Wednesday 4/9/14

• AIM: Why is Gregor Mendel the father of genetics?

• DO NOW: How many chromosomes do you have and where do they come from?

• What would happen if you had an extra chromosome and why?

• HOMEWORK: Text read pages 267-70. Reading check pages 267 and 268, q 1 and 2 pages 270

What is genetics?

Genetics

• The study of inherited traits• Chromosomes are the units of inheritance• Chromosomes carry genes• Genes are the specific direction or code for

your physical trait• Genes: code for proteins• Proteins cause chemical reactions• Chemical reactions lead to physical traits

Where do your inherited traits come from?

Your dads sperm and your moms egg

Homologous chromosome• Similar in size shape and

genetic content• Homologous

chromosomes pair up at fertilization

• n+n=2n

Remember

• Zygote gets one complete set of chromosomes from the egg

• And one complete set of chromosomes from the sperm

• Bringing together homologous chromosomes

Haploid + haploid = diploid

Human Chromosomes

• Total we have 23 pairs• 2(23)=46• 22 of those pairs are

called autosomes• The 23 pair is the sex

chromosomes

Sex Chromosomes

• XX female• XY male

Y chromsome

• Carries the SRY gene• SRY: sex determining

region• If the SRY gene is

turned on, then gonads develop into testis and fetus becomes male

• If not then gonads become ovaries

• AIM: How does the structure of DNA relate to its function?

• DO NOW: How many chromosomes do each of your cells have?

• How many genes does each of your cells have?• How many nuclei does each of your cells have?• Homework: text read pages 293,296,297 and 299.

Answer Reading questions 293,296,297

• Somatic or body cells have 46 chromosomes– Examples of somatic cells

• Cardiac cells lung cells brain cells• Skin cells muscle cells gall bladder cells• Tracheal cells esophagal cells liver cells

• Gametes or sex cells have 23 chromosomes– Male-sperm– Female-ova or egg

• There are thousands of genes in each cell• There is one nucleus in each cell that houses the

chromosomes which carry genes on them• Each cell expresses specific genes to make them specialized

So how do we know anything about genetics and homologous

chromosomes?

Gregor Mendel

• Father of genetics• Looked at the pea plant• Specifically 7 visible

traits• Followed their

inheritance over many generations

• HE KNEW NOTHING ABOUT GENES!!!!!

Mendel was lucky

• Each of the 7 traits Mendel observed was only present in 1 of 2 possible forms– Ex: Plant color was either purple or white

• Pea shape was either round or wrinkled

• Mendel used this when performing his experiments.

Thursday 4/10/14

• AIM: How did Gregor Mendel develop his basic laws of heredity?

• DO NOW: What is genetics? How do we know anything about genetics?

• HOMEWORK: Textbook read pages 276-277. do the reading check on page 277

Genetics

• The study of inherited traits• Chromosomes are the units of inheritance• Chromosomes carry genes• Genes are the specific direction or code for

your physical trait• Genes: code for proteins• Proteins cause chemical reactions• Chemical reactions lead to physical traits

• AIM: How did Mendel develop his basic laws of heredity?

• DO NOW: What is the difference between self fertilization and cross fertilization?

• HOMEWORK: textbook read pages 267-270. 1-Explain the difference between true breeding and hybrid.

• 2- Define P generation, first filial generation and second filial generation.’

• 3- Explain why Mendel studied pea plants

Gregor Mendel’s experiments: Fertilization

• Self-fertilization: egg in the flower is fertilized by the sperm of the same flower

• Cross-fertilization: sperm from a foreign plant fertilizes an egg

Gregor Mendel

• Used both the processes of self fertilization and cross fertilization to experiment on pea plants

• This helped him develop his basic laws of heredity

Definitions

• True breed or pure breed: plants with a trait such as purple flowers that is always inherited by all offspring– Can only produce one type of gamete

• HYBRID:– The offspring of a cross fertilization– 2 parents similar to sexual reproduction– Can produce different types of gametes

Definitions continued

• Monohybrid cross: tracks one trait at a time– Ex: flower color

• Dihybrid cross:

Mendel’s work

• Self fertilized true breed parents for many generations– All offspring gave the

same results• Cross fertilized true

breeds to get an F1 generation

• Self fertilized the F1 and observed the F2 generation

•

Mendel’s Experiment

Parent Generation (P1):Purple true breed X White true breed

First Filial (F1)

100% Purple flowers Self fertilize

Second Filial (F2)75% Purple: 25% White

3:1 ratio

Why were all the F1 generation flowers purple?

Purple Trait is obviously dominant over the white trait

The white trait was hidden but not gone

Why were some of the F2 generation part purple and part white?

The F1 parent was carrying the white trait but it was masked or hidden.White is recessive to purple

Just from looking at these results, what can Mendel conclude?

Mendel’s Conclusions from a monohybrid cross

1- Copies of inherited traits must be separated when gametes are formed

2- When present in 2 forms one form is dominant over the other

3- the recessive trait will show itself when present in two copies

Tuesday 4/22/14

From these experiments, Mendel concluded:

• Traits are determined by physical unit that come in pairs (he did not know these would later be called alleles)

• Gametes separate and carry only 1 allele(copy) for each gene

• The particular allele that ends up in a gamete is caused by chance

• One allele is dominant and one recessive• True-breeding organisms have the 2 copies of the

same allele (homozygous)

• AIM: How can we predict the possible genotypes and phenotypes of offspring?

