mendelian genetics lecture quiz

INTERACTIVE CLASS QUIZLecture on DNA and the Central Dogma of

Molecular Biology

LECTURE OUTLINE

Mendelian Genetics and Heredity

DNA versus RNA and Why DNA is the genetic material?

Crick’s Central Dogma of Molecular Biology

Mendel and the GenesPART 1

HEREDITY AND FAMILY RESEMBLANCE

HEREDITY BEFORE MENDELUNKNOWN: genetic principles that account for the transmission of traits from parents to offspring

“blending” hypothesis: genetic material contributed by two parents mixes

“particulate” hypothesis: parents pass on discrete heritable units called genes

ASSUMPTION 1: CONSTANCY OF SPECIES

heredity occurs within species

e.g. camel + leopard = giraffe (by breeding)

Species were thought to have been maintained without significant change from the time of their creation

HEREDITY BEFORE MENDEL

ASSUMPTION 2: DIRECT TRANSMISSION OF TRAITS

traits are transmitted directly

Information from each part of the body was supposedly passed along independently of the information from the other parts

The child was formed after the hereditary material from all parts of the parents’ bodies had come together

example: red hair parents = red hair children

HEREDITY BEFORE MENDEL

and then there was MENDEL…

WHO IS GREGOR MENDEL?

carried out the first quantitative studies of inheritance

an Austrian monk

educated in a monastery and went on to study science and mathematics at the University of Vienna

BUT…he failed his examinations for a teaching certificate

initiated a series of experiments on plant hybridization (using garden peas)

GUIDING PRINCIPLE FOR MENDEL’S WORK

Variation is widespread in nature

Observable variation is essential for following genes

Variation is inherited according to genetic laws and not solely by chance

Mendel’s laws apply to all sexually reproducing organisms

QUESTION #1:

B

Who was Gregor Mendel?

A. an English scientist who carried out research with Charles Darwin

B. a little known Central European monk

C. an early 20th century Dutch biologist who carried out genetics research

QUESTION #2:

C

Which of the following statements is true about Mendel?

A. His discoveries concerning genetic inheritance were generally accepted by the scientific community when he published them during the mid 19th century

B. He believed that genetic traits of parents will usually blend in their children

C. His ideas about genetics apply equally to plants and animals

WHY THE GARDEN PEA (Pisum sativum)

Earlier investigators had produced hybrid peas by crossing different varieties

can expect to observe segregation of traits among the offspring

Large number of true-breeding varieties of peas were available

Small and easy to grow, and they have a relatively short generation time

can conduct experiments involving numerous plants, grow several generations in a single year, and obtain results relatively quickly

Sexual organs of the pea are enclosed within the flower

fertilization takes place automatically within an individual flower if it is not disturbed, resulting in offspring that are the progeny from a single individual

CROSSING THE

PEA PLANTS

1

5

4

3

2 Removed stamens from purple flower

Transferred sperm- bearing pollen from stamens of white flower to egg- bearing carpel of purple flower

Parental generation (P)

Pollinated carpel matured into pod

Carpel (female)

Stamens (male)

Planted seeds from pod

Examined offspring: all purple flowers

First generation offspring (F1)

STUDIED DISCRETE TRAITS

QUESTION #3:

A

Mendel believed that the characteristics of pea plants are determined by the:

A. inheritance of units or factors from both parents

B. inheritance of units or factors from one parent

C. relative health of the parent plants at the time of pollination

SOME IMPORTANT TERMS

CHARACTER: a heritable feature

e.g. flower color

TRAIT: a variant of a given character

e.g. purple, white, yellow

ALLELES: alternative form of traits

P (purple); W (white); Y (yellow)

QUESTION #4:

D

An allele is:

A. another word for a gene

B. a homozygous genotype

C. a heterozygous genotype

D. one of several possible forms of a gene


Phenotype – observable characteristic of an organism

Genotype – pair of alleles present in and individual

QUESTION #5:

B

Phenotype refers to the ____________________ of an individual

A. genetic makeup

B. actual physical appearance

C. recessive alleles

QUESTION #6:

A

When the genotype consists of a dominant and a recessive allele, the phenotype will be like _________________ allele.

