1 - Mendelian Inheritance and the role of meiosis in determining the pattern of inheritance

Question 1

Who was Gregor Mendel?

Answer 1

Father of genetics

Question 2

what did Mendel’s work with peas lead to?

Answer 2

• discovery of dominant and recessive traits

- concept of the gene, formulation of the basic laws of inheritance

Question 3

character

Answer 3

heritable feature of an individual

Question 4

trait

Answer 4

a variant form of a character (phenotype)

Question 5

What is the law of segregation?

Answer 5

The 2 forms of a gene (alleles) present in each parent segregate independently

Question 6

how did Mendel formulate the law of segregation

Answer 6

by studying the results of monohybrid crosses

Question 7

What is a monohybrid cross?

Answer 7

a cross between two true- breeding individuals differing in only 1 character

Question 8

What did Mendel observe from monohybrid crosses?

Answer 8

• All F1 progeny resembled one of the parents, but both parental traits appear in the F2 generation
• the ratio in the F2 generation is 3:1

Question 9

Monohybrid cross conclusions

Answer 9

1. 1 trait is dominant and the other is recessive

2. the heritable factor for the recessive trait been masked by the presence of the factor for the dominant trait

Question 10

What is Mendel’s model?

Answer 10

1. Variations in inherited characteristics are due to the existence of alternative versions of alleles
2. For each character, an organism inherits 1allele from each parent
3. If the 2 alleles differ, then the dominant allele determines the organism’s phenotype
4. The alleles remain discrete when present in
5. The 2 alleles segregate during gamete formation - and end up in different gametes

Question 11

How do offspring receive genes?

Answer 11

• Each parent has 2 alleles - but only 1 is passed to an individual offspring via the gamete
• Each offspring receives 1 allele from 1 parent and the other allele from the other parent

Question 12

How segregation of alleles can explain the 3:1 ratio seen in the F2 generation

Answer 12

1 homozygous dom,
2 heterozygous dom,
1 homozygous rec.
3:1 ratio of phenotypes

Question 13

What is a punnett square?

Answer 13

A diagrammatic device for predicting the outcomes of crosses between parents of known genotype

Question 14

what are the 3 possible combinations of 2 alleles?

Answer 14

1. Homozygous dominant : GG
2. Homozygous recessive : gg
3. Heterozygous : Gg
   Different genotypes can produce the same phenotype

Question 15

What is a test cross?

Answer 15

A method for determining the genotype of an individual with the dominant phenotype of a trait

Question 16

How do we determine the genotype of an organism with a dominant phenotype?

Answer 16

cross the test species with a homozygous recessive individual

Question 17

What is Mendel’s Law of Independent Assortment?

Answer 17

Each pair of alleles assorts independently of each other pair of alleles during gamete formation

Question 18

What is a dihybrid cross?

Answer 18

a cross between two true- breeding individuals differing in 2 characters

Question 19

What is seen in the F2 generation of dihybrid crosses?

Answer 19

• 2 recombinants in addition to the 2 parental phenotypes

- 9:3:3:1 ratio

Question 20

What would happen if independent assortment did not occur?

Answer 20

• The gametes produced in the F1 would be of only 2 types (YR and yr)
• the F2 would have no recombinant phenotypes - only parentals

Question 21

explanation of LIA observations

Answer 21

• there are 4 possible combinations in each gamete, not 2.

- F2 progeny ratio - 9:3:3:1

Question 22

How to deal with a triple heterozygote

e.g RrYyGg x RrYyGg, how many will have round, yellow, seedsd in yellow pods?

Answer 22

deal with each of the 3 allele pairs separately

Question 23

Meiosis

Answer 23

• results in 4 daughter cells each with half the number of chromosomes of the parent cell
• as in the production of gametes and plant spores.

Question 24

Mitosis

Answer 24

cell division in which the nucleus divides into nuclei containing the same number of chromosomes

Question 25

Comparison of Meiosis and Mitosis

Answer 25

• Mitosis occurs in somatic cells, meiosis occurs in the germ line
• In mitosis there is only 1 cell division, in meiosis there are 2
• Meiosis produces 4 (non-identical) haploid cells (gametes), mitosis produces 2 identical diploid cells
• Synapsis is unique to meiosis
• The role of mitosis is to drive growth and tissue repair; the role of meiosis is to produce haploid gametes and to introduce genetic variability

Question 26

Homologues

Answer 26

The 2 chromosomes of a homologous pair are individual chromosomes that were inherited from different parents
- appear alike under a microscope but have different versions of a gene at some of their loci

Question 27

Chromatid

Answer 27

one of the two identical strands of a newly replicated chromosome

Question 28

sister chromatids

Answer 28

2 identical chromatids held together by a common centromere following replication

Question 29

stages of meiosis I and II

Answer 29

Interphase, Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II

Question 30

How did sutton make the link between behaviour of chromosomes during meiosis and medel’s laws?

Answer 30

He observed that:

• Chromosomes occur in pairs in somatic cells
• Chromosome pairs segregate equally into gametes
• Different chromosome pairs assort independently

Question 31

chromosome theory of inheritance

Answer 31

States that:

• Mendel’s ‘heritable factors’ (or genes) are located at specific positions (loci) on chromosomes
• It is the chromosomes that undergo segregation and independent assortment

Question 32

How does chromosome behaviour in meiosis explain Mendel’s Law of Segregation?

Answer 32

Because each allele is on a different member of a chromosome pair and moves to opposite poles in anaphase I

Question 33

How does chromosome behaviour in meiosis explain Mendel’s Law of Independent Assortment?

Answer 33

Because the arrangement of chromosomes at metaphase I is random