- Slides: 39
Word GENE ALLELE HOMOZYGOUS or Purebred Vocabulary Definition Picture/Example A segment of DNA that codes for a protein Alternate forms of a gene A or a (1 letter) Two alleles are the same. AA or aa
Word Vocabulary Definition HETEROZYGOUS Two alleles are different. Or Hybrid DOMINANT RECESSIVE Picture/Example Aa Trait that is automatically seen even when paired with a recessive allele. AA or Aa (dimples) Trait that is only seen when two recessive alleles are present. aa (no dimples)
Word GENOTYPE PHENOTYPE PUNNETT SQUARE Vocabulary Definition Picture/Example Genetic make-up of an individual. AA, Aa or aa Physical characteristic. How you see the trait. A box that is used to predict the probability of offspring when crossing two parents. Dimples or no dimples
What is genetics? heredity Genetics is the branch of biology that studies _________ or the passing of traits from parent to offspring. Gregor Mendel ___________________ (1822 -1884) today he is considered to be pea plants the father of modern genetics. Worked with _____________. Mendel’s findings led to two laws of heredity: Law of Segregation ___________________ - 2 alleles for a trait separate during meiosis (chromosomes separate) Law of Independent Assortment _________________________ - alleles for different traits separate independently from one another during meiosis. In other words inheritance of one trait does not influence inheritance of another. For example if you have blond hair you will not necessarily get blue eyes. These traits are inherited separately.
Nature vs. Nurture • environment Genes determine the physical trait, but __________can also play a role in how the trait is expressed. – Example 1: Height and weight. Genes determine this trait, but environment can play a big role. If a person has genes for being very tall, but does not have the proper nutrition while growing up, then they may not be as tall as their genes would allow. – Example 2: Fur color in some animals. Genes determine fur color, but some animals have fur that changes depending on the season. The arctic fox for instance has a white coat in the winter but a brown coat in the summer.
Now you practice identifying the genotypes and phenotypes using the following traits and symbols. TRAIT DOMINANT ALLELE RECESSIVE ALLELE Seed shape R = round r = wrinkled Seed color Y = yellow y = green Seed coat color G = gray g = white Flower position A = axial a = terminal Plant height T = tall t = short
Complete the following table using the symbols and traits found above: Trait Genotype (symbol) Phenotype seed shape RR Round seed shape Rr Round seed shape rr Wrinkled plant height TT or Tt tall plant height tt short flower position aa terminal flower position AA or Aa axial seed coat color Gray Gg
Write the correct symbols for the following genotypes. Circle those that are not possible. pure tall stems TT homozygous yellow seeds YY pure short stems tt pure green seeds yy homozygous terminal flowers aa hybrid round seeds Rr pure round seeds hybrid tall stems RR homozygous axial flowers AA homozygous wrinkled seeds rr Tt Heterozygous wrinkled seeds ___ hybrid axial flowers Aa heterozygous short stems__ heterozygous yellow seeds Yy heterozygous seed coat color. Gg • Why are some of these not possible? You cannot have a heterozygous recessive organism. The only way to show a recessive trait is to have two small letters (yy). • Can I always identify the genotype if I know the phenotype? Explain your answer. No, If you know a plant is tall you don’t know if the genotype is TT or Tt.
HOW TO DETERMINE IF A TRAIT CAN BE PASSED ON TO THE OFFSPRING • • • Probability ________ is the likelihood that an event will occur. ____________ Punnett square used to determine the probability that specific traits will be passed down from parent to offspring. __________ cross- a cross that involves one pair of Monohybrid contrasting traits. sperm E e (_____ Female genotype) Ee eggs E e EE Ee Ee ee Ee (_____ - Male genotype) fertilization
PRACTICE PROBLEM: In pea plants, tall is dominant over short. Tt T t t Tt tt tt 50% 0 2 2
PRACTICE PROBLEMS R R r Rr Rr rr 0 4 0 Rr R r R RR Rr r Rr RR rr Rr Rr 1 2 1 3 1
PRACTICE PROBLEMS g G g Gg gg 0 2 2 2
PRACTICE PROBLEMS T T t Tt Tt t T t tt Tt Tt tt Parent genotypes must be Tt x tt A a A AA Aa aa Parent genotypes must be Aa x Aa – both are heterozygous to get ¼ terminal flowers.
