Mendel and Genetics Mr. Nagel

Meade High School

Warm Up Meiosis Review

• Consider the following about Meiosis:

– How many daughter cells are created? – How many chromosomes are in each daughter? – What words could be used to describe the

daughter cells? – What events in Meiosis lead to nearly infinite

possibilities in genetic variation?

IB Syllabus Statements • 4.1.1

– State that eukaryote chromosomes are made of DNA and proteins.

• 4.1.2 – Define gene, allele and genome.

• 4.3.1 – Define genotype, phenotype, dominant allele, recessive allele, codominant

alleles, locus, homozygous, heterozygous, carrier and test cross.

• 4.3.2 – Determine the genotypes and phenotypes of the offspring of a monohybrid cross

using a Punnett grid.

• 10.1.4 – State Mendel’s law of independent assortment.

• 10.1.5 – Explain the relationship between Mendel’s law of independent assortment and

meiosis.

http://click4biology.info/c4b/4/gene4.1.htm

Question?

• What is inheritance? – How does it relate to you personally? – Why does it matter to you and your future

family members?

Inheritance: Passing on traits by transmitting them from parents to offspring

Once Upon a Time…

• Gregor Mendel (1865) – Austrian Monk – A PAIR of factors control the expression of

each inherited trait in an organism

• Modern Thought

– These factors are called GENES and are segments of DNA

• Sutton (1900) – These factors are on chromosomes

Give “Peas” A Chance

• Why use pea plants? – What physical features could you monitor?

Factors Observed by Mendel

Mendel’s First Experiment

• What are the genotypes for each seed?

• Which trait is dominant?

• Which trait is recessive?

• Is the parental Spherical seed homozygous or heterozygous?

Down With the Lingo? • Gene • Allele • Genome • Dominant • Recessive • Homozygous • Heterozygous • Self-Pollination • Cross-Pollination • Parental Generation • Filial Generation • Independent Assortment • Segregation • Genotype • Phenotype

Down With the Lingo? • Gene – segment of DNA on a chromosome that controls a particular

trait • Allele – equivalent of Mendel’s ‘factor’ - several alternative forms of a

gene {one from each parent} • Genome – entire genetic makeup of an organism • Dominant – dominates the other factor of the trait • Recessive – masked in the presence of a dominant factor • Homozygous – when both alleles of a pair are the same • Heterozygous – when both alleles of a pair are NOT the same • Self-Pollination – mating with self (same plant) • Cross-Pollination – mating with a different plant • Parental – original generation • Filial – children (generation of offspring) • Independent Assortment – there is no connection AT ALL between

any given inherited trait (color and height, etc.) • Segregation – two factors (alleles) that a parent possess for a trait

are separated during egg/sperm formation • Genotype – genetic makeup of an organism • Phenotype – external appearance of an organism

Mendel and Meiosis

• Discuss with a partner: – What does independent assortment mean

in terms of what is observed in Meiosis? • Hint: Linkage is when two traits are known to

commonly exist together. – What does segregation mean in terms of

what is observed in Meiosis? • Hint: Disjunction is when the chromosomes

separate, sending one trait to each sex cell.

Punnett Grids • Graphical

representation of possible offspring

• Each parent occupies one side

• Each parental gene occupies one side of a ‘box’

• Based on ideas of Probability – In Meiosis, there is a

50/50 possibility that each trait is passed on. (Think coin flip)

Parental Genes

Mom 1 Mom 2

Dad 1 Kid 1

Kid 2

Dad 2

Kid 3

Kid 4

Punnett Grids

Punnett Grids

• What are the two parental genotypes?

• What are the two parental phenotypes?

• What are the offspring’s genotypes? Ratio?

• What are the offspring’s phenotypes? Ratio?

Homozygous Dominant (YY) x

Homozygous Recessive (yy)

Parental Genes

Dad 1 Dad 2

Mom 1 Kid 1

Kid 2

Mom 2

Kid 3

Kid 4

• What are the two parental genotypes?

• What are the two parental phenotypes?

• What are the offspring’s genotypes? Ratio?

• What are the offspring’s phenotypes? Ratio?

Homozygous Dominant (YY) x

Heterozygous (Yy)

Parental Genes

Dad 1 Dad 2

Mom 1 Kid 1

Kid 2

Mom 2

Kid 3

Kid 4

• What are the two parental genotypes?

