Unit 4 cell division heredity
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Unit 4: Cell Division & Heredity. Part 3 Ch. 14 & Ch. 15 Mendelian Genetics & Chromosomal Basis of Inheritance. I. Genetics As A Science. Genetics = Study of heredity Heredity = How information gets transferred to us from our parents. II. Genetics Vocabulary.

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Unit 4: Cell Division & Heredity

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Unit 4: Cell Division & Heredity

Part 3

Ch. 14 & Ch. 15

Mendelian Genetics & Chromosomal Basis of Inheritance


I. Genetics As A Science

  • Genetics = Study of heredity

    • Heredity = How information gets transferred to us from our parents.


II. Genetics Vocabulary

  • Trait: Characteristic that is different among individuals.

    Eye color, height, skin color


II. Genetics Vocabulary

  • Cross: When 2 individuals mate.

    2 trees, 2 dogs, etc.


II. Genetics Vocabulary

  • Hybrid: Result of crossing individuals with different traits.


III. Discovery of Genetics

  • Gregor Mendel: Used pea plants to explore heredity.


III. Discovery of Genetics

  • Mendel concluded 2 things

    • “Factors” determine what organisms will be like .

      • Genes – determine traits

        1.Height

        2.Hair color


III. Discovery of Genetics

b. Each “factor” can come in different varieties.

1. Alleles- varieties of genes

a. Hair color gene

1. Brown allele

2. Blonde allele

3. Red allele


III. Discovery of Genetics

  • Mendel concluded 2 things…

    • Some alleles are “stronger” than others


III. Discovery of Genetics

  • Law of Dominance: Some alleles are dominant & others are recessive.

    • Dominant: Will always be seen.

    • Recessive: Only seen if dominant is not there.


IV. Mendel’s Work

  • Crossed a tall plant with a short plant.

    • P Generation = Original pair of plants.

      (Parents)


IV. Mendel’s Work

B.Results

  • All tall plants

    F1 = First set of offspring.

    (children)


IV. Mendel’s Work

  • Curious about why none were short.

    1. Crossed 2 plants from the F1. generation.

    Yes, mated 2 siblings!


IV. Mendel’s Work

D.Results

1. 75% Tall

25% Short

F2 = offspring of the F1 generation.

(grandchildren)


V. Explaining the Outcomes

  • The allele for “shortness” didn’t disappear.

    B.The allele for “tallness” was dominant.

    How was the recessive allele able to be “recovered”?


V. Explaining the Outcomes

  • Segregation: Alleles separate from each other during meiosis.

  • Gametes then combine differently during fertilization.

T t

T t

T

t

T

t

T t

T t

t t

T T


VIII. More About Alleles

A. Allele combinations

1. Have 2 alleles for each gene

Height – Tall or short


VIII. More About Alleles

B. Each one represented by the first letter of the dominant allele:

  • Dominant = Uppercase

  • Recessive = Lowercase

    a. Height

    T = Tall (Dominant)

    t = Short (Recessive)


VIII. More About Alleles

a. If 2 of the SAME allele: HOMOZYGOUS

TT = Tall tt = Short

HomozygousHomozygous

DominantRecessive


VIII. More About Alleles

b. If 2 DIFFERENT alleles: HETEROZYGOUS

Law of dominance: If dominant is present, it will “cover” the recessive.

T t = Tall


IX. Looks Can Be Deceiving!

  • Phenotype: Physical appearance (What’s on the outside)

    White, Red

  • Genotype: Genetic makeup (What’s on the inside)

    RR, Rr, rr


X. Punnett Squares

  • Diagrams for predicting results of any cross.

    Genotype of parent 1

    Genotypes of

    offspring

    Genotype of

    parent 2


XI. Single Trait Cross

  • A cross for 1 trait.

    1. Hair color ONLY


XI. Single Trait Cross

Genotype of parent 1

T T

Genotype of

parent 2

t t

T

T

t

t


XI. Single Trait Cross

Results: All 4 combinations are the same.