NOTES: TEST CROSSES Test Cross - Used to determine the unknown genotype of an organism. For example of a plant is tall you don’t know if it is TT or Tt. So you do a test cross to figure it out. You must cross the dominant organism with a _________. recessive Sample test cross: In dogs, there is a hereditary deafness caused by a recessive gene, “d. ” A kennel owner has a male dog that she wants to use for breeding purposes if possible. The dog can hear, so the owner knows his genotype is either DD or Dd. If the dog’s genotype is Dd, the owner does not wish to spend the money to use him for breeding. Assume the male is DD Assume the male is Dd
Test Cross - Used to determine the unknown genotype of an organism. For example of a plant is tall you don’t know if it is TT or Tt. So you do a test cross to figure it out. You must cross the dominant organism with a _________. recessive Sample test cross: In dogs, there is a hereditary deafness caused by a recessive gene, “d. ” A kennel owner has a male dog that she wants to use for breeding purposes if possible. The dog can hear, so the owner knows his genotype is either DD or Dd. If the dog’s genotype is Dd, the owner does not wish to spend the money to use him for breeding. Assume the male is DD d d D D Dd Dd Assume the male is Dd D d d d Dd dd Dd If any of the puppies are deaf, the male’s genotype MUST BE _______; but assuming a litter of at least about 4 to 5 puppies or more, if they can all hear, his genotype is MOST LIKELY DD _______.
Dihybrid Crosses bb. RR What letters would go in Box X? _________ bbrr What letters would go in Box Z? _________ What are the genotypes of the parent’s of this cross? Bb. Rr Bb. Rr _____________ What percent of offspring are expected to have a white coat of fur? 4/16 = 25%
Complex Genetics Term Definition Complete Dominance One allele is dominant over the other. Incomplete Dominance The dominant allele will not fully cover up a recessive allele and the trait will be a result of the two blending or mixing together. Codominance Two different alleles are expressed at the SAME time. RR Rr rr
In carnations, incomplete dominance can be seen in flower color: ◦ red (RR) pink (Rr) Cross two pink carnations. Write the genotypes of the parents white (rr) Rr x Rr R RR r Rr ◦ ◦ ◦ Rr rr Genotypic ratio: 1 RR : 2 Rr : 1 rr Phenotypic ratio: 1 red : 2 pink : 1 white What percent of the offspring are pink? 50% _______
Cross between 2 sickle cell carriers Sickle cell anemia is another example of incomplete dominance. Carriers of the allele have a much milder form of the disease. Normal - (HAHA), Carrier - (HAHS), Sickle cell - (HSHS) Complete a punnett square to determine the chances of two sickle cell carriers having a homozygous normal child? AH S H H Genotype of parents: ____ x ______ HA HS HA H AH S HS HS 25% chance of a homozygous normal child
The allele for red hair (HR) is codominant with the allele for white hair (HW) in cattle. Cattle that have the genotypes HRHW are called roan because their hair is a mixture of red and white hairs. Red (HR HR) Roan(HRHW) White (HW HW)
Codominance Practice Problems HRHR = Red HRHW = roan Cross a red cow and a white bull: HR HR HW HRHW HWHW = White RH R W HW H H ________ X _________ RHR : 4 HRHW : 0 HWHW 0 H What is the genotypic ratio of the offspring? ______ 0 red: 4 roan : 0 white What is the phenotypic ratio of the offspring? ______ What percent of the offspring are roan? 100%
Blood Types TWO Multiple Alleles - A gene that has more than ____ alleles (or forms of a gene). In other words, not just one dominant and one recessive allele (i. e. R and r). Use the same common letter with superscripts to show only one gene is playing a role. O A B AB No antigens A antigen Both A & B antigens
Blood Typing Practice Problem #1 1. A man with type O blood marries a woman with type AB blood, what are the possible blood types of their children? i i IA IA i IAi IB 50% 0%
Blood Typing Practice Problem #2 2. Is it possible for a man with type A blood and a woman with type B blood to have one child with type O blood another child with type AB Blood? Why or why not? Show your work!!! I A i I B IA IB IBi i IA i ii Yes, if both parents are heterozygous.
