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Introduction to Genetics. Biology. Genetics – the study of patterns of inheritance and how traits or characteristics are passed on from parent to offspring. Gregor Mendel. Gregor Mendel – the father of genetics. He used pea plants to study patterns of inheritance.

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slide2
Genetics – the study of patterns of inheritance and how traits or characteristics are passed on from parent to offspring
gregor mendel
Gregor Mendel

Gregor Mendel – the father of genetics. He used pea plants to study patterns of inheritance.

self pollination vs cross pollination
Self-Pollination vs. Cross Pollination
  • Mendel controlled the pollination of pea plants.
  • Pea plants normally reproduce by self pollination (male/female parts from same plant unite)
slide5
Mendel cross-pollinated plants by removing the anthers (male part of plant) and pollinating the stigma (female) part of another plant
pea plants
Pea Plants
  • Mendel studied seven different traits in pea plants
    • Trait – a specific characteristic that varies from one individual to the next.
    • Each trait had two contrasting characteristics (alleles)
slide7
For example:
    • Seed Shape – smooth/wrinkled
    • Seed Color – yellow/green
    • Plant Height – tall/short
mendel s vocabulary
Mendel’s Vocabulary
  • True-breeding – plants that produce only like offspring when self-pollinated.
  • Hybrid – cross between two organisms of different traits
  • P1 Generation – The original pair of organisms in a series of crosses
  • F1 Generation – First generation of offspring as a result of P1 cross.
mendel s work
Mendel’s Work
  • Mendel crossed true-breeding short plants with true-breeding tall pea plants
  • 100% of the offspring were tall
  • Mendel crossed F1 plants (tall plants) to see if recessive trait reappeared
  • 25% of offspring were short; 75% were tall in F2 generation
slide10

Section 11-1

P Generation

F1 Generation

F2 Generation

Tall

Short

Tall

Tall

Tall

Tall

Tall

Short

slide11

Seed Shape

Seed Color

Seed Coat

Color

Pod

Shape

Pod Color

Flower Position

Plant Height

Round

Yellow

Gray

Smooth

Green

Axial

Tall

Wrinkled

Green

White

Constricted

Yellow

Terminal

Short

Round

Yellow

Gray

Smooth

Green

Axial

Tall

mendel s conclusions
Mendel’s Conclusions
  • Every individual receives two factors (alleles) for each trait, one from mom and one from dad.
slide13
Factors can sometimes be dominant or recessive
    • Dominant = one factor masks the presence of another
    • Recessive = factor that is masked by the presence of a dominant allele
slide14
In humans...
    • = Widow's peak: W = widow's peak, w = continuous hairline (which are you?)
    • = Freckles: F = Freckles, f = no freckles (which are you?)
    • = Earlobes: E = unattached, e = attached (which are you?)
    • = Cystic fibrosis C = no CF, c = cystic fibrosis
slide15
Law of Segregation – pair of factors (alleles) are segregated/separated during the formation of gametes
mendel s conclusions con
Mendel’s Conclusions (con.)
  • Law of Independent Assortment – Alleles for different characteristics are distributed to gametes independently
    • Alleles/Traits are not linked to one another
probability
Probability
  • Principle of Probability– the likelihood that a particular event will occur
  • Probability is identified as a ratio, fraction, or percent
    • 50%
    • ½
    • 1:2
probability18
Probability
  • Example – Coin Flip
    • 50% chance of getting heads
    • Could get heads 10 consecutive flips
    • Over many trials results will be near 50%
    • Past coin flips do not affect future coin flips
punnett squares
Punnett Squares
  • Diagrams that apply the principles of probability to predict the outcome of genetic cross
  • Uppercase letters represent dominant alleles Ex. R
  • Lowercase letters represent recessive alleles

Ex. r

punnett squares con
Punnett Squares (con.)
  • Homozygous – organisms with two of the same alleles for a trait (RR or rr)
  • Heterozygous – organisms with two different alleles for a trait (Rr)
  • Genotype – The genetic makeup of an organism (RR, Rr, rr)
  • Phenotype – The physical characteristics of an organism (Round OR wrinkled)
how to use a punnett square
How to use a Punnett Square
  • Monohybrid Cross- “one-trait” cross
  • Identify the genotype for each parent
  • Write the alleles from one parent on the top and the alleles for the other parent on the left side of the square
  • Fill in the table like a multiplication table, capital letter always goes first
slide24
Ex. #2

RR x rr

R R

r

r

analyzing results
Analyzing results

Genotypic ratio-compares possible genotypes

# homozygous dominant: # heterozygous: #homozygous recessive

In Ex. #1 it is 1:2:1

In Ex. #2 it is 0:4:0

analyzing results con t
Analyzing results (Con’t)

Phenotypic ratio-compares possible phenotypes

# with Dominant trait: # with recessive trait

In Ex. #1 it is 3:1

In Ex. #2 it is 4:0

analyzing results con t27
Analyzing results (Con’t)

Percentages-% chance of something occuring

In Ex. #1 there is a 75% chance the plant will be tall and a 25% chance the plant will be short.

patterns of inheritance
Patterns of Inheritance

Complete Dominance: In the heterozygous individual, only the dominant allele is expressed, the recessive allele is present but unexpressed.

slide29
Ex. In pea plant green pods are dominant over yellow pods. Cross two pea plants that are heterozygous for pod color.

