Mendelian Genetics Genetics the branch of Biology that

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Mendelian Genetics

Mendelian Genetics

Genetics the branch of Biology that deals with INHERITANCE (the passing of traits from

Genetics the branch of Biology that deals with INHERITANCE (the passing of traits from parents to offspring) Gregor Mendel ~Austrian monk who studied pea plants in the 1850’s ~theorized that characteristics are inherited as a result of the transmission of “factors” from parents to offspring (he didn’t know about genes & chromosomes!)

n Mendel used pea plants b/c he noticed contrasting traits: n. Tall plants vs.

n Mendel used pea plants b/c he noticed contrasting traits: n. Tall plants vs. short plants n. Green pods vs. yellow pods n. Wrinkled seeds vs. smooth seeds

“Brother Mendel, we grow tired of peas”

“Brother Mendel, we grow tired of peas”

~his work wasn’t valued until the early 1900’s when scientists began observing contrasting traits

~his work wasn’t valued until the early 1900’s when scientists began observing contrasting traits in Drosophila (fruit flies) and when better microscopes led to the discovery of chromosomes

Drosophila have short life cycles and few chromosomes and therefore are easy to study

Drosophila have short life cycles and few chromosomes and therefore are easy to study in genetics

Mendel is considered to be the “Father of Genetics”

Mendel is considered to be the “Father of Genetics”

The garden at Mendel’s Monastery

The garden at Mendel’s Monastery

II. The Gene-Chromosome. Theorychromosomes contain genes which have all the instructions for the traits

II. The Gene-Chromosome. Theorychromosomes contain genes which have all the instructions for the traits of an organism gene- -the unit of hereditary material found on chromosomes - genes are made of DNA allele- another word for gene ex) 2 alleles/genes for flower color: one white, one purple loci- Latin for “place”; the place/position on a chromosome where you find a gene/allele

Loci on fruit fly chromosome Add drosophila loci picture

Loci on fruit fly chromosome Add drosophila loci picture

n Homologous chromosomes: pairs of chromosomes that have genes for the same traits. You

n Homologous chromosomes: pairs of chromosomes that have genes for the same traits. You have 2 genes for every trait and they’re located on homologous chromosomes. XX (double stranded homologs) II (single stranded homologs)

III. Major Genetic Concepts III. Dominant Allele -the allele (gene) that is expressed if

III. Major Genetic Concepts III. Dominant Allele -the allele (gene) that is expressed if present -the “stronger” allele capital represented by a _____letter T example: tallness=______ Recessive Allele- the gene that isn’t expressed if dominant is present. - the “weaker”, rarer allele lower case represented by a _____letter example: lack of tallness (shortness)=_____t

Genotype- the genes (letters) of a trait described as homozygous or heterozygous ex) Dd;

Genotype- the genes (letters) of a trait described as homozygous or heterozygous ex) Dd; heterozygous DD; homozygous dominant dd; homozygous recessive Homozygous- also called pure when both genes are the same, either dominant or recessive. ex) TT, tt, DD, dd

Heterozygous- also called ____ hybrid -when both genes are different; one dominant, one recessive

Heterozygous- also called ____ hybrid -when both genes are different; one dominant, one recessive ex) Dd, Tt Phenotype- the physical appearance of a trait ex) tall, short, curly, straight (the genotype is the musical score and the phenotype is the music we hear) Ataxia video link

~Mendel wondered how he could cross 2 tall pea plants and end up w/some

~Mendel wondered how he could cross 2 tall pea plants and end up w/some tall & some short ~he theorized that the recessive trait can disappear in 1 generation and show up in the next generation as follows:

Genes T, t are SEGREGATED or separated during MEIOSIS Parents: x Tt Tt meiosis

Genes T, t are SEGREGATED or separated during MEIOSIS Parents: x Tt Tt meiosis T t fertilization TT F 1 possibilities Tt Tt tt All of the genes are RECOMBINED RANDOMLY during fertilization (this diagram is a graphical representation of a Punnet Square)

Law of Segregation and Recombination: Mendel explained that “factors” which occur in pairs are

Law of Segregation and Recombination: Mendel explained that “factors” which occur in pairs are separated from each other during gamete formation and recombined at fertilization. Law of Independent Assortment: Mendel concluded that different traits are inherited independently of one another (genes for different traits are separated & distributed to gametes independently of one another when they are on different chromosomes).

He learned this after doing dihybrid crosses which examine 2 traits (like pea color

He learned this after doing dihybrid crosses which examine 2 traits (like pea color & pea plant height); yellow peas aren’t always on tall plants… More on dihybrids to come…. .

