed whenever the allele is present in an individual There are different types of dominance Shown with a lowercase letter An allele that will be masked unless the organism is homozygous for the trait

Homozygous vs. Heterozygous An organism containing two copies of the same allele for a particular trait Homo = Same An organism will have either two dominant alleles or two recessive alleles An organism that contains two different alleles for a particular trait Hetero = Different An organism will have one dominant allele and one recessive allele Can be a carrier of the recessive phenotype for complete dominance traits

Example The gene responsible for producing dimples, or creases in the cheek, is DOMINANT If you have even one copy of the gene you will have dimples (Homozygous Dominant or Heterozygous (carrier)) The no-dimples allele is recessive, which means that TWO copies of the allele must be present if you do NOT have dimples (Homozygous recessive) The dimple characteristic in humans is an example of COMPLETE DOMINANCE because one trait is completely dominant over another (not all characteristics follow this pattern)

Many Genes Can Influence a Single Trait Some characteristics, such as the color of your skin, hair, and eyes, are the result of several genes acting together. Different combinations of alleles can result in different shades of eye color, for example. Many traits do not have a one-to-one relationship between a trait and a gene.

A Single Gene Can Influence Many Traits Sometimes, one gene influences more than one trait. Ex) The trait that affects fur color can also influence eye color in a White Siberian Tiger. Many genetic disorders in humans are linked to a single gene but affect many traits Ex) Sickle Cell Anemia occurs in individuals with two recessive alleles for a certain gene. All of the traits associated with sickle cell anemia are due to a single gene. They have a different protein in their red blood cells to cause them to become crescent shaped when oxygen is low Blood vessels become blocked Spleen is damaged Fewer red blood cells leads to oxygen not being delivered to body’s organs

The Environment Can Influence Traits Environment can influence an organism’s phenotype. Ex) Arctic Fox has a gene responsible for coat color. This gene is affected by light so in the winter the coat is white (less daylight) and in the summer the hairs in the coat grow in brown (more daylight) Acquired traits- traits that are learned in one’s environment, but are not inherited. Ex) knowing how to ride a bike

Exceptions to Complete Dominance Incomplete Dominance Codominance A condition in which two alleles are expressed The phenotype of a heterozygous individual is an intermediate of the phenotypes of the two homozygous parents Ex) When a red snapdragon flower is crossed with a white snapdragon flower, they produce a pink snapdragon flower Ex) Hair texture in humans (Curly hair and straight hair parents have offspring with wavy hair) A condition in which two alleles are expressed The phenotype of a heterozygous individual is a combination of the phenotypes of the two homozygous parents Ex) When a white cow is crossed with a brown cow, they produce an offspring that have brown and white spots Ex) Human Blood Types- A and B types have offspring with AB bloodtype

Incomplete Dominance

Codominance

Punnett Squares

Punnett Squares A graphic used to predict the possible genotypes of offspring in a given cross Each parent has two possible alleles to pass on An offspring receives one allele from each parent A Punnett square shows all of the possible allele combinations in the offspring

Punnett Square Example The possible offspring combinations in pea plants with different flower colors F = Purple flower allele f = White flower allele Parent #1 Genotype: FF Phenotype: Purple flowers Parent #2 Genotype: ff Phenotype: White flowers

Probability & Ratios Probability Ratios The mathematical chance of a specific outcome in relation to the total number of possible outcomes An expression that compares two quantities Written a 1:4, read as “one to four” Use a Punnett square to figure out the probability that any one offspring will get certain alleles Can be expressed as a percentage

Punnett Square Practice Widow’s peak is dominant to no widow’s peak. Determine the genotype and phenotype ratios for a homozygous dominant female and a homozygous recessive male.

Punnett Square Practice Cleft chin is dominant to no cleft chin. Determine the genotype and phenotype ratios for a heterozygous female and a heterozygous male.

Punnett Square Practice Tall plants are dominant to short plants. Determine the genotype and phenotype ratios for a homozygous recessive female and a homozygous dominant male.

Punnett Square Practice Free ear lobes are dominant to attached ear lobes. Determine the genotype and phenotype ratios for a heterozygous female and a homozygous recessive male.

Punnett Square Practice Short hair is dominant to long hair in mice. Determine the genotype and phenotype ratios for a homozygous recessive female and a heterozygous male.

Punnett Square Practice Green peas are dominant to yellow peas. Determine the genotype and phenotype ratios for a heterozygous female and a heterozygous male.

Codominance In some chickens, the gene for feather color is controlled by codominance. The allele for black is B and the allele for white is W. The heterozygous phenotype is known as erminette. a. What is the genotype for black chickens? b. What is the genotype for white chickens? c. What is the genotype for erminette chickens?

Codominance If two erminette chickens were crossed, what is the probability that: a. They would have a black chick? b. They would have a white chick? A black chicken and a white chicken are crossed. What is the probability that they will have erminette chicks?

Incomplete Dominance In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as pink. What is the phenotype of a plant with the genotype RR? What is the phenotype of a plant with the genotype WW? What is the phenotype of a plant with the genotype RW?

Incomplete Dominance A pink-flowered plant is crossed with a white-flowered plant. What is the probability of producing a pink-flowered plant? What cross will produce the most pink-flowered plants? Show a Punnett square to support your answer

Multiple Alleles Another type of non-mendelian trait: Multiple alleles. Human hair color is controlled by one gene with four alleles (with some incomplete dominance): HBr = brown HBd = blonde hR = red hbk = black What do you think your parent’s phenotypes and genotypes for hair color are? What are your phenotype and genotype for hair color? If someone with auburn hair has children with someone with red hair (but whose mother had black hair), what are the genotype and phenotype probabilities for their children?

Punnett Squares Punnett squares can help make predictions about inherited traits in large numbers of offspring Studying human inheritance is more difficult. Scientists cannot perform breeding experiments on people Family histories (or family trees called PEDIGREES) provide one way to gather evidence about inherited traits in humans Studying a pedigree can help us figure out the genotype of individuals in a family

Pedigree A tool to study the pattern of inheritance. Traces the occurrence of any inherited trait through generations of a family. Can be useful in tracing a special class of inherited disorders known as sex-linked disorders. Associated with an allele on a sex chromosome (X or Y) Ex) Hemophilia and Colorblindness are caused by alleles on the X chromosome. Women have two X chromosomes so they may not display the trait, but they could pass it onto their offspring.

Carriers If an individual carries the gene for a disease, but does not express it we say that they are a carrier We use this term for genetic disorders that are recessive in nature (which means that a person must inherit TWO recessive alleles in order to express the trait) The person is Heterozygous for the trait.

Polydactyly

Polydactyly Pedigree

Polydactyly Polydactyly is an inherited condition in which a person has extra fingers or toes. It is caused by a dominant allele of a gene. This means it can be passed on by just one parent if they have the disorder.

Pedigree Practice Make a pedigree for left-handedness using information of the Thomas family: The father, Tom, and mother, Diane, have three children. The two oldest children are Anna and Mary and the youngest child is Teddy. The oldest daughter, Anna, is married and has an older son, Will, and younger daughter, Vanessa. Mary is also married and has a son, Patrick. Teddy is not yet married. Everyone in this family is right handed except the father, the oldest daughter, and the granddaughter. Right-handedness is dominant.

Pedigree Practice A woman’s sister has cystic fibrosis, a disease caused by recessive genes. Neither of her parents has the disease. What chance is there that her mother is a carrier (heterozygous) for the trait? What chance is there that the woman herself is a carrier for the trait?