Patterns of Heredity - Genetics - Sections: 10.2, 11.1, 11.2, & 11.3
Genetics = the study of heredity by which traits are passed from parents to offspring Page. 227
Heredity = The passing of genes/traits from parents to offspring Many of your traits, including eye color, shape of your eyes, texture of your hair, height, weight, resemble those of your parents!
How are traits passed on?.. CHROMOSOMES!
Let s review the structure of a chromosome... A pair of chromosomes are considered homologous (homo meaning same) Homologous chromosomes have the same size, structure, and genetic information (genes).
What is a gene? A unit of heredity that occupies a specific location on a chromosome and codes for a particular protein. It consists of a specific nucleotide sequence
Alleles Alternative forms of a gene that occupy corresponding positions on homologous chromosomes.
Autosomes and Sex Chromosomes We have 23 pairs of chromosomes 1 pair are known as the sex chromosomes, which determines the sex of the offspring (and has other important genetic information too!) Males = XY Females = XX
Think - Pair - Share 1. Does the mother or the father determine the gender of the child? 2. What do you call this set up to the right?
The History of Gregor Mendel Austrian Monk Czech Bred different varieties of garden pea. First to develop rules that accurately predict patterns of heredity. Determined specific units of inheritance = genes and alleles Page. 277 https://www.youtube.com/watch?v=mehz7tcxjse
Pollination - transfer of pollen from anthers to stigma in flowers Two types: 1. Self pollination occurs within the same flower or same plant 2. Cross pollination occurs between two different
Why are pea plants a great subject to use when studying heredity? 1. Several traits exist in two clear different forms. Ex: Flower color was either purple OR white 2. The male and female reproductive parts are enclosed within the same flower. It is easy to control mating by allowing a flower to fertilize itself (self fertilization), or you can transfer pollen to another flower (cross pollination). 3. The garden pea is small, grows easily, matures quickly, and produces many offspring. Results can be obtained quickly with many offspring.
Steps in Mendel s research 1. Allowed each garden pea to self-pollinate for several generations to ensure true-breeding for that particular trait. P Generation = parental generation 2. Mendel then cross-pollinated two P generation plants that had different forms of the trait (purple and white flower). The offspring from that were called the F1 generation. F 1 Generation = Filial generation (of son or daughter) 3. Allowed the F1 generation to self-pollinate and those offspring are called the F2 generation. F2 Generation = Filial generation 2
Mendel s Crosses with Pea Plants P1 parental generation Pure tall plants X Cross F first filial generation Pure short plants Pollination All Tall plants Self Pollination 1 F 2 second filial generation 787 tall plants, 277 short plants 3 to 1 ratio
Ratio of Mendel s Research P Generation had a true-breeding purple and white flower The F1 generation consisted of ALL purple flowers The F2 generation had 705 purple flowers and 224 white flowers. That is a ratio of about 3:1 or 3/1 He found that ratio for all of the traits
Color and texture
Mendel s 3 Principles of Inheritance 1) The Law of Segregation: Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent. 2) The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another. 3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.
Mendel s 3 Principles of Inheritance (Laws) 1. The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant. If an organism has at least 1 dominant allele, that trait will be expressed! Dd
2. The Law of Segregation: The two alleles for a trait segregate into gametes during meiosis
3. Law of independent assortment alleles of different genes separate independently of one another during gamete formation.
Phenotype vs. Genotype Genotype: The set of alleles that an individual has (not always obvious) phenotype: the physical appearance of a trait
Heterozygous vs. Homozygous Different alleles present Two of the same alleles Ex: BB or bb Ex: Bb Homozygous recessive or homozygous dominant
Recessive vs. Dominant Recessive: The trait not expressed when the dominant form of the trait is present Dominant: The expressed form of the trait when present (even if it is just 1 allele)
Example: In dogs, black fur is dominant over white fur color. B = black b = white BB or Bb bb
DO NOW If Chris Hemsworth s phenotype is blonde hair (H=Black, h=blonde) 1. What his genotype? 2. Would his alleles be homozygous dominant, homozygous recessive, or heterozygous? Beyonce s phenotype is brown hair. 1. What is her genotype? 2. Would her alleles be homozygous dominant, homozygous recessive, or heterozygous What are the chances their offspring would have brown hair? Create a punnett square?
Punnett Square A diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross. Crossing only 1 trait is called a monohybrid cross. Crossing 2 traits is called a dihybrid cross.
1. Phenotypic Ratio and %: 2. Genotypic Ratio :
1. Phenotypic Ratio and %: 2. Genotypic Ratio :
1. Phenotypic Ratio and %: 2. Genotypic Ratio :
Probability Probability calculations can predict the results of genetic crosses. It is the likelihood that a specific event will occur. = number of one kind of possible outcome Total number of all possible outcomes Example: If you flip a coin, you will have 1 outcome, but two possible outcomes. Your answer would be ½.
