Genetics

11.1 – Gregor Mendel

Heredity

Inheritance of traitsGenetics - study of heredity

Genetics

Gregor Mendel

Suggested that paired factors, or genes, carry inherited traits.

Predicted how traits were inherited by studying pea plants

The Role of Fertilization

Fertilization - During sexual reproduction, male and female reproductive cells join to produce a new cell.

The Role of Fertilization

The Role of Fertilization

• Mendel had several true-breeding plants

• Self-pollinating and produce offspring identical to parent

• Trait - a specific characteristic of an individual

• Ex) Seed color and shape.

• Varies

The Role of Fertilization

• Mendel studied traits of pea plants.• Hybrids - Offspring between parents with

different traits.

Quick Graded Review – Two Options – 5 minutes

1. Stand and speak Summarize the notes in 15 seconds. Spend the next 3 minutes preparing what

you’ll say. 2. Schoology discussion

Go to Schoology your class Unit 7 11.1 Summary – First Half

Write a summary of the notes so far in at least 3 sentences.

Do not respond to anyone yet.

Genes and Alleles P gen – Parents - Original pair of plants

• F1 - Offspring of P generation.

• In each cross, the nature of the other parent, with regard to each trait, seemed to have disappeared.

Genes and Alleles

• Mendel’s first conclusion -

• An individual’s characteristics are determined by factors that are passed from one parental generation to the next.

• Genes - Factors that are passed from parent to offspring.

Dominant and Recessive Traits

• Mendel’s second conclusion• Principle of Dominance –

Some alleles are dominant, others are recessive.• If an organism has at least

one dominant allele for a trait,it will exhibit the dominant trait.

• If an organism has a recessive allele for a trait, it will exhibit the recessive trait only when there are no dominant alleles present.

Alleles

Different forms of a geneOrganisms have two alleles,

or genes, for each trait.One allele from the

female gamete (egg). One allele from the

male gamete (sperm).

Segregation

• What happened to the recessive alleles?

• Mendel allowed F1 hybrids to self-pollinate. The offspring of an F1 cross are called the F2 generation.

The F1 Cross

• When Mendel saw the F2 plants, he observed the recessive traits reappeared.

• About ¼ of the F2 plants showed the recessive trait.

Explaining the F1 Cross

• Alleles had segregated.

• Mendel suggested the alleles for tallness and shortness in the F1 plants segregated from each other during formation of the sex cells, or gametes.

Recessive trait

Dominant trait

Seed shape

Seed color

Flower color

Flower position

Pod color

Pod shape

Plant height

round yellow purpleaxial (side) green inflated tall

wrinkled green whiteterminal

(tips) yellow constricted short

Quick Graded Review – Two Options – 5 minutes 1. Stand and speak

Summarize this part of notes in 15 seconds. Spend the next 3 minutes preparing what you’ll say.

2. Schoology discussion Go to Schoology your class Unit 7

11.1 Summary – Second Half Write a summary of this part of notes in at least 3

sentences. Or respond and add on to someone else’s response

from First Half with information from notes.

Tongue Roll Dominant trait

Recessive attached ear lobesDominant Free Ear Lobes

Hitch hiker’s thumb

Dominant

Regular thumb

Recessive

Other examples

Chin cleft – Dominant Bent pinky finger – Dominant Dimples – Dominant Blue eyes – Recessive Hand clasp – Left thumb

dominant Widows peak - Dominant

11.2 – Applying Mendel’s Principles

Dominant gene (allele)

Stronger of two genes Represented by capital letter Written first Example: T for tall plant height

Recessive gene (allele)

Weaker of two genes Can be hidden by dominant genes. Represented with lower case letters Example: t for short plant height

Pure (Homozygous)

Two of the same genes (alleles) for a trait

Example: TT (homozygous dominant) or tt (homozygous recessive)

Hybrid (Heterozygous)

Two different alleles for a trait

Example: Tt Tall or short?

Probability

Probability – The likelihood that a particular event will occur.

Example: Flipping a coinProbability of flipping heads?

1

2

Number of total possible outcomes

Number of desired outcomes

Probability

Example: Flipping a coinProbability of flipping heads

three times?