A. the dominant

B. the recessive

C. neither


Homozygous – two alleles of trait are the same (YY or yy)

Heterozygous – two alleles of trait are different (Yy)

Figure 14.6

3

1 1

2

1

Phenotype

Purple

Purple

Purple

White

Genotype

PP (homozygous)

Pp (heterozygous)

Pp (heterozygous)

pp (homozygous)

Ratio 3:1 Ratio 1:2:1


Capitalized traits = dominant phenotypes

Lowercase traits= recessive phenotypes

QUESTION #7:

B

Assuming that both parent plants in the diagram below are homozygous, why would all of the f1 generation have yellow phenotypes?

A. because the f1 genotypes are homozygous

B. because yellow is dominant over green

C. because both parents passed on yellow alleles

QUESTION #8:

C

QUESTION #9:

A

QUESTION #10:

B

DOMINANT & RECESSIVE TRAITS

D

R

QUESTION #11:

3) TT

QUESTION #12:

2) SHORT

QUESTION #13:

2) ALL tt


Generations:

P = parental generation

F1 = 1st filial generation, progeny of the P generation

F2 = 2nd filial generation, progeny of the F1 generation (F3 and so on)


Crosses:

Monohybrid cross = cross of two different true-breeding strains (homozygotes) that differ in a single trait.

Dihybrid cross = cross of two different true-breeding strains (homozygotes) that differ in two traits.

THE OBSERVATIONSP Generation (true-breeding parents) Purple

flowers White flowers

×

F1 Generation (hybrids)

All plants had purple flowers

F2 Generation

EXPERIMENT True-breeding purple-flowered pea plants and white-flowered pea plants were crossed (symbolized by ×). The resulting F1 hybrids were allowed to self-pollinate or were cross- pollinated with other F1 hybrids. Flower color was then observed in the F2 generation.

RESULTS Both purple-flowered plants and white- flowered plants appeared in the F2 generation. In Mendel�s experiment, 705 plants had purple flowers, and 224 had white flowers, a ratio of about 3 purple : 1 white.

BASED ON THE RESULTS…

In the F1 plants, only the purple trait was affecting flower color in these hybrids

Purple flower color was dominant, and white flower color was recessive

BASED ON THE RESULTS…In the F2 plants, a 3:1 inheritance pattern was observed

Possible Heredity concepts:

alleles account for the variation

inherits two alleles, one from each parent

if the two alleles at a locus differ, the dominant allele determines the organism’s appearance

ALLELESAllele for purple flowers

Locus for flower-color gene Homologous pair of chromosomes

Allele for white flowers

The law of segregation - the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes

MECHANISM OF GENE TRANSMISSION

GAMETOGENESIS

alleles segregate

FERTILIZATION

alleles unite

THE PUNNET SQUAREP Generation

F1 Generation

F2 Generation

P p

P p

P p

P

p

Pp PP

pp Pp

Appearance: Genetic makeup:

Purple flowers PP

White flowers pp

Purple flowers Pp

Appearance: Genetic makeup:

Gametes:

Gametes:

F1 sperm

F1 eggs

1/2 1/2

× Each true-breeding plant of the parental generation has identical alleles, PP or pp. Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele.

Union of the parental gametes produces F1 hybrids having a Pp combination. Because the purple- flower allele is dominant, all these hybrids have purple flowers. When the hybrid plants produce gametes, the two alleles segregate, half the gametes receiving the P allele and the other half the p allele.

3 : 1

Random combination of the gametes results in the 3:1 ratio that Mendel observed in the F2 generation.

This box, a Punnett square, shows all possible combinations of alleles in offspring that result from an F1 × F1 (Pp × Pp) cross. Each square represents an equally probable product of fertilization. For example, the bottom left box shows the genetic combination resulting from a p egg fertilized by a P sperm.

THE MONOHYBRID CROSS

Purple (Pp)

Purple (PP)

P p p p

P

P

P

p

F1 generation All purple

White (pp) Purple

(Pp)

Pp Pp PP Gametes

F2 generation ¾ purple, ¼ white

Gametes Gametes

Gametes Pp

Pp Pp Pp pp

THE MONOHYBRID CROSS

MENDEL OBSERVED THE SAME PATTERN IN CHARACTERISTICS

QUESTION #14:

4) none

MENDEL’S LAW OF INDEPENDENT ASSORTMENT

two characters at the same time (DIHYBRID CROSS)

whether alleles at 2 different gene loci segregate dependently or independently

Crossing two, true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters

When gametes form, each pair of hereditary factors (alleles) segregates independently of the other pairs

QUESTION #15:

C

The idea that different pairs of alleles are passed to offspring independently is Mendel's principle of:

A. unit inheritance

B. segregation

C. independent assortment

QUESTION #16:

A

In the diagram, what accounts for the green pea seed in the f2 generation?

