Genetics
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Genetics. Why do we look the way we do? Honors Biology Chapters 9 & 12. Inheritance of chromosomes. Egg + sperm  zygote. egg. meiosis. zygote. mitosis & development. fertilization. sperm. Inheritance of genes. Chromosomes passed from Mom & Dad to offspring are comprised of genes

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Genetics

Genetics

Why do we look the way we do?

Honors Biology Chapters 9 & 12


Inheritance of chromosomes

Inheritance of chromosomes

  • Egg + sperm  zygote

egg

meiosis

zygote

mitosis &development

fertilization

sperm


Inheritance of genes

Inheritance of genes

  • Chromosomes passed from Mom & Dad to offspring are comprised of genes

    • may be same information

    • may be different information

eye color

(blue or brown?)

eye color

(blue or brown?)


Effect of genes

Effect of genes

  • Gene = region of a chromosome that codes for a trait

  • Genes come in different versions for each trait

    • brown vs. blue eyes

    • brown vs. blonde hair

    • A version of a gene = an allele


Genes affect what you look like

Genes affect what you look like

X

bb

BB

Bb

Bb

Bb

Bb

Where did the blue eyes go??


Genes affect what you look like1

Genes affect what you look like…

X

bb

Bb

Bb

Bb

bb

bb

Why did the blue eyes stay??


Genes affect what you look like2

Genes affect what you look like…

X

Bb

Bb

bb

BB or Bb

BB or Bb

BB or Bb

Where did the blue eyes come from??


What did we show here

What did we show here?

  • Genes come in “versions”

    • brown vs. blue eye color

    • alleles

  • Alleles are inherited separately from each parent

    • brown & blue eye colors are separate & do not blend

      • either havebrown or blueeyes, not a blend

  • Some alleles mask others

    • brown eye color masked blue


How does this work

eye color

(blue?)

hair color

hair color

How does this work?

  • Homologous chromosomes have same genes…

    • …but maybe different alleles

eye color

(brown?)


Traits are inherited as separate units

Traits are inherited as separate units

  • For each trait, an organism inherits 2 copies of a gene (2 alleles), 1 from each parent

1 from Mom

homologous chromosomes

1 from Dad


Genetics vs appearance

Genetics vs. appearance

  • There can be a difference between how an organism looks & its genetics

    • Its expressed trait/s = phenotype

      • brown eyes vs. blue eyes

    • Its alleles, or genetic makeup = genotype

      • BB, Bb, bb

2 people can have the same phenotype but have different genotypes: BB vs Bb


Genetics vs appearance1

B

B

B

b

BB

Bb

Genetics vs. appearance

How were these brown eyes made?

eye color

(brown)

eye color

(brown)

eye color

(brown)

eye color

(blue)

vs.


Practice

Practice

If G is the allele forpointy ears and g is the allele for floppy ears, what will be the ear shape phenotypes of the puppies with these genotypes?

The dominant allele is _ for the trait ___________

The recessive allele is _ for the trait ___________

Genotype GG = Phenotype __________

Genotype Gg = Phenotype __________

Genotype gg = Phenotype ___________


Practice1

Practice

G is for pointy ears and g is for floppy ears. Also, H is for a pink nose and h is for a black nose.

Genotype GGHH = Phenotype ______ and ______

Genotype GgHh = Phenotype ______ and ______

Genotype gghh = Phenotype ______ and _______

Genotype GGhh = Phenotype ______ and _______

Genotype Gghh = Phenotype ______ and _______

Genotype ggHH = Phenotype ______ and _______


Practice2

Practice

  • Which of these are traits and which are phenotypes?

  • 1. Finger length

  • 2. Blue eyes

  • 3. Long hair

  • 4. Number of leaves

  • 5. Shape of tentacles

  • 6. Warbling song


Practice3

Practice

  • Which of these are alleles and which are traits?

