Biology Chapter 9 Fundamentals of Genetics

What is Genetics? a.Study of heredity b. Transmission of traits from parent to offspring

Who is the father of genetics? Gregor Mendel

Why was Mendel Successful? 2 reasons 1. He used a garden pea as his test subject Why would he use the pea? 6 reasons a. Small b. Easy to grow c. Produce many offspring d. Mature quickly e. Many varieties f. Easy to fertilize »Self fertilization – within same plant »Cross fertilization – involved two plants

Second reason? 2. He used a quantitative approach

Mendel’s Experiment Step 1 –He produced a parent generation (P) He allowed pea plants to self fertilize for many generations This made sure that he had pure parents that were true breeding or pure Example: He has 1 pure purple pea plant and 1 pure white pea plant for his P generation

Mendel’s Experiment Cont. Step 2 –He produced the 1 st generation (F1) –He cross fertilized two of the P generation pea plants –What was his results? 100% Purple plants, no white

Mendel’s Experiment Cont. Step 3 –He produced the 2 nd generation (F2) –He took 2 of the F1 generation pea plants and self fertilized them. –What were the results? 75% purple, and 25% white

Mendel’s Conclusions Parents transmit information about traits to their offspring Each individual has 2 factors (genes) for each trait, 1 from each parent Factors (genes) are represented by letters or alleles.

Alleles If both alleles are the same, the individual is homozygous for that trait If both alleles are different, the individual is heterozygous for that trait

Traits can be described in 2 ways: Genotype –Alleles that represent the trait –Example: PP, Pp, pp Phenotype –Expression of the trait –Example: purple, white

More about traits Only some traits are seen, others are masked –Dominant – only need 1 letter to be expressed »Represented by capital letters –Recessive – need both letters or its masked »Represented by lowercase letters

Do you understand? Genotype Dom/Rec Homo/HeteroPheno

Mendel’s Law of segregation Members of each pair of alleles separate when gametes are formed. A gamete will receive 1 allele of the other. This occurs in meiosis.

Principle of Independent Assortment Two or more pairs of chromosomes separate independently of one another during the formation of gametes. This is random.

Why did Mendel’s results repeat? 1.Chance and probability -Leads to predictions 1. coins - flipping a head? 2. cards - diamond? - nine? - nine of diamonds? 3. sex of children - having a boy child? - having a girl after having 4 boys in a row?

Monohybrid Crosses Involves 1 trait Crosses 2 alleles on the same locus Uses a 4-boxed Punnett Square Example: Cross a white flowered pea plant with a heterozygous purple flowered pea plant

Monohybrid Example pp x Pp p p P p Genotype % 50% Pp 50% pp Phenotype % 50% purple 50% white

How do you find out whether an individual is BB or Bb? To a testcross –Technique that takes the unknown genotype and cross it with a recessive individual and then look at the results.

Dihybrid Crosses Involves 2 traits Crosses individuals with 4 alleles at 2 loci Uses a 16 box punnett square When both genotypes for both individuals are heterozygous (BbTt x BbTt), the phenotype percentage will be 9:3:3:1 Example: Cross a homozygous purple flowered, heterozygous green pod pea plant with a white flowered, yellow pod pea plant. (Green is dominant over yellow)

Dihybrid Example PPGg x ppgg Must do Foil to get the gametes! –First, Outer, Inner, Last PPGg F = PG O = Pg I = PG L = Pg –FOIL for ppgg are pg, pg, pg and pg –So now take these gametes and place them in the Punnett Square

Dihybrid Example Genotype: 50% PpGg, 50% Ppgg Phenotype: 50% Purple Green 50% Purple Yellow

Dominant Recessive relationships 1.Lethal recessive – homozygous recessive organisms cannot survive (ex. Tay Sachs, Cystic Fibrosis) 2.Incomplete Dominance 3.Codominance

Incomplete Dominance Heterozygote is an intermediate between phenotypes of two homozygotes Blending occurs! Occurs in Japanese 4:00 plants and snapdragons –RR = red –WW = white –So RW = pink! Example: Cross a red flowered Japanese 4:00 plant with a white flowered 4:00 plant

Incomplete Dominance Example Genotype: 100% RW Phenotype: 100% pink

Codominance Two traits share dominance (Ex. Human Blood Types) –Must use special notations when doing these problems I A I A and I A i…………bloodtype A I B I B and I B i…………bloodtype B I A I B ………………….blood type AB ii……………………..bloodtype O Cross a person with bloodtype AB with a person with bloodtype O

Codominance Example I A I B x ii IAIA IBIB i i IAiIAi IBiIBi IAiIAi IBiIBi Genotype % 50% I A i 50% I B i Phenotype % 50% bloodtype A 50% bloodtype B

X linked Genes Also called Sex linked genes Genes that follow the transmission of the X chromosome Always expressed in males, and is considered to be dominant Females may be expressed Hemophilia is an example – special notation for these types of problems

Sex linked notations For hemophilia –Females X H X H normal X H X h carrier/heterozygous X h X h has hemophilia –Males X H Y normal X h Y has hemophilia Example: Cross a hemophiliac man with a female carrier

Sex Linked Example X H X h x X h Y XhXh XhXh XHXH Y XHXhXHXh Genotype 25% X H X h XHYXHY 25% X H Y XhXhXhXh XhYXhY 25%X h X h 25% X h Y Phenotype: 50% normal, 50% hemophiliac