GENETICS & INHERITENCE
GENETICS & INHERITENCE
GENETICS & INHERITENCE
GENETICS & INHERITENCE
GENETICS – the study of heredity.
HEREDITY – the transmission of genes from parents to offspring.
Hey genetics… who’s your daddy?
Gregor Mendel – the father of genetics
Austrian monk in the 1840’s
MENDEL’S EXPERIMENTS:
He studied characteristics of garden pea plants.
WHY PEAS?Easy to growProduce many offspringMature very quicklyCould allow:
SELF-FERTILIZATION – reproduction in the same organism.
CROSS-FERTILIZATION – reproduction between two different organisms.
MENDEL’S EXPERIMENTS
STEP 1SELF-FERTILIZED pea plants for many generations until they produced pure-breeding plants.
PURE BREEDING – trait observed in parent plants shows up in offspring of the offspring.AKA true-breeding / pure breedExample: White flowered plants produce only white flowered offspring.
He called these P1 generationP1 GENERATION – parental generation
MENDEL’S EXPERIMENTS
STEP 2Crossed a purple flowered plant from the P1 generation with a white flowered plant from the P1 generation.He called the offspring of those plants the F1 generation
F1 GENERATION – first filial generation; first generation of offspring
All flowers on plants in the F1 generation turned out to be purple
MENDEL’S EXPERIMENTS
STEP 3He allowed the F1 generation plants to self- fertilize
He called this next generation of resulting plants the F2 generation
He notice that white flowers reappeared.
MENDEL’S CONCLUSIONS
1. Traits are controlled by genes
GENE – small segment of DNA on a chromosome that codes for a trait.
MENDEL’S CONCLUSIONS
2. Genes have alternative forms.ALLELE – alternative forms of a gene
Every individual has 2 alleles for each trait
One from momOne from dad
Example:Purple flowers = PWhite flowers = p
MENDEL’S CONCLUSIONS
3. Alleles can be dominant or recessive
Dominant alleles are always expressed
Recessive alleles can be masked by Dominant ones.
Recessive alleles are expressed only when there are two copies
EXAMPLES:
T- tall TT - tall
t – short Tt – tall
tt – short
MENDEL’S CONCLUSIONS
4. An individual is said to be Homozygous if both of its alleles are the same.
TT or tt
DD or dd
5. An individual is said to be Heterozygous if its alleles are different.
Aa Tt
Bb Dd
MENDEL’S CONCLUSIONS6. LAW OF SEGREGATION - alleles are separated
during the formation of gametes (sex cells—sperm or egg). A gamete can only have ONE allele or THE OTHER
T = Tall
t = short
If a plant has Tt, gametes can either have a T or t in them
If a plant has TT, gametes can only have T in them
If a plant is tt, gametes can only have a t in them
**Remember—letters represent forms of a gene!
MENDEL’S CONCLUSIONS
7. LAW OF INDEPENDENT ASSORTMENT - alleles for different characteristics are distributed to gametes independently.
EXAMPLE: Just because you have one dominant trait (Ex: Brown eyes), does not mean that you have ALL dominant traits.
PUNNETT SQUARESDiagrams used for:
Predicting the result of a cross.Determining the probability of a certain result.
PROBABILITY – the likelihood that something will happen (it is not definite)
Example: Flipping CoinsWhat is the probability of HEADS? 1/2What is the probability of TAILS? 1/2What is the probability of 2 HEADS in a row
1/2 x 1/2 = 1/4Each flip is an independent eventPrevious outcomes DON’T affect future outcomes
MORE VOCAB
Genotype – Refers to the genetic makeup of a specific set of genes
Phenotype – refers to the physical characteristics or traits of an individual.
Essential VOCAB:
DOMINANT
RECESSIVE
HOMOZYGOUS
HETEROZYGOUS
YOU MUST KNOW THESE WORDS TO BE SUCCESSFUL FOR THE
REMAINDER OF THIS CHAPTER: Pop Quiz soon…
Pop Quiz:
1. Phenotype
2. Genotype
3. Heterozygous
4. Homozygous
5. Dominant
6. Recessive
7. Gene
8. Allele
1. Small section of DNA coding for a protein
2. Genetic makeup; ex. Tt
3. Gene that is masked by another; represented by a lower case letter; ex. t
4. Gene that covers up or masks another gene; represented by a capital letter; ex T
5. Two identical forms of a gene: ex TT or tt
6. Two different forms of a gene: Tt
7. Physical appearance of expression of a gene; ex. Brown eyes
8. Different forms of a gene; ex red or white flowers
Pop Quiz:
1. Phenotype
2. Genotype
3. Heterozygous
4. Homozygous
5. Dominant
6. Recessive
7. Gene
8. Allele
1. Small section of DNA coding for a protein
2. Genetic makeup; ex. Tt
3. Gene that is masked by another; represented by a lower case letter; ex. t
4. Gene that covers up or masks another gene; represented by a capital letter; ex T
5. Two identical forms of a gene: ex TT or tt
6. Two different forms of a gene: Tt
7. Physical appearance of expression of a gene; ex. Brown eyes
8. Different forms of a gene; ex red or white flowers
Incomplete Dominance and Co-Dominance
Incomplete Dominance
• Neither allele is dominant over the other.
