Unit 4: Cell Division & Heredity Part 3 Ch. 14 & Ch. 15 Mendelian Genetics & Chromosomal Basis of Inheritance
I. Genetics As A Science • Genetics = Study of heredity • Heredity = How information gets transferred to us from our parents.
II. Genetics Vocabulary • Trait: Characteristic that is different among individuals. Eye color, height, skin color
II. Genetics Vocabulary • Cross: When 2 individuals mate. 2 trees, 2 dogs, etc.
II. Genetics Vocabulary • Hybrid: Result of crossing individuals with different traits.
III. Discovery of Genetics • Gregor Mendel: Used pea plants to explore heredity.
III. Discovery of Genetics • Mendel concluded 2 things • “Factors” determine what organisms will be like . • Genes – determine traits 1. Height 2. Hair color
III. Discovery of Genetics b. Each “factor” can come in different varieties. 1. Alleles- varieties of genes a. Hair color gene 1. Brown allele 2. Blonde allele 3. Red allele
III. Discovery of Genetics • Mendel concluded 2 things… • Some alleles are “stronger” than others
III. Discovery of Genetics • Law of Dominance: Some alleles are dominant & others are recessive. • Dominant: Will always be seen. • Recessive: Only seen if dominant is not there.
IV. Mendel’s Work • Crossed a tall plant with a short plant. • P Generation = Original pair of plants. (Parents)
IV. Mendel’s Work B. Results • All tall plants F1 = First set of offspring. (children)
IV. Mendel’s Work • Curious about why none were short. 1. Crossed 2 plants from the F1. generation. Yes, mated 2 siblings!
IV. Mendel’s Work D. Results 1. 75% Tall 25% Short F2 = offspring of the F1 generation. (grandchildren)
V. Explaining the Outcomes • The allele for “shortness” didn’t disappear. B. The allele for “tallness” was dominant. How was the recessive allele able to be “recovered”?
V. Explaining the Outcomes • Segregation: Alleles separate from each other during meiosis. • Gametes then combine differently during fertilization. T t T t T t T t T t T t t t T T
VIII. More About Alleles A. Allele combinations 1. Have 2 alleles for each gene Height – Tall or short
VIII. More About Alleles B. Each one represented by the first letter of the dominant allele: • Dominant = Uppercase • Recessive = Lowercase a. Height T = Tall (Dominant) t = Short (Recessive)
VIII. More About Alleles a. If 2 of the SAME allele: HOMOZYGOUS TT = Tall tt = Short HomozygousHomozygous DominantRecessive
VIII. More About Alleles b. If 2 DIFFERENT alleles: HETEROZYGOUS Law of dominance: If dominant is present, it will “cover” the recessive. T t = Tall
IX. Looks Can Be Deceiving! • Phenotype: Physical appearance (What’s on the outside) White, Red • Genotype: Genetic makeup (What’s on the inside) RR, Rr, rr
X. Punnett Squares • Diagrams for predicting results of any cross. Genotype of parent 1 Genotypes of offspring Genotype of parent 2
XI. Single Trait Cross • A cross for 1 trait. 1. Hair color ONLY
XI. Single Trait Cross Genotype of parent 1 T T Genotype of parent 2 t t T T t t
XI. Single Trait Cross Results: All 4 combinations are the same. Results vary depending on parents! T T T t T t t t T t T t
XI. Monohybrid Cross F1 Cross: Cross 2 of the “kids”. Results: 1:2:1 Genotypic Ratio 3:1 Phenotypic Ratio T t TT T t T t T t t t
XI. Monohybrid Cross • RULE: According to the Mendel’s Laws, A monohybrid cross of F1 will ALWAYS result in 3:1 p ratio and 1:2:1 g ratio. • If not… something else is acting. - Alternate types of dominance
XII. Dominant/Recessive?? Simple rules of dominance/recessive don’t always hold true. 1. Incomplete dominance: Both alleles present = Intermediate
XII. Dominant/Recessive?? 2. Codominance: Both alleles present = Both appear Brown & White both dominant = both colors appear
XII. Dominant/Recessive?? 3. Multiple alleles: More than 2 alleles for 1 gene Blood Groups
XII. Dominant/Recessive?? 4. Lethal Dominant Traits Monohybrid cross will yield a 2:1 ratio of dominant to recessive. H.D. not viable so does not count in the total offspring. T t TT T t T t T t t t
Sex Chromosomes 44 Autosomes & 2 Sex chromosomes a. Male: 46,XY b. Female: 46,XX
Sex Chromosomes 3. Sperm = X or Y 4. Egg = X only Female X X XX XX 50% female 50% male X Male XY XY Y
Sex-Linked Genes Found on the sex chromosomes, X or Y. Y-linked traits = “maleness” mostly X-linked traits = many traits - Colorblindness
Sex-Linked Genes Males = Y X All X-linked traits will be expressed in males. Only 1 X chromosome, so either YES or NO! Females = X X If trait is dominant, it will be expressed if 1 copy is present. If trait is recessive, it will be expressed if present on BOTH X chromosomes.
More on X Chromosomes Barr body: One of the X chromosomes in females “turns off” during early development. 2. Only in females; Males need the X!! 3. No baby ever born without an X
XIII. Two Trait Cross • A cross that looks at 2 traits. 1. R = right handed r = left handed 2. D = Dimples d = no dimples
The Testcross • A person has brown hair, and brown hair is dominant. How can we tell the genotype? • Testcross: crossing an unknown genotype with a homozygous recessive. • h.r. will always have KNOWN genotype. • gg jj kk ee
The Testcross • If homozygous dominant: • BB x bb = ALL Bb (all brown hair) • If heterozygous: • Bb x bb = HALF Bb, Half bb (half brown, half blonde)
XII. Dihybrid Cross Genotype of parent 1 = R r D d Genotype of parent 2 = R r D d • Figure out the combinations for each parents’ gametes.
XII. Dihybrid Cross Genotype of parent 1 = R rD d FIRST R r X D d R D
XII. Dihybrid Cross Genotype of parent 1 = R rD d OUTSIDE R r X D d R d
XII. Dihybrid Cross Genotype of parent 1 = R rD d INSIDE R r X D d rD
XII. Dihybrid Cross Genotype of parent 1 = R rD d LAST R r X D d rd
XII. Dihybrid Cross Genotype of parent 1 = R rD d Gamete combinations = R D R d rD rd
XII. Dihybrid Cross Genotype of parent 2 = R rD d Same genotype, same gamete combinations = R D R d rD rd
XII. Dihybrid Cross 2. Make a Punnett square: 16 possibilities
XII. Dihybrid Cross 3. Parents’ possible gametes R D R d r D r d R D R d r D r d
XII. Dihybrid Cross 4. Perform Crosses R D R d r D r d RRDD R D RRDd RrDD RrDd R d RRDd RRdd Rrdd RrDd r D RrDd rrDD rrDd RrDD r d Rrdd rrDd rrdd RrDd