Meiosis & genetics (genetics & inheritance) Part 2 - (Week 8)

Question 1

What generation are the ‘true-breeding parents’?

Answer 1

P generation

Question 2

What is the hybrid offspring of the P generation called?

Answer 2

F1 generation

Question 3

What do we call the offspring of the F1 generation?

Answer 3

F2 generation

Question 4

If two contrasting ‘true-breeding’ white & purple flowered pea plants are bred together, what colour will their offspring be?

Answer 4

F1 hybrids (P gen offspring) will all be purple flowers

Question 5

What colour will the offspring of purple flowered F1 hybrids produce?

Answer 5

Flowers purple & white with ratio of 3:1

Question 6

What does the offspring in F1 & F2 generation of pea plants suggest?

Answer 6

Mendel called the purple flower the ‘dominant’ trait and the white flower the ‘recessive’ trait

Question 7

What are alleles?

Answer 7

They are alternative versions of a gene - each gene resides at a specific locus on a specific chromosome

Question 8

For ‘true-breeding’ parents, what type of alleles do they have?

Answer 8

They have alleles at a particular locus that are identical (e.g both dominant/both recessive)

Question 9

Do alleles in F1 hybrids have alleles at identical or different loci?

Answer 9

The two alleles in an F1 hybrid are at loci that are different

Question 10

Give the 4 main ideas that explain the 3:1 inheritance pattern observed in F2 offspring

Answer 10

1. Alternative versions of genes account for variations in inherited characters
2. For each character, an organism inherits 2 alleles, one from each parent
3. If the 2 alleles at a locus differ, then one (dominant allele) determines organism’s appearance, & the other (recessive) has no noticeable effect on appearance
4. The law of segregation

Question 11

What is the law of segregation?

Answer 11

The 2 alleles for a heritable character separate (segregate) during gamete formation (meiosis) & ended up in different gametes (gametes get only one of the 2 alleles present in the organism)

Question 12

What does it mean if an organism is ‘homozygous’ for a gene?

Answer 12

An organism with two identical alleles for a character is homozygous for the gene controlling that character

Question 13

What does it mean if an organism is ‘heterozygous’ for a gene?

Answer 13

An organism that has two different alleles for a gene is heterozygous for the gene controlling that character

Question 14

Homozygotes are not true-breeding. True or false?

Answer 14

False. Homozygotes are true-breeding, heterozygotes are not

Question 15

What is meant by the term ‘phenotype’?

Answer 15

Physical appearance

Question 16

What is meant by the term ‘genotype’?

Answer 16

Genetic makeup

Question 17

How can we determine genotype?

Answer 17

Do a testcross

1. Breed the mystery individual with a homozygous recessive individual
2. If any offspring display the recessive phenotype, the mystery parent must be heterozygous

Question 18

What is dihybrid inheritance?

Answer 18

Simultaneous inheritance of 2 characteristics

Question 19

Using a dihybrid cross, Mendel developed the Law of Independent Assortment. Describe what the means

Answer 19

• Each pair of alleles segregates independently of each other during gamete formation
• Applies only to genes on different, non homologous chromosomes or those far apart on the same chromosome
• Genes located near each other on the same chromosome tend to be inherited together

Question 20

What is the Hardy-Weinberg Principle?

Answer 20

It states that the frequency of dominant and recessive alleles will remain constant from generation to generation provided certain conditions exist

Question 21

What are the certain conditions required for the Hardy-Weinberg Principle to be true?

Answer 21

• No selection is taking place (all alleles are equal)
• No mutations occurring
• Mating is random
• Population is large
• No migration

Question 22

What equation must you use to calculate the frequency of a dominant or recessive allele?

Answer 22

p+q = 1.0

p = dominant allele
q = recessive allele
these frequencies are expressed as %, fractions or decimals

Question 23

How can you calculate the frequency of a genotype?

Answer 23

p^2 + 2pq + q^2 = 1.0

Question 24

What genotype does p^2 represent?

Answer 24

Frequency of the homozygous dominant

Question 25

What genotype does 2pq represent?

Answer 25

Frequency of the heterozygous

Question 26

What genotype does q^2 represent?

Answer 26

Frequency of the homozygous recessive

Question 27

How do you calculate the chance for various genotypes in a multi character cross?

Answer 27

• A multi character cross is equivalent to 2+ independent crosses occurring simultaneously
• To calculate chances for various genotypes, consider each separately
• Multiply each individual probability

Question 28

When does Mendelian inheritance not apply?

Answer 28

When:

• Alleles are not completely dominant or recessive
• A gene has more than two alleles
• A gene productes multiple phenotypes

(However the basic principles still apply)

Question 29

What is complete dominance?

Answer 29

It occurs when phenotypes of the heterozygote & dominant homozygote are identical

Question 30

What is incomplete dominance?

Answer 30

When the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

Question 31

What is codominance?

Answer 31

Two dominant alleles affect the phenotype in separate, distinguishable ways

Question 32

Give an example of incomplete dominance

Answer 32

When two different coloured ‘true-breeding’ parent flowers produce a hybrid offspring with a colour inbetween the two

Question 33

Give an example of codominance

Answer 33

Blood groups in humans. There are 3 alleles: IA, IB, i (IA & IB are dominant, i is recessive)