½ x ½ x ½ = 1/8

Genotype

Combination of alleles or genes for a certain trait

Example: Tt, TT, tt

Phenotype

Physical, visible traits how it looks

Determined by looking at organism

Example: tall, short

Genotype or Phenotype?

TtRoundBlackBBSmoot

hrrTall

Genotype

Phenotype

Phenotype

Genotype

Phenotype

Genotype

Phenotype

In pea plants, green (G) pods are completely dominant over yellow (g).

What are the genotypes?

Homozygous yellowHeterozygous greenHomozygous dominantHybrid

ggGg

GG

Gg

In pea plants, green pods are completely dominant over yellow.

Pure yellow Homozygous recessivePure greenHeterozygous Yellow

gg

gg

ggGg

GG

In guinea pigs, short hair is dominant over long hair

What hair length will be represented by a capital S?

What hair length will be represented by a lower case s?

Short

Long

What phenotypes would result from the following genotypes?

SS ssSs

Short hair

Long hair

Short hair

T

T t

t

Tall plant

Short plant

All tall plants

What are the phenotypes of the parent plants?

If both parents are pure, what are their genotypes?

Which gene or allele can each parent pass on to the offspring?

What is the phenotype of the offspring?What is the genotype of the offspring?

TT t t

In pea plants, round pea pod texture is dominant over wrinkled texture. What is the genotype of the following?

homozygous roundheterozygouswrinkledpure dominanthybrid round

RR

Rr

rr

RR

Rr

In pea plants, round pea pod texture is dominant over wrinkled texture. What is the genotype of the following?

pure recessiveheterozygous roundpure wrinkledhybridpure round

rr

Rr

rr

Rr

RR

Punnett Squares

Punnett squares – used to predict and compare the genetic differences that will result from a cross.

Monohybrid crossesMonohybrid crosses

Heterozygous tall parent

T t

T t

T t

T

t

Heterozygous tall parent

TT Tt

Tt tt

How To Make a Punnett Square for a One-Factor Cross

Write the genotypes of the parents in a cross.

Ex) Cross a male and female bird that are heterozygous for large beaks. They each have genotypes of Bb.

Bb and Bb

How To Make a Punnett Square Draw a Punnett square. Put one parent on the top,

one parent on the left. Put one allele from each

parent on each side of each section.

How To Make a Punnett Square

Fill in the table by combining the gametes’ genotypes.

Mom

Dad

-Determine the genotypes and phenotypes of each offspring.

How To Make a Punnett Square

Probability of having…

A large beak? A small beak? Homozygous dominant? Heterozygous? Homozygous recessive?

3:4

1:4

1:4

2:4

1:4

Independent Assortment

Principle of independent assortment – genes for different traits can segregate independently during the formation of gametes.

Dihybrid Cross

Two factor crossTwo traits involved.

The Two-Factor Cross: F1

Mendel crossed two true-breeding plants:

One produced only round yellow peas

One produced onlywrinkled green peas.

The Two-Factor Cross: F1

The round yellow peas had the genotype RRYY, which is homozygous dominant.

The Two-Factor Cross: F1

The wrinkled green peas had the genotype rryy, which is homozygous recessive.

The Two-Factor Cross: F1

All F1 offspring were round yellow peas. Shows yellow and round alleles are dominant over the alleles for green and wrinkled.

Punnett square shows genotype of F1 offspring as RrYy, heterozygous for both seed shape and seed color.

The Two-Factor Cross: F2

Mendel then crossed the F1 plants to produce F2 offspring.

Crossed RrYy with RrYy

Dihybrid cross instructions

Cross the parent alleles.

Make sure each box has two of each letter, one from each parent

Mom

Dad

The Two-Factor Cross: F2

Alleles for shape segregated independently of those for color.

Genes that segregate independently do not influence each other’s inheritance.

The Two-Factor Cross: F2

Results were close to the 9:3:3:1 ratio the Punnett square predicts.

Mendel discovered the principle of independent assortment – genes for different traits segregate independently during gamete formation.

11.3 - Other Patterns of Inheritance

Incomplete dominance

Alleles BLEND (mix) Neither gene is dominantHeterozygous phenotype

is a blend of the dominant and recessive phenotypes.

