Bellwork: Which fact interests you the most and why?

Genetics Mendelian Genetics & Patterns of Inheritance

Biology And Society: Testing Before Birth – Genetic testing Allows expectant parents to test for possibilities in their unborn child. Includes amniocentesis and CVS. Has risks associated with it.

The Role of Environment – Many human characteristics result from a combination of heredity and environment.

The Chromosomal Basis of Inheritance – The chromosome theory of inheritance states that Genes are located at specific positions on chromosomes. The behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns.

Figure 9.23

Linked Genes – Linked genes Are located close together on a chromosome. May be inherited together. – Sex chromosomes Influence the inheritance of certain traits. Due to linkage

Gregor Mendel The father of genetics

Gregor Mendel He was an Austrian monk. He is important because carried out the first important studies of heredity. He studied plants because plants have male & female parts so that they can reproduce sexually. Was the first person to analyze patterns of inheritance. Deduced the fundamental principles of genetics

Peas In an Abbey Garden – Mendel studied garden peas because These plants are easily manipulated. These plants can self- fertilize.

– Mendel carried out some cross- fertilization. – He also created true- breeding varieties of plants. – Mendel then crossed two different true- breeding varieties. Peas In an Abbey Garden

– Mendel performed many experiments. – He tracked several characteristics in pea plants from which he formulated several hypotheses. Peas In an Abbey Garden

Heredity The passing on of characteristics from parents to children (offspring).

Genetics The branch of biology that studies heredity.

Traits Inherited characteristics Often represented by single letters. Examples Tall plant = T Short plant = t Purple flowers = F White flowers = f

Allele The different forms of a gene for the same trait. For example if we look at a particular plant’s flower color we have two possibilities F (for purple flowers) and f (for white flowers). One allele comes from the female parent, one comes from the male parent.

Homozygous Two alleles of the same trait are the same Example: TT or tt

Heterozygous Two different alleles for the same trait Example Tt

Dominant The allele that is always displayed in a mixed (heterozygous Tt) cross. Represented by an upper case letter ex: T Tongue curling is a dominant trait.

Recessive A gene that is only displayed if both alleles are the same. Represented by a lower case letter ex: t The bent finger is dominant and the straight finger is recessive.

Question Is “W” dominant or recessive? Is “w” dominant or recessive?

Genetic Alleles and Homologous Chromosomes –Homologous chromosomes Have genes at specific loci. Have alleles of a gene at the same locus.

Phenotype What the organism looks like. Memory trick: PH in “phenotype” is like the PH in “photo” Example: red, white, furry, bald.

Genotype The genetic constitution of the organism. In other words the genes of that organism. Memory trick: GEN in “genotype” is like the GEN in “gene” Example: RR, rr, Rr

Question In a heterozygous cross of short plants and tall plants how would you represent the trait with letters?

Question In a heterozygous flower if the dominant trait’s genotype was for a purple phenotype and the recessive trait’s genotype was for a yellow phenotype. What would the flower’s phenotype be?

P Generation The parental generation These are true breeding plants. They will always produce the same traits. They are homozygous for a trait YY or yy

F1 Generation The first generation. These result after a cross from two parents of the P generation with different traits. Heterozygous Yy The F1 generation are often referred to as hybrids as they will have mixed genotypes but the same phenotype.

F2 Generation These are the offspring of a cross between the heterozygous F1 generation Yy X Yy These offspring will have mixed genotypes and phenotypes.

Bellwork 11/18/10 - Week 15 Monohybrid Cross – 1 trait Example: hair color B (blue hair) dominant b (white hair) recessive Make A Punnett Square Genotype Mother = BBWhat is the mother’s phenotype? Father = bb What is the father’s phenotype?

Question How do you set up a Punnett square for this cross?

Make a Punnett I Mother BB ( take one B and put it over each box) Father b b B B b b (colors used in genotypes to help you to see where each one goes in the box) Fill in the genotypes for each offspring B = blue hair b = white hair

Make a Punnett I Mother BB ( take one B and put it over each box) Father b b B B b b (colors used in genotypes to help you to see where each one goes in the box) bBbBbBbB bBbBbBbB What is the phenotype for each offspring? B = blue hair b = white hair

Make a Punnett I Mother BB ( take one B and put it over each box) Father b b B B b b (colors used in genotypes to help you to see where each one goes in the box) bBbBbBbB bBbBbBbB Blue Hair B = blue hair b = white hair

Question 1. How many white haired offspring are there? 2. How many blue haired offspring are there?