Notes: Polygenic Traits many genes. See lots Polygenic Traits are controlled by ________ of variety Eye, skin, hair color, height, weight, Ex: ____________________________
If two parents have a medium skin tone (Aa. Bb. Cc), their children could have: ______________________ By looking at the graph, we can see that it is most likely that their kids will have ______ skin tone.
In humans, other examples of polygenic traits:
Sex-Linked Traits Genes which are located on the sex chromosomes are said to be sex-_______ or ______-linked. Sex-linked traits occur more frequently in ____because they have only ______ X chromosome. Sex-linked traits include: color blindness, hemophilia and muscular dystrophy. XNXN = Normal Female XNY = Normal Male XNXn = Normal Female Carrier Xn. Y = Male with disorder Xn. Xn = Female with disorder
COLOR BLINDNESS _________ (Xn) is a very common sex-linked trait and is recessive to normal vision (XN). More males have this disorder than females. X NY XN XN XNXN Xn Y XNY Xn. Y XNXn ¼ = 25% ½ = 50%
Hemophilia practice problem In humans, hemophilia is a sex-linked trait located on the X chromosome. Normal blood is dominant (XH) to hemophilia (Xh). A heterozygous female is referred to as a carrier. Cross a carrier female with a male with hemophilia. Xh. Y XHXh __________ X _________ h X Y HXh XHY H X X Xh Xh. Xh Xh. Y What percentage of this couple’s sons will have hemophilia? __ 50% What percentage of this couple’s daughters will have hemophilia? ______ 50% What percentage of this couple’s kids will have hemophilia? ______
Well-known Autosomal Genetic Disorders: Disorder Symptoms Pattern of Inheritance Frequency among human births Huntington’s Disease Gradual deterioration of brain tissue in middle age; shortened life expectancy Autosomal Dominant 1/10, 000 Cystic Fibrosis Mucus clogs lungs, liver and pancreas; victims don’t survive to adulthood Autosomal Recessive 1/2, 080 (whites) Sickle Cell Anemia Impaired blood circulation; Organ damage Autosomal Recessive 1/500 (African American) Tay-Sachs Disease at birth, but deterioration of central nervous system begins in infancy; death occurs in early childhood Autosomal Recessive Phenylketonuria (PKU) Inability of the body to break down the amino acid phenylalanine. Failure to limit the amino acid in the diet causes it to accumulate, which leads to problems w/brain development, seizures and possibly mental retardation. Autosomal Recessive 1/1, 600 (Jews-European Descent) 1/15, 000 Caucasians and Asians (less in African Americans)
Well-known Sex-Linked Genetic Disorders: Disorder Symptoms Pattern of Inheritance Frequency among Human births Hemophilia Failure of blood to clot X-linked Recessive 1/7, 000 Muscular Dystrophy Wasting away of muscles X-linked Recessive 1/3500 males Colorblindness Individuals cannot distinguish between certain colors (most common can’t distinguish red from green) X-linked Recessive 1/12 males 1/200 females
Notes: Pedigrees & Genetic Disorders Biologists use charts called pedigrees to study the pattern of phenotypic inheritance in individuals and their family. Some of the most common symbols used:
Pedigrees – family trees that follow a trait/disorder MALE FEMALE Symbols – square = ______, circle = ______ Shaded individual – person has the disorder/trait. GENERATIONS Roman numerals - _________
Determining Inheritance Patterns Using Pedigrees Tips to determining pattern of inheritance in a pedigree: ◦ Autosomal - about ______ HALF males and females shaded MALES are shaded in. ◦ Sex-linked – more ______ ◦ Dominant – for every child with the disease at least one parent is shaded NORMAL (NOT SHADED) parents ◦ Recessive – if one set of parents are ___________________ but kid has the disease.
Pedigree 1 Circle one in each pair: Autosomal or Sex-linked Dominant or Recessive B/c same # of males and females have it. B/c there are unaffected parents but a child with the disease
Pedigree 2 Circle one in each pair: Autosomal or Sex-linked B/c in more females. Dominant or Recessive B/c for every child with the disease at least one parent has the disease.
Pedigree 3 Circle one in each pair: Autosomal or Sex-linked Dominant or Recessive B/c in more males. B/c there are unaffected parents but a child with the disease