Think about colors of paintRed + White = Pink

Incomplete Dominance R R

W

W

RW

www.nerdscience.com 11-3

RW

RW RW

Codominance

Both alleles are dominantHeterozygous

expresses both phenotypes together.

There is NO “blending”Red + White = Red and White

Red cow crossed with white cow results in roan cattle. Roan cattle have both red and white hairs.

Codominance

Codominance

Example: White chicken

(WW) x black chicken (BB) = black and white checkered chicken (BW)

Codominance

Incomplete or Codominance?

A white cow and a red cow produce a roan cow, one that has both white and red hairs.

A red flower and a white flower produce pink flowers.

A black cat and a tan cat produce tabby cats, cats where black and tan fur is seen together.

Codominance

Incomplete

Codominance

Incomplete or Codominance?

A blue blahblah bird and a white blahblah bird produce offspring that are silver.

A certain species of mouse with black fur is crossed with a mouse with white fur and all of the offspring have grey fur.

A woman with blood type A and a man with blood type B have a child with blood type AB.

Incomplete

Incomplete

Codominance

Multiple AllelesSingle gene with

more than two alleles.

example: human blood type

Blood Types (codominant)

Blood type is codominant

IA and IB are dominant.

i is recessive4 different blood

types

Phenotype(Blood type)

Genotype(Alleles or genes for blood type)

A IAIA, IAi

B IBIB, IBi

AB IAIB

O ii

Polygenic Traits Traits controlled by two or more (many)

genes

Polygenic traits often show a wide range of phenotypes.

example: human skin color employs more than four different genes

Skin color genes: AaBbCcDd

Genes and the Environment The characteristics of any organism are

not determined solely by the genes that organism inherits.

Genes provide a plan for development, but how that plan unfolds also depends on the environment.

Both nature and nurture

14.1 – Human

Chromosomes

Karyotype

Chart of chromosome pairs arranged by decreasing size.

Shows unusual number of chromosomesCan detect trisomy 21 (Down syndrome)Identifies male or femaleShows genome – full set of

genetic information.

Karyotype

Normal Female

KaryotypeFemale with Down Syndrome

Sex Chromosomes

X and Y chromosomesDetermine the sex of the

offspringFemales are XXMales are XY

Sex Chromosomes

All other chromosomes are autosomes.

Everyone has 46 chromsomes:2 sex chromosomes and 44 autosomes.

Sex-linked Traits

Traits inherited on X and Y chromosomes.

Most are on the X chromosome (because it’s bigger)

Example) Color blindness is a recessive

sex-linked trait on the X-chromosomeMales show recessive

sex-linked traits more than femalesWhy?

Sex-linked Traits

Males get only one X chromosomeTherefore, males show all

recessive sex-linked traits on X chromosome.

Females have a second X chromosome that carries another allele that can hide recessive traits

Sex-linked Traits

Females who have recessive alleles but show the dominant trait (heterozygous) are called carriers

A woman can have normal vision but carry the recessive allele for colorblindness

X-Chromosome Inactivation If just one X chromosome is enough for

male cells, how does the cell “adjust” to the extra X chromosome in female cells?

In female cells, one X chromosome is randomly switched off, forming a Barr body.

Barr bodies are generally not found in males because their single X chromosome is still active.

Pedigree Study

Method of determining the genotype of individuals by looking at inheritance patterns

Pedigrees illustrate

inheritance

Pedigrees illustrate

inheritance

Male

Female

Affected male

Affected female

Mating

Parents

Siblings

Known heterozygotes for recessive allele

Death

Human Pedigrees This diagram shows what the symbols

in a pedigree represent.

Human Pedigrees This pedigree shows how one human trait

—a white lock of hair just above the forehead—passes through three generations of a family.

The allele for the white forelock trait is dominant.

Human Pedigrees Top of the chart is grandfather with the white

forelock trait. Two of his three children

inherited the trait. Three grandchildren have the trait,

but two do not.

Human Pedigrees Because the white forelock trait is dominant,

all family members lacking this trait must have homozygous recessive alleles.

One of the grandfather’s children lacks the white forelock trait, so the grandfather must be heterozygous for this trait.