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G ENETICS

Learn about Mendel's Laws of Heredity, monohybrid crosses, Punnett squares, phenotypes, genotypes, and more in the study of genetics. Dive into topics like incomplete dominance, multiple alleles, and sex-linked traits.

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G ENETICS

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  1. GENETICS Mendel’s Laws of Heredity

  2. Mendel’s Laws • Law of segregation • The two alleles for ___________________________________ • A parent will pass down ______________, only one allele for each trait • Law of independent assortment • Genes for ______________________________________________________________________

  3. Some Needed Vocabulary • Heredity • Passing on of characteristics ___________________________ • Traits • Characteristics that _________________ • Genetics • The study of Heredity • Gametes • Sex cells • Sperm = male gamete • Egg = female gamete

  4. Gregor Mendel • A monk who studied heredity using garden pea plants • Why garden peas? • ____________________ • ________________________________________ • What did he do? • He transferred pollen from one plant ______________________________________ • This is called “_________________________” • Mendel first “crossed” tall plants with short plants

  5. Mendel’s Monohybrid crosses • Monohybrid cross • Focuses on one (___________) trait • 1st generation • Crossed a ___________pea plant with a ________pea plant • All of the offspring were ____________ • 2nd generation • Crossing the offspring of the 1st generation • _____of the offspring were tall; ______of the offspring were short • _______ ratio (tall to short)

  6. Mendel’s Findings • Mendel found that each chromosome has two factors for each traits… called ________ • Alleles = forms of genes • Types of alleles (mask means hidden) • Dominant • The trait that has the ability to _________the other • Represented with a ____________ letter (A) • Recessive • The trait that will be masked by the dominant trait… it will be there, but will not be show (expressed) • Represented with a _______________ letter (a)

  7. Phenotype vs. Genotype • Phenotype • The way that a___________________; how the trait appears • Tall, short • Genotype • The offspring’s ____________________ • TT, Tt, tt

  8. Homozygous vs. Heterozygous • _______________ (“homo” means “same”) • Having two identical alleles for a trait • TT, tt • ________________ (“hetero” means “different”) • Having two different alleles for a trait • Tt

  9. ____________ square • Short way to find the expected proportions of possible genotypes in the offspring of a ________________.

  10. Mendel’s Punnett Square 1st generation T = Tall t = short TT x tt T T t T t T t t T t T t

  11. Interpreting the Punnett Square T T t T t T t T t T t t • All ____________ are heterozygous tall (Tt) • Ratio • ________ (Tall : Short) • Percentage • ________ Tall • Each offspring box represents _______ of the population of offspring produced Tall = T Short = t

  12. Mendel’s Punnett Square 2nd generation • Homozygous Tall: • Genotype: _______ • How many? ______ • Heterozygous Tall: • Genotype: _______ • How many? ______ • Short: • Genotype: _______ • How many? ______ • TOTAL # OF TALL: _____ • TOTAL # OF SHORT: _____ • Ratio of Tall : Short  __________ • Percentages: • Percent Tall: ___________ • Percent Short: __________ Tall = ____ Short = ___ Parents: _______ x _______ T 1 t Tt Tt Tt 1 T t 1 T TT Tt 3:1 t 75% Tt tt

  13. GENETICS Patterns of Heredity

  14. Simple Mendelian Inheritance • The type of inheritance we have discussed thus far (Mendel’s peas) • Not all patterns in heredity are as simple… • There is more than just dominant and recessive

  15. Incomplete Dominance • The phenotype of the ____________is intermediate (____________) between those of the two __________________. • For Example: • A cross between a particular RED flower and a WHITE flower will produce a _____________ flower

  16. Punnett Square for Incomplete Dominance Cross: (RR) Red flower X (R’R’) White flower RR = Red R’R’ = White RR’ = Pink R R R’ 100% PINK FLOWERS (RR') R R’ R R’ R’ R R’ R R’

  17. ___________________ • The phenotypes of both homozygotes is produced (__________or strips) in the ________________ individual • For Example: • A black rooster and a white hen might produce a chick with some black feathers and some white feathers

  18. Multiple Alleles • Traits controlled by more than ___alleles … • For Example: • ______________alleles are commonly seen in the coat color of rabbits (as well as in dogs, cats, horses, humans, hamsters etc.) • Also… Blood Typing…

  19. Multiple Alleles – Blood Types • Human blood types are determined by the ____________ or __________of certain molecules on the surfaces of red blood cells • There are three alleles for blood type… • IA …………………… written as “A” • IB …………………… written as “B” • i …………………… written as “O”

  20. Sex-linked traits • Traits that are controlled by genes located on sex chromosomes • These traits help explain why some characteristics and disorders are more common in one sex than in the other • Commonly referred to as “X-linked” because the trait is usually linked to the X-chromosome

  21. Background Information • Humans have _______chromosomes; or ________ pairs of chromosomes • Of these, 22 pairs are autosomes auto means “self” (“self” chromosomes for the body) • The last (23rd) pair is different in males & females… these are the ______ chromosomes • Females have two “X” chromosomes (______) • Males have one “X” and one “Y” chromosome (_____)

  22. “Sex-linked” traits Green-eyed male (XbY) X Heterozygous Blue-eyed female (XBXb) B = Blue eyes b = Green eyes X__ Y X__ XBXb XBY X__ XbXb XbY

  23. “Sex-linked” traits Green-eyed male (XbY) X Heterozygous Blue-eyed female (XBXb) B = Blue eyes b = Green eyes Xb Y XB XBXb XBY Xb XbXb XbY • OFFSPRING • MALES (XY) • Blue Eyes • Genotype _______ • How many? _____ • Green Eyes • Genotype _______ • How many? _____ • FEMALES (XX) • Blue Eyes • Genotype _______ • How many? _____ • Green Eyes • Genotype _______ • How many? _____ XBY 1 XbY 1 XBXb 1 XbXb 1

  24. Sex-linked percentages Green-eyed male (XbY) X Heterozygous Blue-eyed female (XBXb) B = Blue eyes b = Green eyes Xb Y XB XBXb Xb XbY • Percentages • When figuring percents for sex-linked punnett squares, you must be careful to only count what is asked for… • % of females with blue eyes • % of males with blue eyes • % of females with green eyes • % of males with green eyes 50% 50% Females Males 50% 50%

  25. Polygenic Inheritance • When a trait is controlled by more than one gene • For Example: • Skin color is actually the accumulation of dominant genes for pigment in the skin

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