GENETICS - CLUTCH CH.2 MENDEL'S LAWS OF INHERITANCElightcat-files.s3.amazonaws.com/packets/admin_genetics-18-genetic… · 1. Assume you have mated a homozygous dominant purple, square

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GENETICS - CLUTCH

CH.2 MENDEL'S LAWS OF INHERITANCE

CONCEPT: MENDELS EXPERIMENTS AND LAWS

Mendel’s Experiments

● Gregor Mendel was an Austrian monk who studied Genetics using pea plants □ Mendel used pure lines meaning that all offspring produced by pure line mating will be ___________ for that trait

- Ex: Yellow-seeded pure line mating will produce yellow-seeded offspring

□ Mendel labeled each ___________________________ in a specific way

- Parental (P) Generation: Is the first mating that occurs

- First Filial (F1) Generation: is the offspring produced from parental mating

- These often undergo self-mating where one plant’s pollen is used to fertilize itself

- Can also undergo cross-fertilization where one plant’s pollen is used to fertilize another plant

- Second Filial (F2) Generation: is the offspring produces from F1 mating

EXAMPLE: One of Mendel’s Crosses

X Parental

F1 F1 were “selfed” – meaning self-mating

F2

6022 2001 = 8023 total F2 plants ¾ ¼ 3:1 ratio

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Each F2 plant was “selfed”

1. F3 from yellow F2 ¾ ¼

2. F3 from green F2 100% Then, he did a different cross. He mated a F1 yellow with a green X ½ ½ At the end of these crosses he knew

1. Yellow seeded plants always produced at least some yellow seeded offspring 2. Selfed, green seeded plants only produced other green seeded offspring 3. The green seeded plant trait could skin generations

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Mendel’s Laws ● By studying pea plants, Mendel came up with certain properties and __________________ that govern inheritance □ The properties include:

- There is a heredity factor (gene) that is necessary for producing a certain trait

- This gene comes in two forms (alleles)

- One form (allele) is dominant to the other

□ Mendel’s Laws include:

1. Law of segregation: Alleles separate (during meiosis) to form gametes.

- Each gamete contains a ____________________ allele for each trait

2. Law of Dominance: Some alleles are dominant, and others are recessive

3. Law of independent Assortment: Genes for different traits segregate into gametes independently

- Genes are randomly, and independently, put into gametes

EXAMPLE: A cross of white (W) and red (R) flowers

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PRACTICE:

1. Which of the following Mendel’s postulates states that alleles separate in the formation of gametes? a. Law of segregation b. Law of dominance c. Law of independent assortment d. Law of dividing cells

2. True or False: Breeding two pure-lines of yellow-seeded flowers will always produce yellow-seeded offspring a. True b. False

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3. What is the official genetics term for the second generation of offspring? a. Parental generation b. F1 generation c. F2 generation d. Grandchildren

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CONCEPT: DIPLOID AND HAPLOID GENETICS

Diploid Genetics

● Understanding allele combinations is extremely important in understanding genetics □ There are many important _____________________ to remember:

- Alleles are variants for a particular trait, in diploid organisms there are two alleles per gene

- Alleles can be dominant or recessive; The dominant trait is always seen when it is present

- Homozygous means that there are two of the same alleles; heterozygous means two different alleles

- Each gene sits at a specific chromosomal locus

EXAMPLE: Alleles

□ Genes lie on _________________________________

- In Diploid cells, there are two chromosome copies

- Each chromosome contains one allele

- During meiosis these chromosomes are replicated once, but divided into daughter cells twice

- Creates four haploid gametes (sex cells)

Identical Allelesat 1 gene locus(Homozygous) Heterozygous

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EXAMPLE: Chromosomes and Meiosis

A a

Homologous Pair

Replication

A aA a

Tetrad

Dyad

Division #1

AA a a

1 cell (n) 1 cell (n)

1 cell (2n)

1 cell (2n)

Sister Chromatid

Division #2

A A a a

1 cell (n) 1 cell (n) 1 cell (n) 1 cell (n)

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□ Chromosomes have a distinct ___________________________

- A centromere is a condensed region of the chromosome

- It can be metacentric (in center), submetacentric (off-center), acrocentric (at one end),

- The p arm is the shorter arm and the q arm is the longer arm

- Determined by the length between centromere and end of chromosome

EXAMPLE:

