Genetics and the Work of Gregor Mendel Gregor

Genetics and the Work of Gregor Mendel

Gregor Mendel l Modern genetics began in the mid-1800’s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas l l Used experimental design Used mathematical analysis l l Collected and counted peas Scientific method

Vocabulary to know l l l True breeding – when self-pollinated they produce offspring identical to themselves Genes- chemical factors that determine traits (usually come in two forms) Alleles – different forms of a gene Dominance – alleles that mask another allele, so that you only see that trait Cross-pollination- pollinating males and females from two different plants

Where are genes located? l On chromosomes! l Remember chromosomes are made up of DNA located inside of the nucleus

Every individual receives one copy of each gene from both parents T = Tall allele t = short allele Father Mother TT T tt T t sperm Tt You t egg

Mendel’s Work l Bred pea plants l l l Cross-pollinated Raised seed and then observed traits Allowed offspring to selfpollinate and observed next generation.

Mendel collected data for 7 traits

What two things were observed for each trait? l Genotype: the genetic make up that create the trait. (TT, tt, etc) l Phenotype: the observable characteristic of an organism that results from the interaction of its genotype. Physical Pheatures

What did Mendel’s Findings mean? l Some traits mask others l For example: Purple & white flowers are separate traits that do not blend l l Dominant allele – LAW OF DOMINANCE l l l Purple x white ≠ light purple “dominates” or masks recessive alleles In genetics they are represented by an up case letter Recessive allele l l An allele that will not be expressed if paired with a dominant allele In genetics they are represented by a lower case letter.

Homozygous vs Heterozygous l l l “Homo” = two of the same “Hetero” = two different Heterozygous: When a dominant and recessive allele is represented in a trait Homozygous recessive: When two recessive alleles are represented in a trait Homozygous dominant: When two dominant alleles are represented in a trait

Making Crosses l Alleles are represented as letters l l l flower color alleles P (dominant) or p (recessive) True breeding purple flowers = PP True breeding white flowers = pp PP x pp Pp

Mendel’s system is just TOO easy! l l l Peas are genetically simple Most traits are controlled by a single gene Each gene he observed only had 2 versions l l 1 completely dominant 1 recessive

Punnett Square Practice l Work like the game battleship or chess.

Punnett Square Practice

Punnett Square Practice

YOU PRACTICE: l l l Cross a Heterozygous Brown eyes (Bb) with recessive blue eyes. (bb). What are the possible genotypes? What are the possible phenotypes? B b b b

You practice l l Stripes is dominant and solid color is recessive. Cross a heterozygous stripped cat with a solid color cat. What are the genotypes? Phenotypes?

You practice l Complete a cross of these traits: PP by p. P. What are the results of the F 1 generation?

STOP and practice

Dihybrid Crosses A breeding experiment that tracks the inheritance of two traits. l Mendel’s “Law of Independent Assortment” l l l a. Each pair of alleles segregates independently during gamete formation b. Formula: 2 n (n = # of heterozygotes)

Question: How many gametes will be produced for the following allele arrangements? l Remember: 2 n (n = # of heterozygotes) l 1. Rr. Yy l 2. Aa. Bb. CCDd l 3. Mm. Nn. Oo. PPQQRrss. Tt. Qq 22

Answer: 1. Rr. Yy: 2 n = 22 = 4 gametes RY Ry r. Y ry 2. Aa. Bb. CCDd: 2 n ABCD ABCd a. BCD a. BCd = 23 = Ab. CD ab. CD 8 gametes Ab. Cd ab. Cd 3. Mm. Nn. Oo. PPQQRrss. Tt. Qq: 2 n = 26 = 64 gametes 23

Dihybrid Cross Traits: Seed shape & Seed color l Alleles: R round r wrinkled Y yellow y green l l Rr. Yy RY Ry r. Y ry x Rr. Yy RY Ry r. Y ry All possible gamete combinations 24

Dihybrid Cross RY Ry r. Y ry 25

Dihybrid Cross RY RY RRYY Ry RRYy r. Y Rr. YY ry Rr. Yy Ry r. Y ry RRYy Rr. YY Rr. Yy RRyy Rr. Yy Rryy Rr. Yy rr. YY rr. Yy Rryy rr. Yy rryy Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9: 3: 3: 1 phenotypic 26 ratio

Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9: 3: 3: 1 27

Stop Dihybrid practice

Incomplete dominance l Hybrids have an “in-between” appearance l l l RR = red flowers rr = white flowers Rr = pink flowers l Make 50 % less color

Incomplete dominance

Codominance l Equal dominance l l Human blood ABO blood groups 3 versions l l A, B, i A & B alleles are codominant Both A & B alleles are dominant over the i allele The genes code for different sugars on the surface of red blood cells l “Name tag” of the red blood cell

Many genes, one trait l Polygenic inheritance l l Additive effects of many genes to create one observable trait Humans l l l Skin color Height Weight Eye color Intelligence behaviors

Human Skin Color Aa. Bb. Cc x Aa. Bb. Cc l l l Can produce a wide range of shades Most children = intermediate skin color Some can be very light, some can be very dark

Human Skin Color

Environmental Effect l Phenotype is controlled by both the environment and genes altering the p. H of the soil = Blue flowers appear when the soil has an acidic p. H of 5. 5 or lower

Coat color in Arctic animals is influenced by the environment.

Sex-linked Traits l Traits (genes) located on the sex chromosomes l Sex chromosomes are X and Y l XX genotype for females l XY genotype for males l Many sex-linked traits carried on X chromosome 38

Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes fruit fly eye color XX chromosome - female Xy chromosome - male 39

Sex-linked Trait Problem l l Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X RY l l l x X r Remember: the Y chromosome in males does not carry traits. Xr Xr RR = red eyed Rr = red eyed R X rr = white eyed XY = male Y XX = female 40

Sex-linked Trait Solution: Xr Xr XR XR Xr Y 50% red eyed female 50% white eyed male 41

Stop Practice: l 1. Complete the foldable on all types of inheritance: You need five sections labeled: Monohybrid crosses, Dihybrid crosses, Incomplete dominance, Codominance, and sexlinked. In each flap you need to: l l 1. 2. 3. Define what it is, what type of cross it is. Give an example trait with Punnett square. Explain with an example what the genotypes in this type of cross could be and what the phenotypes are.