• What are the two parental phenotypes?

• What are the offspring’s genotypes? Ratio?

• What are the offspring’s phenotypes? Ratio?

Heterozygous (Yy) x

Heterozygous (Yy)

Parental Genes

Dad 1 Dad 2

Mom 1 Kid 1

Kid 2

Mom 2

Kid 3

Kid 4

• What are the two parental genotypes?

• What are the two parental phenotypes?

• What are the offspring’s genotypes? Ratio?

• What are the offspring’s phenotypes? Ratio?

Warm Up Intro to Genetics Review

• How are Mendel’s laws associated with our

understanding of Meiosis? – Independent Assortment? – Segregation?

• Consider the trait for silliness. S (silliness) is dominant over s (serious). Create a Punnett Grid of a mating of two parents that are silly but produce a serious child.

IB Syllabus Statements • 4.3.2

– Determine the genotypes and phenotypes of the offspring of a monohybrid cross using a Punnett grid. • 10.2.1

– Calculate and predict the genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes.

• 4.3.3 – State that some genes have more than two alleles (multiple alleles).

• 4.3.4 – Describe ABO blood groups as an example of codominance and multiple alleles.

• 4.3.5 – Explain how the sex chromosomes control gender by referring to the inheritance of X and Y chromosomes in humans.

• 4.3.6 – State that some genes are present on the X chromosome and absent from the shorter Y chromosome in humans.

• 4.3.7 – Define sex linkage.

• 4.3.8 – Describe the inheritance of colour blindness and hemophilia as examples of sex linkage.

• 4.3.9 – State that a human female can be homozygous or heterozygous with respect to sex-linked genes.

• 4.3.10 – Explain that female carriers are heterozygous for X-linked recessive alleles.

• 4.3.11 – Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any of the above patterns of

inheritance.

http://click4biology.info/c4b/4/gene4.3.htm

Dihybrid Cross Parental Genes

Dad 1 Dad 2 Dad 3 Dad 4

Mom 1 Kid 1 Kid 2 Kid 3 Kid 4

Mom 2 Kid 5 Kid 6 Kid 7 Kid 8

Mom 3 Kid 9 Kid 10 Kid 11

Kid 12

Mom 4

Kid 13 Kid 14 Kid 15

Kid 16

Homozygous Dominant (TTYY) x

Homozygous Recessive (ttyy) Parental Genes

Dad 1 Dad 2 Dad 3 Dad 4

Mom 1 Kid 1 Kid 2 Kid 3 Kid 4

Mom 2 Kid 5 Kid 6 Kid 7 Kid 8

Mom 3 Kid 9 Kid 10 Kid 11

Kid 12

Mom 4

Kid 13 Kid 14 Kid 15

Kid 16

Heterozygous (TtYy) x

Heterozygous (TtYy) Parental Genes

Dad 1 Dad 2 Dad 3 Dad 4

Mom 1 Kid 1 Kid 2 Kid 3 Kid 4

Mom 2 Kid 5 Kid 6 Kid 7 Kid 8

Mom 3 Kid 9 Kid 10 Kid 11

Kid 12

Mom 4

Kid 13 Kid 14 Kid 15

Kid 16

Codominant I

• Imagine a cat that is black, and another that is white. – What if all the

offspring were gray?

– What if half the offspring were gray and half were white?

Parental Genes

Dad 1 Dad 2

Mom 1 Kid 1

Kid 2

Mom 2

Kid 3

Kid 4

Codominant II

• Consider two parents, one with type A blood and one with type B. – How could a child

of this mating have type O blood?

Parental Genes

Dad 1 Dad 2

Mom 1 Kid 1

Kid 2

Mom 2

Kid 3

Kid 4

Sex-Linked I

• Imagine a colorblind mom mating with a non-colorblind dad. – What predictions

could you make about the offspring?

– What do you notice about the boys?

Parental Genes

Dad 1 Dad 2

Mom 1 Kid 1

Kid 2

Mom 2

Kid 3

Kid 4

Sex-Linked II

• Imagine a hemophilic dad mating with a non-hemophilic mom. – What predictions

could you make about the offspring?

Parental Genes

Dad 1 Dad 2

Mom 1 Kid 1

Kid 2

Mom 2

Kid 3

Kid 4

Testcross

• What if we know the offspring phenotypes and/or genotypes, but don’t know one of the parents?