Metacentric

submetacentric

acrocentric

p arm

q armCentromere

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Haploid Genetics

● In haploid cells, there is only one ___________________ per gene □ Wild type and mutant alleles have different symbols

- WT allele looks like a+ ; Mutant allele looks like a

- When opposite mating types fuse – it creates a diploid combination (a+/a) called a meiocyte

- These can be replicated and divided into haploid cells containing either a+ or a

EXAMPLE: Haploid cell creation

a+ a

Fuse

a+/a

a+/a+/a/a

a+ aa+ a

Replicate

Divide

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PRACTICE: 1. Which of the following describes an acrocentric chromosome?

a. The p arm is longer than the q arm b. The centromere is located at the center of the chromosome c. The centromere is located at the end of the chromosome d. The p arm and q arm are the same length

2. In diploid organisms there are _______ chromosomal copies. In haploid organisms there is _______ chromosomal copy.

a. One, two b. Two, one c. Two, four d. Four, two

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3. After a diploid cell undergoes meiosis, it divides to produce… a. Two diploid cells b. Two haploid cells c. Four diploid cells d. Four haploid cells

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CONCEPT: MONOHYBRID CROSS

● A monohybrid cross is a mating between two organisms with different alleles at a single gene □ Remember: The alleles can be presented in different ways

- Dominant, recessive (A=dominant, a=recessive)

- Wild Type, Mutant (+ = WT, a = mutant)

1. Two heterozygous purple plants 2. WT winged fly with mutant short-winged fly

Genotypes Genotypes

Mother: ________________ Mother: ________________

Father: _________________ Father: _________________

Phenotypes Phenotypes

Mother: ________________ Mother: ________________

Father: _________________ Father: _________________

Genotypes _______________________________ Genotypes ______________________________ Phenotypes _______________________________ Phenotypes ______________________________

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PRACTICE

1. A black and white rabbit were mated. All F1 offspring were black, and the F2 offspring is made up of approximately ¾ black and ¼ white rabbits.

a. Draw out two Punnet squares detailing both matings. b. Supposed two white F2 offspring were mated. What would be the phenotype and genotype of the F3

offspring? (a) White, aa (b) White, Aa (c) Black, Aa (d) Black AA

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2) Green scales (G) in a particular species of fish is dominant over blue scales (g). The following crosses are carried out, producing the progeny shown. Write out all possible genotypes of the parents in each cross.

Parents Progeny Genotypes of Parents

a) Green x Green 4 green, 2 blue __________________ b) Green x Green 8 green __________________ c) Green x Blue 12 green __________________ d) Green x Blue 3 green, 1 blue __________________ e) Blue x Blue 2 Blue __________________

3) Which of the following offspring ratios is expected from a Mendelian heterozygous cross examining one gene?

a) 2:2 b) 3:1 c) 9:3:3:1 d) 4:2:1

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4) Human albinism is a simple recessive trait. Determine the genotypes of the parents for each offspring combination i. A wild-type male and albino female have 6 wild-type children

a. AA x aa b. Aa x Aa c. aa x aa d. AA X AA e. AA x Aa

ii. A wild-type male and albino female have 8 children, 4 wild-type, and four albino a. AA x aa b. Aa x Aa c. Aa x aa d. AA X AA e. AA x Aa

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CONCEPT: DIHYBRID CROSS

Punnet Square

● A dihybrid cross is a mating occurring between organisms containing two different traits

□ Typically written like BbSs (heterozygous)

□ Done for genes that independently assort

- Inheriting one trait will not affect the inheritance of the other trait (Ex. color and shape)

□ Two methods of doing a dihybrid cross

1. Punnet Square

2. Branch Diagram

1. Punnet Square

Starting Genotypes

Mother: Yy Rr

Father: Yy Rr

Starting Phenotypes

Mother: Yellow, round

Father: Yellow, Round

1. What is the probability of having a yellow round offspring? ________________

2. What is the probability of having a yellow wrinkled offspring? ________________

3. What is the probability of having a green round offspring? ________________

4. What is the probability of having a green wrinkled offspring? ________________

□ The common dihybrid ratio is 9:3:3:1

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Branching Diagram

2. Branching Diagram

□ Branching diagram uses math to calculate the the probability of certain genotypes?

