Genetics A study of inheritance

Gregor Mendel Father of modern genetics

Gregor Mendel Father of modern genetics Researched with pea plants

Gregor Mendel Father of modern genetics Researched with pea plants Developed ideas of dominance and trait segregation

Phenotype –Physical characteristics

Genotype Phenotype –Physical characteristics Genotype –Genes we inherit from our parents

Phenotype –Facial structure Notice the similarities:

Phenotype –Facial structure –Eyes Notice the similarities:

Phenotype –Facial structure –Eyes –Smile Notice the similarities:

Phenotype –Facial structure –Eyes –Smile –Ears Notice the similarities:

Phenotype –Facial structure –Eyes –Smile –Ears –Nose Notice the similarities:

Phenotype –Facial structure –Eyes –Smile –Ears –Nose –Neck Notice the similarities:

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH Pod color - yellow or GREEN

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH Pod color - yellow or GREEN

Mendelian Genetics We will work with the following three: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH Pod color - yellow or GREEN Flower position - terminal or AXIAL

Mendel's Four Hypotheses 1) There are alternative forms of “heritable factors” (what we now call genes). –Alternative forms are called alleles. In our flowers we have two alleles for color, purple and white. 2) Each individual inherits two copies of these alleles. These may be two of the same (e.g., two alleles for purple), or two different ones (one for white, one for purple). –- if an individual has two of the same alleles, it is termed “homozygous” –- if an individual has two different alleles, it is “heterozygous”.

Mendel's Four Hypotheses 3) If the two alleles are different (the individual is a heterozygote), then one of –the alleles will determine the individual's appearance. This is the "dominant“ allele. –- the other allele essentially has no effect on the individual, and is called “recessive”. 4) a gamete carries only 1 allele for each trait (because alleles separate from each other during production of gametes.

Homozygous –Homo means "same or common". –Homozygous means that both alleles are the same. Genotypes such as BB, bb, B1B1 are homozygous.

Heterozygous –Hetero means "different". Heterozygous means that the two alleles are not the same. Thus, genotypes such as Bb, are heterozygous

Predicting Inheritance To determine the chances of inheriting a given trait, scientists use Punnett squares and symbols to represent the genes. UPPERCASE letters are used to represent dominant genes. lowercase letters are used to represent recessive genes.

Predicting Inheritance For example: T = represents the gene for TALL in pea plants t = represents the gene for short in pea plants So: TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two genes for every trait!

Predicting Inheritance For example: T = represents the gene for TALL in pea plants t = represents the gene for short in pea plants So: TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two genes for every trait! Mendels’ Principle of Dominance Some genes (alleles) are dominant and others are recessive. The phenotype (trait) of a dominant gene will be seen when it is paired with a recessive gene.

Predicting Inheritance Let’s cross a totally dominant tall plant (TT) with a short plant (tt). Each plant will give only one of its’ two genes to the offspring or F 1 generation. TT x tt TTtt

Predicting Inheritance Let’s cross a totally dominant tall plant (TT) with a short plant (tt). Each plant will give only one of its’ two genes to the offspring or F 1 generation. TT x tt TTtt Mendels’ “Law” of Segregation Each gene (allele) separates from the other so that the offspring get only one gene from each parent for a given trait.

Punnett Squares TtTtTt The genes from one parent go here. The genes from the other parent go here.

Punnett Squares TT tTtTtTt t

Punnett Squares TT tTtTtTt tTtTt

Punnett Squares TT tTtTtTtTt tTtTtTtTt

TT tTt tTtTtTtTt

Punnett Squares TT tTt t

Punnett Squares TT tTt t F 1 generation

Interpreting the Results The genotype for all the offspring is Tt. The genotype ratio is: Tt - 4/4 The phenotype for all the offspring is tall. The phenotype ratio is: tall - 4/4

Punnett Squares Tt T?? t Your Turn!!

Punnett Squares Tt TTTTt t tt F 2 generation

Punnett Squares Tt TTTTt t tt Next, give the genotype and phenotype ratios of the offspring (F 2 generation).

Punnett Squares Tt TTTTt t tt Genotype ratio: TT - 1

Punnett Squares Tt TTTTt t tt Genotype ratio: TT - 1, Tt - 2

Punnett Squares Tt TTTTt t tt Genotype ratio: TT - 1, Tt - 2, tt - 1

Punnett Squares Tt TTTTt t tt Genotype ratio: TT - 1, Tt - 2, tt - 1 Phenotype ratio: Tall - 3

Punnett Squares Tt TTTTt t tt Genotype ratio: TT - 1, Tt - 2, tt - 1 Phenotype ratio: Tall - 3, short - 1

Punnett Squares Tt TTTTt t tt This is a monohybrid cross. We worked with only one trait. The height of the plant.

Punnett Squares Tt TTTTt t tt This is a monohybrid cross. We worked with only one trait. The height of the plant.

Nondisjunction Nondisjunction is the failure of chromosome pairs to separate properly during meiosis or mitosis.meiosismitosis

Examples of Nondisjunction: A. Down's Syndrome: 47 chromosomes with 3 #21 chromosomes. B. Triple-X Syndrome: 47 chromosomes caused by 3 X chromosomes. –Can cause women to be taller C. Klinefelter's Syndrome: 47 chromosomes caused by 2 X chromosomes and 1 Y chromosomes. –Men are unable to have children D. Turner's Syndrome: 45 chromosomes with 1 X chromosome (caused by the absence of one of the X chromosomes or a Y chromosome). –Women can not have children and may be shorter.