Results vary depending on parents!

T

T

T t

T t

t

t

T t

T t


XI. Monohybrid Cross

F1 Cross: Cross 2 of the “kids”.

Results: 1:2:1 Genotypic Ratio

3:1 Phenotypic Ratio

T t

TT

T t

T

t

T t

t t


XI. Monohybrid Cross

  • RULE: According to the Mendel’s Laws, A monohybrid cross of F1 will ALWAYS result in 3:1 p ratio and 1:2:1 g ratio.

  • If not… something else is acting.

    - Alternate types of dominance


XII. Dominant/Recessive??

Simple rules of dominance/recessive don’t always hold true.

1. Incomplete dominance:

Both alleles present =Intermediate


XII. Dominant/Recessive??

2. Codominance:

Both alleles present = Both appear

Brown & White

both dominant =

both colors

appear


XII. Dominant/Recessive??

3. Multiple alleles:

More than 2 alleles for 1 gene

Blood Groups


XII. Dominant/Recessive??

4. Lethal Dominant Traits

Monohybrid cross will yield a 2:1 ratio of dominant to recessive.

H.D. not viable so does not count in the total offspring.

T

t

TT

T t

T

t

T t

t t


Sex Chromosomes

44 Autosomes & 2 Sex chromosomes

a. Male: 46,XYb. Female: 46,XX


Sex Chromosomes

3. Sperm = X or Y 4. Egg = X only

Female

X

X

XX

XX

50% female

50% male

X

Male

XY

XY

Y


Sex-Linked Genes

Found on the sex chromosomes, X or Y.

Y-linked traits = “maleness” mostly

X-linked traits = many traits

- Colorblindness


Sex-Linked Genes

Males = Y X

All X-linked traits will be expressed in males.

Only 1 X chromosome, so either YES or NO!

Females = X X

If trait is dominant, it will be expressed if 1 copy is present.

If trait is recessive, it will be expressed if present on BOTH X chromosomes.


More on X Chromosomes

Barr body: One of the X chromosomes in females “turns off” during early development.

2.Only in females; Males need the X!!

3.No baby ever born without an X


XIII. Two Trait Cross

  • A cross that looks at 2 traits.

    1. R = right handed r = left handed

    2. D = Dimples d = no dimples


The Testcross

  • A person has brown hair, and brown hair is dominant. How can we tell the genotype?

  • Testcross: crossing an unknown genotype with a homozygous recessive.

    • h.r. will always have KNOWN genotype.

      • ggjj kk ee


The Testcross

  • If homozygous dominant:

    • BB x bb = ALL Bb (all brown hair)

  • If heterozygous:

    • Bb x bb = HALF Bb, Half bb (half brown, half blonde)


XII. Dihybrid Cross

Genotype of parent 1 = R r D d

Genotype of parent 2 = R r D d

  • Figure out the combinations for each parents’ gametes.