Starting Genotypes

Mother: Yy Rr

Father: Yy Rr

Starting Phenotypes

Mother: Yellow, round

Father: Yellow, Round

Steps

1. What is the probability of the offspring being yellow? Or green?

2. What is the probability of the offspring being round? Or wrinkled?

__________ Yy , Yellow

__________ yy, Green

Rr round

rr wrinkled

rr wrinkled

Rr round

Yellow Round

Yellow Wrinkled

Green Round

Green Wrinkled

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PRACTICE

1. Assume you have mated a homozygous dominant purple, square plant with a homozygous recessive pink, spherical plant. What is the proportion of purple and spherical plants that would be produced in the F2 generation?

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2. Write out all of the following gametes that can be produced from individuals with the following genotypes.

a. AaBB

b. AaBb

c. AaBbCc

d. AaBbcc

3. Two organisms with the genotypes Aa bb Cc Dd Ee and Aa Bb Cc dd Ee were crossed. Use the branch method to determine the proportion of the following genotypes in the offspring.

I. aa bb cc dd ee a. 1/256 b. 1/64 c. 1/16 d. 1/4

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II. Aa bb Cc dd ee a. 1/256 b. 1/64 c. 1/16 d. 1/4

III. AA BB CC Dd ee

a. 1/256 b. 1/64 c. 1/16 d. 0

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3. In melons, spots (S) are dominant to no spots (s) and bitterness (B) is dominant to sweet (b). Answer the following questions that arise from a crossing of a homozygous dominant plant with a homozygous recessive plant. Assume Mendelian inheritance.

I. What is the F2 phenotypic ratio if the F1 generation is intercrossed? a. 12:3:1 b. 4:3:2:1 c. 9:3:3:1 d. 3:1

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CONCEPT: SEX-LINKED GENES

● Humans have two ________________ chromosomes, X and Y

□ The Y chromosome has certain characteristics

- The Y chromosome contains only a few dozen genes

- SRY gene determines maleness

- It is hemizygous because there is only one Y chromosome

□ The X chromosome, unlike the Y, contains hundreds of genes for multiple _______________________ functions

- Both the X and Y have pseudoautosomal regions 1 and 2, which help pair the X and Y together

- During meiosis, the X and Y act as a pair, so that they can segregate equally into sperm

- Nondisjunction occurs when chromosomes fail to separate properly

- XXX, XXY, XO, OY

EXAMPLE:

□ Sex-linkage is when genes located on the sex chromosomes show certain _______________________ patterns

- X-linkage is when there are mutant alleles on the X chromosome

- Y-linkage is when there are mutant alleles on the Y chromosome

- Sex-limited inheritance is when expression of a phenotype is absolutely limited to one sex

- Example: Different coloration or size in males/females

- Sex-influenced inheritance is when the sex of an individual influences the expression of a phenotype

- Gene expression is dependent on male/female hormones

- Example: Pattern Baldness

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EXAMPLE: X-Linkage and eye colors in Drosophila

P

F1

Cross F1 males and females F2

Red-eyed female w+/w+

White-eyed male w/y

X

Red-eyed females/males w+/w or w+/y

Red-eyed males/females 3/4

White-eyed males 1/4

3

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EXAMPLE: X-linkage and eye colors in Drosophila - reciprocal cross P

F1

F2

X

White-eyed female w/w

Red-eyed male w+/y

Red-eyed Females w+/w 1/2

White-eyed males w/y 1/2

Red-eyed females/males w+/w or w+/y

1/2

White-eyed females/males w/w or w/y

1/2

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PRACTICE

1. Which of the following sex chromosome pairs is caused from nondisjunction? a. XX b. XY c. ZZ d. XXY

2. Which of the following is an example of sex-limited inheritance? a. Pattern baldness in humans b. Male doves are white, while female doves are brown c. Klinefelter’s disease d. Men tend to be taller than women

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CONCEPT: PROBABILITY AND GENETICS

● To predict the genotypes and phenotypes of offspring, geneticists use probability ____________________ □ Product Law – multiply the probability of independent events occurring together

- Ex: Tossing a penny and a nickel – each has a ½ chance of being heads

- Probability of both being heads will be ½ x ½ = ¼ or 25%

- Use this when two independent events are occurring together

□ Sum Law – add the probability of independent occurring together

- Ex: Tossing a penny and a nickel – each has ½ chance of being heads

- Probability of one being heads and other being tails will be ¼ + ¼ = ½ or 50%

- Use this when the events could occur in more than one way

□ Binominal Theorem: Used when there are alternative ways to achieve a combination of events

