8) Principles and laws of mendelian genetics

Question 1

Mendelian genetics

Answer 1

Foundation of modern genetics

Question 2

Mendel’s laws

Answer 2

• Monogenic traits
  
  • Environmental factors rarely influence the phenotype
  • The trait is either present or not
• Segregation of traits during crossing
  
  • Independent combinations

Question 3

Monogenic traits

Answer 3

Single major genes (Alleles)

Question 4

Generation: P

Answer 4

Parent

Question 5

Generation: F1

Answer 5

First generation

Question 6

Generation: F2

Answer 6

Second generation

Question 7

Monohybrid cross

Answer 7

• Cross of two different purebred strains (homozygotes)
• Differ in a single trait

Question 8

Reciprocal cross

Answer 8

• Cross of two chains reversed
• If the results are the same, the trait is not sex linked

Question 9

Dihybrid cross

Answer 9

Cross of two homozygotes that differ in two traits

Question 10

Gene/locus

Answer 10

DNA sequence which determines a trait

Question 11

Allele

Answer 11

A variant of a gene

Question 12

Genotype

Answer 12

Pair of alleles carried by an individual at a particular locus

Question 13

Homozygous

Answer 13

Genotype where both alleles are the same

AA,aa

Question 14

Heterozygous

Answer 14

Genotype where the alleles are different

Aa

Question 15

Dominant

Answer 15

One copy of an allele is enough to express the phenotype

AA, Aa = expressed

Question 16

Recessive

Answer 16

Two copies are needed to express the phenotype

aa

Question 17

Genetic polymorphism

Answer 17

More than two alleles identified in a population

Question 18

Semidominance/incomplete dominance

Answer 18

Both alleles expressed to a certain degree

Question 19

Codominance

Answer 19

Both alleles fully expressed

Question 20

Overdominance

Answer 20

Heterozygotes are more fit than homozygotes

Question 21

List Mendel’s laws

Answer 21

• Law of segregation
• Law of uniformity and reciprocity
• Law of independent assortment

Question 22

Law of segregation

Answer 22

1. Alternative versions of alleles account for inherited variance
2. For each characteristic, the offspring inherit 2 alleles
3. Alleles for each characteristic segregate during gene production

• Each gamete has one allele for each gene*
• Allow maternal and paternal alleles to be combined → Variation*

Question 23

Law of uniformity and reciprocity

Answer 23

• F1 have identical genotype + phenotype
  
  • Independent of genetic dominance
• F1 heterozygote reproduces
• P characteristics reappear in F2
• Offspring will not be uniform

Question 24

Law of independent assortment

Answer 24

• Gamete formation:
  
  • Segregation of allele pairs is independent of other alleles
  • The inheritance pattern of one trait will not affect the inheritance of the other
• One trait give: 3:1 ratio
• Two traits give 9:3:3:1 ratio

Question 25

Summarise mendelian genetics

Answer 25

• Genes are heredity determinants
• Alleles form gene pairs
• Gene pair segregate into gametes, carrying only one member of the gene pair
• Gametes unite in random