Answer or 4/4

Answer Both parents are Bb They both have blue hair

Mendel’s First Law This law states that allele pairs separate or segregate during the formation of eggs and sperm (gamete formation), and randomly come back together (unite) at fertilization. The Law of Segregation

Mendel’s Second Law Different traits are inherited separately (independently) of each other. The Law Of Independent Assortment

Mendel’s Third Law If a homozygous dominant parent (TT) is crossed with a homozygous recessive parent (tt) the offspring will ALWAYS be Tt, displaying the dominant phenotype. The Law Of Dominance

Question So how do we predict the probability of offspring types between two parents? Think about how we predict a coin flip: With a coin flip. 1 in 2 that it will be heads.

Punnett Square Used to show all possible combinations.

Question There are two parents who are both heterozygous for hair color, where blue was B and white was b What is the genotype for each parent? What is the phenotype for each parent?

Make a Punnett II Mother Bb ( take one B and put it over each box) Father B b B b b B (colors used in genotypes to help you to see where each one goes in the box) Fill in the genotypes for each offspring B = blue hair b = white hair What is the phenotype for each offspring?

Question 1. How many white haired offspring are there? 2. How many blue haired offspring are there?

Dihybrid Cross Used for two traits Example: R (round) dominantY (yellow) dominant r (wrinkled) recessivey (green) recessive Genotype Mother = RyrYWhat is the mother’s phenotype? Father = RyrYWhat is the father’s phenotype?

Dihybrid Cross Used for two traits Example: R (round) dominantY (yellow) dominant r (wrinkled) recessivey (green) recessive Genotype Mother = RYryWhat is the mother’s phenotype? Father = RYryWhat is the father’s phenotype?

Make a Punnett Mother RrYy ( take one allele pair and put it over each box) Father Rr Yy RYRY RYRY (colors used in genotypes to help you to see where each one goes in the box) Fill in the genotypes & phenotypes for each offspring R = round r =wrinkled Y = yellow y = green rYrY RyRy ryry rYrYRyRyryry

Question 1. How many round & yellow peas are there? 2. How many round & green peas are there? 3. How many wrinkled & yellow peas are there? 4. How many wrinkles & green peas are there?

Using a Testcross to Determine an Unknown Genotype – A testcross is a mating between An individual of unknown genotype and a homozygous recessive individual.

–The rule of multiplication states that The probability of a compound event is the product of the separate probabilities of the independent events. The Rules of Probability

Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall (TT & Tt) 25% short (tt) INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods

Incomplete Dominance, Codominance, Sex-Linked Traits & Multiple Alleles Beyond Mendel

Variations On Mendel’s Laws – Some patterns of genetic inheritance are not explained by Mendel’s laws.

Incomplete Dominance F1 hybrids in betweenphenotypes F1 hybrids have an appearance somewhat in between the phenotypes of the two parents. Example:snapdragons (flower) Example: snapdragons (flower) red (RR) x white (rr) RR = red flower rr = white flower r r RR

Incomplete Dominance r rRR All _____ = pink (heterozygous pink) produces the _____ generation

Incomplete Dominance

ABO Blood Type: An Example of Multiple Alleles and Codominance – Multiple alleles are traits that are controlled by more than two alleles.

Multiple Alleles continued Note: An individual can only have two alleles for any given trait, but the population can have many different alleles for that trait, sometimes over 100 different alleles for a single trait! Examples: Rabbit coat color, feather color, human hair color.

Codominance – Two of the human blood type alleles exhibit codominance. Both alleles are expressed in the phenotype.

Codominance Two alleles are expressed (multiple alleles) in heterozygous individuals. Example: blood type 1.type A= I A I A or I A i 2.type B= I B I B or I B i 3.type AB= I A I B 4.type O= ii

Codominance Problem Example:homozygous male Type B (I B I B ) x heterozygous female Type A (I A i) IAIA IBIB IBIB i

Another Codominance Problem Example:Example: male Type O (ii) x female type AB (I A I B )

Codominance Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) X girl - type AB (I A I B ) boy - type O (ii) X girl - type AB (I A I B )

Polygenic Inheritance – Polygenic inheritance is the additive effects of two or more genes on a single phenotype.