  • 1. Eye color

  • 2. Bone integrity

  • 3. i

  • 4. Insulin shape

  • 5. B

  • 6. Na


Practice4

Practice

  • Which of these are phenotypes and which are genotypes?

  • 1. Curly hair

  • 2. Jj

  • 3. PP

  • 4. Arthritic knees

  • 5. Type B blood

  • 6. Spotted fur and a pink nose

  • 7. HHGg

  • 8. Purple leaves and spiny stem


Genetics the work of mendel

Genetics&The Work of Mendel


Gregor mendel

Gregor Mendel

  • Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas

    • used good experimental design

    • usedmathematicalanalysis

      • collected data & counted them

    • excellent example of scientific method


Mendel s work

Mendel’s work

Pollen transferred from white flower to stigma of purple flower

  • Bred pea plants

    • cross-pollinate true breeding parents

    • allowed offspring to self-pollinate& observed next generation

all purple flowers result

self-pollinate

?


Genetics

Mendel collected data for 7 pea traits


Looking closer at mendel s work

true-breeding

purple-flower peas

true-breeding

white-flower peas

100%

purple-flower peas

1st

generation

(hybrids)

100%

75%

purple-flower peas

25%

white-flower peas

3:1

2nd

generation

Looking closer at Mendel’s work

X

Parents

F1

self-pollinate

F2


What did mendel s findings mean

What did Mendel’s findings mean?

  • Some traits mask others

    • purple & white flower colors are separate traits that do not blend

      • purple x white ≠ light purple

      • purplemaskedwhite

    • dominant allele

      • functional protein

        • affects characteristic

      • masks other alleles

    • recessive allele

      • no noticeable effect

      • allele makes a non-functioning protein

allele producingfunctional protein

mutant allele malfunctioningprotein

homologouschromosomes


Mendel s results and conclusions

Mendel’s Results and Conclusions

RESULT:

  • Whenever Mendel crossed two P plants, one of the traits disappeared in the F1 plants.

  • The missing trait reappeared in the F2 plants in a 3:1 ratio pattern

    CONCLUSION: LAW OF DOMINANCE

  • One trait is dominant because it masked or dominated the other trait

  • One trait is recessive because it “hid” behind the dominant one. It can only be seen when the plant has no dominant alleles.


Mendel s results and conclusions1

Mendel’s Results and Conclusions

  • CONCLUSION: LAW OF SEGREGATION

  • Pairs of alleles segregate (separate) during the formation of gametes (meiosis—homologous pairs separate)

  • A parent only passes one allele for each gene onto a zygote


Mendel s results and conclusions2

Mendel’s Results and Conclusions

  • CONCLUSION: LAW OF INDEPENDENT ASSORTMENT

  • Factors for different characteristics are distributed to gametes independently or randomly.

  • Which allele is passed for one one gene doesn’t affect which allele is passed down from other genes


Mendel s legacy

Mendel’s Legacy

  • DNA and chromosomes weren’t discovered until many decades after Mendel’s death

  • Today, we understand the genetic mechanisms that underlie his mathematical discoveries…


Gamete formation

Gamete Formation

  • Suppose there’s a gene for eye color, with the alleles B for brown eyes or b for blue eyes.

  • A man has the genotype Bb, which gives him the phenotype brown eyes.

  • Meiosis produces his gametes…

He can make gametes that are EITHER B or b.

Half of his gametes will be one, half will be the other.

We simplify, saying that he produces either B or b allele sperm. Equal chance of each.

b

b

b

S Phase

b

b

b

b

1st Cytokinesis

2nd Cytokinesis

B

B

B

B

Normal cell in G1

B

B

B

Four Gametes


Practicing the law of segregation

Practicing the Law of Segregation

(Some gametes are written with more than one letter. If Dad’s genotype is LTLt, he will make a sperm that has the LT allele or a sperm that has the Lt allele.)

Genotype YY makes what gamete/s?

Genotype Tt makes what gamete/s?

Genotype bb makes what gamete/s?

