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This chapter covers the basics of genetics, including vocabulary terms, Mendel's experiments, predicting traits using Punnett squares, and an introduction to human genetics, including sex-linked disorders.
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GENETICS Chapters 11, 12-4 & 14
INTRO TO GENETICS Chapter 11
I. Genetics Vocabulary A. GENETICS = STUDY of howtraits are passed from parent to offspring B. HEREDITY = passing of traits from parents to offspring C. TRAIT=inherited characteristic
D. GENE – located on chromosomes, control traits. E. ALLELE – different forms of same gene/trait Ex: Trait = hair color Alleles = black, brown, blonde, red
1) Dominant = masks/hides recessive trait • use CAPITAL letters 2) Recessive–ishidden if dominant allele is present; can only be seen when both are present • use lowercase letters
Ex: Brown hair (B) is dominant over blonde hair (b) • Bb_______ • bb_______
F. Genotype = genetic makeup of organism • usually have 2 alleles • Ex: Bb, Tt, Gg, Hh
1) Homozygous = both alleles are alike (Purebred) Ex: CC, aa 2) Heterozygous = alleles are different (Hybrid) Ex: Tt, Bb
G. Phenotype = physical appearance determined by genotype Ex: Brown hair, tall, green eyes, curly hair.
II. History of Genetics A. GregorMendel = “Father of Genetics” (1850’s)
1) Mendel’s Conclusions Bb a. Every trait has 2 factors. b. Law of Segregation 1. Genes are separated during the formation of gametes Example B b
c. Law of Independent Assortment = Genes for different traits are distributed to gametes independently
III. Predicting the Traits of Offspring A. Punnett Square = predicts probability of inheriting certain traits
To do Punnett Square problems, there are 4 major steps. You must show all 4 steps to get full credit!!!
Example 1) In fruit flies, long wings (L) are dominant to short wings (l). Two heterozygous long-winged fruit flies (both Ll) are crossed. What are the possible genotypes of their offspring? What are the phenotypes?
1. Make a key: L = long wings l = short wings 2. Show the cross between the parents: Ll x Ll
3. Draw the Punnett Square: L l L LL Ll Ll ll l
4. Answer the question: Genotypes = Phenotypes =
Example 2) In peas, the color yellow is dominant to the color green. A homozygous yellow pea plant is crossed with green plant. What will the genotypes and the phenotypes of all the possible offspring be?
1. Make a key: Y = yellow pea plant y = green pea plant 2. Show the cross between the parents: YY x yy
3. Draw the Punnett Square: Y Y y Yy Yy y Yy Yy
4. Answer the question: Genotypes = _______ Phenotypes = ________
IV. Other Genetic Possibilities A. Incomplete dominance = 2 alleles influence phenotype • neither allele is dom. • 2 alleles BLEND
Ex: Red flowers (RR) crossed with white flowers (rr) make pink flowers (Rr). What percent of the offspring would be red, white and pink when you cross two pink flowers?
Key: RR = red rr = white Rr = pink Cross: Rr x Rr
Punnett Square: R r RR Rr R rr Rr r
Answer: 25% = red (RR) 50% = pink (Rr) 25% = white (rr)
B. Codominance – both alleles are expressed in phenotype • neither allele is dom. • NOBLENDING of alleles Ex: red x white ---> red & white spottedflowers
C. Multiple Alleles = traits controlled by 3 or more alleles of the same gene Ex: Human blood types • 3 diff. alleles: A, B & O • 4 blood types: A, B, AB & O • A & B codominant; both dominant over O
D. Polygenic Trait = trait controlled by more than one gene and therefore more than two alleles. Can change over life time • Most traits are polygenic • Ex: skin color, eye color, hair color, height, etc.
Dihybrid Crosses A. Def: cross between 2 pairs of contrasting traits * Use a 16-box Punnett Square!!
Ex: In pea plants, the color yellow (Y) is dominant to green (y) and round texture (R) is dominant to wrinkled (r). Give the phenotype ratios when you cross two plants with YyRr genotypes.
Key: Y = yellow y = green R = round r = wrinkled Cross: YyRr x YyRr
Before you do the Punnett square, you need to determine the gametes 1st to put across the top/down the side! DO NOT PUT ONE LETTER PER ROW/COLUMN!
yR yr YR Yr YYRR YYRr YyRR YyRr YR YYRr YYrr YyRr Yyrr Yr YyRR YyRr yyRR yyRr yR yr YyRr Yyrr yyRr yyrr
Answer: 9 Yellow & Round pea plants 3 Yellow & Wrinkled pea plants 3 Green & Round pea plants 1 Green & Wrinkled pea plant
I. Vocab: A. Genes on chromosomes #1-22 = AUTOSOMAL B. Pair #23- Genes on sex chromosomes = SEX-LINKED
II. Human Genome Project A. Completed in 2003 • International scientific project • Identified over 92% of our genes • HUGE science advancement
HUMAN GENOME PROJECT • VIDEO CLIP
III. Sex Linkage A. If sex-linked, it is X-linked (on X chr.) or Y-linked(on Y chr.) B. X chr. much LARGER than Y chr., so it carries more genes.
IV. Sex-linked Disorders A. Colorblindness = cannot distinguish certain colors (red-green most common) • recessive X-linked • males more likely to be colorblind
WHY? • males only need 1 recessiveX to be colorblind • females must have 2recessiveX to be colorblind
B. Hemophilia = disorder where blood does not clot • recessive X-linked • men more likely to have hemophilia
SEX LINKED DISORDERS • VIDEO CLIP- Hemophilia