Mendelian Genetics

Question 1

Who was Gregor Mendel?

Answer 1

Born in 1822 in Czech Republic (formerly Czechia), died 1884
discovered inheritance

Question 2

What did Mendel study and what did he show?

Answer 2

studied peas (Pisum sativum) in 1850’s

• Have dichotomous traits (traits with only 2 forms)
• Coined the term hereditary units didn’t know they were called genes

Showed inheritance is “particulate”, not blending

Ex a black cat x white cat does not produce a grey cat

Question 3

Why did Mendel use peas?

Answer 3

Readily available at monestary

Flowers have both male and female structures

Self-fertilize

Can manually fertilize plants by removing male anthers (ie artificial cross-fertilization)

Short life cycles

Question 4

Self-fertilize

Answer 4

Reproduction by organisms that contain both male and female reproductive structures; the natural reproductive mechanism on many plants, including pea plant

Question 5

artificial cross-fertilization)

Answer 5

A controlled cross between plants made by an investigator who transfers pollen from one plant to fertilize the other plant.

Question 6

Pure-breeding (true breeding):

Answer 6

strains that consistently produce the same phenotype

the parents would produce offspring that would carry the same phenotype
he parents are homozygous for every trait.- the parents must be both dominant or both recessive.

Question 7

Parental (P) generation:

Answer 7

pure-breeding parent plants in a cross

Each parent has alternative forms of the trait

Pink parent plant will only produce pink offspring

Question 8

First filial (F1 )

Answer 8

progeny(offspring) produced from a parental cross

Self-fertilised or crossed to produce the next generation

Mendel would measure the phenotypes in this generation

Question 9

Second filial (F2 )

Answer 9

progeny produced from the cross of F1

Mendel would then measure the phenotypes produced here too

Question 10

Replicate crosses

Answer 10

produced 100’s of F1 plants and thousands of F2 plants

Repeated crosses involving parents with the same genotypes and phenotypes

Question 11

Reciprocal crosses:

Answer 11

Plants with the same phenotypes crossed but the sexes of the donating parents were swapped

Plant donating the egg in one cross, donated the pollen in the next

Question 12

Test-crosses

Answer 12

crosses designed to identify the alleles carried by an organism whose genetic make-up (genotype) is not known

Question 13

Genes

Answer 13

determinants of traits (ie, eye colour)

The physical unit of heredity, composed of a DNA sequence that is transcribed and encodes a polypeptide or another functional molecule.

Question 14

Alleles

Answer 14

alternative forms of genes (ie gene variants)

Gene for pea seed colour has alleles that code for Yellow (Y) or green (y) seeds

Question 15

Phenotype

Answer 15

trait that you can measure

Ie appearance, biochemistry (eg amount of enzyme), behaviour

Question 16

Genotype

Answer 16

Genetic make-up of an organism that results in its phenotype

Determined by combination of alleles

Diploid organisms have 2 alleles for each gene (one from mom and one from dad)

Question 17

Genotypic ratio

Answer 17

relative proportions between organisms with different genotypes

Mendel’s peas had a 1:2:1 genotypic ratio for GG:Gg:gg \homozygous and heterozygous

Question 18

Phenotypic ratio:

Answer 18

relative proportions between organisms with different phenotypes

Mendel’s peas had a 3:1 phenotypic ratio for purple: white flowers

Question 19

What are Mendels genotypic and phenotypic ratios?

Answer 19

Mendel’s peas had a 1:2:1 genotypic ratio for GG:Gg:gg \homozygous and heterozygous
Mendel’s peas had a 3:1 phenotypic ratio for purple: white flowers

Question 20

Homozygous

Answer 20

both alleles code for the same phenotype (ie both YY or yy)

Question 21

Heterozygous

Answer 21

Each allele codes for a different phenotype (Yy)

Question 22

Dominant allele

Answer 22

alleles that mask the effect of the other alleles

Ie Yy results in yellow seeds since Y (yellow) masks y (green)

Question 23

Recessive allele:

Answer 23

alleles that are masked by other alleles

Phenotype is only seen in the homozygous state (ie yy, green)

Question 24

Monohybrid cross

Answer 24

cross between two organisms that have the same heterozygous genotype for a gene

Question 25

What happened when Mendel performed a monohybrid cross?

Answer 25

reveal the segregation of alleles
When Mendel bred two true-breeding parents, the resulting F1 progeny were all the same phenotype as the parent with the dominant trait

When Mendel crossed the F1 , the resulting F2 showed the appearance of the recessive trait (1:2:1 genotype ratio and 3;1 phenotype ratio)

Question 26

Law of Segregation

Answer 26

proven by the monohybrid cross
Two alleles of the same gene separate from one another during the formation of gametes
explained phenotypes

Meiosis I!- separating out the sister chromatids during anaphase

When an organism makes gametes, each gamete receives just one gene copy, which is selected randomly.

Question 27

Monohybrid cross ratio

Answer 27

F2- 1:2:1 genotypic ratio and 3:1 phenotypic ratio

Question 28

What did Mendel predict to be the genotype for the F1 progeny what was done to prove it?

Answer 28

He predicted all the F1 progeny were heterozygotes, but needed to prove it

Performed a test-cross (always with the recessive parent)

F1 (dominant phenotype) x true-breeding recessive parent

If F1 was heterozygous, the resulting F2 would have a phenotypic ratio of 1:1

Question 29

What did Mendel predict about the F2 generation?

Answer 29

that the F2 plants with the dominant phenotype would produce twice as many heterozygotes as homozygous dominant individuals
 Ie 3⁄4 of the offspring would be yellow seeds, 1⁄4 green seeds (phenotypic ratio)

Question 30

What was the result of self fertilization in the F2?

Answer 30

Homozygous dominant plants would produce offspring that were homozygous dominant (ie all yellow)
 Heterozygous plants would produce some plants with yellow seeds and some with green seeds
 3:1 phenotypic ratio

Question 31

Dihybrid crosses

Answer 31

two traits and their simultaneous transmission (inheritance)

Mendel began each dihybrid cross with pure -breeding parentals

F1 will be heterozygous for both traits (ie dihybrids)

Question 32

Independent assortment

Answer 32

The segregation of alleles of one gene is independent of the segregation of alleles of the other gene

*Law of segregation occurs during
anaphase I of meiosis I since the two alleles will segregate independently of each other during gamete formation and have equal opportunity of inclusion in the gamete

supported by dihybrid cross

Question 33

What does Crossing the F1 heterozygotes produce

Answer 33

Crossing the F1 heterozygotes produce a 9:3:3:1 phenotypic ratio in the F2

Question 34

Trihybrid crosses

Answer 34

involve three independently assorting traits

Question 35

Dihybrid cross features

Answer 35

Parental and nonparental phenotypes in the F 2 differ from one another ie 9:3:3:1

Compare that to the monohybrid cross

Monohybrids in F2 generation will have a 3:1 ratio

hen we look at each trait independently, we still get the 3:1 phenotypic ratio

Question 36

Conditional probability

Answer 36

 Probability prediction that is dependent on another previous event having taken place
 i.e. “What is the probability that F2 yellow-seeded progeny plants are heterozygous like their parents”?
 We know that F2 progeny will be 3⁄4 yellow and 1⁄4 green, and of the 3 yellow, 2/3 will be Gg and 1/3 will be true-breeding GG