Genotype Ii makes what gamete/s?

Genotype K1K2 makes what gamete/s?


How do we say it

B

B

B

b

b

b

BB

Bb

bb

How do we say it?

2 of the same allele=

Homozygous

BB= brown eyes

bb= blues eyes

homozygous dominant

homozygous recessive

2 different alleles=

Heterozygous

Bb= brown eyes


Practice5

Practice

  • Identify each of these genotypes as being homozygous or heterozygous.

    • GG ____________Ss ________

    • Yy ___________Vv ________

    • kk ____________


Practice6

Practice

  • Identify each of these genotypes as being homozygous dominant, homozygous recessive, or heterozygous.

    • ee ____________CC ________

    • QQ ___________pp ________

    • Ll ____________


Practice7

Practice

  • Suppose that the I allele codes for orange fins and the i allele codes for yellow fins.

    • The heterozygous genotype: __

    • The homozygous dominant genotype: __

    • The homozygous recessive genotype: __

    • A fish with yellow fins must have a _____________ genotype.

    • A fish with orange fins could be either _____________ or ___________________.


Punnett squares

B

b

B

b

Punnett squares

Bb x Bb

male / sperm

X

BB

Bb

female / eggs

Bb

bb


Genetics and probability

Genetics and Probability

  • Figuring out offspring is a matter of chance.

    • A Punnett Square provides the probabilities of two parents producing particular zygotes.

    • An example, using coins:


Punnett squares1

Punnett Squares

  • Using the letter H to stand for heads…

    • If you flip a coin that’s heads (H) on both sides, what are the chances that it will come up heads (H)?


Punnett squares2

Punnett Squares

  • If it’s a normal coin, heads (H) on one side and tails (h) on the other…

    • What are the odds that it will come up heads (H) on a flip?


Punnett squares3

Punnett Squares

  • If you flip TWO normal coins, what are the odds that you will get heads (H) on both flips?


Punnett squares4

Punnett Squares

  • The first flip will be either heads (H) or tails (h):


Punnett squares5

Punnett Squares

  • The second flip will also be either heads (H) or tails (h):


Punnett squares6

Punnett Squares

  • These are the possible combinations that you could have produced:


Punnett squares7

Punnett Squares

  • These are the possible combinations that you could have produced:


Punnett squares8

Punnett Squares

  • These are the possible combinations that you could have produced:


Punnett squares9

Punnett Squares

  • These are the possible combinations that you could have produced:


Punnett squares10

Punnett Squares

  • These are the possible combinations that he could have produced:

H

H H

H

H

H


Punnett squares11

Punnett Squares

  • 1 in 4 possible outcomes would be both heads (HH). The chance of getting heads on both flips = 1/4 = 25%

H

h

H

H H

H h

H h

h h

h


Punnett squares12

Punnett Squares

  • What are the odds of getting heads on one flip, tails on the other?

h

H

H

H H

H h

H h

h h

h


Punnett squares13

Punnett Squares

  • 2 of 4 possible outcomes = 1/2 = 50%

h

H

H

H H

H h

H h

h h

h


Punnett squares14

Punnett Squares

  • What if you flip two different coins:

    • One coin has two heads

    • The other is normal, one heads and one tails

    • What are the odds of getting heads on both flips?


Punnett squares15

Punnett Squares

H

H

  • 2/4 = 1/2 = 50%

  • This is called a Punnett Square.

    • Punnett Squares display all possible gametes and possible offspring.

H H

H

H H

H h

H h

h


Punnett squares16

Punnett Squares

  • The top and side boxes show possible gametes. The middle boxes show possible zygotes (offspring) they would create.


Step by step instructions

Step-By-Step Instructions

  • Sample problem: What are the chances that a heterozygous brown-eyed father and a blue-eyed mother would have a blue-eyed child? (Use letters B/b)

  • 1. Figure out Mom and Dad’s genotypes.

