Transcript Mendel & Genes

Mendel & the Gene
Idea
Gregor Mendel – Pea-rific!
 Bred garden peas in monastery
 Character – heritable feature
 Trait – variant for a character
 Cross-pollinated true-breeding varieties of pea
plant (hybridization)
 “Parents” – P generation
 Offspring – F1 generation
 F1 offspring – F2 generation
Mendel’s Work
 P: purple & white
 F1: all purple
 F2: 75% purple
25% white
 How?
 Hypothesis…
Mendel’s Work
1.
2.
Alternative versions of genes (alleles)
account for variations in inherited
characteristics
For each character, you inherit one allele
from each parent
Mendel’s Work
3. If the two alleles differ…
 Dominant allele
- fully expressed
 Recessive allele
– no noticeable
effect on
appearance
Mendel’s Work
4. Two alleles segregate (separate) during
gamete production
 Each gamete gets one
 This is the Law of Segregation
 Determined by Punnett square
Vocabulary to know
 Homozygous – have two of same allele
 Heterozygous – two different alleles
 Phenotype – physical appearance &
physiological makeup
 Genotype – genetic makeup
 Testcross – test unknown with homozygous
recessive to determine unknown genotype
Test Cross
Law of Independent Assortment
 Each different pair of alleles will segregate
independent of any others during gamete
formation
 F1 produced for single character – monohybrid
 F1 produced for two characters – dihybrid
 Result of dihybrid cross - 9:3:3:1
Math Rules
 Rule of Multiplication
 Probability two independent events happen
at same time – multiply each probability
 Coin: H & H = ½ x ½ = ¼
 F1 is Pp – chance F2 is pp?
 Gamete has P = ½
 Gamete has p = ½
½ x ½ = ¼
Math Rules
 Dihybrid crosses
 YyRr x YyRr
 Probability of YYRR
 Do a Punnett square for Yy x Yy
 Get ¼
 Do another for Rr x Rr
 Get ¼
 ¼ x ¼ = YY AND RR = 1/16
Math Rules
 Rule of Addition
 Probability of event that can occur two or more
different ways – add sum of separate probabilities
 Example: cross two Heterozygous for flower color
 probability that the offspring is heterozygous?
 1)Mom’s recessive egg with dad’s dominant
sperm – ¼
 2)Dad’s recessive sperm with mom’s dominant
egg – ¼
 #1 OR #2  ¼ + ¼ = ½
Mendel & Beyond
 Incomplete Dominance
 F1 hybrids have
intermediate
characteristics
 Ex: snapdragons
 Not blending
Mendel & Beyond
 Codominance
 Two alleles in hybrid are BOTH expressed
 Ex: blood types
Mendel & Beyond
 Multiple Alleles
 Blood type
 A, B, AB, O
 Three alleles – Ia, Ib, i
 Presence or
absence of carbo
on surface
 Wrong blood type –
agglutination
Mendel & Beyond
 Quantitative characters
 Characters that vary along a continuum
 Ex: human skin color
 Indicates polygenic inheritance
 Additive effect of two or more genes on
single phenotypic character
 Nature vs Nurture
 Both often have an effect on gene expression
Human Inheritance
 Chart with a pedigree
Human Inheritance
 Recessively Inherited Disorders
 Need homozygous recessive to have
 Heterozygous are carriers & can pass on to
offspring
 Ex: Cystic fibrosis, Tay-Sachs, sickle-cell
disease
 Read details in text
Human Inheritance
 Dominantly Inherited Disorders
 Achondroplasia (dwarfism), cluster
headaches
 Affects homozygous dominant &
heterozygous
 If lethal, much less common – die before
reproducing
Human Inheritance
 If late-acting, can pass on dominant disorder
 Ex: Huntington’s disease
 Multifactorial Disorders
 Genetics & environment play a role
 Ex: diabetes, cancer, some mental illness
Technology
 Fetal Testing
 Amniocentesis
 Chorionic
villis
sampling
(CVS)
 Ultrasound