Laws of Inheritance

Question 1

Who cares about genetics and inheritance?

Answer 1

• dog breeders care
• owners of pedigree animals care
• farmers care
• increasing part of the conversation relating to treatment

Question 2

What are the Three Laws of inheritance?

Answer 2

• First Law = Law of segregation
• Second Law = Law of independent Assortment
• Third Law = Law of dominance

Question 3

What is the First Law - Law of segregation?

Answer 3

• every individual organism contains two alleles for each trait, and that these alleles segregate (separate) during meiosis such that each gamete contains inly one of the alleles

Question 4

What is the Second Law - Law of independent Assortment

Answer 4

• Alleles for separate traits are passed independently of one another from parents to offspring

Question 5

What is the Third Law - Law of dominance

Answer 5

• recessive alleles will always be masked by dominant alleles

Question 6

Are the Three Laws always correct?

Answer 6

• no there are always variants

Question 7

What is a locus?

Answer 7

• position of gene on a chromosome
• loci (plural)

Question 8

What are alleles?

Answer 8

• alleles are varieties of the same gene

Question 9

Describe the position of alleles:

Answer 9

• alleles are always in the same position on the chromosome (locus)

Question 10

How are alleles created?

Answer 10

• they are created by mutations in the DNA

Question 11

What can allele mutations cause?

Answer 11

• these mutations can give a different phenotype

Question 12

What is a phenotype?

Answer 12

• phenotype can be both a physical appearance or the biochemical ability e.g., enzyme production

Question 13

What does a diploid individual contain?

Answer 13

• contains two copies of each gene
• one from each parent

Question 14

What does a homozygous individual contain?

Answer 14

• contains two identical copies

Question 15

What does a heterozygous individual contain?

Answer 15

• contains two different copies (alleles)

Question 16

A phenotype is an expression of genotype - what does this include?

Answer 16

• morphology
• biochemistry
• behaviour

Question 16

What is a genotype?

Answer 16

• alleles of a particular gene or genes
• present in a particular individual

Question 17

What are the exceptions to the first law?

Answer 17

• prokaryotes (bacteria and archaea) - binary fission instead
• clonal reproduction
• haploid organisms
• sex chromosomes

Question 18

Describe a gamete:

Answer 18

• haploid
• contains one copy of each parent gene
  determined at random

Question 19

Describe a zygote?

Answer 19

• diploid
• formed by fusion of two gametes
• from same or different individuals
• develops into diploid individual

Question 20

Independent assortment should lead to …

Answer 20

• no bias

Question 21

What are the exceptions to independent assortment?

Answer 21

• clonal reproduction - entire genome is inherited
• genes on the same chromosome - more likely to be inherited together = linkage

Question 22

When does crossing over (recombination) happen?

Answer 22

• crossing over happens in prophase 1 of meiosis - only in the production of gametes

Question 23

What happens if crossing ever happens after the gene?

Answer 23

• there is no recombination (not for that gene anyway)

Question 24

What happens if recombination (crossing over) happens between the centromere and gene?

Answer 24

- there is recombination

Question 25

The further the alleles are apart there is more chance of what?

Answer 25

- the more chance there is of recombination

Question 26

In complete dominance the phenotype of recessive allele is only expressed when?

Answer 26

- only when homozygous for recessive

Question 27

In the Law of dominance if there is complete what will happen to the recessive?

Answer 27

- if there is complete dominance the dominate allele will mask the recessive allele in phenotype

Question 28

What happens if there is incomplete dominance?

Answer 28

- phenotype of heterozygote is intermediate between two homozygotes - roan horses

Question 29

What happens if there is co-dominance?

Answer 29

- both alleles contribute to the phenotype - the effects of both alleles are seen to their full extent

Question 30

What is a second cross?

Answer 30

- between two individuals from F1 generation

Question 31

What is a first cross?

Answer 31

- between two individuals

Question 32

What does autosomal mean?

Answer 32

- the gene is located on one of the numbered or non-sex chromosome