PUNNETT SQUAREPredicts possible outcomes of a genetic cross T T Segregation. Only 1 gene

PUNNETT SQUAREPredicts possible outcomes of a genetic cross T T Segregation. Only 1 gene from each parent is passed along due to meiosis TT OR t Tt tt Results: 75% dominant 25% recessive Filling in the squares represents fertilization Which recombines genes

Problems: 1. If a heterozygous freckled person marries a non-freckled person, what is the

Problems: 1. If a heterozygous freckled person marries a non-freckled person, what is the chance that they will have a non-freckled baby? Freckles (F) no freckles (f) F f f Ff ff 50% chance of Non-freckled (ff) baby

2. The gene for brown eyes (B) is dominant over the gene for blue

2. The gene for brown eyes (B) is dominant over the gene for blue eyes (b). Show the results of a cross between a hybrid brown-eyed woman and a hybrid brown-eyed man. B=brown b=blue B b phenotype B BB Bb bb genotype 75% brown 50% Bb 25% blue 25% BB 25%bb

3. Normal skin pigmentation (A) is dominant over albino (a). Show the cross of

3. Normal skin pigmentation (A) is dominant over albino (a). Show the cross of an albino man with a woman who is homozygous normal. A= normal a=albino A a a A Aa Aa phenotype 100% normal genotype 100% heterozygous

Ff tt Bb hh +, + mm CC freckled non taster brown no disease

Ff tt Bb hh +, + mm CC freckled non taster brown no disease has blood factor light skin color vision

Ff freckeld TT Taster bb blond hh no disease +, - has blood factor

Ff freckeld TT Taster bb blond hh no disease +, - has blood factor mm light skin Cc color vision

ff tt BB Hh no freckles non taster brown hair has disease -, MM

ff tt BB Hh no freckles non taster brown hair has disease -, MM cc doesn’t have blood factor dark skin color blind Can’t tell if he was Ff or ff yes FF Can’t tell if parents were Tt or tt Can’t tell if parents were Bb or bb yes brown dark Can’t tell if parents were Cc or cc

Intro to dihybrid crosses (not in note pkt) As Mendel continued his study of

Intro to dihybrid crosses (not in note pkt) As Mendel continued his study of peas, he noticed that different traits (pea color, pea shape) were inherited independently of one another. When he crossed yellow x yellow, the F 2 smooth generation had : yellow, green, green smooth wrinkled

We know now, that during meiosis, genes for different traits are separated and distributed

We know now, that during meiosis, genes for different traits are separated and distributed to gametes independently of one another. (when they’re on different chromosomes). Genes located on the same chromosome do NOT sort independently (aka gene linkage). Breeding experiments that examine 2 different traits are called dihybrid crosses

Dihybrid Crosses In guinea pigs, black coat color (B) is dominant to albino (b);

Dihybrid Crosses In guinea pigs, black coat color (B) is dominant to albino (b); coarse coat (R) is is dominant to smooth (r). Two animals are selected for breeding. Their genotypes are BBRR and bbrr. Give the results of the following including expected genotypes and phenotypes of: a) the F 1 generation b) the F 2 generation c) offspring produced from a cross of an F 1 pig with one having genotype BBRr

a) BBRR x bbrr BR br Bb. Rr 100% black course pure parents gametes

a) BBRR x bbrr BR br Bb. Rr 100% black course pure parents gametes F 1 generation

b)F 2: Bb. Rr x Bb. Rr BR Br b. R br BR BR

b)F 2: Bb. Rr x Bb. Rr BR Br b. R br BR BR Br b. R br possible gametes Br b. R br BR BBRr Bb. RR Bb. Rr BBrr Bb. Rr Bbrr Bb. RR Bb. Rr bb. RR bb. Rr Bbrr bb. Rr bbrr Br b. R br Key B=black b=albino R=Coarse r=smooth Phenotype results 9 black coarse 3 black smooth 3 albino coarse 1 albino smooth 9: 3: 3: 1

c)Bb. Rr x BBRr BR Br b. R br BR Br BR BBRr Br

c)Bb. Rr x BBRr BR Br b. R br BR Br BR BBRr Br BBRr BBrr b. R Bb. Rr br Bb. Rr possible gametes Bbrr Phenotype results 6 black coarse 2 black smooth

Statistically: If x = the number of traits in the cross x 2 =

Statistically: If x = the number of traits in the cross x 2 = # phenotypes x 3 = # genotypes x 4 = # individuals Monohybrid Results: 2 phenotypes 3 genotypes 4 individuals Tt x Tt