Bellwork Pre-AP Biology A red flower (RR) is crossed with a white flower (rr). 1. In the case of codominance what is the phenotype of the offspring? 2. In the case of incomplete dominance what is the phenotype of the offspring? 3. What generation is the offspring?

Sex-linked Traits Traits (genes) located on the sex chromosomes Traits (genes) located on the sex chromosomes Sex chromosomes are X and Y Sex chromosomes are X and Y XX genotype for females XX genotype for females XY genotype for males XY genotype for males Many sex-linked traits carried on X chromosome Many sex-linked traits carried on X chromosome

Sex-Linked Genes – Sex-linked genes Are any genes located on a sex chromosome. Were discovered during studies on fruit flies.

Sex-linked Traits Sex Chromosomes XX chromosome - femaleXy chromosome - male fruit fly eye color Example: Eye color in fruit flies

Sex-linked Trait Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X R Y x X r X r Remember: the Y chromosome in males does not carry traits. RR = red eyed Rr = red eyed rr = white eyed Xy = male XX = female XRXR XRXR y XrXr

Sex-Linked Disorders in Humans – A number of human conditions result from sex-linked (X-linked) genes.

Is characterized by a malfunction of light-sensitive cells in the eyes. Red-Green Color Blindness

Is characterized by a progressive weakening and loss of muscle tissue. Duchenne Muscular Dystrophy

Is a blood- clotting disease. Hemophilia

Female Carriers What is a carrier? Why are females usually carriers?

Pedigree Charts The family tree of genetics

Family Pedigrees – Mendel’s principles apply to the inheritance of many human traits.

A family pedigree Shows the history of a trait in a family. Allows geneticists to analyze human traits.

What is a Pedigree? A pedigree is a chart of the genetic history of family over several generations. Scientists or a genetic counselor would find out about your family history and make this chart to analyze.

Constructing a Pedigree Male Female

Connecting Pedigree Symbols Fraternal twins Identical twins Examples of connected symbols:

Connecting Pedigree Symbols Married Couple Siblings Examples of connected symbols:

Example What does a pedigree chart look like?

Symbols in a Pedigree Chart Has the trait X-linked Autosomal carrier Deceased

Interpreting a Pedigree Chart 1. Determine if the pedigree chart shows an autosomal or X-linked disease. – If most of the males in the pedigree are affected the disorder is X-linked – If it is a 50/50 ratio between men and women the disorder is autosomal.

Example of Pedigree Charts Is it Autosomal or X-linked?

Interpreting a Pedigree Chart 2. Determine whether the disorder is dominant or recessive. – If the disorder is dominant, one of the parents must have the disorder. – If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

Example of Pedigree Charts Dominant or Recessive?

Example of Pedigree Charts Dominant or Recessive?

Summary Pedigrees are family trees that explain your genetic history. Pedigrees are used to find out the probability of a child having a disorder in a particular family. To begin to interpret a pedigree, determine if the disease or condition is autosomal or X- linked and dominant or recessive.

Pedigree Chart -Cystic Fibrosis

Human Disorders Controlled by a Single Gene –Many human traits Show simple inheritance patterns. Are controlled by genes on autosomes.

Recessive Disorders – Most human genetic disorders are recessive. Individuals can be carriers of these diseases.

Figure 9.14

Dominant Disorders – Some human genetic disorders are dominant. Achondroplasia is a form of dwarfism. Huntington’s disease is another example of a dominant disorder

Evolution Connection: The Telltale Y Chromosome – Sex chromosomes Influence the inheritance of certain traits. The Y chromosome of human males is only about one-third the size of the X chromosome. Biologists believe that X and Y were once a fully homologous pair. Major episodes of change have rearranged pieces of the Y chromosome.

– Researchers recently used comparisons of Y DNA to confirm that the Lemba tribe in Africa descended from ancient Jewish people. Evolution Connection: The Telltale Y Chromosome

Off to the computer lab!!!! A Tour of Genetics