    • In the example: Dad = ___, Mom = __


Punnett squares17

Punnett Squares

  • 2. Figure out Mom and Dad’s gametes.

    • Dad’s gametes = __ and __

    • Mom’s gametes = __ and __

  • 3. Set up a square.

    • For a monohybrid cross (studying only one gene), make a normal tic-tac-toe board.


Punnett squares18

Punnett Squares

  • 4. Write Dad’s gametes on one side, and Mom’s on the other.

    • It doesn’t matter whether Mom or Dad is on the side vs top, just keep both eggs together and both sperm together.


Punnett squares19

Punnett Squares

  • 4. (continued)

    • Like a genotype, if there’s a dominant allele, put it first.

a

a

A

a

A

A

a

A


Punnett squares20

Punnett Squares

  • 5. Complete zygote genotypes.

    • Remember to put dominant allele first, if there is one.

  • 6. Write out all the zygote genotypes as fractions.

    • I.e. 1/4, 2/4, 3/4, 4/4


Punnett squares21

Punnett Squares

  • 7. Reduce fractions if possible, and convert fractions to percentages.

    • For instance, if two of the four zygotes are AA, the probability of genotype AA is 2/4 = 1/2 = 50%

  • 8. If applicable, rewrite offspring genotype results as phenotype results.


Punnett squares22

Punnett Squares

  • If you did the problem correctly, it should EITHER look like this, OR…

Genotype Probabilities

BB = 0/4 = 0%

Bb = 2/4 = 1/2 = 50%

bb = 2/4 = 1/2 = 50%

Phenotype Probabilities

Brown eyes = 2/4 = 1/2 = 50%

Blue eyes = 2/4 = 1/2 = 50%

Final Answer

50% probability of a blue-eyed child

B

b

Bb

bb

b

b

Bb

bb


Punnett squares23

Punnett Squares

  • …OR like this.

    • Notice that results are the same.

Genotype Probabilities

BB = 0/4 = 0%

Bb = 2/4 = 1/2 = 50%

bb = 2/4 = 1/2 = 50%

Phenotype Probabilities

Brown eyes = 2/4 = 1/2 = 50%

Blue eyes = 2/4 = 1/2 = 50%

Final Answer

50% probability of a blue-eyed child

b

b

Bb

Bb

B

b

bb

bb


Practicing with punnett squares

Parents – Tt and tt

Tt

t Tt tt

t Tt tt

Offspring:

50% Tt – tall

50% tt – short

Parents – TT and Tt

TT

T TT TT

t Tt Tt

Offspring:

100% TT or Tt – tall

Practicing with Punnett Squares


Practicing punnett squares

Practicing Punnett Squares

  • Show a monohybrid cross, with all genotype and phenotype probabilities, for parents who are HH and hh.


Practicing punnett squares1

Practicing Punnett Squares

  • Show a monohybrid cross, with all genotype and phenotype probabilities, for parents who are Ll and Ll.


Practicing punnett squares2

Practicing Punnett Squares

  • If Dad’s genotype is Rr and Mom is homozygous recessive, what are the odds of having homozygous dominant offspring?


Practicing punnett squares3

Practicing Punnett Squares

  • If both parents are heterozygous, and they have ten offspring, how many of those offspring would you predict will be homozygous recessive?


Practicing punnett squares4

Practicing Punnett Squares

  • Suppose black fur is dominant and white fur is recessive. Two parents, one with black fur and one with white fur, have many offspring. Roughly half of their babies are black-furred, and half are white-furred. What were the genotypes of the parents?

    • Hint: when a question asks you to figure out parental genotypes, make test crosses, Punnett Squares for every possibility, then see which one gives you offspring results that fit.


Testcross

Testcross

  • Dominant phenotypes can have either BB or Bb genotypes. How do you know?

  • Perform a test cross, or a cross with a known recessive genotype (bb)

    • If any recessive offspring appear, unknown must be heterozygous

    • If no recessive offspring appear, unknown can be homozygous.


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