• DO NOW: 2- if I cross fertilized a true breed green seed pea plant by a true breed yellow seed pea plant, what phenotypes do I expect to get?

• HOMEWORK: Textbook read pages 272-273. answer questions 1,2,3 on page 275

Create a list• 7 traits observed by Gregor Mendel

1- Flower color2- Plant size3- Flower position4-Seed color5- shape of pod6- Pod color7- Seed shape

Each of these traits has a dominant and a recessive phenotype

•

Seed color

• Dominant phenotype: green• Recessive phenotype: yellow• Genotype Phenotype

– GG– Gg– gg

Mendel had no idea about the following

• We know we get 2 copies of genes– 1 from sperm– 1 from egg

• Allele: is a copy of a gene• Homologous chromosomes carry alleles

Monohybrid Cross

• Tracked one (mono) trait at a time

Mendel’s work

• Cross fertilized two true breed parents that displayed opposite traits.(P or Parental generation)

• All First filial or F1 offspring were purple

What happened to the white color?

Self-fertilized F1

• Second filial or F2 generation yielded about ¼ white and ¾ purple

• So the white flower color was not lost just masked

Self-fertilized F2

• Saw that all white flowered F2 yielded all white F3 but the purple still yielded 3:1 ratio of purple to white

• Therefore the white allele was not lost but rather hidden or masked by the purple allele

From these experiments, Mendel concluded:

• Traits are determined by physical unit that come in pairs (he did not know these would later be called alleles)

• Gametes separate and carry only 1 allele for each gene

• The particular allele that ends up in a gamete is caused by chance

• One allele is dominant and one recessive• True-breeding organisms have the 2 copies of the

same allele

Thursday 4/24/14• AIM: why did Mendel

decide to perform a dihybrid cross?

• DO NOW: Let A represent the allele coding for terminal flowers and a axial flowers. Complete the following table:

• HOMEWORK: text read pages 274-275. answer questions 3 and 4 page 275

Genotype Phenotype

AA Homozygous dominant

terminal

Aa Heterogygous terminal

aa Homozygous recessive

axial

Mendel’s Law of dominance

• When two different alleles are present, the dominant alleles gives the resulting phenotype and masks the trait of the recessive allele

• However the recessive allele is still present• Homozygous Dominant and heterozygous organisms

display the same phenotype• Recessive alleles are only displayed when present in

2 copies– Homozygous recessive

Mendel’s Law of segregation

• Pairs of alleles on homologous chromosomes separate from each other during gamete formation

• Gametes receive only one allele from a homologous pair.

• Fertilization produces offspring with a copy of one allele from mom and one from dad

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Mendel’s Hypothesis were consistent with his results

• 2 plants that look alike may actually carry different combinations of alleles

• Genotype: the combination of alleles carried by an organism– Homozygous Dominant: AA– Heterozygous: Aa– Homozygous recessive: aa

• Phenotype: The physically observable feature

• So a homozygous dominant individual and a heterozygous individual will display the same phenotype but have different genotypes

• The only way for the recessive phenotype is observed is if the individual is homozygous recessive

Mendel was not satisfied• He wanted to see if alleles could be inherited together• He asked himself are all round seeds yellow?• Are all green seeds wrinkled?• He looked at two traits at the same time• Dihybrid cross • Ex: seed shape and seed color• His results were inconclusive which means all round

seeds were not yellow all wrinkled seeds were not green

In order to investigate, Mendel performed a dihybrid cross

• Dihybrid cross: crossed plants that differed in more than one trait

• Specifically Mendel looked at seed shape and seed color

Cross Fertilization

Homozygous Dominant Homozygous recessive

ALL heterozygous

Both Dominant traits

Dominant shape

Recessive colorDominant color

Recessive shape Both recessive traits

• • R-round• r-wrinkled• Y-Yellow• y-green

•

Friday 4/25/14

Mendel’s dihybrid cross

• P: true breed RRYY(Round Yellow) x rryy(wrinkled green)

• All F1: RrYy (Round Yellow)• Allowed F1 to self-fertilize which yielded the

following phenotypic ratio• F2: 9:3:3:1 ratio ofRound Yellow: Round green: wr Yellow: wr,green

• F1: Self Fertilization

• F1: self fertilization

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• Display of all possible genotypes

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Law of independent assortment

• Multiple traits are inherited independently of each other because alleles of genes are distributed independently during gamete formation

• Genes found on different chromosomes assort independently of each other during gamete formation

• Genes are inherited independently

What was the major question Mendel was trying to answer when he performed his dihybrid cross?

Mendel asked himself if two characteristics were inherited together.Specifically is seed color inherited with

seed shape?

Testcross

• Cross fertilize a dominant phenotype plant with a homozygote recessive plant

• WHY?• Purpose is to analyze the

ratio of the offspring• This will tell us the parents

genotype(homozygous dominant or

heterozygous)

What do we call this type of cross ad why would we perform it?

Test cross

• Determines the genotype of a dominant displayed phenotype

Testcross

• The only way to display the recessive phenotype is to have a homozygous recessive genotype

• After performing a testcross, If the f1 offspring display ALL dominant phenotypes then I know the Parent genotype is homozygous Dominant.

• If the offspring display 50% dominant phenotype and 50% recessive than the Parental genotype is heterozygous