• Heterozygous individuals have a phenotype that is in between the homozygous individuals
• Don’t use CAPS and lower case b/c neither is DOM/rec*
• Example: Blue and Red (B and R, or B and B´) BR=purple
SnapdragonsIn snapdragons, flower color can be red, pink, or white. The heterozygous condition results in pink flowers
WW RWRR
Hair texture can follow the incomplete dominance pattern.Curly: _______________Straight: _______________Wavy: _______________Cross wavy with wavy_______________ X _______________
Complete a Punnett Square
Co-dominanceBoth alleles are expressed equally
Neither allele is recessive
Both expressed as if they are a mixed dominance.
Erminette chickens
Roan Cows/Horses
Co-Dominance Erminette Chicken
P generation
Black chicken X White chicken
F1 generation = erminette (checkered patterned)
Key:B =BlackB1 (or W)=White
B B
B1
B1
B
BB
B B1
B1
B1
B1
Phenotype: 4:0 or 1:0100% erminette
Genotype: 4:0 or 1:0100% heterozygous
Multiple Alleles
• So far every trait has had only 2 variations (like tall or short)
• Some traits have more than two versions
ex. Blood types, coat color in rabbits
• Individuals still have only 2 alleles (1 from mom, 1 from dad), there are just more choices available
• Hierarchy of dominance (one is most dominant, another is second most dominant, etc.)
What other genotypes could result in Chinchilla fur?
Multiple Alleles
C= full color Dominant to all other alleles
cch = Chinchilla recessive to C dominant to c
ch = Himalayan recessive to both C and cch. Dominant to c allele
c= albino, no color recessive to all other alleles.
C > cch > ch > c
Dominant Recessive
What’s your type?
Blood Type Percentages
Data from CDC 2002
in
Codominance AND Multiple Alleles: Blood Types
Blood type refers to the antigens on the surface of your red blood cells. You can have 2 different antigens (___ or ___), or none. (3 choices=multiple alleles)
Antigens A and B are both seen when present. Neither is dominant over the other and there is no mixture or blending of phenotypes. (______________________)
Blood Type Inheritance
Key can change:
Dominant: I with superscript A or B or just A and B (for A or B antigens, respectively)
Recessive: i or O (for no antigens)
Blood type
Cross a male type A with a female type AB.
Complete 2 Punnett Squares (the father has two possible genotypes).
Cross 1: _____X_____
Cross 2: _____X_____
Analyze the possible offspring phenotypes and genotypes for each cross.
Richardson is of mixed race, with Nigerian and English heritage, while the father is white. A genetics expert at Oxford University says such births are rare, as the genes that cause skin color normally mix together. In this case, he says, it appears the genes for skin color didn't combine for some reason and the boys may have inherited different genetic codes from their mother.
AP updated 7:15 p.m. ET, Fri., Oct . 27, 2006
LONDON - A pair of British twin boys has been born with different skin color, a rare genetic occurrence according to experts.In an interview with Britain's Sky News program, mother Kerry Richardson said that the boys were both born white but as they've gotten older one of the boys got darker and the other lighter.Today, she says, the twins attract attention wherever they go.
Polygenic traits--Traits that are controlled by more than 1 gene.-Example—there are at least 4 different genes that code for skin color.-Multiple genes controlling a single trait produce a wide variety of phenotypes
Which karyotype is from a male? Female?Which symbol represents male? Female?
A B
Sex ChromosomesSex chromosomes determine gender.
X and Y chromosomes both contain genes to develop into a male or a female.
There are other genes found on the sex chromosomes… we call those sex-linked traits.
X X X Y
The Classic Baldness in Males
What they try to do to cover it up!
What they should do.
Sex linked traits
XB Xb
Xb XBXb
XbXb
Y XBY XbY
B = normal hairb = baldness
XBXb x XbY
½ females normal½ females carrier ½ males normal½ males bald
Hemophilia H = normal bloodh = hemophilia
XH Xh
XH XHXH XHXh
Y XHY XhY
XHXh x XHY
2/2 females normal½ males normal½ males hemophilia
Think!
So, where do sons get sex-linked, recessive traits from?
Why is it more common to have males with hemophilia (or any other sex linked gene) than females?
A Little Info on Hemophilia•Hemophilia occurs when a factor (protein) in the blood is missing.
•The factor is needed to clot blood.
•Hemophiliacs bruise very, very, easily.
Most common is red/green colorblindness.
What number do you see to the right?
Color blindness
CALICO CATS… another sex-linked trait
Let’s see what you’ve learned!
In cats there is a gene for coat color, which is codominant and sex linked. There is one gene for brown and one gene for black. The heterozygote has a coat that is brown and black which is called tortoise-shell or calico.
Cross a black female with a brown male.
Need some help?
BB-black
WW-brown
BW- tortoise or black & brown
XBXB x XWY
XB XB
XW XBXW XBXW
Y XBY XBY
Two female tortoise-shell and two black males.
•Only females can express both colors at the same time according to the Punnett Square. •Can male cats ever be calicos or tortoise?
•Hint: Think back to meiosis and how Down Syndrome occurs.
Another one…. Ear hair in older men!
Albino people occur approximately 1 in 17,000. Most have serious eye problems.