XII. Dihybrid Cross

Genotype of parent 1 = R rD d

FIRST

R r X D d

R D


XII. Dihybrid Cross

Genotype of parent 1 = R rD d

OUTSIDE

R r X D d

R d


XII. Dihybrid Cross

Genotype of parent 1 = R rD d

INSIDE

R r X D d

rD


XII. Dihybrid Cross

Genotype of parent 1 = R rD d

LAST

R r X D d

rd


XII. Dihybrid Cross

Genotype of parent 1 = R rD d

Gamete combinations =

R D R d rD rd


XII. Dihybrid Cross

Genotype of parent 2 = R rD d

Same genotype, same

gamete combinations =

R D R d rD rd


XII. Dihybrid Cross

2. Make a Punnett square: 16 possibilities


XII. Dihybrid Cross

3. Parents’ possible gametes

R D

R d

r D

r d

R D

R d

r D

r d


XII. Dihybrid Cross

4. Perform Crosses

R D

R d

r D

r d

RRDD

R D

RRDd

RrDD

RrDd

R d

RRDd

RRdd

Rrdd

RrDd

r D

RrDd

rrDD

rrDd

RrDD

r d

Rrdd

rrDd

rrdd

RrDd


XII. Dihybrid Cross

5. Results: 9 = right handed w/dimples

R D

R d

r D

r d

R D

RRDD

RRDd

RrDD

RrDd

R d

RRDd

RRdd

Rrdd

RrDd

r D

RrDd

rrDD

rrDd

RrDD

r d

Rrdd

rrDd

rrdd

RrDd


XII. Dihybrid Cross

5. Results: 3 = Right handed, no dimples

R D

R d

r D

r d

R D

RRDD

RRDd

RrDD

RrDd

R d

RRDd

RRdd

Rrdd

RrDd

r D

RrDd

rrDD

rrDd

RrDD

r d

Rrdd

rrDd

rrdd

RrDd


XII. Dihybrid Cross

5. Results: 3 = Left handed w/dimples

R D

R d

r D

r d

R D

RRDD

RRDd

RrDD

RrDd

R d

RRDd

RRdd

Rrdd

RrDd

r D

RrDd

rrDD

rrDd

RrDD

r d

Rrdd

rrDd

rrdd

RrDd


XII. Dihybrid Cross

5. Results: 1 = Left handed, no dimples

R D

R d

r D

r d

R D

RRDD

RRDd

RrDD

RrDd

R d

RRDd

RRdd

Rrdd

RrDd

r D

RrDd

rrDD

rrDd

RrDD

r d

Rrdd

rrDd

rrdd

RrDd


XII. Dihybrid Cross

5. Results:

The probability of having a child with dimples and being left-handed?

3/16 = r r D D

r r D d

r r d D

Out of 16, 3 should be left handed and have dimples.


XII. Dihybrid Cross

6. Independent Assortment

a. New combo’s were made

b. Traits didn’t affect each other

c. Gene for right hand/left hand independent from gene for dimples… why?


XII. Dihybrid Cross

6. Independent Assortment

d. On different chromosomes!

* Different genes can assort without affecting each other if they are on different chromosomes.


XII. Dihybrid Cross

Phenotypic Ratio is always:

9:3:3:1

If not… something else is going on… Alternate type of dominance, sex linked trait…


Probability

A. Punnett squares can get too large if we look at more than 2 traits. Using rules of probability are much easier!

1. Rule of multiplication

a. signaled by the word “AND”

- what’s the probability I will have a boy and he will have blue eyes?


Probability

1. Rule of multiplication

boy = XY girl = XX blue eyes = gg

GgXX (mom) x GgXY (dad)

Do one trait at a time, then multiply both.

Blue eyes = gg… what’s the prob. Of gg? ¼

Boy = XY… what’s the prob of XY? ½

¼ x ½ = 1/8 prob of boy w/ blue eyes.


Probability

2. Rule of addition

a. Signaled by the word “OR”

simplest example: what’s the prob. Of getting a boy OR a girl?

XX x XY

prob. of a girl = ½ prob of a boy = ½

½ + ½ = 1 (100%)

Obviously!


Probability

3. Combining the rules

P genotypes: GgTtff x GgTtFf

What’s the prob. Of a green eyed, short, freckled child?

1. Green eyes:

can be GG or Gg

GG = ( ½ x ½) = ¼

Gg = ( ½ x ½ ) + ( ½ x ½ ) = ½

GG( ¼ ) + Gg ( ½ ) = ¾


Probability

3. Combining the rules

P genotypes: GgTtff x GgTtFf

What’s the prob. Of a green eyed, short, freckled child?

2. Short:

can only be tt

tt = ( ½ ) x ( ½ ) = ¼


Probability

3. Combining the rules

P genotypes: GgTtff x GgTtFf

What’s the prob. Of a green eyed, short, freckled child?

3. Freckled

Can be Ff or FF (but looking at the parents, FF will not be a possibility!)

(1) x ( ½ ) = ½


Probability

3. Combining the rules

P genotypes: GgTtff x GgTtFf

What’s the prob. Of a green eyed, short, freckled child?