Dihybrid Tt. Bb x Tt. Bb 2 Results: (2) = 4 phenotypes (3)2= 9

Dihybrid Tt. Bb x Tt. Bb 2 Results: (2) = 4 phenotypes (3)2= 9 genotypes 2 (4) = 16 individuals Trihybrid Tt. Bb. Rr x Tt. Bb. Rr Results: (2)3= 8 phenotypes 3 (3) = 27 genotypes 3 (4) = 64 individuals 9: 3: 3: 1

Dihybrid Problems…. answers 1. L= long l = vestigal G = gray g =

Dihybrid Problems…. answers 1. L= long l = vestigal G = gray g = ebony F 1 llgg x LLGG LG lg Ll. Gg 100% Ll. Gg; long, gray

F 2 Ll. Gg x Ll. Gg LG Lg l. G lg LG LLGg

F 2 Ll. Gg x Ll. Gg LG Lg l. G lg LG LLGg Ll. GG Ll. Gg Lg LLGg LLgg Ll. Gg Llgg l. G Ll. Gg ll. GG ll. Gg lg Ll. Gg Llgg ll. Gg llgg 9 long gray 3 long ebony 3 vest. gray 1 vest ebony

2. R= red r = yellow T = tall t = dwarf F 1

2. R= red r = yellow T = tall t = dwarf F 1 RRtt x rr. TT Rt r. T Rr. Tt 100% Rr. Tt; tall, red

F 2 Rr. Tt x Rr. Tt RT Rt r. T rt RT RRTt

F 2 Rr. Tt x Rr. Tt RT Rt r. T rt RT RRTt Rr. TT Rr. Tt Rt RRTt RRtt Rr. Tt Rrtt r. T Rr. Tt rr. TT rr. Tt rt Rr. Tt Rrtt rr. Tt rrtt 9 red tall 3 red short 3 yellow tall 1 yellow short

3. T = taste t = non taste N = normal pigment n =

3. T = taste t = non taste N = normal pigment n = albino from his mother from her father Mom: tt. Nn x Dad: Ttnn t. N tn Tn Tt. Nn Ttnn tn tt. Nn ttnn 25% taster, normal 25% taster, albino 25% non-taster, normal 25% non-taster, albino

4. B= bark b = silent E = erect ears e = droopy ears

4. B= bark b = silent E = erect ears e = droopy ears Ee. Bb x eebb eb EB Eb e. B Ee. Bb Eebb ee. Bb eb eebb 25% each: erect barking erect silent drooping barking drooping silent

Intermediate Inheritance Many genes do not follow the patterns of dominance: may produce a

Intermediate Inheritance Many genes do not follow the patterns of dominance: may produce a trait between the 2 parents. INCOMPLETE DOMINANCE (blending) red flowers + white flowers = pink flowers “R” + “W” = “RW”

OR May produce a trait that expresses 2 dominant alleles at the same time

OR May produce a trait that expresses 2 dominant alleles at the same time : CODOMINANCE red fur + white fur = red & white fur C R+ CW = C RC W Ex) blood type AB: IAIB

Test Cross: Consider a phenotypically tall organism. What is it’s genotype? Is it TT

Test Cross: Consider a phenotypically tall organism. What is it’s genotype? Is it TT or Tt? To answer this question, you would do a test cross: definition: when an organism showing the dominant trait is crossed with a pure recessive to determine if that dominant organism is homozygous or heterozygous *By observing the phenotypes of the offspring, we can trace back to the genotype of the parent: If the genotype of the parent was homozygous (TT), T all the offspring are tall: T t Tt Tt If the genotype of the parent was heterozygous (Tt), T 50% of the offspring are tall and 50% are short: t Tt tt t

Problem: 1. A cattle rancher buys a black bull which is supposed to be

Problem: 1. A cattle rancher buys a black bull which is supposed to be a purebred. Black coat is dominant to red. The new owner decides to be sure he has gotten a good deal by mating the bull with several red cows. Such crosses are called test crosses. If the farmer really got a good deal, what color calves should be born? B B b Bb Bb b B= black b= red They should all be black

Multiple Alleles: ~when there are more than 2 (“multiple”) alleles for a trait ~example:

Multiple Alleles: ~when there are more than 2 (“multiple”) alleles for a trait ~example: Human blood groups have 3 alleles: IA where I is dominant IB and i is recessive i ~the possible combinations of these 3 blood alleles are as follows: Blood type Phenotype genotype A IAIA or IAi B IBIB or IBi AB IA IB ii O

Problems: 1. A couple preparing for marriage have their blood typed along with the

Problems: 1. A couple preparing for marriage have their blood typed along with the other required blood tests. Both are type AB. They ask what types of blood their children may have. What will you tell them? I I A I B A A A I I A B I I I B A B I I B B I I Phenotype Genotype 50% AB IAIB 25% A IAIA 25% B IBIB

