Genetic analysis 1+2

Question 1

What was Mendel’s experiment with smooth and wrinkled phenotypes of peas?

Answer 1

1) Cross-bred 2 true breeding pea varieties (smooth seeds, wrinkled seeds)
2) F1 progeny all had smooth seeds
3) Self fertilise F1 progeny
4) Wrinkled seeds reamerged in a definite proportion

Question 2

What is co-dominance?

Answer 2

• Simultaneous expression of 2 phenotypes determined by a gene having more than 2 alleles
• Eg. blood groups

Question 3

What is Mendel’s first law?

Answer 3

• 2 alleles segregate during gamete formation
• Half of gametes carry one allele and half the gametes carry the other
• No blending, only dominant or recessive phenotypes

Question 4

Which one of Mendel’s laws did Hunt Morgnan violate?

Answer 4

Mendel’s second law

Question 5

What did Mendel do?

Answer 5

• Grew pea plants

- Set up an experimentsal system of breeding different strains of pea plant

Question 6

What were Gregor Mendel’s ideas?

Answer 6

• Genes were discrete, physical entities which function independantly of each other and determine specific characteristics (distinct phenotypes)

Question 7

What is genetic recombination?

Answer 7

• Crossovers occurring between chromosomes during gamete formation, producing non-parental recombinant combinations of alleles
• Every chromosome involved in at least one crossover during meiosis
• Occurs at the ends of chromosomes

Question 8

What is Mendel’s second law?

Answer 8

• Un-linked genes controlling different characteristics are assorted INDEPENDANTLY into gametes
• Different genes R/r Y/y lie on different chromosomes

Question 9

What did Mendel miss in his experiments?

Answer 9

• Some genes have more than 2 alleles
• Some alleles are not completely recessive or dominant
• Many genes don’t show independent assortment as they lie on the same chromosome
• In-complete dominance
• co-dominance

Question 10

What is a ‘true breeding’ organism?

Answer 10

An organism which always passes down certain phenotypic traits to offspring

Question 11

What did Thomas Hunt Morgan discover?

Answer 11

• Backcross grey-normal winged drospohila with a mutant ebony-vestigal winged parents
• Expected 4 phenotypes in EQUAL proportions
• BUT there were 4 phenotypes in UNEQUAL proportions

Question 12

What were Huntt Morgans conclusions?

Answer 12

• Both genes are on the same chromosome so they are linked and inherited together
• Carry both dominant genes on one chromosome and both recessive genes on a different chromosome

Question 13

What were Mendel’s conclusions?

Answer 13

• In the gametes there is one allele of each gene

- The gamete combine randomly to form the progeny

Question 14

What was Mendel’s 2nd experiment?

Answer 14

• Looked at yellow/green and wrinkled/smooth
• Breed heterozygotes plants for both traits with homozygous recessive parents - this is a backcross
• Observes phenotypes in 4 equal proportion
  (rY Ry RY ry) not (Rr rr yY yy)

Question 15

What can measuring the recombination frequencies allow?

Answer 15

Allows genetic maps before genome sequencing

Question 16

What are the number of recombinants proportional to?

Answer 16

The physical distance between the two linked genes on the same chromosome
(further apart = more recombinations)

Question 17

Why did Mendel use pea plants?

Answer 17

• Simple characteristics which we easy to identify
• Very fertile so can produce large numbers
• Hermaphroditic (self-fertilising) - true breeding
• Easy to grow

Question 18

What is incomplete dominance?

Answer 18

F1 heterozygote phenotype is the intermediate between the two homozygote parental phenotypes
- Eg. snapdragons have red, white, and PINK phenotyes