Mendel and Genetics Mr. Nagel

Meade High School

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

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.

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?

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?

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

Gizmo

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

Beyond Mendel…

• What other systems exist for gene expression? – Simple Dominance (A or a) – Co-Dominance (equal expression of alleles) – Sex-Linked (alleles only on X chromosome)

• Girls = XX = two alleles • Guys = XY = one allele

• How do we test for unknown genotypes? – Testcross to determine AA or Aa

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 Purple.

• ALL the offspring are Blue.

• ALL of the sons are red.

Parental Genes

Dad 1 Dad 2

Mom 1 Kid 1

Kid 2

Mom 2

Kid 3

Kid 4

Intro

• http://www.ndsu.edu/pubweb/~mcclean/plsc431/mendel/mendel9.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?

Polygenes

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