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Ch. 8 Heredity. GLE 0707.4.3 Explain the relationship among genes, chromosomes, and inherited traits TB 234-240. Explain how traits are inherited Identify Mendel’s role in history of genetics Use Punnett Squares to predict the results of the crosses

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ch 8 heredity

Ch. 8 Heredity

GLE 0707.4.3 Explain the relationship among genes, chromosomes, and inherited traits

TB 234-240

what you ll l earn

Explain how traits are inherited

  • Identify Mendel’s role in history of genetics
  • Use Punnett Squares to predict the results of the crosses
  • Compare and contrast the difference between an individual’s genotype and phenotype

Why You Need To Know It…

What You’ll Learn…
  • Heredity and genetics help explain why people are different
i inheriting traits

Heredity – passing of traits from parent to offspring

  • What is Genetics?
  • Genes on chromosomes control organism’s form, function, and traits
  • Different forms of traits that make up a gene pair = alleles
  • Meiosis = pair of chromosomes separate, alleles also separate into different sex cells
  • Every sex cell has 1 allele for each trait
  • Study of how traits are inherited through interactions of alleles = science of genetics
I. Inheriting Traits
ii mendel father of genetics

Gregor Mendel

  • Austrian Monk
  • 1865- studied pea plants to predict possible types of flowers and fruits resulting from cross breeding
  • 1st to trace on trait through several generations
  • 1st to use math = probability to explain heredity

http://www.brainpop.com/science/cellularlifeandgenetics/heredity/

II. Mendel: Father of Genetics
iii genetics in a garden

Mendel studied specific traits

  • Crossed 2 plants with different expressions of that trait
  • New plants all looked like one of the 2 parents
  • New plants called hybrids = received different genetic information (Diff. Alleles) for a trait from each plant

2. Organism that always produces the same trait generation to generation = purebred

EX: Tall plants that always produce tall plants = purebred

III. Genetics in a Garden
iii genetics in a garden1

Dominant and Recessive Factors

  • Cross pollination- pollinate one trait with opposite trait

Ex: Purebred tall plants with purebred short plants

2. Dominant Allele = trait that covers up/dominants other form of that

trait

Ex: Tall gene covered short gene in plants

3. Recessive Allele = trait that is covered by the dominant trait

http://www.brainpop.com/health/geneticsgrowthanddevelopment/genetics/

III. Genetics in a Garden
iii genetics in a garden2

B. Using Probability to Make Predictions

  • Probability- math that helps you predict the chance of something happening

Ex: Coin toss – heads or tails – 50/50 chance

2. Mendel worked with a large number of plants – helped make predictions more accurate. Also increased the chances of seeing a repeatable pattern

3. Valid science conclusions need to be based on results

III. Genetics in a Garden
iii genetics in a garden3

C. Punnett Squares

  • Letters represent dominant and recessive alleles
  • Uppercase letter = dominant allele
  • Lowercase letter = recessive letter
  • Letter – A code (genotype) = Genetic make-up
  • The way an organism looks or behaves is a result of genotype = phenotype

Ex: Brown hair = phenotype of hair color = brown

III. Genetics in a Garden
iii genetics in a garden4

D. Alleles Determine Traits

  • Most cells have 2 alleles for every trait
  • Alleles are located on chromosomes in nucleus of the cell
  • Organism with the same 2 alleles = homozygous trait

EX: both tall alleles ( TT )

4. Organism with that has 2 different traits

EX: 1 tall and 1 short ( Tt )

5. Mendel produced heterozygous hybrids for height = Tt

III. Genetics in a Garden
iii genetics in a garden5

E. Making a Punnett Square

  • Letters representing 2 alleles from 1 parent are written along the top of the grid
  • Those of the 2nd parent are placed down the side of the grid

(1 letter per section )

3. Each square of the grid is filled with 1 allele donated by each parent

4. Letters represent genotypes of possible offspring that parents could produce

T

t

T

T

III. Genetics in a Garden
iii genetics in a garden6

F. Principles of Heredity

  • Traits are controlled by alleles on chromosomes
  • An allele’s effect is dominant or recessive
  • When a pair of chromosomes separates during meiosis, the different alleles for a trait move into separate sex cells

https://www.khanacademy.org/science/biology/heredity-and-genetics/v/punnett-square-fun

III. Genetics in a Garden