2. A type A person marries a type A person. Their firstborn has type

2. A type A person marries a type A person. Their firstborn has type O blood. What are the genotypes of the parents and the child? parent ___ IA i I A IA IA IA i parent ___ IA i child ___ i i i IA i ii Each parent must have a recessive gene to give to the child

3. A wealthy, elderly couple die together in an accident. Soon a man shows

3. A wealthy, elderly couple die together in an accident. Soon a man shows up to claim their fortune claiming that he is their long lost son. Other relatives dispute the claim. Hospital records show that the deceased couple were blood types AB and O. The person claiming to be their son was type O. Do you think the man is an imposter? i IA IB A B I i 50% A 50% B He was an imposter! i A I i B I i

Sex Determination: ~there are 2 types of chromosomes: sex chromosomes (1 pair) autosomes (all

Sex Determination: ~there are 2 types of chromosomes: sex chromosomes (1 pair) autosomes (all other pairs) ~in each diploid human cell this looks like: sex chromosomes 1 pair autosomes 22 pairs 46 23 homologous pairs or _____chromosomes female ~The genotype XX represents a ________ male ~The genotype XY represents a ________ sperm ~The sex of an individual is determined by the ________ at fertilization the time of____________. X chromosomes while the human ~The human egg contains only ______ X or _______ Y chromosomes. sperm can contian either ______ X XX XX Y XY XY Every time a man and woman have a child there is a 50 / 50 chance it ____ will be a boy or girl.

Sex Linkage: ~sex-linked traits are caused by genes found on the X chromosome ~sex-linked

Sex Linkage: ~sex-linked traits are caused by genes found on the X chromosome ~sex-linked traits are recessive ~since they are recessive, fewer females are afflicted with these traits because they have another X chromosome which is dominantly normal. Males have only one X chromosome so when they have a sex-linked gene, they’ll display the trait. ~the genotype of a sex-linked trait is represented as_____ X or X (can also be represented as Xh, where h is the trait) ~females with one gene for the trait ( X X ) are called_______ carriers ~examples of sex-linked traits: hemophilia, colorblindness

1. A man normal for blood clotting marries a woman who is a carrier

1. A man normal for blood clotting marries a woman who is a carrier for hemophilia. What are the chances they will have a child with hemophilia? X X Y XX H or X XY H H X Y XX XY or XHXh X h. Y 25% chance of a child with hemophilia: 25% normal female (XX) 25% carrier female (XX) 25% normal male (XY) 25% hemophila male (XY)

2. What is the probability that a woman with normal vision who marries a

2. What is the probability that a woman with normal vision who marries a colorblind man will have a colorblind child? X XX XX Or XHXh Y XY X HY XHXh XY X HY 0% chance: 50% carrier females 50% normal males

3. A man with a normal vision and a woman with normal vision have

3. A man with a normal vision and a woman with normal vision have 3 sons. Two of the sons have normal color vision and one of them is color-blind. What are the probable genotypes of the parents? X X XX or Xh. XH X XX X HX H Y XY Xh. Y XY X HY XY and XX ; The gene for color blindness must be hidden/carried by mother to be passed on

The Y chromosome

The Y chromosome

Pedigree charts: used to show he presence or absence of certain trait in families

Pedigree charts: used to show he presence or absence of certain trait in families through several generations. **they’re kind of like a “genetic family tree” Bb bb bb Bb Bb bb Bb a

1 X X X Y XX XY 3

1 X X X Y XX XY 3

Human Pedigree A diagram showing the transmission of a trait through several generations of

Human Pedigree A diagram showing the transmission of a trait through several generations of a family is called a pedigree. In Figure 1, generation 1 is made up of grandparents, generation II is their children, and generation III is their grandchildren. 1. Study the pedigree diagram and the key in Figure 1 to learn the symbols.

1. How many generations are shown? _____ 3 5 2. How many men are

1. How many generations are shown? _____ 3 5 2. How many men are shown? _____ women? _____ 3. How many women have cystic fibrosis? _____ 9 2 4. How many men have cystic fibrosis? _____1 5. How many marriages are shown? _____ 4 5 6. How many single women are in the family? _____ 4 7. How many children are there? _____ 5 8. How many grandchildren are there? _____ 9. Do you think the gene for cystic fibrosis is dominant or recessive? ___________________________ Recessive b/c it remains “hidden” in several people

Use A to represent the allele for the ability to taste PTC, a dominant

Use A to represent the allele for the ability to taste PTC, a dominant allele. Use aa for the PTC nontaster, who exhibits the recessive trait. Aa aa aa aa Aa Aa