What is the phenotypic ratio?

What is the genotypic ratio?

answer
ANSWER

Genotypic ratio: 1:2:1

Phenotypic ration is 3:1

exceptions to mendel s rules not all traits are clearly dominant or recessive
Exceptions to Mendel’s Rules: Not all traits are clearly dominant or recessive
  • Incomplete Dominance – One allele is not completely dominant over another
    • Example: Japanese Four O’Clock Plant
      • RR = Red Flowers
      • RW = Pink Flowers
      • WW= White Flowers
ratios
Ratios

Find genotypic ratio the same way we did for complete dominance

Now there are 3 phenotypes so the ratio is

# Dom: # Heterozygous: # Rec

Find Genotypic ratio and phenotypic ratio for the previous problem

Genotypic ratio: 0:4:0

Phenotypic ratio: 0:4:0

slide35
Codominance – In a heterozygote both alleles are dominant and are expressed at eh same time. Example: coat color in cattle
      • RR = Red Coat
      • RW = Roan Coat
      • WW = White Coat
slide36

RR = Red

WW = White

RW = Roan

ex cross 2 roan coat cows
Ex. Cross 2 roan coat cows.

Genotypic Ratio- #RR: #RW: #WW

1:2:1

Phenotypic Ratio- #red: #roan: #white

1:2:1

dihybrid cross
Dihybrid Cross
  • Cross involving two traits (hair color & eye color or pod color & pod shape)
  • Traits assort independently of each other
  • Mendel used to discover the principle of independent assortment
slide39

Dihybrid Cross

Go to Section:

how to use a dihybrid cross
How to use a Dihybrid Cross
  • Identify the 2 traits
  • Assign a capital letter to the dominant form of the first trait and the same lower case letter for the recessive form.
  • Choose a different letter and do the same for the second trait.
  • Identify the genotype for each parent
slide41
5. Identify the gametes for each parent

Combine:

1st letter with 3rd letter

1st letter with 4th letter

2nd letter with 3rd letter

2nd letter with 4th letter

6. Fill in the Punnett Square

-ABC order

-keep like letters together

-capital always goes first

analyze using phenotypic ratio
Analyze Using Phenotypic Ratio

1st trait dominant, 2nd trait dominant:

1st trait dominant, 2nd trait recessive:

1st trait recessive, 2nd trait dominant:

1st trait recessive, 2nd trait recessive

In previous example, the phenotypic ratio is 9:3:3:1

sex linked traits
Sex-Linked Traits

Sex-linked traits are determined by genes found only on the sex “X” chromosome

REMEMBER:

XX-Females Xy-Males

EX. Red-Green Colorblindess

genotypes
GENOTYPES

Possible female Genotypes

XBXB-normal

XBXb-normal (carrier)

XbXb-colorblind

Possible male genotypes

Xby-normal

Xby-colorblind

ex cross a female carrier with a normal male
Ex. Cross a female carrier with a normal male

What is the % chance they will have a colorblind son?

50%

multiple alleles
Multiple Alleles

Multiple Alleles: Having more than 2 alleles for a trait.

Ex. Human blood type

human blood type
Human Blood Type

3 alleles: A, B, and O

A and B are codominant

O is recessive

possible blood type combinations
Possible Blood Type Combinations

GENOTYPES PHENOTYPES

AA-homozygous dominant Type A

BB-homozygous dominant Type B

AO-heterozygous Type A

BO-heterozygous Type B

AB-codominant Type AB

OO-homozygous recessive Type O

slide51
EX. Cross a mother who has type O blood with a father who has typeAB blood. What are the possible phenotypes?

Answer: Type A and Type B (both are heterozygous)

polygenic traits
Polygenic Traits
  • Polygenic Traits – traits can also be controlled by more than one gene
    • Example – Skin color is controlled by 3 to 6 genes that control melanin production

Polygenic traits: stature, body shape, hair and skin color

pedigrees
Pedigrees

Pedigree: diagram that shows how a trait is inherited over several generations.

Symbols

Circle: female

Square: male

Diamond: unknown sex

pedigrees con t
Pedigrees (con’t)
  • Shaded in shape =person exhibits the trait
  • Half shaded=the person is a carrier
  • Not shaded=the person is unaffected
  • Marriage line-horizontal line from male to female
  • Child line-vertical line which extends from the marriage line
karyotypes
Karyotypes

Karyotype-picture of an individual’s chromosomes

-Review of chromosome structure

a-centromere

b-sister chromatids

-

slide57
-In normal human body cells, there are 2 copies of each chromosome which makes 23 pairs or 46 total chromosomes

-Each pair of chromosomes are called homologous chromosomes

karyotype con t
Karyotype (Con’t)
  • In a Karyotype, 1-22 pairs are called autosomes.
  • The 23rd pair are called sex chromosomes.
  • XX-female, Xy-male
  • Gender is determined by sex chromosomes

Use a Punnett Square for the following cross:

XX (mom) x Xy (dad)

What is the % chance for a girl? Boy?

50%, 50%

karyotype con t60
Karyotype (con’t)
  • Karyotypes can be analyzed to find genetic disorders.

Ex. Down’s Syndrome (trisomy 21)