Chapter 2: Traits and How They Change Section 2: Genetics Heredity x Genetics Mendel s experiments Punnett Square For the test: study power point and textbook
Important Info to remember :
We inherit 2 alleles per gene One allele comes from the father and another from the mother
1)What is Heredity? 2)What is genetics? Heredity is the passing of traits from parents to offspring. ** Genetics is the branch of Biology that studies genes, heredity, and the variation of inherited traits in living organisms.
Mendel Austrian monk, lived in the 1800s The Father of Genetics He was the first to describe the inheritance of traits in an offspring As a result of his observations, he developed 3 basic principles of genetics, studying pea plants
HE used pea plants because they reproduce quickly and the inheritance of traits can be observed in a short period of time
1st Principle Mendel s Principle of Dominance Traits are determined by different factors. Each trait is determined by at least two factors. One factor is dominant over the other Today we call factors genes and alleles
What are dominant and recessive alleles? Dominant alleles will show their effect on the phenotype whenever they are present in the genotype. Recessive alleles will show their effect on the phenotype only when two of them are present in the genotype.
2 nd Principle: Mendel s Principle of Segregation Mendel also concluded that for each trait: Organisms receive ONE allele from the father and ONE from the mother. This allows for many different allele combinations AND explains why variation exists among the offspring of the same parents.
Mendel s 3 rd principle : Law of Independent assortment Alleles for one trait have no effect on the inheritance of alleles of another trait
Vocabulary not in the book! Homozygous or Purebred an organism that has two identical alleles for a trait Heterozygous or Hybrid an organism that have two different alleles for a trait
**Representing alleles Letters are used to represent alleles Capital letters are used for dominant alleles and lowercase letters are used for recessive alleles Ex: short and tall tall is dominant and short is recessive TT homozygous or purebred = organism is tall tt homozygous or purebred = organism is short Tt heterozygous or hybrid = organism is tall (it has the dominant allele, that will always show in the phenotype)
Punnett Square Tool to predict the genotype and phenotype of an offspring Ex: cross a pink flower with a white flower. Pink is dominant Steps: 1) Represent alleles 2) Do the Punnett square 3) Interpret the results in % for the genotypes and phenotypes
More examples: Mendel s experiments : Mendel named: P - Parental generation (1 st cross) F1 generation - the result of 1 st crossing (2 nd cross) F2 generation - result of the 2nd crossing ( 3 rd cross) ****IMP: No matter what trait he was working with, Mendel observed that there was a pattern in the inheritance of traits.
Discovering the Patterns: EX: Tall and short plants tall is dominant -Cross two homozygous for the dominant trait -Cross two homozygous for the recessive trait -Cross two heterozygous
Discovering the Patterns: RESULTS BELOW ARE ALWAYS THE SAME NO MATTER THE TRAIT -Cross two homozygous for the dominant trait = 100% with the dominant trait -Cross two homozygous for the recessive trait = 100% with the recessive trait -Cross two heterozygous = 75% with the dominant trait and 25% with the recessive trait
Practicing Punnett Square - Pea plants with different seed color Dominant yellow seed what is the genotype? Recessive green seed what is the genotype? 1)Homozygous yellow x homozygous green 2)Heterozygous yellow x heterozygous yellow 3)green x green 4)Heterozygous yellow x green 5)Homozygous yellow x homozygous yellow Identify Genotypes and phenotypes for all crosses Page 47 Applying math
Non-Mendelian Inheritance not in the book use power point to study
The inheritance of traits not always follows Mendel's rules Mendel studied traits determined by one gene with 2 pair of alleles and one allele is always completely dominant over the other This type of inheritance is called Complete Dominance
Nowadays we know that there are other types of inheritance: Incomplete dominance or Codominance Multiple Alleles Polygenic Inheritance Sex-Liked traits
Incomplete dominance- Snapdragon traits determined by genes with alleles that are neither dominant nor recessive. The offspring show a phenotype that is a blend of the parents phenotype (pink flower)
Snapdragons: A plant that is homozygous for the red allele will have red flowers A plant that is homozygous for the white allele will have white flowers A plant that is heterozygous will have pink flowers Neither the red nor the white alleles are dominant, so the phenotype of the offspring is a blend of the phenotypes of the two parents.
Incomplete dominance- Snapdragon Representing the alleles: (only capital letters) C R C R red C W C W white C R C W pink
Incomplete dominance- Snapdragon Punnett Square : C R C R red versus C W C W white C R C W pink versus pink
Incomplete Dominance in horses C C C C C W C W C C C W - Chestnut homozygous - White homozygous - Palomino heterozygous
Incomplete Dominance in horses C C C C C W C W C C C W - Chestnut - homozygous - White homozygous - Palomino heterozygous Do a Punnett Square to cross: Palomino with Palomino Palomino with Chestnut
Co-Dominance Codominance is a type of incomplete dominance. Codominance would show both alleles equally. It is not a blend of the traits as seen in incomplete dominance.
Blood Type AB in humans is a case of Codominance Blood types are: A,B,AB,O Blood AB: A and B are proteins called antigens, present in the blood and they are both a dominant trait In Blood AB - both proteins are present in the phenotype. (not a blend)
Multiple Alleles: another type of inheritance The trait is determined by a gene that has more than 2 alleles, so the phenotype is also a combination. Ex: Blood type case of multiple alleles (and codominance for type AB ) There are: 2 dominant alleles: alleles for type A and alleles for type B One recessive for type O
Blood type alleles and how to represent them: i recessive I A and I B are Codominant (when present, both will show in the phenotype Blood type AB)
Cross type AB with Type O 50% A heterozygous 50% B heterozygous Cross heterozygous A with heterozygous B Cross heterozygous A with recessive O
Polygenic Inheritance Many traits are determined by more than one gene. EX: height, eye color, skin color More difficult to study because of the wide variety of phenotypes (range) that the different gene combinations can produce
SKIN COLOR: 3 Genes and 6 Alleles the skin gets lighter when more recessive alleles are present in the genotype
Different genotypes and phenotypes
Sex-Liked traits X and Y chromosomes determine the sex Remember, if you have: 2 chromosomes X you are a female (XX) 1 chromosome X and one Y you are a male (XY) Ex of sex-linked traits: Color-blindness, hemophilia both recessive traits
What are Sex-Liked traits? are traits linked with the X or Y chromosomes linked means that the chromosome carries the allele for that trait Sex linked traits are usually X-linked Y-linked traits very rare
Sex-Liked traits Conditions for the trait to show in the phenotype: Females need to be homozygous to have the disease, males have to have only one chromosome to be affected by the disease.
The alleles in the Sex-linked traits EX: Hemophilia bleeding disorder that slows the blood clotting process it is recessive To be hemophilic women need two lower case h and man needs one lower case h
What is a carrier? Is an organism that carries the allele for a certain trait but does not have the trait expressed in the phenotype.
The alleles in the Sex-linked traits EX: Colorblindness - it is recessive to be color blind woman needs 2 lower case c and male needs 1 lower case c.
Examples Punnett Square: 1) Mother is carrier for hemophilia and father is hemophilic 2) Mother is color blind and father is not color blind: 3) Mother is carrier for color blindness and father is color blind