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.