How do you write a ratio? When flipping a coin and it lands on tails ½ or 1:2 Genotypic ratio: What is genetically written. Phenotypic ratio: what physical traits you would see
Relate probability to a Punnett Square 1. What is the phenotypic ratio? 2. What is phenotypic %?
Test Cross In a test cross, an individual whose phenotype is dominant, but whose genotype is not known, is crossed with a homozygous individual. Ex: Brown eyes are brown, but can be BB or Bb. To find out if the person with brown eyes is homozygous or heterozygous, you cross it with a recessive person's genotype and the outcome will tell you depending on the ratio
Spongebob squarepants doesn t know whether or not he is Homozygous Dominant or Heterozygous for his yellow color. The recessive trait is a white sponge. Let s say that we perform a test cross on spongebob (spongebob + a white female sponge) and all of the baby sponges are yellow. What would spongebob s genotype be?
Pedigree - a family history that shows how a trait is inherited over several generations.
You can see how a genetic disorder runs in a family. Carriers are individuals who are heterozygous for an inherited disorder but do not show symptoms. Carriers can pass the allele for the disorder to their offspring
DO NOW Fill in possible genotypes!
Types of Inheritance
Incomplete dominance a trait that is intermediate between two parents
Codominance Neither trait is dominant instead, both traits are shown (No Blending) Ex) Roan Cows Red + White = RED AND WHITE
Codominance two dominant alleles are expressed at the same time.
Determine Blood Type Determine the possible offspring of the following crosses below 1. AB and O 2. AA and BO 3. AB and AB
Multiple alleles genes with 3 or more alleles
Polygenic Traits several genes influence a trait A wide range of variability! Genes can be located on different chromosomes
Sex-Linked Traits Red-green colorblindness Male Pattern Baldness Hemophilia Compare: Male : XhY X HY Female: XHXH X HX h X hx h
Autosomal vs. Sex-Linked
What do you see?
Pleiotropy The single gene controlling or influencing multiple, possibly unrelated, phenotypic traits. Ex: albinism
Polyploidy Occurrence of one or more extra sets of all chromosomes in an organism. Ex. A triploid organism (3n) - means that it has three complete sets of chromosomes.
Gene Linkage When two genes are close to each other on the same chromosome and tend to be passed on together There are several genes on a chromosome
Gene Linkage cont... Linked genes usually do not segregate independently because they are so close together on a chromosome.
Traits can be influenced by the environment! Hydrangea Flowers: When in acidic soil, they bloom blue flowers When in basic soil, they will bloom pink flowers Arctic Fox Enzymes will make pigments during a certain time of the year.
Genetic Disorders Sickle Cell Anemia Cystic Fibrosis (CF) Hemophilia Tay- Sachs Disease Huntington s Disease (HD) Hypercholesterolemia In Groups, you will research a specific disease and present it to the class.
Sickle Cell Anemia - Red blood cells are c-shaped or sickled. This disease lacks the correct amount of hemoglobin. Cystic Fibrosis (CF) - A thick mucus is constantly created in the lungs and intestinal tract. It is a recessive disorder. Hemophilia - Specific protein for blood clotting is not created, thus making it very hard to stop cuts. Bruising and internal bleeding occur. SEX LINKED! Tay- Sachs Disease - Breaks down nerve cells, brain cells, and deteriorate the spinal cord. A recessive disorder. Huntington s Disease (HD) - Symptoms appear later in life and is a dominant disorder. Movement and cognitive ability is impaired.
Treating Genetic Disorders Most genetic disorders cannot be cured, although progress is being made. Families who have a history of genetic disorders are recommended to undergo counseling before having a child. They can find out how it could affect their offspring. Some genetic disorders can be treated if diagnosed early enough, such as PKU (lacking a certain enzyme). If known, that child can be put on a certain diet and medicine routine.
Gene Therapy May soon allow scientists to correct certain recessive genetic disorders by replacing defective genes with copies of a healthy one. First step of gene therapy is to isolate a copy of the gene. Scientists are trying to input that gene into the cell by attaching it to a cold virus. Attempts in humans have not been successful. However, the outlook is promising.
What is genetic mapping? Genetic mapping - also called linkage mapping - can offer firm evidence that a disease transmitted from parent to child is linked to one or more genes. It also provides clues about which chromosome contains the gene and precisely where it lies on that chromosome. Genetic maps have been used successfully to find the single gene responsible for relatively rare inherited disorders, like cystic fibrosis and muscular dystrophy. Maps have also become useful in guiding scientists to the many genes that are believed to interact to bring about more common disorders, such as asthma, heart disease, diabetes, cancer and psychiatric conditions.