1. What is the probability that in family with four children, two will be male and two will be female?

Option 1

- (a + b)n a = male probability = ½ and b = female probability = ½

- (a + b)4 = a4 + 4a3b + 6a2b2 + 4ab3 + b4

- Each of these terms represents a different outcome

- a4 = probability of having four males

- 6a2b2 = probability of having two males, two females

6(1/2)2(1/2)2 = 3/8

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Option 2

- N = s + t ; n=total number of events, S = # of times a occurs t = # of time b occurs

- 4 = 2 + 2

PRACTICE

1. Use the product law to calculate the probability that mating two organisms with the genotype of AaBbCcDd will produce offspring with the genotype of AA bb Cc Dd?

a. 1/4 b. 1/16 c. 1/64 d. 1/128

4!2! 2!

(1/2)2 (1/2)2

p = 3/8

p =

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2. In a family of five children what is the probability that… I. Three are males and two are females

a. 0.31, 31% b. 0.5, 50% c. 0.25, 25% d. 0.10, 10%

II. All are females a. 0.031, 3.1% b. 0.31, 31% c. 0.25, 25% d. 0.10, 10%

III. Two are males and three are females a. 0.31, 31% b. 0.5, 50% c. 0.25, 25% d. 0.10, 10%

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3. In a family of six children, where both parents are heterozygous for albinism, what is the probability that four are normal and two are albinos?

a. 0.50, 50% b. 0.25, 25% c. 0.30, 30% d. 0.10, 10%

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CONCEPT: PEDIGREES

● A pedigree is a map of human matings □ A propositus is the family member who first comes to the attention of a geneticist

□ Pedigrees use many symbols

□ In Genetics, you’ll be given a pedigree and asked to identify the inheritance pattern

Male

Female

Mating

Parents and

Chidlren

Twins

Affected Male

Affected Female

Heterozygotes forautosomal recessive

Death

Propositus

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Autosomal Inheritance

1. Autosomal Recessive Disorders

- Affected individuals appear in offspring of unaffected parents

- Affected offspring include both males and females

- There are only a few affected offspring

EXAMPLE:

2. Autosomal Dominant Disorders

- Phenotype appears in every generation of pedigree

- Affected parents pass the phenotype to their children

- Are rare, but normal allele is recessive

EXAMPLE:

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3. Autosomal Polymorphisms

- Polymorphism existence of two or more common phenotype of a trait

- Examples include: widow’s peak, tasting PTC, attached/free earlobes

- Inherited in standard Mendelian manner

EXAMPLE:

Sex-linked inheritance

4. X-Linked Recessive Disorders

- More males than females are affected

- An affected male parent will not have affected offspring, but all daughters will be carriers

- Sons of affected males will not pass it to their offspring

- Ex: red-green colorblindness

EXAMPLE:

Nontasters (tt)

Tasters (Tt or TT)

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5. X-linked Dominant Disorders

- Affected males pass condition to all daughters, but no sons

- Affected heterozygous females who mate with unaffected males pass condition to ½ of all offspring

EXAMPLE:

6. Y-linked Disorders

- Only males inherit it

- Very rare

EXAMPLE:

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Pedigree Flowchart

Do all affected individuals have an affected parent?

Yes No

Does the trait affect mostly males?Do all the affected males have an affected mother

Yes No NoYes

X-Linked Recessive

Autosomal Recessive

Autosomal Dominant

Does an affected fatherproduce daughters who areall affected?

YesNo

Does an affected fatherproduce sons who are all not affected?

Yes

No

X-LinkedDominant

Are all the sons ofan affected fatheralso affected?

Y-Linked

No

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PRACTICE:

1. This pedigree exhibits which of the following inheritance patterns? a. Autosomal Dominant b. Autosomal Recessive c. X-linked Dominant d. Autosomal Polymorphism

2. This pedigree exhibits which of the following inheritance patterns? a. Y-Linked b. Autosomal Recessive c. X-linked Dominant d. Autosomal Polymorphism

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3. This pedigree exhibits which of the following inheritance patterns? a. Autosomal Dominant b. X-linked Recessive Recessive c. X-linked Dominant d. Autosomal Polymorphism

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GENETICS - CLUTCH CH.2 MENDEL'S LAWS OF INHERITANCElightcat-files.s3.amazonaws.com/packets/admin_genetics-18-genetic… · 1. Assume you have mated a homozygous dominant purple, square