• Breed with a homozygous recessive!

Parental Genes

Dad 1 Dad 2

Mom 1 Kid 1

Kid 2

Mom 2

Kid 3

Kid 4

Fun With Traits • Pick a few traits from the list

below: – Dominant

• Widow’s peak • Dimples • Bent little finger • Mid-digital hair • Dwarfism • L-over-R Thumb folding • Detached Earlobes • Tongue Rolling

– Recessive • Hitch-hiker’s Thumb (90’) • Chin cleft

– Sex-Linked • Hemophilia • Red-green Colorblindness • Male Pattern Baldness

– Co-Dominant • Blood type • Flower Color (Red/White)

• Map out a Punnett Square based on the trait you selected, where mom and dad are both heterozygous for the condition or trait.

Where are Genes Located?

• http://www.ncbi.nlm.nih.gov/books/NBK22266/

Assessment • Imagine a parent

that is blue and another that is red. – Construct a Punnett

Square for each that demonstrates this mating if:

• ALL the offspring are Blue.

• ALL the offspring are Purple.

• HALF of the offspring are Red. (2)

Parental Genes

Dad 1 Dad 2

Mom 1 Kid 1

Kid 2

Mom 2

Kid 3

Kid 4

Warm Up Genetics Review

• Consider a parent with type A blood.

– What type of parental mating would determine the parent’s genotype? What is called?

– The parent is found to have the genotype Ao. List the possible offspring with a parent with genotype AB.

– What was the probability of having a child with the type blood:

• AB • A

Gizmo

• Observe outcomes predicted in Punnett Grids for: – Single Trait – Two traits – Aliens – Codominance

Warm Up Genetics Review

• Consider the following situation.

– Two parents, one possessing Nagel’s Disease and one perfectly healthy, mate. Describe the mode of inheritance and construct a Punnett Grid if:

• None of the children are visibly affected. (2 possible) • Half of the children are visibly affected. • Only the male offspring have the disorder.

IB Syllabus Statements • 4.3.12

– Deduce the genotypes and phenotypes of individuals in pedigree charts.

http://click4biology.info/c4b/4/gene4.3.htm

Pedigrees

http://www.sciencecases.org/hemo/hemo.asp

Pedigrees • Let’s take a look at

Queen Victoria’s son Leopold’s family. His daughter, Alice of Athlone, had one hemophilic son (Rupert) and two other children—a boy and a girl—whose status is unknown. – What is the probability

that her other son was hemophilic?

– What is the probability that her daughter was a carrier? Hemophilic?

– What is the probability that both children were normal?

Pedigrees • Now for the Spanish

connection: Victoria’s youngest child, Beatrice, gave birth to one daughter, one normal son, and two hemophilic sons. – Looking at the pedigree of the

royal family, identify which of Beatrice’s children received the hemophilic gene; why can you make this conclusion?

• Notice that Beatrice’s daughter, Eugenie, married King Alfonso XIII of Spain and had six children, one of whom was the father of Juan Carlos, the current King of Spain. – Would you predict that Juan

Carlos was normal, a carrier, or a hemophilic?

– What is the probability that her unnamed son was hemophilic?

Pedigrees • Lastly, the royal line of

Russia. – What are the

probabilities that all four of the girls were carriers of the allele hemophilia?

– Supposing Alexis had lived and married a normal woman, what are the chances that his daughter would be a hemophiliac?

– What are the chances his daughters would be carriers?

– What are the chances that his sons would be hemophiliacs?

Pedigree Practice

• Use the worksheets in small groups to determine the genotypes and phenotypes of the given subjects.

Warm Up Chi Square Test for Dihybrid Cross

• Chi Square Problem: An ear of corn has a total of 381 grains, including 216 Purple & Smooth, 79 Purple & Shrunken, 65 Yellow & Smooth, and 21 Yellow & Shrunken.

• Hypothesis: This ear of corn was produced by a dihybrid cross (PpSs x PpSs) involving two pairs of heterozygous genes resulting in a theoretical (expected) ratio of 9:3:3:1.

• Objective: Test the hypothesis using chi square and probability values. In order to test your hypothesis you must fill in the columns in the following Table.

http://waynesword.palomar.edu/lmexer4.htm

Warm Up Chi Square Test for Dihybrid Cross

• Chi Square Problem: An ear of corn has a total of 381 grains, including 216 Purple & Smooth, 79 Purple & Shrunken, 65 Yellow & Smooth, and 21 Yellow & Shrunken.