1. Green eyes = ¾

2. Short = ¼

3. Freckled = ½

¾ x ¼ x ½ = 3/32


A Closer Look at Meiosis

Crossing over: Parts of a homologous chromosome cross to the other homologous chromosome.


Recombination

  • Case 1: Recombination of genes that are on different chromosomes (Unlinked).

    YyRr (yellow, round) x yyrr (green, wrinkled)

    ¼ YyRr (yellow, round) ¼ yyrr (green, wrinkled

    ¼ Yyrr (yellow, wrinkled) ¼ yyRr(green,round)

    ½ Parental Pheno. ½ Recombinant Pheno.


Recombination

Case 1: Recombination of genes that are on different chromosomes (Unlinked).

50% recombinant offspring is the EXPECTED value for unlinked genes.

It is also the MAXIMUM value


Recombination

Case 2: Recombination of genes that are on the same chromosome (Linked).

Any number less than 50% means the genes must be on the same chromosome.

The LOWER the number = the CLOSER the genes are to each other.


Recombination

  • Equation for calculating recombination Frequencies & distance the genes are from each other.

    Freq. R = # recombinants/ total offspring

    Practice Problem


Human Traits & Diseases

1. Pedigree Charts: Diagram used to follow inheritance patterns of genes.


F. Human Disorders

  • Recessive disorders

    • Cystic Fibrosis

      Symptoms: Excess mucus in lungs, digestive problems, prone to infections.

      Most Affected: Northern European ancestry.


F. Human Disorders

  • Recessive disorders

    • Cystic Fibrosis

      Cause: Deletion of 3 bases = no phenylalanine.

      CFTR protein malfunctions = mucus builds up.

      Treatment: Nebulizer = Thins mucus in lungs.


F. Human Disorders

  • Recessive disorders

    • Cystic Fibrosis

      Frequency: 1 in 2,500

      Diagnosis: Tested before birth or once symptoms are noticed.


F. Human Disorders

  • Recessive disorders

    b. Sickle Cell Disease

    Frequency: 1 in 400 African Americans

    Other races affected but primarily African Americans.


F. Human Disorders

  • Recessive disorders

    b. Sickle Cell Disease

    Causes: Substitution on an incorrect amino acid in hemoglobin protein.

    Symptoms: Blood cells are misshapen and clot irregularly.

    Treatments: Blood transfusions.


F. Human Disorders

  • Dominant disorders

    a. Achondroplasia

    Symptoms: Dwarfism, shortened limbs

    Most affected: Uncertain; Studies show men being affected more.


F. Human Disorders

  • Dominant disorders

    a. Achondroplasia

    Cause: FGFR3 gene = abnormal cartilage formation.

    Treatment: Growth hormones


F. Human Disorders

  • Dominant disorders

    a. Achondroplasia

    Frequency: Not known in USA; International = 1 in 15,000- 40,000.

    Diagnosis: Before birth, after birth.


Sex-Linked Disorders

1. Muscular Dystrophy: Weakening of muscles, loss of coordination. 1/3500 males.

2. Hemophilia: Poor blood clotting, smallest injuries can be fatal.


Chromosome Disorders

  • Nondisjunction: Homologous chromosomes don’t separate during meiosis.

  • Incorrect number of chromosomes.


Chromosome Disorders

  • Down Syndrome

    a.3 copies of chromosome 21


Chromosome Disorders

  • Turner’s Syndrome

    • One X chromosome = 45,X

    • Sterile, females

  • Klinefelter’s Syndrome

    • Extra X chromosome = 47, XXY

    • Sterile, males


G. Genetic Testing

Testing for alleles

Test parents

Fetal testing

Amniocentesis

CVS

c. Newborn Screening


Influences on Genes

Polygenic Traits: Traits that are controlled by more than 1 gene.

Eye color

Skin color


Influences on Genes

B. The Environment

1. Plant height

2. Human weight


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