L9 Principles of Inheritence

Question 1

What is a gene?

Answer 1

Gene is a unit of information that
codes for a protein
codes for genetic traits that are heritable

Question 2

Define genotype and phenotype.

Answer 2

Genotype is the combination of alleles present in your chromosomes.
Phenotypes refer to the physical appearance of a trait.

Question 3

Explain Mendel’s 3 Laws

Answer 3

1. Law of Dominance
   In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. Offspring that are hybrid for a trait will have only the dominant trait in the phenotype.

2.Law of Segregation
During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then “recombined” at fertilization, producing the genotype for the traits of the offspring.

3. Law of Independent Assortment
   Alleles for different traits (alleles) are distributed to gametes or sex cells (& offspring) independently of one another. The third Mendel law only applies when we are talking about two traits which are controlled by two different genes located on different chromosomes.

Question 4

Explain what is the test cross.

Answer 4

Geneticists use the test cross to determine unknown genotypes
Mating between an unknown genotype and a homozygous recessive can reveal the unknown’s genotype.If you have a homozygous dominant all the offspring will have dominant trait but if u have heterozygous the offspring will have a 50 50 mix of traits.

Question 5

What are germline mutations?

Answer 5

Germline mutations are errors that occur in DNA of cells that produce sperm or egg causing disease to run in the family.

Question 6

Why are sex linked recessive diseases more likely in men?

Answer 6

Males are more likely as they only have one X chromosome thus do not have a second X chromosome like women to override the mutation.

Question 7

Explain a recessive and dominant pedigree.

Answer 7

For those traits exhibiting recessive gene action:
unaffected parents can have affected offspring
affected progeny are both male and female

For those traits exhibiting dominant gene action:
affected individuals have at least one affected parent
the phenotype generally appears every generation
two unaffected parents only have unaffected offspring

Question 8

What are the 4 assumptions to Mendel’s Laws?

Answer 8

Mendel’s 3:1 monohybrid ratio and 9:3:3:1 dihybrid ratio are based on the following assumptions:
  Each allele is dominant or recessive
  Segregation occurs
  Independent assortment occurs
  Fertilization is random

Question 9

Explain incomplete dominance and codominance.

Answer 9

1. Incomplete Dominance
   A cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits
2. Codominance
   A cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together. (E.g. A and B phenotype in blood type)

Question 10

Does having a Gene Means the Trait Will be Developed?

Answer 10

A gene gives only the potential for the development of a trait.
How this potential is achieved depends partly on the interaction of the gene with other genes.
But it also depends partly on the environment