A. On average, 1 out of 4 offspring of heterozygous parents will be homozygous recessive

B. The yellow allele is dominant over the green one

C. The f1 generation parents are homozygous yellow

QUESTION #17:

C

The idea that for any particular trait, the pair of alleles of each parent separate and only one allele from each parent passes to an offspring is Mendel's principle of:

A. independent assortment

B. hybridization

C. segregation

DIHYBRID CROSSYYRR P Generation

Gametes YR yr ×

yyrr

YyRr Hypothesis of dependent assortment

Hypothesis of independent assortment

F2 Generation (predicted offspring)

1⁄2 YR

YR

yr

1 ⁄2

1 ⁄2

1⁄2 yr

YYRR YyRr

yyrr YyRr

3 ⁄4 1 ⁄4

Sperm

Eggs

Phenotypic ratio 3:1

YR 1 ⁄4

Yr 1 ⁄4

yR 1 ⁄4

yr 1 ⁄4

9 ⁄16 3 ⁄16 3 ⁄16 1 ⁄16

YYRR YYRr YyRR YyRr

Yyrr YyRr YYrr YYrr

YyRR YyRr yyRR yyRr

yyrr yyRr Yyrr YyRr

Phenotypic ratio 9:3:3:1

315 108 101 32 Phenotypic ratio approximately 9:3:3:1

F1 Generation

Eggs YR Yr yR yr 1 ⁄4 1 ⁄4 1 ⁄4 1 ⁄4

Sperm

CONCLUSION The results support the hypothesis ofindependent assortment. The alleles for seed color and seed shape sort into gametes independently of each other.

EXPERIMENT Two true-breeding pea plants— one with yellow-round seeds and the other with green-wrinkled seeds—were crossed, producing dihybrid F1 plants. Self-pollination of the F1 dihybrids, which are heterozygous for both characters, produced the F2 generation. The two hypotheses predict different phenotypic ratios. Note that yellow color (Y) and round shape (R) are dominant.

DIHYBRID CROSS

LAWS OF PROBABILITY× Rr

Segregation of alleles into eggs

Rr Segregation of

alleles into sperm

R r

r R

R R

R 1⁄2

1⁄2 1⁄2

1⁄4 1⁄4

1⁄4 1⁄4

1⁄2 r r R r

r

Sperm

×

Eggs

SUMMARY OF MENDEL’S EXPERIMENTS

Genes are distinct entities that remain unchanged during crosses

Each plant has two alleles of a gene

Alleles segregated into gametes in equal proportions, each gamete got only one allele

During gamete fusion, the number of alleles was restored to two (FERTILIZATION)

MENDEL AND HUMAN TRAITS

EXCEPTIONS TO MENDEL’S LAWS

INCOMPLETE DOMINANCE

P Generation

F1 Generation

F2 Generation

Red CRCR

Gametes CR CW

× White CWCW

Pink CRCW

Sperm

CR

CR

CR

Cw

CR

CR Gametes 1⁄2 1⁄2

1⁄2

1⁄2

1⁄2

Eggs 1⁄2

CR CR CR CW

CW CW CR CW

Neither allele is dominant and heterozygous individuals have an

intermediate phenotype

QUESTION #18:

B

What is the ratio of F2 heterozygotes during incomplete dominance?

A. 1

B. 2

C. 3

CODOMINANCE

Neither allele is dominant and both alleles are expressed in heterozygous individuals

QUESTION #19:

C

If your blood type is AB what is the dominant allele?

A. A

B. B

C. both

POLYGENIC TRAITS

traits that are not controlled by a single gene locus, but by the combined interaction of many gene loci

Polygenic traits often show continuous variation, rather then a few discrete forms

example: eye color, hair color, skin color

POLYGENIC TRAITS

EPISTASISalleles at one gene locus can hide or prevent the expression of alleles at a second gene locus

PLEIOTROPYThis is when a single gene locus affects more than one trait

QUESTION #20:

hair, skin or eye color

Give an example of a polygenic trait…

mendelian genetics lecture quiz

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