• Hypothesis: This ear of corn was produced by a dihybrid cross (PpSs x PpSs) involving two pairs of heterozygous genes resulting in a theoretical (expected) ratio of 9:3:3:1.

• Objective: Test the hypothesis using chi square and probability values. In order to test your hypothesis you must compare your value to that on the chart.

• Degrees of Freedom = ???

http://waynesword.palomar.edu/lmexer4.htm

Probability Lab

• Using pennies, we will model births to determine population statistics…

• Then we will use math to make similar predictions…

• Lastly, we will use pedigrees to illustrate why inbreeding allows recessive traits to become expressed frequently!

Warm Up Inheritance

• Given the parents AaBbCcDd and aabbccdd: – What are the chances of a child aabbCcDd? – What are the chances of a child AaBbCcDd? – What are the chances of a child AABBCCDD? – What are the chances of a child aaBbccDd?

IB Syllabus Statements • 10.3.1

– Define polygenic inheritance. • 10.3.2

– Explain that polygenic inheritance can contribute to continuous variation using two examples, one of which must be human skin colour.

http://click4biology.info/c4b/10/gene10.3.htm

Polygenes

• Polygenes have an additive effect… the more dominants you have, the more intense the feature: – Fingerprint Ridge Count – Eye Color – Skin Color

Warm Up Meiosis

• What event in Meiosis I accounts for the shuffling of traits amongst non-sister chromatids?

• Given a parent AaBb, what is the probability that AB will be passed on? – Which of Gregor Mendel’s laws dictates this? – Could this rule ever be broken?

IB Syllabus Statements • 10.2.1

– Calculate and predict the genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes.

• 10.2.3 – Explain how crossing over between non-sister chromatids of a

homologous pair in prophase I can result in an exchange of alleles.

• 10.2.4 – Define linkage group.

• 10.2.5 – Explain an example of a cross between two linked genes.

• 10.2.6 – Identify which of the offspring are recombinants in a dihybrid

cross involving linked genes. http://click4biology.info/c4b/10/gene10.2.htm

Heterozygous (TtYy) x

Heterozygous (TtYy) Parental Genes

Dad 1 Dad 2 Dad 3 Dad 4

Mom 1 Kid 1 Kid 2 Kid 3 Kid 4

Mom 2 Kid 5 Kid 6 Kid 7 Kid 8

Mom 3 Kid 9 Kid 10 Kid 11

Kid 12

Mom 4

Kid 13 Kid 14 Kid 15

Kid 16

What would you do?

• William Bateson & R.C. Punnett (early 1900s)

• Sweet pea plants – PpLl x PpLl

• P = purple eyes • p = red eyes • L = long pollen • l = round pollen

Phenotype Expected (9:3:3:1)

Observed

Purple, Long 3911 4831

Purple, Round 1303 390

Red, Long 1303 393

Red, Round 435 1338

TOTAL 6952 6952

Why does this happen? • Genes located on the same chromosome exhibit this

behavior if they are close to each other, but… • Genes on far ends of the same chromosome act ‘nearly

independent’… thus Gregor Mendel got really lucky!

Trait Phenotype Alleles Chromosome

Seed form round-wrinkled R-r 7

Seed color yellow-green I-i 1

Pod color green-yellow Gp-gp 5

Pod texture smooth-wrinkled V-v 4

Flower color purple-white A-a 1

Flower location axial-terminal Fa-fa 4

Plant height tall-dwarf Le-le 4

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/L/Linkage.html

A A a a B B b b

Read about it!

• http://biology.clc.uc.edu/courses/bio105/sex-link.htm

So what?

• Genes can be mapped based on their distance apart – Closer = less likely crossing over occurs

• A map unit is 1 cM, or centimorgan, and represents a 1% cross over rate – Shout out to Morgan’s work with flies and

discovering crossing over

Gene Maps In The Modern Age

• http://www.ncbi.nlm.nih.gov/books/NBK22266/

Recombinants

• Recombinants – Products of meiosis with allelic combinations

different from those of the haploid cells that formed the meiotic diploid.

– RESULT OF CROSSING OVER! • Re-combined DNA

– These appear as the lower than expected values in the observed matings